I bought a midpipe setup from Random Tech for the C5 that will mate up to my TTi downpipes (I'll have to get them reduced a little bit to get a tighter fit) but has 3" piping after the cats.

Who makes a 3" cat back for our cars, and where do you get gaskets to fit the larger flanges?

3" pipes have around 30%-40% more area than 2.5" pipes so I figured to a point, that bigger pipes would be better for a TT.

 

Stainless Works has a 3in cat. back.

 

Looks like LG has 3" pipes coming soon but no pictures or price. So far all the 3" pipes are not to my liking, at all.

I am not afraid to experiment, so here's the solution I've come up with so far. Just gotta make it fit. Running the 3" pipes all the way to the back where the catback meets the midpipe. In that vicinity, 3" cut-outs will be installed and necked down to 2.5". OEM 2.5" exhaust flanges will be welded to the end of the neck so the 3" exhaust can mate with any exhaust made for the C5.

I may even run the OEM Z06 exhaust instead of an aftermarket exhaust since the idea is to open the cut-outs when I really want to make noise and make power. There's nothing wrong with a 600rwhp silent/stealth cruiser, especially when I can uncork the exhaust and end up with a 750rwhp killer.

 

Wicked!!

 

Don't get too crazy on blowing out all your exhaust fumes, you still want the turbos to have some back pressure so they'll still work in the sweet spot. If you PM the Dr. he'll confirm this, well atleast it was always true on the import side.

 

Not for sure.. but, didn't APS say they were doing some higher-flowing catbacks in the 3" variety?


Arnel

 

Yes, there are a few guys doing some 3" exhausts now that weren't doing them a while ago. Well, I should say not for sure as well, but I thought I heard the same thing you did. Who knows, too much info on this forum and it's hard to keep up sometimes.

Jay -- regarding backpressure... the Z06 Ti exhaust is restrictive (no doubt) and it does cost power and torque. This has been verified on the dyno. Simply swapping to a Borla Stinger picked up in the vicinity of 50/50 on hp/tq on my convertible. I plan on running some big 3" Random Tech cats so dumping exhaust out of cut-outs probably would not represent a "too little" backpressure scenario, and would probably be a little better than just Stingers on top of cats.

 

I've always believed that turbos do not like backpressure. The reason why a turbo spins is the result of the pressure difference between the areas before the exhaust blades and after. Take a look at the import drag cars...the real monsters...they have very short exhausts with side exits. Another example is the Dodge Neon SRT-4, it doesn't come with a muffler from the factory!!!! Decreasing backpressure usually allows faster spool.

One wouldn't want an exhaust that was so fat that scavenging would be compromised, but larger than stock and open should be better. If the LS6 came with a 2.5" stock...the LS7 with a 3" stock...then what would be appropriate for 600hp? or 600rwhp??? 700rwhp???

I find it strange that the aftermarket hasn't gone to 3" on the catbacks for the LSX motors sooner, especially modded ones. Sure the midpipes/x-pipes come up to 3", but it seems almost pointless when it's capped with a 2.5" exhaust...especially for turbo/SC/HC cars. How effective is necking down a 3" x-pipe to fit a 2.5" exhaust?

JMHO,
Tom

 

Well, we already know from real-world dyno data on this combo that a 2.5" midpipe to 2.5" Z06 Ti exhaust will yield around 650rwhp at current boost pressure and tuning levels. This is with no cats.

Also know from real world dyno data that pulling the Z06 Ti exhaust and putting a more free flow exhaust (Borla Stingers) yielded on the order of 50hp/tq extra.

So, my expectation is that by going to the 3" midpipes and adding cats back in, exhaust that goes through the Z06 Ti at current boost/tune will probably yield slightly less than 650rwhp. I'll increase backpressure with the cats but probably offset that with the 3" pipes.

But then when I open the cut-outs, well... I expect that will flow much better than Borla Stingers because the cutouts will be at the back of the mid pipe. If you were to straighten out the pipes on our exhaust systems (remember, they jump over the axel in a bend, then shoot out to the side of the car in a bend, then go into a muffler (once agian, bending) and then come out the rear just before (you got it! bending!))... the end of the midpipe would be about the mid point in all the exhaust plumbing. Not to mention all the bending I just mentioned. I think exhaust dumps at that location are going to be real, real healthy for turbos and getting rid of exhaust gas.

 

Pressure and heat makes a turbo spin. You do not want pressure on the outlet side of the turbo.

I think you are going through a lot of effort on this 3" exhaust. I would suggest monitoring exhaust backpressure after the turbo with the Borlas and dual 2.5". I think you will be surprised...

The cutouts are a great idea... I like it how Nick has his set up.

 

Noob, The stainless works setup is a major pain in the A$$. I used a random tech X with the Stainless works exhaust on a Chicago car I did. Made great power (900+) and had a decent sounds but it banged on just about everything no matter how you adjusted it and it always seem to need adjustment .

Phil