I have a T5 with 0.76 OD in my 1963 with a 3.73 rear, and 29” tires, and a great running 230. It will cruise along at 2100 RPMs at 62-65 MPH. I rarely need to downshift. I hooked up a vacuum gauge to the intake manifold to watch performance. The conclusion was that lower RPMs will not necessarily give better MPG. I have all the power I need but my engine is probably not in the ideal RPM range for power. So the lack of HP at lower RPMs translates into lower MPG than you might expect. There may be less engine wear, but no actual fuel economy.
Fancyt,
If I were you, I’d do the math and keep the RPMs above 2500 in 5th at highway speeds. Your engine will perform properly with the needed HP and you will not need to downshift on hills as often.
The 0.63 OD can be found in V8 Camaro T5s but the 27% drop in RPMs is a HUGE drop and usually only works well for lighter vehicles with V8 horsepower.
Last edited by Lugnutz; 01/25/2020 9:21 PM.
