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Old 05-30-2013, 09:50 AM   #6
FR-S Matt
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Join Date: Nov 2012
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The cats have nothing to do with a restriction... you may see 1-3 whp difference from catted vs catless. The restriction is a combination of the stock header and a tune which increases the flow drastically. The header alone frees up some horsepower, but not near as much without the tune as well.
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