The ST started with a 2,3 big bore version of the 2,2 street motor with Biral cylinders. Then the street motor became 2,4 with the long stroke. The big bore became a 2,5 long stroke. Then they experienced flywheel failures due to vibrations at high speed. They went back to the 66mm stroke crankshaft and used the biggest bore cylinders (only made possible with thin walled Nickasil technology from the 917) to arrive at just a couple cc's less than the long-stroke 2,5. The short stroke 2,5 had the same power and torque (a lot
) and revved quick and fast but was reliable.
Some STs used MFI.
The best ST engine would be a 2,5 short stroke (89.5mm bore x 66mm stroke) Magnesium case, Nickasil cylinders, and for the most power and best throttle response, MFI.