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Old 01-18-2000, 01:23 AM   #14
Scooby Specialist
Member#: 607
Join Date: Dec 1999
Location: SF Bay Area, CA

Imprezer writes:

"1. High EGT's will literally cause engine internal to melt. I think the magic number not to go above on pump gas are 900C and 1650F."

--Corect, very high exhaust gas temps are not good. Not only can they damage engine internals (usually exhaust valves) and turbos, they can also trigger serious detonation which, of course, is the end to any engine. Hot exhaust gas temps can also fool you (and your a/f ratiometer) into believing that the car is running richer than it really is. This is why an EGT gauge is so critical with high output forced induction engines.

"2. Detonation (ping, knock) will destroy the pistons, bent conrods and amage the valves due to the extereme stress caused by the self-igntiting a/f mixture happening anywhere in the cylinder."

-- Yes. This is what likely happened in the case of those dead STi/22B motors. They knocked themselves to death. Terrible way to go. The owners must have heard it and ignored it. Afterall, most people don't expect a stock turbo car to ping. Also, ping can be quiet and hard to hear-- especially when the car is revving at 8500rpm.

"3. Too much boost with high compression will cause head gasgets and rings to blow due to the extreme cylinder pressure."

-- This, I'm not to sure about. Although some will swear that combustion pressures brought about by "extreme" power outputs have caused their engine to fail, I'm more willing to believe that knock was the true underlying culprit. Detonation is an order of magnitude more stressful to a engine than any normal combustion. Temps and pressures sky-rocket instantly. Literally, it's an explosion. This is why everything all comes back to guarding against detonation above anything else.

4. Increased power output will put excessive stress on engine's internals and destroying them.

-- In most situations, this is not true. Power loads aren't very stressful in the big scheme of things. In fact, the load a rod goes through just after TDC is far more stressful than the load caused by engine output. This is why raising maximum engine speeds can be far more stressful to an engine than introducing boost. Rule of thumb: You can add boost but leave the redline where it is.

But like everything else in life, there are no absolutes. So take everything with a grain of salt...

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