Okay right now I have the HKS 2.75 inch downpipe on my car. I recently ordered a 10.5 hotside (not installed yet). This is what I'm wondering, since I'm going to be upgrading to the 10.5 hotside and 3inch turbo ouetlet pipe, should I spend the extra cash to also upgrade to a 3inch downpipe. Is it worth the money? Is it necessary?

 

Save your money. Coat the DP that you currently have.

 

I wouldn't bother if you still had the stock o2 housing.

But I may be tempted to since you have the 3 inch o2 housing, and you never went a neck in the exhaust.

 

Works 3" O2 housing ?
Its counterproductive go from 3"(O2H) to 2.75"(dp)
It should be done biggest at the back of the tail pipe to the smallest at the turbo kinda like a bell shaped or just 3" turbo back is what i like .

 

Those 2.75 DP's are good for applications up to about 375whp and like 4bngr said, would even be better coated. If it will fit to your new O2 house then I wouldn't worry bout it. I would atleast go with aftermarket catdelete or CB 3 or 2.75 - restrictive stock.

Smaller DP may be advantagous, more clearance for tie bars and less heat transfer to your oil case, etc. Also the exhaust gases are hotter in the area, less dense, faster moving so bends and area are less of a factor in exhaust restriction when compared to CB.

Keep it if it works, you might have a good thing.

However it deffinately wont be worthwhile at all if your O2 housing inside diameter is much larger than where it meets the 2.75 DP - this will clog things really bad and cause knock up top