H/P to weight question
 

Is there a formula for weight to horsepower? How much h/p would a 283 have to make to run high 12s in a 3300 lb car?

Re: H/P to weight question
 

If you plug those numbers into the Wallace power speed calculator you will need about 320 HP to run 12.80 at that weight.

Re: H/P to weight question
 

http://www.wallaceracing.com/et-hp-mph.php


Scroll down and pick you formula

Re: H/P to weight question
 

12.90 @ 3300 lbs = 304 hp
Not sure if that is 304 rear wheel or flywheel hp

Re: H/P to weight question
 

304 at the tires will easily run 12.90 in a 3300 lb car.

Re: H/P to weight question
 

i'm curious if this is wheel or flywheel hp too, and my other curiosity is if your mph show significantly less hp than e.t. at the same weight does that just mean you have a efficient car?

Re: H/P to weight question
 

It looks like the Wallace link uses NET flywheel power. Then they make assumptions to translate that to rear wheel power which is what move the car. Note they say the formula is just approximate, eg they don't even ask what transmission you have.


If MPH is low it can mean a bunch of stuff
1. Running out of fuel on top (common in my old junk)
2. Running out of revs
3. Brick-like aero or headwind (a 5mph headwind will reduce trap speed about 1mph - varies by car of course)
4. Other


If you have open headers, not too many belt drives, a big air filter, and cold air coming in, NET horsepower will get really close to GROSS horsepower. Still some losses to get to the rear wheels, no way around that.

Re: H/P to weight question
 

well a amx isn't the most aerodynamic car i can think off and the ets and mph i was using were from a day when we were driving in to a 20 mph head wind but it was good cool air.

Re: H/P to weight question
 

In a somewhat strange mathematical coincidence, optimal ET x MPH in 1/4 mile tends to equal 1320 (example 10.00 ET x 132 MPH = 1320, 11.00 ET x 120 MPH = 1320) so you can use that number as a baseline. As we know, MPH tells you how much HP you are making, the 1320 number gives you a reasonable idea of how well you are getting it to the ground. Not surprisingly, high HP cars tend to be a little over the 1320 number, low HP cars under but usually not by much.

Jim Caughlin
SS 6019

Re: H/P to weight question
 

Very good explanation.