10-05-2009, 09:38 PM
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Registered User
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Join Date: Jun 2007
Location: Richmond, CA
Posts: 256
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 Quote:
Originally Posted by BradGTV
i will soon be making up a plenum/airbox, now does it need to be made to evenly as possible share the air between the two carbies/4 inlets? or do the carbies suck enuf air them selves to get an even amount of air if it was a simple box?
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FWIW, from fiddling extensively with Mitsubishi's EVO turbos, turbo engines seem to respond much more dramatically to changes in the exhaust side than changes in the intake side. In other words, almost all power, boost response and throttle response gains were made by careful modifications to the exhaust manifolds, turbo housings, etc. Little or no power gains were found by swapping intake manifolds with larger aftermarket ones.
So, I'd spend more time and money making a better flowing merge-collector exhaust manifold (not a log), and don't sweat the details of the intake plenum.
Most OEM turbo intake plenums are surprisingly small, and almost all have the throttle body on one end, which seems to work just fine, and will be much easier to package on an Alfa engine. The small size gives better throttle response. And make it out of round material; square shapes just don't flow well.
Same with the intercooler... too big, and you'll loose throttle response. For a 200-ish HP, 8 psi engine, I'd keep it relatively small for 2 reasons: better throttle response, and less blocking of your radiator... which will be critical, since you'll be fighting detonation and want lower coolant temps.
Big shiny parts get you bragging rights, but smaller parts often make for a better driving experience.
George
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