Best shift is 6,000 rpm

This conclusion is buried in my 1/2 mile drag race post. All my runs ended up with about 115 mph trap speed. However, I deliberatly tested four shift rpms in this order: 7,500; 7,000; 6,500; and 6,000. Each step was a bit faster then the previous test. The biggest speed increase was seen on the 6,000 rpm run. It was more then one mph faster then the 7,500 rpm test.

1986 Mondial 3.2 QV coupe

 

I have a supposition on this and it has to do with stradling the torque curve. That seems to be what happens when I shift at about 6,000+ rpms which then drops down to about 4,500 in the next gear. I believe the peak torque is about 5,400 rpm.

Having always been delighted with red line shifts I was surprised when each lower rpm switch was a bit faster then the previous higher shift. Not by much. For instance, the 7,500 shift produced a speed of just over 113 mph and the 6,000 shift produced a speed just under 115 mph. That would only make a difference in a timed drag race. A 1.5 mph terminal advantage in a 1/ 4 race mile is not much.

However, I have always believed the 4,500 - 6,000+ rpm sewing machine smooth rush more satsfying then the full-boat 7,700 rpm cacaphony of mechanical torturer. Besides, I once scattered a clutch plate doing that!

 

A perfect start only matters in a timed race or for very high hp cars that can spin their tires in lower gears. Hell, I could stall the car at the starting gate, roll forward 15 ft, declutch, restart, and get the same end speed. The end speed is directly proportional to the total time under full power. For instance, I did a hard launch on my first run shifting at 7,500 rpm and that was my slowest run. However, if the run was timed that little leap forward couid have taken .25 seconds of my time. A full throttle dropped clutch burn out coud take off .50 seconds. AND - drum roll, the run would have half a second less of full throttle.

Its why older 911s were much faster on a drag strip then at stop light racing. All that rear weight bias just slung them out of the starting gate when you dropped the clutcH.

PS - I was tempted to try full throttle power shifts at 6,000 rpm and, assuming I did not miss a shift or scatter the engine would probably gotten a full 115 mph. I only needed about 1/3 more mph. But I may leave that goal for next year and using a full throttle drp clutch start and power shifting would almost surely get that extra third!