1. a custom header is generally used, and the pipes are as short as possible to keep the turbo as close to the head as can be. Turbos depend on taking heat out of the exhaust stream and converting it to inertial energy. If you put the turbo too far away and the pipes cool the exhaust first, then you've lost energy before you can extract it.
2. the intake air for the turbo comes from the air filter, gets compressed in the housing, goes into and out of the intercooler, then gets piped to the carb. A bolt-over housing is used to seal the pressurized air into and through the carb.
3. generally, 8:1 compression is about the highest normally used for a turbocharged engine. You can go higher, but the cost and technology increase exponentially. You need to remember that pressurizing air on the outside of the motor gets the same results as just increasing the compression alone. An example would be if you pressurized an engine intake to 1 atmosphere (about 14 psi boost), that would be the same as stuffing twice the regular amount of air and fuel into the cylinder. If the turbo engine is 8:1, then the equivalent aspirated ratio is 16:1. That's a big increase. That's why the general rule of thumb for turbochargers on STOCK engines is a doubling of flywheel horsepower for each atmosphere of boost. There's some other info that I'm leaving out, of course, dealing with head flow rates, cam profiles, intake and exhaust considerations, etc. that can substantially increase those numbers.
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David
newbie #4153
