What's a good rule of thumb maximum DCR for Iron and Aluminum heads figuring premium 93 octane gas. Thanks

For the average motor, limit an iron headed motor to 8:1 and an aluminum headed motor to about 8.25:1. Those numbers are not set in stone though. Assuming you have good heads with better chambers and quench is properly set at or very near .040 and the cooling system properly does its job as well as the tuneup, 8.2 with iron and about 8.5 with aluminum is do-able. And, some people take it even further by thermal heat coating the piston tops and valves to even further reduce the sensitivity to detonation and take the numbers even further than that. It takes some good engineering, but if you picked up the issue of hot rod with the pump gas drags, many of those cars were in the nines and some in the eights supposedly on 93 octane fuel, so you can push the limits, but once again, for the average buildup in a heavy street car that will be driven in different situations and conditions, its probably safest to go with the first set of numbers(8:1 iron and about 8.25:1 for aluminum).

Thanks, that's the info I was looking for.

Empirical testing of the upper end of street DCR's:

8.6 is barely doable with great quench, old porous GM alm heads, and a motor that makes best power at 200 degrees. To wit, even with all the 'stars lined up' 8.5 is too high, not giving you any margin for the occasional bad batch of fuel.

Greg's numbers are good point estimates.

Toluene messes with the needle and seats! :( Always carry spares with added aromatics.

mine came out at 8.19 I have .043 quench and Canfield out of the box heads. I run 91 octane at 35 deg.

BTW, as for the pump gas drags, it says right in the article " SPECIALLY BLENDED 93", For the 20 guys that pulled it off, 1,000 more will explode their stuff trying.


Mike

how about for Iron-headed on 87 octane?

This gets into the 11+ to 1 CR. motors that can run 87 octane if you want to read up on it by searching under my name.

A Tech. School Class even did a build-up of a 502 with Mr. Jim Fuelings BB truck, Torque-Heads on it that was above 12 to 1!!!

BUT these build-ups are by no stretch race motors, but rather work horses!!

Mr. Ray Bohaz(Sp?) wrote two articles on the 502 build-up and I have talked to him personally several years ago on the subject.. Great Tech Writer imho..

pdq67

Back again, his name is Ray T. Bohacz!!

I forget but figure he wrote the articles for PHR if they have an article archive at their web site??

pdq67

Old Gold's burnout (http://gallery.godragracing.com/photos/etown/IMG_0262.jpg)

Originally posted by Motor Martyr:
Old Gold's burnout (http://gallery.godragracing.com/photos/etown/IMG_0262.jpg) :confused:

click the picture jason :D i was trying out the link.

Cool pic :D

deleted. They are right: ignorance = bliss.

Originally posted by 66 283:
And my rant about DCR :rolleyes: That's like trying to measure rpm by counting tire revolutions at the finish line. If it could be calculated it wouldn't be dynamic now, would it? LOL There are more important things that will determine the octane requirement - LOAD for instance. Don't be governed by these artificial feel-good laws of the universe! :D
Crap man you are starting to sound like me :D

Uh, 66 283, I dont know if that was supposed to be a bash or what, but if you read my whole post, I used quite a few different numbers for some common DCR levels........ Kinda hinting at the fact that the numbers DONT say it all(actually I said it, not hinted at it), otherwise I woulda said "this is the only way to go". It kinda sounded like you were tying to say Im wrong by using an arguement that agrees with mine? As far as me saying supposedly 93 octane, I say that cause I wasnt there, nor did I send out an order for a gallon of that fuel so I can test it in hopes to bring up a case on the pump gas drags. So Im in no place to say, yes it was definitely 93 octane. My point was that many things, including DCR dictate how a motor responds to a given octane. If it was a totally useless number, I doubt any of us would concern ourselves with static compression numbers either, cause they are both forms of compression. One is theoretical, and the other is real world and does vary, but it works off of the theoretical number along with everything else. As far as your motor, if you give me your rod length, stroke lenght, and intake valve closing angle, I could figure out what the calculators say your DCR is with 11:1 compression, and Im guessing itll be a lower number. That number might not matter to you cause it sounds your plenty happy with the way things worked out reguardless, but I bet whatever number it is, it partially contributes to the fact that you can run so much nitrous through your motor on 93 fuel. If it dont matter, run a much smaller cam with no other changes, or just boost the static compression a couple points and see if it still works out as well as it does now. If I misinterpreted your post, than I apologize, but if not, than I am a little confused cause I though I made it pretty obvious that the numbers arent an exact science and can vary in every situation(like you said) depending on many things of which I listed just a few.

..

66 283, I don't care and many others don't care if you think the DCR concept is bunk. The choice of term is unfortunate but it is used by two rather authoritative sources. David Vizard goes into some length about it in his book on Cams and Valvetrains (using the term Dynamic Compression Ratio (p20-21)). Smokey Yunick talks about it, using the same term, in his Power Secrets book (p74) "When you use a long cam--which will have a late intake closing--much of the mechanical pressure developed during the compression phase will escape past the open intake valve. As a result, the dynamic compression--the thing that really counts--will be reduced." [italics added] Notice that no mention is made of the load on the engine, the weight of the car, or the rpm of the engine.

Without doubt Effective Compression Ratio would be a better term for it. DCR is a calculated value, just like static is. The only, I repeat, only difference is that it is calculated using the position of the piston at intake closing rather than the full stroke of the crank. Very few engines can run at more than 8.5:1 compression without detonating. The catch is that this 8.5:1 CR is the running or effective compression (DCR as used here) and that has to take the cam (read--intake closing point) into account. If it didn't, we all might be running engines with 8.5 static and cams that close the intake at BDC. This would severely limit the rpm and power output potential of our engines.

I think you are confusing Cylinder Pressures--which can vary widely due to a number of factors--with this compression ratio. Which is fixed when the engine is built. I do think the word dynamic does create some confusion.

I personally feel that the DCR calculator was a big help in choosing my cam. Either that, or you come here and get others opinions on "help me pick a cam". As far as detonation goes, it's trial and expensive error. My wife's Escort@5 speed, pings on 91 octane. Fat Tony.

66283,

I'm only stating EXACTLY what the mag article said , that was their exact words. I think it's great guys run fast on pump gas, but I hate to see it portrayed as easy. Think about a new hotrodder reading that article then throwing himself together a 12-1 motor and spraying it on pump gas...KABOOM. That's what i hate to see happen to people.

I can't remember exactly, but there was a blue Chevelle with a HUGE BBC from Canada that was wicked fast, was that your car ?

..

I am glad that your engine has held together for you, too bad about the wrist pin. I'm also glad that you have a much better understanding of the internals of an operating Otto cycle engine than two professional automotive mechanical engineers that have built, dynoed, and raced cars for their entire adult lives. You think it is bunk, fine. Glad to hear it. Enough said!

Bunk or not Ryan, I shot for 8.3, overshot to 8.6. And now have occasionally issues which I know I would'nt have had if it stayed at 8.3:1.

But you're right that when adding an oxidizer, it might indeed be bunk.

Great tool for designing a street motor BTW.

..

Ryan, I really wasn't asking your opinion. Seems to me that you have plenty!

..

I didn't "plagiarize" these photos. They were sent to me, along with the text, by an automotive engineer and builder.

..

This goes to show everyone, dont argue with 66 283, or he will attack everything you believe is correct about tuning or building engines. Man I'm glad I dont have a website for him to attack, 'cause I would be next.

66 283, Reher Morrison builds RACE engines, I run a Street/strip pump gas engine, not a race engine. Pats info has been very helpful to me and others who are also running pump gas street/strip engines.

I currently get away a DCR of 8.6:1 with pump 93 but just barely -- same as 427L88.

I optimized a friend's NA 327 last winter for a better DCR and he actually dropped .3 off his ET with a smaller cam. We went from 200cc Iron Eagles and a Comp XE284 to 200cc Pro Topline aluminum heads and a Comp Magnum 282s. He used to run race fuel now runs pump gas.

It ain't bunk . . .

I don't know, but there's a lot of rookies out here like me. We don't have the time, money or resources to dyno-tune our engines. We're not professional drag racers, but we are enthusiasts that want to pick a cam that will fit our combo. We don't want to have hot-rodder illness and accidentally pick a cam that's too huge or way too small for our motor. But we don't have a dyno, so we read books written by men that lived dyno pull after dyno pull and we take what we can from their research.

That's it, its that simple. You can call it what you want it but that's the way hot rodding is. Kudos to the people that have access and money for dyno-tuning as you get the average enthusiast one step closer to where they were before, while still being several steps ahead of them.

Oh, and plug reading- Maybe not all of us have someone to teach us how to read plugs?

Originally posted by red68chevL:
This goes to show everyone, dont argue with 66 283, or he will attack everything you believe is correct about tuning or building engines. Man I'm glad I dont have a website for him to attack, 'cause I would be next. From reading this post, I think he is not attacking, but rather trying to show you that DCR is not a be-all end-all, that it is something fun to play with, and may aid you in cam selection. I see Mike (wolfplace) agrees with him, and I can see his point, theres to many variables.

Wow :eek: , all this from my original one line question.

edited - beyond help.

Eric, I looked up the basic specs on those two heads you mention:

Iron eagle 200cc -> 222cfm intake, 175 exhaust
Pro topline 200cc-> 286cfm intake, 202 exhaust.

The protoplines outperformed the iron eagle peak flow number by .300" lift!

Yes, you can attribute 3 tenths to the magic number! LOL :rolleyes: Like I said - if it picked up THAT much it must have been common sense.

Ryan - I'd like to get your permission to use your picture on my website dragstuff.com and any others you'd like to share. Specifically I'm looking for pictures of plugs that have problems and what caused the problem. Too fat, too lean, too much timing, not enough for example.

I'm working on a new plug reading article with some more samples of plugs showing various issues to try and help people diagnose their tuneups. I've already got quite a few of my own showing Fat and way fat, detentation, etc. I'd like to put together a great article showing a lot of examples.

That one article you referenced has some good points, but Larry does call somethings a bit different than other people do and it doesn't take into account how many pulls/passes are on the plugs.

I think a few of you guys are taking Ryan's comments WAY too personally. What happened to the days when men could discuss or argue things and not get thier feelings hurt. He's not making fun of your wives or kids for God's sake. He is not "attacking" anybody, grow up and wipe the milk off your chin.

As for his comments about DCR, for guys like him who push the window of performance it is worthless. Ryan will spend a lot of money on flowing his heads (not to mention the upfront cost of a set of big Chiefs), researching nitrous to fuel ratios, countless hours on the dyno, etc, etc. For the guy who is far less knowledgable about engine dynamics, who just wants to know if he is probably ok with the cam, compression, etc he wants to choose the DCR can be a useful tool.

.

DCR IS a VALID number. Changes in cylinder pressure throughout the rpm range is one thing, but its still the IDENTICAL exact same number from idle to eighty billion rpm. To figrue dynamic compression ratio, you must first know static compression ratio. From there, figure in your intake valve closing angle. If you have a 3 inch stroke and an intake valve that closes 60 degrees after bottom dead center, you have lost basically 30 percent of your stroke cause ya cant compress anything to any great extent when the intake valve is open. So the calculated dynamic stroke length would be basically 2 inches, not three. If you would rather do it this way, do all the math to calculate static compression, only instead of using your 3 inch stroke(like for a static compression calculation) use your new dynamic stroke lenght of roughly 2 inches(piston dwell at top and bottom dead center and rod angularity will affect the roundness of my numbers, but its close enough to get the point across), and after you do that calculating, you end up with a new compression ratio number that is lower than your static compression, but also a solid unchanging number just like static. This number is dynamic compression and it CANNOT be changed, so all the nitrous in the word added to that motor wont change DCR, itll only change cylinder pressure. This is cause when the engine is running your crank stroke wont get longer or shorter as you run through the rpm range, your connecting rods wont grow or shrink, the piston tops wont change shape, and the intake valve closing angle wont change, so neither will dynamic. The only way it could change is if we are talking about a variable valve timing engine, but were not, were talking pushrod motors.

Its true that cylinder pressure changes over the rpm range, but thats not because of changes in dynamic compression ratio(cause DCR cant change, its a solid number), cylinder pressure changes due to the higher volumes of air packed into the chamber at higher rpm. You could have 5 psi of cylinder pressure at idle with 8:1 DCR and that 5 psi will be compressed 8 times. At peak rpm you could have 4000psi(keep in mind, these are all just random numbers for the sake of comparison) and the 4000psi of air will be compressed 8 times as well(same ratio of compression). But, compressing 4000 psi eight times over is gonna provide a much higher final pressure than compressing 5 psi 8 times. Obviously the volume of air entering the cylinder before compression rises as rpm rises, but DCR dont change, the density of the volume being compressed does so you get higher cylinder pressure numbers as rpm increases with the same compression ratio.

Finally(I know, its long) the reason that its good to have baseline numbers for DCR and everything else is due to the similarities between the average street buildups. Think about it, all of us only have so many different fuel choices at the pumps, your average street bound hi performance cylinder head falls between 180 and 200cc usually for a small block, and they have similar chamber designs, flow numbers, and valve sizes as well. You mostly see hi rise dual plane intakes, 650-750 cfm carbs, similar timing curves between motors, similar header lenght and diameter, and compression that is somewhere around 9.75-10.25 with even similar drivetrains in the average street car. Look at a hundred different 400 horsepower small block chevies and most all of them will fall under these catagories(or very near). With all this including the type of fuel we have available in mind, isnt it fair to say that the average motor that usually falls under these catagories would also like a fairly common amount of compression? And, since dynamic compression ratio is the amount of compression that the engine actually sees when it is running, it is much more of an important number than static compression ratio. And obviously, if your engine doesnt follow these rules, the average DCR number for the average motor wont be optimal, but your motor still follows some set of rules, so there is in fact a particular number for DCR that will be closer to optimial than another number that doesnt quite fit the bill.

Thanks Ryan, I'm sure the pic's will be helpful for many people down the road. Please send the pics when you get them to admin@dragstuff.com.

John

.

No, thats not true. Im not trying to represent what you seem to think is a totally dynamic event with a static number. Dynamic compression and static compression are the same exact thing...they are both ratios of compression, thats all it is. Static compression is the assumed amount of compression ratio that the motor could make if the valves never open, and the piston rises from bottom dead center to top dead center in the bore. Obviously this is a real number. Dynamic compression is also a real number that comes from figuring how much compression ratio the motor ACTUALLY makes based on valve timing events. You are taking the term dynamic to literally, it doesnt mean that is a number that constantly changes in a given engine, its a number that always stays the same, but differs from static compression in that particular engine due to the dynamics of the intake valve closing angle, and that angle always stays the same, static always stays the same, and dynamic always stays the same. The dynamic number will always be lower than the static number unless your valves never open, and the DCR number will vary depending on your IVCA, but once you pick a cam, youve got a number and it dont change, you can make it higher or lower by changing the valve timing events, but once you change it, it is once again set in stone until you change the valve timing again. And no, dynamic compression does not determine octane reqirement along, just like ignition timing does not determine octane requirement by itself, but it plays a part in the grand scheme of things just like every other part of your tuneup and you can have average numbers to go by, cause there are too many similarities among average motors(I covered that before). Let me ask you a question and maybe it will click as to what we are trying to say after you think about it. With your given engine and the amount of nitrous and static compression you run now, what do you think would happen if you put a stock camshaft in that engine, but made no other changes? I do not doubt your skills by any means, so dont think I think you dont know what you are doing, but given your static compression and the volume of nitrous you use, do you think you can tune out the issues you would have with running that much compression and that much nitrous still on pump fuel? Probably not, and the idea is blasphemy to even try something like that unless your purpose is to see how many holes you can make in the oil pan and block and possibly how high a given set of heads will fly into the air under a full throttle nitrous explosion. But what is your opinion on why this would or would not work. I can tell you, that just like you add or remove fuel from the tuneup, add or remove timing to acheive proper cylinder pressure for your combo, adding and removing the length of the intake valve closing angle will also work as a tuning aide for any motor just like every other change you can possibly make to an engine, and to not take it into account is just the same as ignoring your spark plugs on the tuneup......its something you should not do cause it can come back to bite you if its not right. Bottom line, you cant compress anything until the intake valve closes(which is why it closes), and once it closes you compress something at the same ratio every time, and a given octane can only take so much pressure reguardless of the tuneup and dynamic compression is the real deal that has a hand in dictating cylinder pressure so it helps to know a little bit about it. My logic does not say that you can run as much juice as you want on a given octane, my logic is just common sense that says you cant compress anything til your valves are closed shut, and the longer they are closed, the higher the ratio of compression, and in turn, the higher the cylinder pressures will be with no other change to the engine. If the higher pressures dont work out for you, than you now have one new place to look for a change to make it work.

Greg
How is DCR and its effects,affected by weather conditions and valvetrain deflection in relationship to detonation????

Changine weather conditions dont affect DCR itslef. The DCR number itself will stay the same, but what can change is cylinder pressures themsleves along with the change in the quality of the air in different weather situations. For example, standard sea level pressure is 14.7 psi. Lets say your dynamic compression is 8:1 DCR, and lets say you have exactly 14.7 psi of pressure in your cylinder(numbers are for example only, the actual pressure can vary when the engine is in motion even though the outside air pressure is 14.7 or whatever). In this example, as the piston rises, you compress that 14.7psi volume to a volume that is 8 times smaller than its original size. Now, in another example, you still have 8:1 DCR, but you go out driving tomorrow and the temp is a lot hotter, and the air is thinner, holding a lower pressure of 12.2 psi and you have exactly that much in your cylinder in this case as well. So now you are compressing the same volume, but that volume holds a lower pressure. In both cases, pressure will rise as its compressed, but in the case where the pressure that you started with is smaller, it will be smaller after its compressed than the higher value will be after it is compressed. So, even though the final pressure is different in both cases due to just the difference in the air, both volumes were still compressed from their original size by a ratio of 8:1 in turn making them one eighth their original size. See what I mean. The amount they were compressed is still the same, but the final compression number differs depending on all the variables. As far as valvetrain deflection, thats tough to measure cause you have to know how much a given valvetrain deflect, when it deflects, and what that equates to in crankshaft degrees of rotation. It can make a difference, but not enough to worry about. Lifters can make a difference as well. Lets just say for example, your intake valve is just about to touch the seat(maybe 15 degress of rotation away) and your hydrualic lifter collaples, dropping the valve on the seat right now and the valve does not bounce. Since the valve closed earlier, the engine starts compressing sooner, making for a higher dynamic compression number. Thats just a random occurence of events, but do you see what I mean. Lets say your rocker arm flexes under adverse conditions. The rocker flexing upwards from its pivot point will cause the valve to close sooner and that also makes higher DCR. Probably never enough to worry about or measure though, cause if anything in your valvetrain ever flexes enough to make a significant and noticeable change in your valve timing events, something will probably break long before you ever have a reason suspect that the motion of the valves isnt coinciding with the cam spec card. The weather is the important one to consider. If you live in an area with predominantly high temperatures and humidity and high altitude with lower pressures, your engine could tolerate more compression on a given fuel type than the exact same engine could on the exact same fuel that is located in an area with predominantly higher pressures and cooler temps cause of the air density. If the air is not as dense, it takes higher compression ratios to acheive the same final amount of cylinder pressure as the same combinaiton of parts needs with denser air.

.

Dynamic Compression Ratio is probably a poor name for it; a better name might be Effective Compression Ratio. Who names these things? The valve closing timing is certainly important. Do a compression test on two engines with different intake valve closing times. The engine that closes the valve first (same SCR) will have the higher pressure. I think DCR is a useful tool for understanding the relationship of the intake closing to static compression. I think DCR is a useful tool for determining a TUNABLE engine configuration.

WOW!!

Reading right long...

But everybody went right by my 87 octane/11 to 1 CR. info stuff...

pdq67

Sorry bout the punctiation. I was getting a little too into it. Anyways, we are getting somewhere now. First of all, I havent been trying to be mean here, and Im trying not to take anything too personally either. With that said, here an excerpt from your most recent post.

-You do not understand why it is NOT so simple. The incoming charge will have MOMENTUM and the amount of it that will be "stacked and remain in the cylinder" when the valve closes depends on many factors which cannot be reduced to a single number ie efficiency of head, bore and stroke, cam profile, engine RPM. Just because you can calculate where the piston is when the intake valve closes does NOT mean that you will capture the same number of molecules of air/fuel for each cycle.

Anyways, that was the first time that you actually provided some valid info alongside of your arguement. Every other post so far, you basically just bashed the whole concept with no good reasons as to why you feel the way you do, except for "because I said so", and that was not helping the cause.

Just so you know, I completely agree with what you have said in the your last post. It is true that the DCR number wont dictate how much air and fuel can and will enter the cylinder with a given combo. It just determines how much that value is compressed. Here is where the confusion between us may lie. In any motor, you wont know what is going to happen to the density of the volume of air just by changing the IVCA a few degrees. There is no easy way to know whats happening in there before you make any changes. This seems to be the point you are trying to make, and that point is that the DCR number does not matter, because we cant calculate what the difference in air density and volume is actually going to be, even though we know what the new compression number will be right? Well, even though we dont know the actual difference, here is where the problems can arise. Assuming that you make no other changes but to the IVCA, its possible that even with a smaller IVCA you can still pack the same amount of air into the cylinder as before. We dont know for sure, but it can happen. Maybe that is because you had a slightly larger than necessary IVCA for the particular engine. Well, if it happens like that, the volume and density dont change, but the amount of time its compressed becomes longer with a shorter IVCA. This does result in higher cylinder pressures.
Going back to what this thread initially started as, the original poster wanted to know the maximum safe DCR for pump fuel. You think It does not matter, but I still say it does matter, and you can get close. I said this before, but the average street motor follows a pretty common recipe, or guidelines if you will. There are about 5 sets of aftermarket cylinder heads that really get used a lot, and compression numbers and camshaft specs dont vary to a great degree from one hot street motor to another. Because of the similarity in the combos, there is a similarity in how much air any 10 similarly build motors can push into the cylinder. Because of this, their is also a similarity of detonation resistance with a particular fuel. Because of all these similarities, you really can come up with good and safe guidelines for a compression estimate, so there is a fairly accurate group of DCR numbers that do in fact fit into the mold of a particular motor. You might not think so, but it is true, and testing by many experts have come up with good numbers that work well with the dynamics of your average street motor. I provided those numbers earlier on. In a max effort application, these numbers might be no good cause the better top end combo is capable of forcing more air into the chamber than the average street motor, but still, the higher the pressure you acheive witout detonation, the better you run. If you are not careful and push the compression envelope too high, it is very possible that you can put yourself in a position where your engine is not safe with a partucilar grade of fuel and a tuneup for max power. Pulling out ignition timing and adding fuel to the mix to compensate for high compression is not my idea of a good tuneup. Its a crutch for something that could have possibly been taken care of before you ever put the motor together. Anyways, thats about all Im gonna say on the subjet(for now....probably hehe). If you cant see what Im trying to say here, than I guess you just wont see it. I can say that reguardless of whether you agree or not, neither of us are incorrect, we just have different views, and are applying the ideas on two very different levels. You seem to be talking max effort here, but I am talking for the general street guy.

Whats Mike Lewis's opinion about this thread???????? :eek:

Originally posted by 1968 hot rod:
Whats Mike Lewis's opinion about this thread???????? :eek: =

Funny you should ask,,, I was considering weather to post some of my thoughts as I was composing & eatin my popcorn,,, so,,, :D


Ok,,, just to add my thoughts regarding DCR here as my name was mentioned earlier as agreeing with Ryan which I pretty much do but,,,,

Just to be clear, the difference is I NEVER said it was meaningless.

I do not presume to know all there is to know in the universe regarding engines.
Fact is after about 40 years I find out daily how much I don't know.

I have posted at different times my thoughts on DCR as it is used here & here is a couple of them:

DCR or more correctly "effective compression ratio as Dynamic implies something in motion or transition as used in Pat's DCR calculator is a very important part of the equation when it come to cylinder filing,, or lack of cylinder filling but,,,.
There is a bit more to cylinder pressure than just when the intake valve closes.

At low RPM, DCR as it is being used here will suffice when trying to run crap gas with high compression.

But, when you start getting up near peak torque & the VE is starting to climb everything changes & you better damn well have fuel with enough octane to support the cylinder pressures you are making.

This is not as simple as where the intake valve closes, it now becomes, what I feel at least is truly what Dynamic compression ratio is all about & includes where the intake valve closes ALONG WITH how much cylinder filling you have done taking into account all the other factors like how efficient the intake & exhaust system is at a particular RPM, which is essentially what volumetric efficiency or VE is about.

VE is a ratio of how much you filled the cylinder verses what you could have filled the cylinder (100%) at atmospheric pressure & in a well tuned system (or forced induction) can reach well over 100%.
IE: "overfilling"

Here is the rest of the post:

"First let me say I think that Pat's DCR calculator is an excellent tool when used with a bit of common sense.

Here's some of my thoughts about DCR & high compression that I have posted before.

With a big cam you will see lower cranking compression but you also have to use a little common sense with the slam a big cam & lower the DCR syndrome
It may have low cylinder pressure at cranking & low rpm's but somewhere it is going to start getting efficient & the engine is going to see whatever compression you have.
If the fuel isn't good enough when this happens ugly things can & eventually will happen.

My own opinions are that the calculator as a tool needs to be used properly & as I said before, with a bit of common sense.

Unfortunately I feel there just is no set compression for either aluminum or cast heads.
As was stated there are way too many variables.
It would be nice if engines could read all the theory & behave accordingly but it doesn't always seem to work out that way :D

I don't really care what RPM you are at, detonation can & will occur if the fuel doesn't have the octane or is to lean for the circumstances at the time.
This is true of gas, alcohol or nitro.
The heavier the load & the lower the rpm the more likely it is to detonate but it can happen at 8000 or 3000 if things ain't right.
As for hearing it on a dyno, you usually will not unless it is really bad.
You will probably see it if you happen to be measuring crankcase pressure & you will see it in the torque curve when the power goes to hell again if it is bad.
The exhaust temps may or may not go up & sometimes they will go down.
The best deal is the in cylinder pressure measurement stuff that is available but it starts around $25-30,000 for one cylinder,,,,

Short of that, it pays to keep an eye on plugs & start on the rich side with conservative timing just like at the track.

I used to drive a blown alcohol dragster & you would not hear detonation but you would hear & feel the engine "lay down" & it was a good idea to consider getting out of the throttle at this point if it wasn't a race ;)
This was usually on the top end so the rpm was definitely on the high side as this thing went through the lights well over 10,000 rpm.

If the plan is to use & lean on your engine with pump gas most of the time I would prefer to limit the static compression with aluminum heads at 10.-10.5 for 91 octane & 10.5-11 for 93 & change the cam accordingly.
There are combos that can & do run higher & some that will not tolerate this much but I feel the risks far outweigh the advantages of pushing the limits with compression.

You are right in that cranking compression which is part of the DCR is determined from when the intake valve closes.
The higher the static compression, the higher the cranking compression will be the sooner you close the intake valve.
This I think we all agree on.

Now there is a lot of other things that will effect dynamic cylinder pressure, like VE, RPM, Barometric pressure, cam intensity, engine temp, air temp, humidity & probably a lot of other little things I missed as well.

Here's another thought to screw up the works,,
You can build an engine with say 13.0 & overcam the crap out of it & on paper the DCR will tell you it will run on 91 octane.
The problem comes when that engine gets up in the rpm & becomes efficient & starts actually seeing that 13.0. Now that "DCR number" becomes less of an issue as you are starting to keep pressure in the cylinder & with enough load without proper fuel, it will detonate.

The load part is why lighter low gear cars will usually tolerate more compression than a heavier or higher geared car.

It also works the other way.
We do restricted engines you just could not put a load on at low rpm in most cases.
Small cam hi compression deals like 13.5+ with a cam of say 240 or so @ .050 & at low speeds they will detonate themselves to death if you ain't careful but from say 4000-4500 up they will never see that 13.5 compression as the intake is too small to let enough air in to fill the cylinders :(
Is this enough confusion yet??

Anyway, you are only compressing what is in the cylinder from the time the intake valve closes & this can be completely different depending on a number of things but most of them are listed above I think :confused:

Ok,,, these are just a few of my uneducated thoughts on the merits of just using when the intake valve closes to calculate DCR.

Someone else can pick up the VE, quench, swirl, chamber efficiency & timing issues :D "

Bottom line in my opinion is we are using a term that I at least do not feel is a proper one even though I realize a lot of people including me at times have used it
I feel that Dynamic Compression Ratio would more aptly be named "effective compression ratio" as this is what we are usually discussing here, the effect the intake valve closing has on compression.

In reality I suppose it is just a matter of semantics' but as I said before, Dynamic implies something in motion or transition & I feel this is what Ryan is referring to,,,, as do I,,, usually.

I agree completely, a bad term. Over the next couple weeks I'm going to change the program name and all references from DCR to ECR. That might get rid of some of the confusion (while creating some during the transition smile.gif ). I noticed you use Dynamic Compression (without the Ratio part) in many places. I think part of the problem is the ratio part of the term, which cannot be change while the engine is running but the amount of fuel compressed while running can change. This is what is confusing. All the factors you mentioned, VE, quench, swirl, ect. are part of the dynamics of a running engine and have a huge part in the cylinder pressures created in the engine.

I think the name "dynamic" is a poor word choice. AZCamino has better name in that 'Effective compression ratio' is more appropriate. Cylinder pressure will build up when the intake valve closes.

DCR really only applies to engines that are not running power adders like nitrous or forced air induction (blowers or turbo). It is a basic base point to begin with for us less experienced for getting a feel of what may work or may not. I do feel that too much focus is put on DCR and not the whole combination.

Just because you have found a cam / crank stroke /rod length/ piston combo that has a DCR of X.XX does not mean that you do not have to do any tuning or planning. You could get the ideal DCR and still have a terrible turd of an engine. Why, because the devil is in the details. A large quench height, improper jetting of carb, wrong secondary spring choice, timing, camshafts that do not work in the rpm range you want, etc. These all reduce the potential of an engine. I think this is what 66 283 is talking about

I tuned my 406 on the dyno. It was a great learning tool. I could see the fuel ratio and change the jetting for optimum power, see what changes in timing did, experiment with spacers. But if I did not have done the tuning on the dyno, I would be doing it on the road. Reading the plugs, trying different secondary springs, changing timing, etc.

P.S. 66 283, you did not kill the bunny, you only hit the leg. I saw that 3 legged gimp running across the road yesterday. ;)

OK!! Great..

Gonna start using ECR from here on out, if I don't forget and use the old DRC term???

My 2 cents in here too..

I figure the reason a light car can tolerate more ECR is b/c being a lighter load to be moved, the crank can accelerate away from TDC faster which, imho, gives less time for detonation to rear it's ugly head.

A dump truck pulling 8 tons of rock up a hill at 3500 rpm has to constantly work, pushing the crank around b/c the crank doesn't want to accelerate down the cylinder, therefore the sucker will detonate more under load b/c it's taking longer to push it down away from TDC!!!

How's that for looking at that part of this???

Anyway, GREAT THREAD EVERYBODY!!!

Yes, I tend to be conservative and don't max. out my CR. b/c of poor gas and good gas costs in general. Plus only use it as a sim. program like D2K and DRAG by watching the trends b/c I am no expert at all when the motors get maxxed out..

But am sure glad there are guy's around with alotta more experience on this then me AND like to share their thoughts on it..

pdq67

One of the things I have found to be of interest is the calculated displacement given the valve closing event. Effective Comp Ratio aside, when you look at some of the figures, it hits home just how much displacment is given up with a long cam.

Here's a CAFE study with some interesting graphs of wave pressures in an engine:

http://www.cafefoundation.org/aprs/EPG%20PART%20IV.pdf

BOY :eek: Are you guys analytical or what.I have to wonder for what these guys are doing is it really necessary to get this scientific. All the professionals will offer these thoughts on ECR....BUT IN SIMPLE TERMS from my experience keep static to 10.5:1 and cranking pressure to 180lbs or less and you should be fine. That being said I agree with Mike and Gregs data smile.gif

He, He!! Joe...

I thought the same thing about that artice AND I'm an ME!!

BUT I am glad somebody know's what's going on better then me..

pdq67

He, He!! Joe...

I thought the same thing about that article AND I'm an ME!!

BUT I am glad somebody know's what's going on better then me..

pdq67

Ooop's sorry for the double post...

My bad.. I tried to put the l in article and didn't make it is all.....

pdq67

pdq67, you and your dump trucks! ;)

I'm sure DCR figures can be related to proven Octane requirements on basic engine combinations, but I'm also sure the top professional race engine builders using uncommon trick flowing heads and uncommon cams, pistons, strokes, etc. have seen radical DCR figures that work well despite common disbelief. Burn rates, exhaust scavenging, cylinder head flow, engine temps, etc. all factor in on how an engine runs and when detonation will set in. And I think maybe that is what 66 283 was trying to say. For the average Joe choosing parts, calculating DCR is a very handy thing. JMO- I'm not a professional engine builder, for sure.

Great info...Thanks Mike, after all these years(not that many) with playing with 'DCR' and knowing that VE plays an effect, the light finally came on. I think I have found the cause for a few detonated to death engines that according to the calculators should of been fine.

"It may have low cylinder pressure at cranking & low rpm's but somewhere it is going to start getting efficient & the engine is going to see whatever compression you have.

Hey baddbob71, thats it basically. 66 283 was definitely talking about your not so average and ordinary, trick race motor. But, I have a feeling the original poster that started this thread was not. You gotta read between the lines a bit. I mean, a lot of the guys that come on any message board and ask for advice(like me as well) are often looking to build a fast car that can do double duty at the track or regularly on the street If Jeff K was in the process of building an 8 second 1/4 mile car, I doubt his biggest question would be about DCR. Thats why you gotta read between the lines. I figured that like many of us, he wanted to put together a good motor that runs fast with common, off the shelf stuff, and not end up having any big probs in the end. So, I gave common examples that do work well in this sorta environment. For some reason though, 66 283 seemed to be completely stuck on his experience for what he probably normally builds(trick, real fast motors), but unfortunately, thats not what were talking about and I dont know why he didnt want to see that. It seems that he was the only apple in the pear tree in that arguement, if ya know what I mean.

I am glad you guys have everything all figured out!

gross generalizations + democratic consensus = fact. :rolleyes: To hell with common sense.

Next time I have a technical decision to make I know where to ask.

If nothing else from all of this, I learned how to properly read a spark plug! Thanks Ryan for correcting that.

Been gone a couple days -- wanted to respond to this

Originally posted by 66 283:
Eric, I looked up the basic specs on those two heads you mention:

Iron eagle 200cc -> 222cfm intake, 175 exhaust
Pro topline 200cc-> 286cfm intake, 202 exhaust.

The protoplines outperformed the iron eagle peak flow number by .300" lift!

Yes, you can attribute 3 tenths to the magic number! LOL :rolleyes: Like I said - if it picked up THAT much it must have been common sense. Your flow numbers are way out there (ie: WRONG). The Iron Eagles flow 234/174 @ .500 according to CHP site and slightly better than that after a good valve job when tested locally. The ProToplines flow much less than you claim at the lifts we are talking about. Yeah right, 286 cfm :rolleyes: even ProTopline doesn't claim that -- 260/186 @ .500 is what is on their website. You bet the better heads helped, but the key is he went from RACE FUEL to PUMP FUEL in the process of making the change.

The iron headed combo needed either less compression or more cam to run pump gas. The Pro Toplines are aluminum and would run pump gas at that compression. Its that simple.

I don't credit "the number" for the improvement and if you are going to attack me or anyone else here you ought to at least get your facts straight.

http://smileys.smileycentral.com/cat/4/4_15_3.gif

:"Originally posted by Eric68:
Your flow numbers are way out there (ie: WRONG). The Iron Eagles flow 234/174 @ .500 according to CHP site and slightly better than that after a good valve job when tested locally. The ProToplines flow much less than you claim at the lifts we are talking about. Yeah right, 286 cfm :rolleyes: even ProTopline doesn't claim that -- 260/186 @ .500 is what is on their website. You bet the better heads helped, but the key is he went from RACE FUEL to PUMP FUEL in the process of making the change.
I don't credit "the number" for the improvement and if you are going to attack me or anyone else here you ought to at least get your facts straight.You are a jackass for making these ridiculous claims of 3 tenths with only changes in your DCR and then not posting any specs to back it up to begin with... (you called it 4 tenths on camaros.net and 2 tenths on dragraceresults so what was it REALLY?

I searched again - want to compare them at .500" lift:

The iron eagles are 222 @ .500" lift link said Flow specs are from Dart's website as of 01/08/04 and are out of the box flow numbers.

What I found really interesting is that a quick search revealed that YOU flowed them yourself and got 220 but are quoting magazine numbers? :rolleyes: :D Funny how you use whatever numbers suit your purpose! The NEW iron eagles flow more - so your buddy took off brand new iron eagle heads or the ones you flowed? You were posting about them in 2001 so somehow I think you were twisting the facts...

http://smileys.smileycentral.com/cat/4/4_15_3.gif


8/10/2004, camaros.net
Eric68
PS. we flowed a set of 200cc Iron Eagles once and they were WAY off . . . after a 3 angle valve job they flowed right about 220/180 at .500"...

The prolines from their website are 260.51 @ .500". I guess 40 cfm = same to you.


"The iron headed combo needed either less compression or more cam to run pump gas. The Pro Toplines are aluminum and would run pump gas at that compression. Its that simple."
Based on what? Your experience? Or your magic DCR number? Did you actually tune for the fuel? And I don't mean tuning on desktop dyno. You see, there are these things called spark plugs... oh, nevermind. You said NO RACE ENGINES so it must not be worth tuning.

"At THAT compression." At WHAT compression? Another detail left out intentionally :rolleyes: You also went from a very old grind 236/236 @ .050" to a modern 240/246 @ .050". Now that wouldn't make any difference either. :rolleyes:

Just because it might like less timing on pump doesn't mean it won't make power. Of course you know pump gas burns faster and can make more power if you don't need the octane.

You have wasted MORE than enough of my time comparing apples to watermelons and contradicting yourself so I'm OUTA HERE. Insert your witty response here and I'll clap in advance.

graemlins/hurray.gif

:D

Reading these posts is great entertainment :D I get a grin again and again......even though I may accept the theory that Greg and Mike share I've never applied it myself but sometimes there are guys that just have a sixth sense for this stuff and do just as well as the textbook guys :D

Originally posted by joespanova:
Reading these posts is great entertainment :D I get a grin again and again......even though I may accept the theory that Greg and Mike share I've never applied it myself but sometimes there are guys that just have a sixth sense for this stuff and do just as well as the textbook guys :D =
Hey Joe,,,,
I think you need to reread my post if you think I am in complete agreement with Greg :confused:

I don't think you have ever seen me post on the merits of using just the intake valve closing event to either build an engine or pick a cam for a particular engine to keep it out of detonation,, rather what I have normally said is what I feel is a reasonable static compression ratio for most street combinations & the reasons for not using just the DCR number which is also if I am not mistaken what you posted a few posts back in very simple terms that I do happen to basicly agree with ;)

But I am certainly glad to hear I am helping to keep you entertained :D

Weight and gear ratio makes a huge difference in what compression ratio you can run. My dodge V10 three quarter ton truck weights 6700 lbs. With 3.55s it pings going up hills on 87 octane unless I turn off the overdrive. My truck has less than 8:01 compression. Where I live the altitude is 6000 ft.

Ok, Im just wondering what some of you guys will have to say about this. First, of all, I never claimed to be the super-expert on this topic. And second of all, I understand how the other variables come into play and never would say that DCR is the end all be all. We are obviously not going to change each others mind, but I think this deserves a look anyways. L

Lets look away from DCR for a minute and take a look at static compression numbers cause people tend to agree with those more anyways. Pick any bunch of camshafts, mechanical, hydraulic, its up to you. Now, crane cams and isky cams websites(just an example) both have all the cam spec card numbers right in front of you. And along with the cam card specs, they also reccomend numbers for what static compression ratio they think you should use for the particular cam in question. I picked a bunch of different cams at random from both cam makers, all from stock street to somewhat radical camshafts. The tamer cams reccomed between 8:1 and 9:1 for example, and the more wild cams reccomended between 10.5:1-11.75:1 compression for example.

Anyways, maybe I am wrong, but I assume the compression estimates they give with the cam card are good guidelines to use if you arent sure yourself. And since all the cams I picked had specs that would be common in different levels of street engines, Im sure the static compression estimates were also provided with the average street motor in mind(only makes sense right, cause thats probably the environment the cam will be used in).


Now we will go back to DCR for a minute. This is where you guys should try it yourself just to see what I mean. Pick out a bunch of different camshafts, and then plug in the numbers for the motor of choice(I used all small block 350's and 400's in my own tests). Anyways, when you plug in the numbers in pat kelleys calc, be sure to make the static compression for the imaginary motor equal the highest estimate for static compression that the particular cam grinder reccomends using with the cam in question. So if it says use 9.5:1-11:1 static compression with said cam, make your motor show 11:1 static compression in the calculator(highest reccomended amount of static comp). Next, get the specs for that camshafts intake valve closing angle and calculate DCR with your imaginary motor. What you will find is that almost every cam using the maximum reccomended static compression(from the cam maker) falls almost exactly at 8:1 DCR every time, which Ive heard is a good safe limit for iron heads in most applications(once again, iron heads are pretty common items on the street). Some were a tick over 8:1DCR, but still less than 8.2:1. Im sure there are some exceptions too, but I didnt find any.


So, I have no idea why the cam grinders reccomend any particular amount of static compression to use with a particular cam. Maybe its common sense, educated guessing, real world testing, who knows but I bet there is a reason. Reguardless of the reason, it just so happens that if you do choose to follow the reccomended guidelines imposed by the cam grinder, those static compression numbers end up creating a DCR number that falls right in line with what seems to be the safe norm for DCR in a street motor. Maybe its an accident, and maybe its not, but it kinda seems to me that for the AVERAGE street motor that the average guy would build, their is a little bit of a common ground that you CANNOT avoid IF you simply follow the cam grinders guidelines for static compression. And, I bet the average street guy trying to build a good, trouble free motor will listen to their cam grinder advice and use the reccomended static compression numbers for said cam. In turn, also creating DCR numbers that are very common. So, if you are not sure and you do the smart thing and follow the rules for static compression imposed by your cam grinder, you cant get away from common DCR numbers even if you want to. I would hope that the guys who grind our cams know more about a camshaft than I do, and it seems that their are trends in their numbers probaly created by the grinder.

For those of you who disagree with me thus far, I would like to hear what you have to say. If by chance you say that the numbers come out this way because most people dont take the time to really get into the motor and tune it to work, and that these limits are imposed to keep the average builder safe, you are exacly right. Its not uncommon for the average street engine builder to know how to put his motor together and maintain it to an extent, but not really have the facilities or skills to really do a top notch tuneup all the way through. And for this reason, safe guidelines are implied for static compression ratios by the cam makers to keep their customers happy. And following those static comp guidelines also just happen to create those safe and common DCR levels based on the valve timing specs of whatever cam it is were talking about. Do you now see that I am merely trying to show that their is a little bit of a trend out there that people are following even if they dont know what DCR is. You still may not agree and thats fine, but for what I am trying to say about the AVERAGE street motor, it seems that I have crane and isky on my side so far in every example I tried myself. Maybe they are confused like me and dont realize that no one person knows more than another about an engine, and that everyone is completely capable of tuning a motor as well as the next guy.


I dont think its an accident, or a magic number at all. If it is, they are at least consistent with their mistakes. It seems to me that the cam grinders probably have a good idea of how much air/fuel their cam(s) can move in the reccomended rpm range, running in the average motor that they are intended to be in. So I would think they taylor the valve timing events to create a safe environment for the average fuel/air mix that they presume should occur with the cam(s)in question, running inside of the presumed engine in question(part of that environment is the DCR). Maybe it is an accident though that the numbers come out the way they do almost every friggin time, but its hard to be that consistent when your not tryin.....hint hint. This post started with a guy who I think probably wants to safely build a fast street motor and I was doing my best to take that into account. I dont think anybody ever said weight and gearing and everything else just dont matter, so go with the number. No, thats not true, all these things do matter a lot, and that is why I said go with the lower numbers cause the cam grinders themselves grind em that way to have a large margin of error. If you hate the idea of DCR and dont want to think of it that way, when you pick a camshaft, go with the most suitable static compression numbers if that makes you feel better. But I gotta tell you, by doing this you will still accidentially end up being at or below common, safe DCR numbers almost every time unless you get a custom ground cam cause it dont seem that they make many that dont fit the mold right off the shelf.

OMG, I know said I was done and that this is getting petty - but then I found this little jewel:

eric68, drr.com 1/18/2004
My friend's 327. 8.48:1 DCR, 10.8:1 static. Went from iron heads to aluminum the same time as the cam swap and picked up .5 in the 1/4 mile.Now you have said your friend's car as a result of this magic DCR picked up:
2 tenths on an old drr post
3 tenths yesterday on chevelles.com
4 tenths on camaros.net!
5 tenths the post above!

And quoted the highest flow numbers you could find for the latest iron eagle heads when you had the actual flow numbers all along?!

And sorry greg - nobody is reading your long winded philosophical posts. You registered this month and I've been here since 2001 and I think you have written more words on here than I have! :eek: Why don't you call Reher Morrison or Pat Musi or Scott Shafiroff and see if they use DCR?

Jeez. 66 283, cant you just realize that we are not all up to your level of expertise(that is not a bash either, Im being serious). Most of the guys who are working to learn enough and afford enough to hopefully stick their cars in the 12's are not working a day job building motors for Pat Musi or whomever else. Of course maximum safe anything does not matter to these guys. If it blows up, grab that one off the stand. If that one blows up, get this one out of the box. If this one blows up too, get that one in the corner. The rules are different when youve got the time, money, and facilities to make whatever you want happen. I would not expect you to ever be able to know what I know about things that I do in my life that you never have experienced. Or at least have limited experience with. For example, air traffic controlling. Unless you are doing it now, you probably dont a whole lot to say to me about it that I dont already know. If thats the case, I would not fault you for not knowing about the field like I do. Many people dont know motors like you do, and cant tune like you can, and probably dont have a facility like yours. So for them, its best to take the safe route cause they cant just put something together on a whim and make it work every time. So once again, their are safe limits imposed, and I mean imposed, the cam grinder does it for you under the assumption that you dont know any better. Read my above post and you will possibly see what I mean by that last statement. If you dont like it at all, than thats just how it is, but I think you will at least start to get where Im coming from with all of this. Or maybe not. And by the way, Pat Musi's career could be based on dynamic compression ratio but he wouldnt tell you that cause you'd yell at him, and he doesnt need that.

You know 66 283 again you have your data F'd up. We went from the XE grind to the Magnum not vice versa.

You keep trying to distract from the point with your irrelevant arguements and attacks about flow numbers and ETs.

And once again you are missing the point which I so nicely put in BOLD for you on my other post. We went from RACE GAS to PUMP GAS which is what this whole thread is really about.

Easy, easy, easy, guy's!!

Heck, we're all just supposed ta be having fun here!!

That's why Ed isn't around... AND I'm still a fan..

pdq67

Mike, my comments were not directed at you :D I think it should be obvious that Greg is just explaining the principles of a theory that is a tool to use in addition to the other resources that an individual my have access to, including the individuals own experience.I dont really understand why there is a debate over this issue :rolleyes:

Originally posted by greg_moreira:
What you will find is that almost every cam using the maximum reccomended static compression(from the cam maker) falls almost exactly at 8:1 DCR every time, which Ive heard is a good safe limit for iron heads in most applications(once again, iron heads are pretty common items on the street). Some were a tick over 8:1DCR, but still less than 8.2:1. Im sure there are some exceptions too, but I didnt find any.
Greg, that's good information. Thanks for crunching the numbers.
Ken

Originally posted by Eric68:
You know 66 283 again you have your data F'd up. We went from the XE grind to the Magnum not vice versa.

You keep trying to distract from the point with your irrelevant arguements and attacks about flow numbers and ETs.

And once again you are missing the point which I so nicely put in BOLD for you on my other post. We went from RACE GAS to PUMP GAS which is what this whole thread is really about. I will say it again - his original combination would have gone quicker on pump gas if you had a clue how to tune. (and no, desktop dyno doesn't count). Your claim to fame - running 11:1 on pump gas? I ran more 15 years ago with iron heads back in high school and I know others who run over 12:1 on 91 octane.

You are avoiding the fact that you got caught in your lies about the flow numbers and the ET. Why? :rolleyes:

You are a nobody and a detriment to others - over 10,000 posts on this site and others making yourself out as an automotive authority while regurgitating internet advice to others about things that you have never done for yourself.

And many others here - you are guilty of being lemmings, blindly believing much of this bunk and accepting it as fact. Would you follow medical advice on the internet w/o asking your doctor?

graemlins/boring.gif I'M heading to the garage now - I suppose you use a computer simulator to get your hands dirty too? tongue.gif

not to mention that he swapped from a hydraulic flat tappet to a solid flat tappet, and he thinks DCR is why it went quicker.

66 283, CLASS act. You are total CLASS. Way to make yourself look cool, build a fast car, insult others . . . good job tough guy.

If you ever grow the nads to have a real technical discussion you come let me know. I'd like to hear why you think the relationship between cam timing events and static compression ratio is so useless.

Speaking of lemmings, Hi Brian!

Ya know , I admit I'm still a newby here... sort of... but in the two someodd years and roughly a thousand posts here I cant recall ever getting involved in a DCR / ECR /SCR / whatever CR thread...

Now you know why.......
-----------------------------------------------

Some like blonds... some like Brunetts...

Some like loud exhausts ...some like quiet.

Some like hyd cams others like mechanical cam...

Some like low gears ..some like to cruize...

Some say tomato some say tomayto....

Gee sure sounds like everything is normal in the world....

So why get all worked up over this..... why not back off and put her in overdrive and cruize for a while ? We all learned something.... take the positive from this and go from there.... getting hot under the collar aint gonna help nuthin....

Cruize.... ya know 180 MPH in 7th gear ..doing oh say 2300 RPM.... pulling 18 in of vacuum.... Listening to some tunes..... :D

A real technical discussion? Similar to the one where your friend the "lemming" over here, explained to you how to set up your spring heights and equalize the pressures? All while explaining the best type of springs to use (if you wanted to) and explaining why installed height readings are critical.

Eric, its rediculas to make 3 changes, then attibute the difference in gas/ET to one thing.

you went from Iron heads to Aluminum, A small hydraulic to a larger Solid, and the heads have completely different cylinder filling abilities, yet you attribute your ability to use pump gas solely to a DCR number?

Not to mention that until you tear down the motor, inspect the bearings and pistons, along with plug inspections after each pass, in all different weather conditions, that you REALLY DONT KNOW if the car is capable of using pump gas safely.

You're the same guy who thinks that torque production under the FLASH RPM doesnt matter. LOL.

Dont they have a different chamber design as well?

you take all my advice, yet have never offered me a compliment, instead insult me on such things as the burnout picture i was proud of, and you wonder why i get irritated with you.

Holy Crap,,, is this still goin' graemlins/sad.gif

Hey Brian,, cool pic, graemlins/beers.gif
missed it in all the "conversation"


Here's one for you LOL
http://wsm.ezsitedesigner.com/share/scrapbook/19/190264/Camaro_1.JPG
Fremont Raceway a long time ago


In my professional opinion,,,,, I think everyone should have no more that 7.9999981 DCR & we should all have to drive Nash Ramblers painted lime green graemlins/boring.gif

http://www.usfamily.net/web/hoffbug/popcorn.gif

Nice!

Mike your a hoot :D Looks like 1970 vintage pro stock.......what was the combo and times...I love vintage pro stock and modified production graemlins/thumbsup.gif

Originally posted by joespanova:
Mike your a hoot :D Looks like 1970 vintage pro stock.......what was the combo and times...I love vintage pro stock and modified production graemlins/thumbsup.gif =

Thanks Joe,

Yea, it ran Pro, A&B/MP, CG & ProGas in NHRA & A&B/HR in AHRA & a lot of bracket stuff too.
Bests were 9.67/139, pretty consistent 9.80's to 10.0's depending on weight.
Engines were 427, 433, 468, 482 at different times.
Weighed about 3350 with me in it at it's lightest.
4 speed, or Clutchflyte at different times & normally 4.88, 5.13 or 5.38 gears.
Tried 5.57's a few times but they kept breakin'
M22's didn't last real long either :(

Can't believe what I did to an original 69 DZ car,,, if I only knew :rolleyes:

Can't really recall the DCR :D

Sorry,,, couldn't resist,,,,

This threads gonna be 160 post long pretty soon. Just when its about done.......hehe

Thanks Mike......those were the good old days :D

You know, I just ran a make-believe, generic, 10 to 1 CR., 327 and 350 through Boost Calculator using a 270, 108/108, .450 hy-cam and I always figured that the best cam to use was just that...

Seems the ECR calculator say's 7.94 and 7.97 which is right at the limit TO ME for a good motor running pump gas..

Funny thing is that there are many, many cams bigger AND smaller but only the 268, 270 and 272 cams that fall in this catagory!! Why in the world would there be so many different cams both bigger AND smaller to choose from if for no other reason so that if you have a motor like these two are and want to run pump gas, if you don't buy a 268/270/272 cam , you will be buying at least two maybe three cams until you do hit that magic cam instead of buying one of the 268/270/272 cams first!!

So the cam companies won't sell as many cams if you believe the sim. program!!

And they sure don't want that to happen or their bread and butter money-maker cams will drop off and profits will drop too..

pdq67

Hmmm... just thinking. Wouldn't the actual dynamic WOT compression ratio be the static CR times the volumetric efficiency at the particular RPM the engine is turning? If so, then the VE tables that the engine simulators spit out could be very useful.