I've never heard the 3 chambers, but I would recommend getting the 2 chambers. They sound pretty good on my car. If you do get turndowns put on with the 2 chamber flowmasters, your car should sound pretty mean. All you'll need after that is an x/h-pipe.
As for my earlier question, I don't know how much gain I'll pick up since my clutch has really been whining at me lately. I was hoping to get into the 9.30's with the gears. With a new clutch and some DR's, I think I should be able to run in the low 9's.
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1997 GT Flowmasters,K&N,3.27 gears
RedSOHC