GT/KA ? What class?

[Bill Harris]

The HP calculator is just a ball-park since there really is no way to do an accurate estimate of the peak HP for a racecar. The Chrysler estimates were developed back in the '60s and are roughly based on a constant acceleration model that would give an estimate of power at the flywheel. The equation uses basic Newtonian physics to determine the power needed to accelerate a given mass to a given speed in a given time and then padded to account for observed performance. Anyone who has a data aquisition system can see at a glance that the acceleration of a racecar is anything but linear which makes a constant acceleration model a rough estimate at best.

There are other ET estimators out there that use similar equations but with some variation of the "200" constant. For example, the TCI website (www.tciauto.com/Products/TechInfo/Calculators.asp) has a calculator that is the same as the Chrysler estimates except that the constant is 193 instead of 200. It goes though the intermediate step of calculating the MPH and then the ET, but the end result is that the estimated HP is weight*193/(ET^3). These results are of course lower than the Chrysler results, but not by a lot. The difference is around 15 to 20HP for various weights and HP ratings.

The spreadsheet was originally developed to allow me to figure out which GT classes I could run with various engine/body combos when I was planning my adventures into the realm of super stock competition. The HP stuff was added to give a relative measure of how much power I would need to make at the different weights. It is more of a measure of which legal class is more attractive from a power standpoint than a target to shoot for in the dyno cell. I found it useful and thought that others trying to decipher the GT class mess might also benefit, so I shared it with the forum.

I am pretty certain that the classes that the spreadsheet reports are accurate given the NHRA indexes, rules and user input, but there are no guarantees. The HP stuff is for entertainment purposes only.. if you get my drift.

Enjoy, or not....