.....to push a '71 Malibu hardtop into the 11's?

Try this site ... figure around 3600 -3700lbs with driver.
http://www.race-cars.net/calculators/et_calculator.html

At 3800 lbs and with a chassis that works and traction it will take about 440 HP. The less efficient the chassis and driveline the more power it will take to get there.

Don't put too much faith in those calculators. I ran my car on a dynojet (370 hp). Weighed it on a scale at an NHRA track(Maple Grove) 3880lbs with me in it. Actual ET/MPH 11.92/114. The calculator says I should be making 443RWHP. If I plug in actual weight/RWHP it predicts a 12.70/107mph. Either my car is making more HP than the Dyno jet shows or it is using what it has to good advantage. This probably doesn't help answer your question of how much power to run 11's in a Chevelle.

From what I hear (take that as a disclaimer) automatics skew chassis dyno #'s so much that they are almost useless for telling true power, they are only good for comparing things when you already have a baseline..

matt

Many of the calculators say "RWHP" when in actuality it would be closer to flywheel HP. In any event I have only run across 1 performance calculator that is fairly close.

As another example, my 3600 lb car (w/driver) used to run 7.30's in the 1/8th(~11.50 in the 1/4) with "only" 365 RWHP.

I'd like to build a 550 hp sbc but that's probably gonna take some serious $$

My motor made 440hp@5300 and 500ft-lbs@4000 on an engine dyno and is basicly there. The car is all steel with a full interior. I did run light weight wheels. The calculator says the engine is making 400hp (at the flywheel). A 40 hp loss for the water pump, fan, alt and exhaust sounds about right.
The other piece of the puzzle is making sure you put the power to the ground and I have spent time and money on that part of it too.

I was reading an article in CHP...this kid has a '70 with a 406/TH350 and he's running in the low 12's/mid to high 11's! They said his engine's not been dynoed but it's guestimated to be making 475 hp but I dunno if that's at the flywheel or the rear wheels.

Originally posted by chvl71402:
If I plug in actual weight/RWHP it predicts a 12.70/107mph. Maybe you just had a hell of a tail wind that day at the track? :D
only kiddin' ;)

From what I hear (take that as a disclaimer) automatics skew chassis dyno #'s so much that they are almost useless for telling true power, they are only good for comparing things when you already have a baseline..

matt I agree.. I made 340rwhp, 210ftlbs on a chassis dyno that came to town (His accuracy is debatable)

That weekend I went to the track (Unchanged) and ran 121mph.. Full weight 68 Chevelle..

Chasis Dyno numbers can be all over the place, I agree to only use them as a baseline to measure improvments...

That being said, I'd have to say a 450hp sbc will get you there.. Just get it to 60' graemlins/hurray.gif

Gene

the rwhp numbers and timeslips you guys are throwing around are way off...look at a late model camaro for example similar or less weight...similar numbers but times that are much slower...I know their are other unaccounted factors such as gearing traction etc but the numbers are bogus the calculators are actually more accurate becuase they are using proven physics equations...

Doggy69,

I beg to differ. :rolleyes:

There is only one online HP/ET predictor that has shown to be close. That was at http://www.smokemup.com. That sight now requires registration though. All of the other calculators WAY, WAY overestimate power or call flywheel HP - RWHP.

Thanks to the wonders of bench racing and everyone making 500, 600, 700 HP or more out of 9:1, 350 SBC's it is always assumed that it takes piles of power to run even in the 11's. That simply is not the case. As I stated before, it only takes about 440 HP at the flywheel to push a 3800 lb car in the 11's if the car is properly set up for the track. No if's and's or but's. If traction is not there, or you don't run the right converter, etc. then it will take more power to make up for it.

Look at 68Chevelle533's post. He's already proven it.

Peak numbers also do not tell the whole story. While my old underachieving 383 combo "only" made 365 RWHP it did put down 460 RWTQ. That did help alot in pushing 3600 lbs. to mid 11's. I also ran adjustable suspension components, 28x10 ET Drags, 4.56 gears, and an ATI 8" MRT Treemaster converter.

Look at what a ZZ502/502 runs in a 4000 lb Chevelle - low 12's/high 11's. That has been done over and over. What do those "derived from bogus physics" online bench racing estimators say a ZZ502/502 is pumping out?

Just because a late model that is not set up for the track can't do it doesn't make it impossible. I've raced LS1 Camaro's at the track that trap the same MPH (ie equal power), yet I've crossed the line about 4 cars ahead of them. All the power in the world does no good unless you can put it to the ground.

Originally posted by doggy69:
...look at a late model camaro for example similar or less weight...similar numbers but times that are much slower...It's called aerodynamics.
The late models have less drag and are more efficient than our blunt nosed Chevelles.
Example...my stock '02 C5 convert runs only 13.5x but at nearly 106 mph in the quarter.

Don't look at ET, look at MPH. Biggest indicator of HP. An LS1 making 300-310 RWHP usually runs around 105-108 MPH.

I make 340 RWHP on a dynojet at 3550 lbs and go high 11's.

Jason is right on about most of the calculators.

The Prestage calculator is or was using a formula that is for engine HP. Haven't been there in a while so they might have changed it.
I emailed them twice about it & got no answer so I guess it ain't real important to them. :confused:

Virtual 2000 supposedly gives engine HP I believe, all I can tell you is to do a few calculations & see if it makes sense to you.

If that calculator was right a 204 mph Pro car would be making over 1500 rear wheel HP assuming about 20% loss??

I have posted this before but here it is again & it is fairly accurate for engine HP in the real world.

Here is a little formula that has been around since at least the 70's & was used by Chrysler Corp. in their drag racing program & written up in the American Journal of Physics in 1973
HP=(.00426*MPH)cubed * WGT
I add about 50 HP to the number because MPH is measured differently now than it was in the 70's.
This was brought to my attention by a gentleman who posts on another board & here on occasion named Harold Sutton. (Thanks Harold graemlins/thumbsup.gif )


I find this formula works pretty fair until you get into some of the very hi end cars like Pro Stock. I find with cars like these it will give you a higher HP number than you usually see, especially adding 50HP as they are so efficient.

This formula might be old but I believe most of the laws of physics still apply,,,,,,unless of course you are using that "Good LA air" when you dyno :D :D

Also, remember, your MPH is very dependant on weather at the time of your run & the dyno numbers will be corrected to sea level & good air so you have to take this into account when attempting to compare dyno numbers to real world numbers.

I don't use any of the ET calculators for HP, if you have the MPH, the ET is up to you :D

And in the end,, you need to realize these are estimated numbers,, nothing to get real excited about ;)

Yeah those calculators are WAY off. My bro in laws 69 Chevelle made 330rwhp and 411rwtq on the dynojet. The prestage calculator said he needed 409 rwhp to hit 11.99. Well he went 11.92 at 111.
So just shoot for about 330rwhp on the dyno and get the sucker to dead hook!

You may find this an interesting read
http://www.camaros.net/forum/ultimatebb.php?ubb=get_topic;f=4;t=008471

I wouldnt put any faith in online calculators, i've seen compression calculators that are higher then normal, much higher.

Even most of the calculations in the books dont give an accurate calculation and are typically high.

The RPM for MPH calculators are off as well, even when you adjust for converter slip, they come up low on RPM.

Originally posted by Motor Martyr:
I wouldnt put any faith in online calculators, i've seen compression calculators that are higher then normal, much higher.

Even most of the calculations in the books dont give an accurate calculation and are typically high.

The RPM for MPH calculators are off as well, even when you adjust for converter slip, they come up low on RPM. Brian,
The only way a MPH/RPM calculator will be right is if you are running a clutch car & then negate tire growth.
Put three different converters in the same car & you will get three different readings in the lights.
Change tire pressure or rim/tire combo & it will also effect the outcome to a small degree.
You have to estimate tire growth unless you have some way to measure it.
Guess you could ride in the trunk with a laser & measure the distance to the ground in the
lights :D
When I ran a Lenco the tach & mph were very close if I assumed about 1/2" radius of tire growth which was what Goodyear said was a realistic estimate given the MPH, tire/rim combo & speed.
The reverse of this is you can estimate your converter efficiency by using the approx rpm you should be versus what it actually is.

On compression calculators, a lot do not take into account the actual diameter of the head gasket & most don't calculate the area above the rings which will skew the actual measured results.
Mine does as well as Pat Kelley's now.
The one I use is the same one AERA sends it's members that use their PROSIS software program.
They feel it is accurate enough to recommend it to their members.
It is the Performance Trends one. Very accurate.

What I am saying is that the numbers guys are spitting from there dynos mean ****...simply put...you dont have to believe what the calculators are right..but if they are using the right equations they are dead on...no arguement...but ppl arent always using the right equations and they arent considering traction and other ineffieciencies.....dyno numbers are garbage bc different correction factor make huge power differences....and you should also consider time is not an accurate measure of power due to poor reaction time shift times etc...trap speed is much more accurate and helps account for these other unaccounted for variables...saying that man x runs 11's is great bc he has 350 hp too like a camaro..but he also mentioned he has much more torque you cant just spit out a number and say it will run a time it has to do with the whole combo...bottom line is the calculator's work fine...different power curves,combos, and riving styles make the time..not a set number and the problem....

I agree smokemup's 1/4 mile speed seems to be pretty close to real world horsepower numbers. E.T. predictors seem optimistic on this site. To 71chvl your 370 RWHP number comes to 462 Flywheel with the commonly accepted 20% loss of an automatic/torque converter car(not 443). If you get an unrealisticly low H.P. or torque number on a Dynojet look for slippage somewhere.

The car is using radial slicks, and they dont grow, or its very, very minimal. With an automatic car, i dont think the calculators are accurate unless you play with the numbers.

We had the same findings on the compression, the area above the top ring, and also i think the valve pocket CC ratings in many pistons are not as accurate as i would like.

Originally posted by DragRacer:
At 3800 lbs and with a chassis that works and traction it will take about 440 HP. The less efficient the chassis and driveline the more power it will take to get there. A '71 Malibu HT doesn't weigh that much does it? I was thinking maybe around 3400.

How possible would it be to extract those numbers from a 350? I know a good set of heads/cam/intake/exaust would be in order.....what else am I missing?

Harold,
Your right. I checked the MPH calculator at the smoke em'up site and it seem to give numbers very close to what I have seen in the REAL world. 114mph in my 3880lb car is 380 rwhp. That is with 22% drivetrain slip. Making about 460-480 at the crank, depending on the slip and weather parameters I use. I believe that to be accurate.

Check out the new HotRod magazine.Its gotta good article on chassis dynos & how they work.
I recall one sentence where it says something about the ratchet tie-downs.
"one extra click on the ratchet tie-downs was worth a 10HP loss"(or something like that) graemlins/clonk.gif