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mppickett mppickett is offline
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Join Date: Oct 2005
Location: Barrington, RI
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It is very difficult to predict exactly because the actual amount of boost developed in the intake manifold depends on the flow characteristics of your motor. For example, at a given RPM, if you put on a smaller throttle body, sometimes you see the amount of boost measured in the intake go up. In this example, counter-intuitively, the horsepower delivered is less even though you show more boost than if you were using a larger throttle body that was more closely matched to the rest of your engine (valve size, lift, header restrictiveness, muffler restrictiveness, etc).

Since the supercharger manufacturers don't really know how much backpressure their blowers will encounter, they can't easily show you how much boost you'll see. Their maps usually give you a pretty good sense of how much air the blower will flow at an RPM and some sense of how much heat it will add at a particular RPM and boost level.

A faster way to estimate the best pulley size to use is to ask what others with a similar application are seeing. This doesn't have to be an exact match, but you can use it to get a reasonable start. I've seen boost levels vary by 2-3 psi between identically sized engines depending on the throttle body, valve, header, muffler, and inlet air flow (to the blower) characteristics.

Just remember, it is all about air flow. Your goal is to flow the most amount of air at the LOWEST boost you can because boost = heat (and heat = a less dense air charge and a higher likelihood of engine knock).

Sorry if my answer isn't very helpful in this particular case (pretty much - ask someone who's running your blower what kind of boost they're seeing). Sometimes it helps to understand the interactions at play. I'd give some guess from my own experience, but it has all been with Eaton blowers and on Miata engines.

Have fun. Blowers give you the feel of an instantly larger engine!
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Last edited by mppickett; 03-09-2008 at 04:46 PM..
Old 03-09-2008, 04:42 PM
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