I called Ron to ask him why the Megacams are rated at .007" open /.010" close.

First of all, let me say, Ron is a GREAT guy. He took 10 minutes to talk to me (a nobody) on the phone to answer my question and provide additional info. I was very impressed by the fact that he seems to genuinely care about helping the "little guy".

Anyway, Ron tells me that that is just the way they do it. He said most of thier other hydraulics are rated at .007"/.007", but he said the Megacams are a bit slower closing, so they decided to rate them a little different. He said they ARE asymmetrical lobes.

I told him I wanted to know what duration at .004 and/or .006 was, so that I could make meaningful comparisons to the "other guys" for DCR calculation purposes. He said that the megacams at .007/.007 would typically add 3 deg to advertised numbers, and add another 2 for .006/.006. So basically, .001/deg on the ramp. That means a 270 Megacam rated the Comp way is actually a 275 cam.

Regarding DCR, he said not to get to hung up on those numbers. He said that the amount of air flowing in or out of the cylinder at lifts less than .010" doesn't amount to much, and if you calculate the DCR at .006", .008", or even .010", the engine really won't see that much of a difference based on the minimal flow area. In other words, you still build cyl pressure when the valve is open less than .010", since the "leak" flow area is very small.

He also told me that Isky grinds 3 deg advance into thier cams to account for timing chain wear-in. He said that some amount of chain stretch occurs pretty quickly, and that if they grind it 3 deg advanced, and the chain stretch retards it 1.5-2 deg, it will still end up slightly advanced (though it may be retarded after 90k miles). He said that if you want a 108 LSA cam to actually RUN at a 104 ICL, you better plan on instaling it on a 102.

All-in-all, I found Ron to be very informative, and he was more than happy to discuss this stuff on the phone, without me feeling rushed (and I am sure he is a busy man). Thumbs up to Isky for customer service! graemlins/thumbsup.gif

Originally posted by novadude:
All-in-all, I found Ron to be very informative, and he was more than happy to discuss this stuff on the phone, without me feeling rushed (and I am sure he is a busy man). Thumbs up to Isky for customer service! I know what you mean. I have talked to Ron several times, one time it was for 30 or 40 minutes, on his dime after returning my phone call.

He was the main reason I choose an Isky cam about 4 years ago. Excellent customer service. Talked to several cam companies for info on there cams and they seemed irritated to talk to me. Ron was very helpful and informative.

I think they are hard to beat but for good quality, reliable valve train components. graemlins/thumbsup.gif

Originally posted by novadude:
Regarding DCR, he said not to get to hung up on those numbers. He said that the amount of air flowing in or out of the cylinder at lifts less than .010" doesn't amount to much, and if you calculate the DCR at .006", .008", or even .010", the engine really won't see that much of a difference based on the minimal flow area. In other words, you still build cyl pressure when the valve is open less than .010", since the "leak" flow area is very small.I mean no offense but DCR is a phenomenon that is pretty much only discussed widely on this board due to Pat K's extremely easy to use program and his write up. I think that those who have become familiar with DCR and the calculation programs that are out there need to understand that everyone in the world has not come up to speed with it yet. Also, obviously there are some who are up to speed but don't necessarily agree 100% with the concept, like Ron at Isky. It's good that Pat also wrote the article so that when new folks come to this board someone can direct them to it so they can get some understanding of the concept rather than be lost when the DCR term is thrown around so much.

Pat's calculator is really good guide, but it does not take into account how more aggresive profiles, or race profiles, will generate alot more cyl pressure than a typical street hydraulic profile, even with comparable duration numbers. Nor does it take into account the efficiency of the intake tract. For example a cyl head with a lazy intake port, will not generate nearly the cyl pressure than that of a properly chosen, designed, ported, and otherwise optomized head. JMO

The DCR concept has been floating around a while. In fact I was first introduced to this concept through Vizards book in 1991-1992. I even walked through the tedious calculations. Pat's excellent program makes it easy! smile.gif

Ron didn't say he did not agree with it... he just pointed out that whether you are looking at Crane's numbers (.004"), or Isky's IC numbers (.010"), the valve is STILL OPEN, but probably not enough to flow any significant amount of air. To REALLY do an accurate DCR calc, you'd need to know exactly when the valve hits the seat, closing up the cylinder, and those numbers just aren't commonly available.

Pat's program is a great tool, BUT, it will just get you in the ballpark, which is closer than many will get when they do NOT consider DCR. smile.gif

EDIT: also remember that inertia plays a big role, and this is much too complicated a phenomenon for a simple calc (as stated above about port efficiency).

Originally posted by novadude:
I called Ron to ask him why the Megacams are rated at .007" open /.010" close.

First of all, let me say, Ron is a GREAT guy. He took 10 minutes to talk to me (a nobody) on the phone to answer my question and provide additional info. I was very impressed by the fact that he seems to genuinely care about helping the "little guy".

Anyway, Ron tells me that that is just the way they do it. He said most of thier other hydraulics are rated at .007"/.007", but he said the Megacams are a bit slower closing, so they decided to rate them a little different. He said they ARE asymmetrical lobes.

I told him I wanted to know what duration at .004 and/or .006 was, so that I could make meaningful comparisons to the "other guys" for DCR calculation purposes. He said that the megacams at .007/.007 would typically add 3 deg to advertised numbers, and add another 2 for .006/.006. So basically, .001/deg on the ramp. That means a 270 Megacam rated the Comp way is actually a 275 cam.

Regarding DCR, he said not to get to hung up on those numbers. He said that the amount of air flowing in or out of the cylinder at lifts less than .010" doesn't amount to much, and if you calculate the DCR at .006", .008", or even .010", the engine really won't see that much of a difference based on the minimal flow area. In other words, you still build cyl pressure when the valve is open less than .010", since the "leak" flow area is very small.

He also told me that Isky grinds 3 deg advance into thier cams to account for timing chain wear-in. He said that some amount of chain stretch occurs pretty quickly, and that if they grind it 3 deg advanced, and the chain stretch retards it 1.5-2 deg, it will still end up slightly advanced (though it may be retarded after 90k miles). He said that if you want a 108 LSA cam to actually RUN at a 104 ICL, you better plan on instaling it on a 102.

All-in-all, I found Ron to be very informative, and he was more than happy to discuss this stuff on the phone, without me feeling rushed (and I am sure he is a busy man). Thumbs up to Isky for customer service! graemlins/thumbsup.gif =
Now you know why I like dealing with Isky & recommend them a lot ;)

As I said in your previous post of a few days ago, Ron will usually call me back in the evening at home so we can talk a while without interruptions or using up his valuable time during the day & there are times we have talked for quite a while "on his dime" about these things we like to think we understand & I usually come away the better for it....
Of course he usually comes away with more of my money :D

Good products, good people graemlins/thumbsup.gif

And if anyone is needing Isky products, just email me as I can usually save you a buck or two on them ;)

I have also spoke with Ron on several occasions, and agree that he is a great guy. FWIW, I have one of their 274 mega cams (226@.050, .490 lift 108 lca) and it measures 274 at .010/.007, and 281 at .006/.006, and IIRC, about 287-288@.0045/.0045. Seems to relatively mild on the seat, but pretty aggressive from .050 and above.

Like I said, no offense meant!

Pat's calc. is great along with the others that are out there.

Originally posted by novadude:
The DCR concept has been floating around a while. In fact I was first introduced to this concept through Vizards book in 1991-1992. I even walked through the tedious calculations. Pat's excellent program makes it easy! smile.gif

Ron didn't say he did not agree with it... he just pointed out that whether you are looking at Crane's numbers (.004"), or Isky's IC numbers (.010"), the valve is STILL OPEN, but probably not enough to flow any significant amount of air. To REALLY do an accurate DCR calc, you'd need to know exactly when the valve hits the seat, closing up the cylinder, and those numbers just aren't commonly available.

Pat's program is a great tool, BUT, it will just get you in the ballpark, which is closer than many will get when they do NOT consider DCR. smile.gif

EDIT: also remember that inertia plays a big role, and this is much too complicated a phenomenon for a simple calc (as stated above about port efficiency). Vizard is where I was first introduced to the concept, too. I found his calcs difficult to work with and difficult to transfer to a general formula. I took a different path using trig rather than the percentages he used.

What everyone has said is true. Nothing in it addresses VE, port efficiency, or any of the other conditions mentioned. The calculator was written because so much of the info around, particularity concerning running pump gas in a higher compression engine, was anecdotal. I just made the Vizard's calculations easy to use. When I was testing it, I compared the results to a couple charts posted on Isky's web site. They don't appear to be there anymore but these charts are available HERE (http://cochise.uia.net/pkelley2/ncrank1.pdf) and HERE (http://cochise.uia.net/pkelley2/ncrank2.pdf). These charts give the piston location for various closing angles and rod lengths. Notice on chart "ncrank1.pdf" on the right panel (highlighted line), with a closing angle of 85º ABDC and 5.7" rods the piston has moved up 2.162". My calculator gives 2.1616, which rounds to 2.162", so the calcs are accurate. As for how useful they are, I'll leave that up to others. It really is nothing more than putting a number where speculation existed before. For advance builders, their own experence is their best guide. For novices and casual builders, it can help with matching up a cam to a CR. But throwing 58cc 305 heads on a pop up pistoned 350 then putting in a big ass cam, even if the DCR check out, will still not make a 7500 rpm screamer. As said, there are a lot of other factors to consider.

Oh yea, no offence taken by me. Vizard is the real culprit :D .

He, He!!

(Me and my 305 heads and all. Oh, no! That was Bruce Crower and the big domed pistons...).....

I know, I know... He, He....

Great site Pat!!!

pdq67