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Registered
Join Date: Jul 2001
Location: Portland Oregon
Posts: 7,007
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Hi Doug:
I don't need to tell anyone that the C.A.R.B. really didn't do anyone any favors when they downgraded the pump premium from 92 to 91 and thats simply not good enough for many cars in hot weather. Many 911 owners now know to use some unleaded race gas in hot weather as SOP.
The air-cooled 911 is one of the most sensitive and susceptable powerplants in the world as cylinder head temps and therefore detonation thresholds change with ambient temperatures. In other words, 91 octane fuel is simply not up to what Porsche specified and you must simply mix some race gas with pump premium in hot weather. Failure to so will result in a whole bunch of broken rings. The knock-sensors do not have a real wide range to handle that fuel.
Octane boosters have a few serious drawbacks.
First, you cannot achieve a homogenous mix in the tank so each and every tank is different and inconsistent. Second, octane boosters make a mess inside the engine and leave deposits on plugs, valves, and piston crowns. Lastly, they really do not offer a very big gain in octane for the dollars spent. Race gas is FAR cheaper and much more effective.
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