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Old 08-27-2011, 06:35 AM
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Lead and octane rating

If you have no detonation problem with 93 octane pump gas with the initial timing advanced as far as possible and will still allow the engine to start, there is only one reason to use high octane leaded racing fuel. That is if you have over 125 lb. valve spring seat pressure. Leaded racing fuel will prevent the exhaust valve spring seats from premature erosion. IMO, using leaded racing fuel is an expensive way to keep the seats from being pounded out when it could be avoided just by using valve springs with no more than 110 - 115 lb. seat pressure.

High compression ratio and high valve spring seat pressure pressure is for race cars that do not see any street use. When 104 octane leaded gasoline was available at the pump, it was common to see cars with 125-150 lb. seat pressure and 11:1 compression ratio from the factory.
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