11-29-2006, 10:40 AM
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CC Member
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Join Date: Aug 2006
Location: San Diego,
CA
Cobra Make, Engine: SPF1715, Roush Built 434 ci Stroker, Dart Block, Ported AFR 205 Heads... 561 hp / 547 tq, Former Roush Show Car, Completed and Prepped By Olthoff Racing.
Posts: 1,066
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Not Ranked
FYI, I was running a 50/50 mix of F&L 111 and 91 octane in my Roush 434 (very similar to the 427) and it did not run well. The motor has 10.25 compression and had a problem on the top end. It would not run to the limiter on extended high rpm runs and it felt like either a fuel or ignition problem.
I took the car to a local mechanic who builds motors and does a lot of SPF motor installs who also works closely with Roush. He spoke with Eric at Roush who said he thought it was a problem of running fuel that was to high in octane which burns to slow for a low compression motor. Sure enough after getting rid of the race fuel and running some pump 91 octane fuel through the car the problem went away. I was worried about detonation with the pump gas, but It turns out I was creating a problem with using the race fuel.
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