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Old 11-16-2018, 07:56 AM   #9
The Radium King
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Join Date: Apr 2010
Location: Canada
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if going oem, realise that the exhaust manifold tubes are not equal length, and the flow merging leaves a lot to be desired. further, gutting the cats creates an area where the flow expands and then contracts again, using energy and potentially causing exhaust gas pulses.

note also that this is a tuned system and efforts to achieve max hp (improving flow) may actually impede torque at lower rpms; if this is a concern then oem is a good choice.

if you are looking for max hp, try to put any restrictions as far downstream as possible. at the muffler if you can. if you need to have emissions then keep the secondary cats on the mid-pipes and extend your o2 sensors to downstream of these. as others have noted, first step is the headers - you can go cheap and take a risk (the cheap chinese stuff is obx, and a number of other resellers) or pay bigger money for better product. with ebay and paypal, warranty protection is pretty good on this stuff these days, however.

finally, as also previously stated, regardless of the route you go, you will probably see more of a performance increase from the weight reduction (10 lbs = 1 hp give or take) than from any improvements to exhaust gas flow.
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