1st gen coupe exhaust system options.

[Drummer]

My 93 grand prix GTPs exhaust system has 2 holes after the y pipe going to the drivers side muffler, and rather than replacing sections of pipe I'd like to just get a new catback exhaust system.  Where can I get a decent exhaust system from?  Are the 1.5 gen or 2nd gen systems compatible?  

[l67ss]

95-99 z34 exhaust fits. Can do a lil bit o nodding to a 2nd gen and it'll fit....mainly around where it goes around the gas tank. Have to lengthen there about 9" and shorten by where it bolts to cat about 9"

[Padgett]

Odd thing is that for a normal six cylinder engine from a power standpoint you are better off with a single large exhaust than duals. It is only when you start using aggressive cams and turn over 5,000 rpm (e.g. LQ1) that duals make sense.

 

This is because for a six (or a 12 treated as two sixes) both the intake and exhaust can be tuned for uniform flow with one cylinder shutting down just as another starts. It takes a 120 degree separation for this to work (why the best 90 degree V6s use offset cranks to produce "even fire").

 

Of course this requires attention to every phase of operation and frankly both the Chev 60 degree V6) 2.8-3.1-3.4 and the Buick 90 degree (3.3-3.8-3800 have pretty good intakes and terrible exhaust manifolds where the exhaust gas is the hottest and needs the smoothest flow.

 

This is why boost is so popular: with the right intake pressure, the exhaust will be forced out of the cyl regardless. You just need to be careful not to go sonic aka choked flow. A NA engine is much more sensitive to flow: this is why both Mercedes and Chrysler use tuned multistage intakes, free flowing exhaust manifolds and dual catalysts to get 300hp (Net) out of a 3.5-3.6 V6. When they add direct injection (DI) and turbosupercharging (boost) figure 400hp from a mid-sized V-6 and 30 mpg at 70. Of course this also takes a 4 valve head, DOHC and VVT I&e.

 

Which is part of the reason I am a sucker for a good 6 and particularly a 24 valve DOHC 6 with a manual trans, even a kludge like the LQ1.

 

All of this is just background to the original question but the answer is really the cat back part really does not matter, you already lost most of the power back at the exhaust manifold and collector. If you had a L67 it would not matter so much but you have either a 3.1 or 3.4. 3,1 does not matter that much but the LQ1 is being choked pretty bad at high RPM (why the torque peaks at 4k rpm with 215 lb ft instead of 260 lb-ft at 5k like my Jeep).

 

So to open up a LQ1 we really need dual output free flowing manifolds and dual catalysts. Except the computer has no provision for dual O2 sensors. WOT does not matter but for a decent lean cruise (MPG on the road) you would need a signal from both. Modern cars have heated O2 sensors on both ends of the catalyst but that is not necessary if your nose works.

 

So ending back around to the original question, from the cat back it really does not matter what you do, it isn't going to hurt anything.

[Imp558]

Excellent explanation, and it should be mentioned that when he talked about exhaust pulse timing that works into a principal known as "scavenging" where we can see the exhaust pulses actually pulling each other along and helping to move the exhaust flow more rapidly then even just open headers would when it works correctly.

[wlkstout]

I got my replacement dual mufflers for my 91' 3.1l Cutlas Supreme from RockAuto. They were Walkers. I had to replace mine from the Y back. Direct fit no modding necessary.