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CVD · 03-03-2006

Think velocity. For one thing you would need a smooth transition to maximize gains. For another, you are allowing the gases to expand to fill a 4" diameter pipe and then "compressing" them back down into a 3" pipe. Regardless of how you look at it that will take energy, and I think you would agree that it would be a waste of energy. So, you MAY see gains from an ass-backwards setup like that, but they will be very inefficient gains.

I actually had a 2.5" downpipe on the stock catback. This setup was basically to keep the car quiet on the street. The catback was to be removed at the track. Did I see gains over running the stock DP? Well, yes. Not significant gains though, where I would say "this is a decent upgrade for poor kids like me" and probably due in part to the amount of exhaust leaking where they met. If you think you need that size piping, then run it all the way back.

So from my theory based perspective and my real world experience, I think you should just get a whistle tip. They go woo woo.

03-03-2006	#3
CVD Sten Sniper Join Date: Oct 2003 Location: New Hope Drives: Evo VIII RS Posts: 1,385	Re: Proof of larger DP/ Fluid Dynamics Think velocity. For one thing you would need a smooth transition to maximize gains. For another, you are allowing the gases to expand to fill a 4" diameter pipe and then "compressing" them back down into a 3" pipe. Regardless of how you look at it that will take energy, and I think you would agree that it would be a waste of energy. So, you MAY see gains from an ass-backwards setup like that, but they will be very inefficient gains. I actually had a 2.5" downpipe on the stock catback. This setup was basically to keep the car quiet on the street. The catback was to be removed at the track. Did I see gains over running the stock DP? Well, yes. Not significant gains though, where I would say "this is a decent upgrade for poor kids like me" and probably due in part to the amount of exhaust leaking where they met. If you think you need that size piping, then run it all the way back. So from my theory based perspective and my real world experience, I think you should just get a whistle tip. They go woo woo.