"... The constant is 224 not 225, and MPH is calculated by dividing 224 by the cube root of the lbs.-per-HP ratio ... .
"... It was the result of 40 or 50 road and strip tests of many different cars. What I would do is test the car with an accelerometer - and several complex equations - to determine the true peak HP delivered at the clutch under accelerating conditions, usually in a gear giving the HP peak between 60 and 90 mph, to make it easier to get consistent accelerometer readings. (The gear effect was compensated by using a factor to allow for engine and drive line rotating inertia.) Anyway, the car was tested on a quarter-mile to accurately determine the terminal speed at the end of the quarter. Using the gross weight of the car and the tested true clutch HP, the lbs-per-HP ratio was derived ... and this was plotted on a graph vs. trap speed. The above formula is the average line through the plotted points. And actually there was amazing correlation.
"Note that I only tested cars with trap speeds between 70 and 115 mph. The curve is extrapolated above 115 mph.
"Incidentally, I did the same thing with a formula for quarter-mile e.t. That one is a constant of 6.29 times the cube root of the lbs.-per-HP ratio. However, there was more scatter in the plotted points here, due to wider variations in traction between cars. Minimum tested e.t. was 12 seconds.
"Anyway, I know I was the first to derive ths type of equation, based on true net HP. It represented many hours of work and tedious slide rule calculations over a period of 10 years."
|Goodness of Fit (R2)|
|Predicted MPH||Predicted ET|
|LRT "best fit"||0.9301||0.9076|
The LRT Formulas
Patrick Hale's Formulas
Geoffrey Fox's Formulas
|Comparison of Formula Estimates and Actual Track Performance|
|3000GT VR4 / Stealth R/T TT weighing 3900 lbs with driver|
|320||14.003||101.27||14.427||99.94||13.405||101.68||14.2 - 13.4||99 - 102|
|350||13.684||104.05||14.002||102.97||13.011||104.77||13.5 - 13.0||103 - 105|
|400||13.221||108.33||13.393||107.66||12.444||109.53||13.3 - 12.5||107 - 109|
|450||12.827||112.25||12.877||111.97||11.965||113.92||12.9 - 12.0||111 - 114|
|500||12.483||115.88||12.433||115.97||11.552||117.99||12.2 - 11.7||115 - 118|
|550||12.181||119.26||12.044||119.72||11.191||121.80||12.1 - 11.3||118 - 122|
|600||11.911||122.43||11.700||123.24||10.871||125.38||11.5 - 11.2||122 - 125|
|650||11.668||125.42||11.392||126.57||10.585||128.78||11.2 - 11.0||125 - 128|
|700||11.448||128.26||11.114||129.74||10.326||132.00||11.0 - 10.8||128 - 132|