The basic theory of these devises is that they "fool" the engine into thinking the intake manifold is larger (very common trick on carburater engines, where spacers under the carbs are used). Generally any improvement in peak power is at the expense of the power band width (ie, low end torque), there by making the car less responsive in street conditions.
As you can tell, I don't like these kinds of tricks on street cars, but it isn't just my bias. Clearly if it were this easy with no down side, GM would have done it in the stock build up.
Though it is not a perfect analogy, when we retired my Shelby from full time bracket racing, we had trouble on the street until we removed the spacers, which greatly improved low end and throttle response.
Hope this is helpful.
PS, this is not in cradiction to Greg's responsive above, I don't think because I think he is addressing an issue of airflow, not plenum size.
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Regards, Art in Baton Rouge, LA
"May The Horsepower Be With You."
1991 ZR-1, Red, Saddle, all Original, and Retired bracket race Shelby Cobra replica. "Working on" '63 Split Window Coupe
"ZR1991" or "Cobra65", depending on the mood and the weather!
www.artcolleys.net
Last edited by ArtZR1991; 08-05-01 at 06:44 PM.
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