I've just started reading up on the mods many people intially do to their regals. I know very little about this so far, but I see eliminating the U-bend is a necessity. I realize there are a few mods to do all at once and not just this, but I was surfing and see a company sells the 3" downpie with free flowing CAT. My question is: Is the 3" all the way? Do I stay 3" all the way, including a new 3" inlet and outlet muffler? Or should I neck down from the 3" at some point?

Steve

Welcome to AF.

I'm assuming you are referring to '97 -'04 Regals.

Which model are you referring to. A GS or LS? Therefore any benefit will depend on certain factors like which engine - L36 normally aspirated or or L67 supercharged.

>>>Which model are you referring to. A GS or LS?<<<

Sorry, '97 GS.

Personally I prefer headers over a 3" downpipe but the 3" downpipe and hi-flow CAT is a good alternative. The power gains won't be great but better than nothing. The main purpose on a L67 SII 3800 of going to exhaust mods like the bigger downpipe is to help reduce knock retard (KR) when doing supercharger mods such as a smaller pulley to increase boost. A combination of intake and exhaust mods will reduce KR and net a hp gain. The downpipes are typically 3" from the flange for the exhaust manifolds to the output of the hi-flow CAT.

The other problem you will run into is the PCM module should be re-programmed to take advantage of the mods. You can get re-programmed PCM module from either DHP, ZZP or Intense. I would start there or do it in conjunction with the other mods. Cold air intake (CAI/FWI) is another consideration and PEMs.

The most popular sites for mods are 3800performance.com, ZZPerformance.com and PFYC.com.

Thanks a lot for the info bnaylor.

Steve