To determine best shift points you should be able to get *very* close by doing arithmetic with the torque curve (not hp) and percentage change in gear ratio. For example, in an m40/41 (which I know in John's case, is not what he's using) you'd use 1.99 second gear, 1.36 third, and factor out what rpm you run before and after a shift, and figure out which would supply the better end torque:

-the engine wound well past peak, but multiplied through the 'box, or

-the engine at or closer to peak but with its output less multiplied (significantly so: I'm getting 46% less multiplication by my quick calc!).

One needs to find *driveshaft torque* (not hp).


What tends to get lost in these discussions as soon as they go into engineering speak, is that in chasing HP which looks so appealling on paper, ends up in RL with the baby getting thrown out with the bathwater. (more in a sec)

Torque drives the car- if you change gears or change axle ratios, and the car accelerates more rapidly, you haven't changed the HP, you've changed the torque recieved by the tires. Axle torque is what is desired, get that how you may.

Looking for torque (or area under the curve of a HP graph) is the solution for street cars, not just in itself, but because of some of the aspects that come with using that as your ideal.

I'll post a graph I saved off the net, explaining why a very successful engine builder was finding he was running smaller cams, intake port volumes, and header tubes than the competition he was beating. Smaller cams have higher 'standing vacuum' in the intake manifold. This equates to better ability to transition from part throttle to full power.

Another idea as an example of where this thought can head: suppose there is, as measured by conventional thought, a perfect header tube size for achieving peak HP in a given engine package. One car is set up with that size, and one set up a bit smaller. At transition from part throttle to full, or at anything less than peak RPM, the smaller tube will scavenge better, and allow the engine to pull better.