HP to ET Math question

[tes87gn]

Ok here is one for a little fun for all you number crunching gear heads out there. How much Horsepower does it take to run a certin ET. Ex. ( not accuate/ stock GN NO mods rated at 245 HP avg. track time 13.8 to 14.5 depending on track conditions ). So to say approx 250 HP will get you to high to mid 13's. Now as ET times get faster it seems Horsepower ratings rocket as compaired to ET times slowly go down. Seems 100 hp at a time to shead tenths off track times. So does anyone have a basic formula to figure these values now I do know that the figures are somewhat inaccurate due to track conditions tires( radials, drag radials or slicks) 60ft. times, powertrain resitance, the tune of the car ect. , ect. , but i know that there has to be some basic equation if keeping some varibles a constant for simplisity sake. Ex. to go 12.0,11.0,10.0,9.0 it would take X amount of power. I know this may seem to be a dumb drawn out quetion to some but it's something that just came across my mind while working on my car the other day. Happy calculating

 

[ponch]

Try this link for some number crunching.

Click here

 

[2quiktocare]

Is a very good question, but the equation to even get near what happens in real world is so full of variables, it would be hard to factor them all in without having someone with a large amount of physics and calculus experience to do it. By the time you work out a formula, someone could run any number of passes and tell you in real world what's up.

 

[ijames]

Well, if you make the assumption of constant acceleration you can derive the formula hp=197*weight in lbs / (et * et * et) for average rear wheel hp. Since our cars have such a flat torque curve this actually works pretty well in the cases where people have posted dyno numbers and track info (+/- 10-20 hp at 500 hp is what I mean by pretty well). [If anyone wants to see the derivation I posted it a year or so ago.] Even if the actual number is off some, this is still very useful for trends as you track your car's performance over a series of modifications, especially seeing how much losing weight helps the et. If you make the same assumption you can derive et = 1450 or more / mph, which is way off. I've seen about 1365 used in the Moroso calculator, I think. I fit all 130 or so et's that were 13.50 or quicker (down to the 7's) from the reader's rides page at gnttype.org and got et = 1356 / mph, +/- about 0.2 sec. Most of this variance is probably from not knowing who locked their converter. For slower cars I got a different constant. Because the et is so dependent on traction, I like to take the mph and run it through the formula to get an et, and then use that in the hp equation.

For the original poster, assuming 3800 lbs going down the track (car and driver), you get:
et hp
12 433
11 562
10 749
9 1027
8 1462

For grins, that same 562 hp in a 3000 lb car would run 10.17 - start that diet today .

 

[EightSecV6]

Todd,
Your setup should produce around 575-600 hp, I think your car is about 3600 with you in it, looks like you would be "capable" of running 10.25 at 129.5 according to the ATI slide rule. Since you are skeerd, I would bank on a 12.50........
Bill

F.O.A.D.!!!!! Todd!

 

[tes87gn]

Thanks Billy as always your imput is always a great help F.O.A.D. once again you've lost me way to go!

Thanks Todd

 

[bishir]

I've never found a calculator that could accurately tell me my #s.

That's probably because my car dynoed with much higher torque #s than HP #s..

For instance, most HP calculators will say a 300hp car is high 13s or 14s, but most 300 HP Turbo Buicks are in the 400+ torque range and since Horsepower is only a derivitive of Torque wouldn't it be more accurate to use torque #s anyways? Then again why not use both?


James