Hi All... building a street performance engine for my '53 +4 Morgan Roadster. Now have a TR4 (not 4A) cylinder head. <span style="font-weight: bold">For 91 Octane pump gas, what is the optimal compression ratio?</span> I read the Kas manuals, he suggests ll.7 to 1, but this may be dated (assuming higher Octane gas). This will be a 5k RPM engine, 89mms, 3/4 cam, headers & SU's. Must be drivable in low RPM's...I owe beers to whoever has the answer..