H/P to weight question

[Jim Caughlin]

Originally Posted by DeuceCoupe

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.

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

[Hans Olsson]

Originally Posted by Jim Caughlin

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

Very good explanation.

[DrHP]

The relationship between E.T. and MPH is offen refered to as the "Hook factor". Normally if you're 1340 to 1355 its acceptable, if you use this factor to anaylze your performance levels, remember its just a yardstick for comparsion purposes, but not a bad one. Also works for 1/8th mile when you use approximately 670 to 680. I run my customers performance levels through this exercise to evaulate their baseline, then continue to monitor the HF as we improve the performance. High and low powered cars upset the apple cart a tad, but its still a useful tool.


Dennis Baccus - Dynamic Power, Walla Walla WA