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2.5" exhaust vs stock exhaust

267 Views 2 Replies 3 Participants Last post by  DC Clark
Hi all
I have a 2000 Pontiac Grand Prix GTP
I have the original exhaust but thinking about to change it to a 2,5" exhaust.
I have a 3" downpipe and 2,5" Flowmaster mufflers already.
What will the result of changing this exhaust to a bigger one?
Will you feel it? Better for the engine?
thanks for your answers
1 - 3 of 3 Posts
Your choking off your exhaust going from a 3" downpipe to the stock 2.25". I would absolutely go at least 2.5" preferably with mandrel bent piping. 3" would be even better especially if you plan on doing a lot more modding to your GTP. The larger piping will help take down your knock retard and that will help your engine run better. You should also feel a little more power freed up in the mid-upper rpm range.
I have ZZP full header setup with 2.5 catback, on a 2002 GS with new long block from Summit racing(their last one) it was actually overkill until I installed ZZP stage 2 IC and ZZP Billet Fuel rails and 3.0 pulley and a tune. That's when the exhaust really woke up. Installing the headers was time consuming but time is irrelevant when its the outcome that matters. Now its asking for more and I have already maxed out the stock #33 injectors. Waiting on ZZP to restock 42.5# injectors and another tune. Its a big relief to look at my scan guage and see no KR at all even over 100MPH in no time
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