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Re: Boost level and fuel Posted by Ari [Email] ![]() ![]() In Reply to: Boost level and fuel, Andrew ![]() |
Fuel octane level is directly related to octane rating. The octane rating is a measure of how resistant the fuel is to knock. The APC dials back boost if it detects knock. So if the octane rating is such that the engine knocks at full boost, the APC will dial the boost back to half-yellow.
In general, the car was designed to get full boost at 93 octane, but still run without damage (base boost) at 87 octane. Those are US measures of octane, which is different from Europe.
However, your son's car is now 15 years old. Things change. Some engines become more prone to knock with age, and some less so. So each engine is different. My '88 9000T will run at full boost on 87 octane. Well, that's just great. My '86 900T had basically the same engine, but it needed 93 to get full boost. Anything less would cause knock and reduced boost. It wasn't anything magic about 900 vs 9000, or a two year difference; it was the individual engine.
If you're getting less the full boost, the FIRST thing you should do is run higher octane fuel. If that cures the problem, then you know it's a knock issue. Yes, you may want to look further - make sure the timing is right, that the spark plugs are in good shape and the right kind and gap, and that you don't have any vacuum leaks. But some engines, especially as they get old, will require the octane stated in the manual (93) to get full boost.
posted by 140.157.4...
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