I have no idea. I think the R&P is 2.20? I'm running 285/30R18s on the rear. At a GPS verified 75mph in 5th the engine is spinning 2200 rpm.

 

I got 22mpg average going to SITM and back from Atlanta (235/40-18 and 285/30-18), that's with the 2.73 R&P and a supercharger. A properly running stock LH 5-speed with a 2.2 R&P should be getting 24 - 25mpg, that's what my former '86 got with stock tire sizes.

Dan
'91 928GT S/C 475hp/460lb.ft