Ford Focus Forum, Ford Focus ST Forum - View Single Post - anyone using premium gas ?
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Old 12-07-2011, 07:22 PM   #38
Dgc333
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Quote:
Originally Posted by zak404 View Post
So you're saying premium gas won't advance the spark curve for better low end power?
No it won't. It might keep it from being retarded but it won't advance it beyond what the engine was tuned for. Plus an engine needs less timing advance at low RPMs than at high RPMs. The engine needs the most timing advance at light load cruising when the throttle is barely open. Under this condition the cylinder does not fill with air/fuel efficiently so the spark has to happen sooner to ensure max cylinder pressure occurs at the approx 20 degrees ATDC i mentioned previously.

In the old days distributors had mechanical advance that was strickly rpm dependent, more rpms, more advance. They also had vacuum advance that added more timing in high manifold vacuum conditions such as light load cruising.
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