[wolfehunter]

I read in another post that a horsepower estimate can be given from trap speed and was wondering what my engine might be pushing out. I ran 100.3, 100.4 and 98. something the 3 times I ran my Chevelle in the quarter this summer. It weighs a little over 3900 with me in it(getting a belly!). Or do I need to furnish more info?

Thanks

 

[blown70]

http://www.angelfire.com/fl/procrastination/quarter.html
Calculate all you want...

 

[67RS502]

that calculator is way off...
it says my motor is makin 719hp - yea right!
it dynoed at 626hp, thats almost 100hp off.

The HP formula is:
HP=(mph / 234)cubed x WT.

 

[smitty454]

I dont think I have 269 HP from that estimator. At least I hope not. I did that formula too but im bad at math and I know I dont have 560 hp either.

 

[blown70]

that calculator is way off...
it says my motor is makin 719hp - yea right!
it dynoed at 626hp, thats almost 100hp off.

The HP formula is:
HP=(mph / 234)cubed x WT.

OOPS!Yeah that ain't no good!...Unless your bench-racin'!

 

[wolfehunter]

So the fromula HP=(mph divided by 234) cubed x weight comes out to 308 HP if I did the math correctly. Is that at the wheels? My engine builder told me that I should have 1 HP per cubic inch and since my 402 was bored out to 408 I was hoping for a little higher number. I'm sure he meant at the crank so is there that much of a drop in HP until it hits the wheels?

 

[GRN69CHV]

Scott,

Last summer ('04) when I made some runs with my 408 I ran similiar MPH. Using the calculators it put me in the low 300 - 330 range. This is net HP with all accessories as installed in the car for the air temp of the day with all HP loss including trans, gearing, etc. - really gets eaten up. Also, keep in mind, a lot of it has to do with where the motor RPM's through the traps. A 400HP oval port 408 motor is probabaly making peak power in the 6000 RPM range, but if the motor only sees 4500 at the traps due to gearing, you are not going to go through the traps at peak HP, the difference could easily be 50HP.

When I was serious about racing, first thing we would do is establish the MPH / ET we targeted, then take into consideration the motor & veh wt.. Last thing involved was the gearing. As we played with motors, the gearing would get changed to suit. 5.38's to 5.13's, finally to 4.88's. A typical 408CI street combo might run 3.73's with a 28" tall tire (that's what I have anyway). This motor really needs about a 4.56 to run correct in the 1/4. Peak HP in top gear should occur right at the trap, otherwise the car is not accelerating the entire length of the 1/4. Take a look at one of the speed/mph/hp calculators [check out www.tciauto.com, racing calulators]. Plug in your info and see what the gearing/rpm combo should be.

 

[66ElkyBB]

My 1973 Peterson Publishing Power Sliderule says approx. 320HP from 100mph and 3900 pounds.

My 1975 Pocket Dyno book says 301HP.

I believe these are power figures at the rear wheels pushing your car through the traps.

 

[67RS502]

Why would they care about rear wheels in '73 or '75?
This is gross engine power.

 

[Wolfplace]

My 1973 Peterson Publishing Power Sliderule says approx. 320HP from 100mph and 3900 pounds.

My 1975 Pocket Dyno book says 301HP.

I believe these are power figures at the rear wheels pushing your car through the traps.

=
This is engine HP Not RWHP. It is also the HP you had under those conditions not corrected to sea level.
I don't care what most of the on line calculators tell you, they are incorrect.
Here is an old post I have done probably 20 times:

The info has been around forever & is still valid within reason,,,

Most online calculators supposedly gives RWHP 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 a generous 10% loss we are talking almost 1700 engine HP????

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 used to add about 50 HP to the number because trap speed is measured differently now than it was in the 70's but Harold Sutton posted this multiplier a while back.
I got the multiplier from the Meaux Racing Heads site and think it's pretty good. It is (1.072 x the new MPH = the old MPH),
which is probably a lot more accurate given where it came from.

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.

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

 

[Harold Sutton]

Why would they care about rear wheels in '73 or '75?
This is gross engine power.

I think your right Rafel, it's most likely flywheel horsepower. My power speed calculator showed a little over 300 H.P., something like 305 or so. I find the best calculator to be the one at Smokemup.com and only use the speed one as the E.T. one is way optimistic.
Before recent upgrades my son car made about 825-830 H.P. and ran a best trap speed of 140.27 on the motor and made 646 RWHP on the Dynojet. I find that both ends of the horsepower calculation formula seem to be a little off. That speed formula with an automatic transmission works best if you substitute 230.5 for the 234 figure. The 234 figure seems O.K. for a standard transmission so i guess the difference is slippage in the converter.

 

[Harold Sutton]

=
This is engine HP Not RWHP. It is also the HP you had under those conditions not corrected to sea level.
I don't care what most of the on line calculators tell you, they are incorrect.
Here is an old post I have done probably 20 times:

The info has been around forever & is still valid within reason,,,

Most online calculators supposedly gives RWHP 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 a generous 10% loss we are talking almost 1700 engine HP????

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 used to add about 50 HP to the number because trap speed is measured differently now than it was in the 70's but Harold Sutton posted this multiplier a while back.
I got the multiplier from the Meaux Racing Heads site and think it's pretty good. It is (1.072 x the new MPH = the old MPH),
which is probably a lot more accurate given where it came from.

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.

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

Wolfy, you missed the other zero again. ( New MPH x 1.0072 = Old MPH). Your definately right about the formulas not being too accurate at the high end of the scale as they are a couple hundred horsepower high on the upper end of the scale. Low on the bottom and about right in the middle horsepower numbers. I did the Chevelle in the first post, after converting the MPH, and came up with 311.7 H.P.

 

[littlehop]

How accurate is these formulas http://marylandperformance.com/calculator.html

 

[Harold Sutton]

How accurate is these formulas http://marylandperformance.com/calculator.html

It appears that the one being called rear wheel is actually flywheel H.P. within about 5 H.P. and the other one is a daydream.

 

[67RS502]

Wolfy
I was wondering when youre gonna jump in, and set things straight - again...

Harold
Glad to be on a board that you post on again, did you see my excuse
to start posting here, its on my webpage - old Gomer (the gold one)

Think of it this way guys. Its a simple formula that some engineer came up
with, which takes into account mass, distance, speed, and HP. There can
only be ONE right formula, not 20...
If a Nasa scientist was trying to figure out how much thrust it will take
for the shuttle to clear the atmosphere, he would have to know the mass,
distance, speed, gravity for a simplified formula. Once this was figured out, he
could make a "simplified" formula for thrust needed. There wouldnt be 20
different formulas that told him he needed anywhere between 1000 - 10000000
lbs of thrust now would there. Its all simple math/physics.

Just let Wolfy explain it a few more 1000 times to everyone on the internet,
and I'm sure they'll get it right one of these days. Looks like your gonna be
busy for the next few yrs Mike

 

[GRN69CHV]

I can still remember an article in one of the mags (way back now), entitled "Where does all the horsepower go?". THe negative power per acessory was incredible. Something like 10HP per belt. toque converter, auto trans, driveshaft, underhood air, exhaust system. If you have 5 things that take 10 HP each to dirve, that's 50HP down the tubes.

 

[Wolfplace]

Wolfy, you missed the other zero again. ( New MPH x 1.0072 = Old MPH). Your definately right about the formulas not being too accurate at the high end of the scale as they are a couple hundred horsepower high on the upper end of the scale. Low on the bottom and about right in the middle horsepower numbers. I did the Chevelle in the first post, after converting the MPH, and came up with 311.7 H.P.

=
Damn your picky,, it's only a zero

Thanks Harold,
Don't know why I keep forgetting the extra zero :clonk: I'll go rewrite my draft so it's in there

Hi Rafal :waving:

 

[Harold Sutton]

=
Damn your picky,, it's only a zero

Thanks Harold,
Don't know why I keep forgetting the extra zero :clonk: I'll go rewrite my draft so it's in there

Hi Rafal :waving:

Hi again Wolfy, Just picking on you a little. We're both getting old so we have to keep each other straight. Glad to see Rafel on here again as i've changed internet providers and haven't "e" mailed anyone for quite a while. My old one dropped his service and now i've picked up net zero. My new address is [email protected]. At least i think that's it. Nice to see you'all again Wolfy and Rafel.

 

[69-CHVL]

Did anybody have the combo dynoed and then run at the track, and then try one of these formulas to see how accurate they are?

 

[mr 4 speed]

Did anybody have the combo dynoed and then run at the track, and then try one of these formulas to see how accurate they are?

I believe Chris "cmt454" dynoed his motor at 490/HP 530 ft./lbs. TQ @ the crank and the car went 12.81 @ 107 MPH

We both had almost identical combos,except his cam is installed 4* advanced(mine is straight up) and his has the 2.19/1.88 valves and I have 2.06/1.72
We both had the same gear/convertor

My MPH is 105.7 but I never dynoed my motor