So what is it? How many inches, 2.25'?

 

it changes. from 2.5 to 2.25

 

Def not...


OP it's roughly 2.85" through and 'crimps' down to about 2.75 over the axle

 

how do you know that it crimps down in size and starts at 2.85in?

 

Why do we use 2.5" downpipes if there smaller then stock?
Why do we use 2.5" catbacks if there smaller then stock?

 

so the stock catback is 2.5in? Not smaller not larger? Trying to figure this out

 

I thought stock was 2.5".. sure I read that somewhere.. not sure where all this other 2.85 n crap is coming from /shrug

 

Member on here had it I.D.'d when he cut the TC 3 bolt flange off to put a 2 bolt flange for his LSJ

Look where you're at and try again

And stock LSJ DP is 2.75 and tapers down to 2.5 at the end of it.

The GMPP exhausts are 2.25 and post gains on cars...there's more to exhaust than size

Must be true if it's on the internet

 

umm keeping in mind that this is in the LNF sub-forum;

http://www.modernperformance.com/081...c-473_599.html

Most assuredly seems to me that there is no aftermarket 2-1/2" catbacks/downpipes...

 

whats more to exhausts than size? resonator? bends in the catback? Restriction (or lack of) r/t to muffler?

 

Smooth bends.

That's how the smaller GMPP exhaust shows gains on the L61/LE5/LSJ cars.

Stock exhaust on the LNF is real good, but it doesn't hurt to throw on a 3" exhaust...you're not going to see much gain if any at all.

 

imho the stock head pipe blows goats.

you most certainly are going to see gains from a mandrel bent 3" system aft the headpipe;
any restriction removed from the car's exhaust is going to allow the engine to breathe better;

I haven't a clue why you would think that you would see nominal at best gain from upgrading the exhaust system.

 

There is 1 2.5" catback for LNF's
https://www.cobaltss.net/forums/supporting-vendor-deals-group-purchases-133/agency-power-catback-exhaust-system-cobalt-ss-tc-209066/

 

I wasnt serious.

I figured out all the downpipe/exhaust stuff awhile back.

 

hmm... look at that.

Ok, I'm proven wrong on that point.

smaller OD will help low rpm flow - but once rpm's are brought past the point of gain, it then becomes a power hindrance - because of the increased back pressure...
at least that's how I've understood it.

 

For most cars, dropping a bunch of cash on a cat-back system isn't going to change much other than sound. Cars come from the factory with free-flowing exhaust systems; manufacturers want to get the best fuel ratings they can after all. The TC comes stock with a 2.5 inch exhaust, which means that should support at least 300 hp before it starts becoming a restriction. If there was a gain to be had, it would be from the downpipe. Anything after the cat isn't going to give you a significant gain until you've increased the power considerably. Plus, the TC has the learn-down deal anyways, so you would need to be tuned before an aftermarket exhaust would make any sense anyways.

 

Theres a reason adding an aftermarket exhaust doesn't net very much power on the stock turbo, maybe
5whp if your lucky. But if some of you want to be stubborn and drop a lot of cash on a full after market exhaust more power to you. It would be cheaper for you to have either a different resonator or muffler welded on at a muffler shop.

Theres dyno numbers floating around somewhere with the difference between the factory exhaust vs. bolting on an aftermarket one.

 

I personally did an apple to apple comparison a while back between the stock 2.5" exhaust and an aftermarket 3" on a dynojet dyno.. The ONLY thing that made any difference in whp numbers was swapping out the stock dp (in this case it was catless.. I didn't have a aftermarket catted dp to compare).

Unless you are upgrading to a larger turbo setup, or just want/like the sound of the 3" exhaust (which sounds sweet on our cars btw), save your money and put it elsewhere. You just won't see the gains from a 3" catback alone

 

what do you guys think of swapping out the stock muffler for an aftermarket one, doing something resonator wise?

 

Sometimes automakers will keep an exhaust just a bit on the small side and/or shape it a certain way to maximize the Scavenging Effect.

Basically, while cruising the air leaving the exhaust leaves in pulses and has a low pressure area behind it as soon as it leaves. By creating a high-speed flow of exhaust (such as with a non-3" exhaust), it "sucks" out the extra exhaust left in the cylinder "for free", leaving room for more fresh air and enhancing cruising efficiency. This is part of the reason that you increase cam overlap while cruising.

When you want more power, then you decrease cam overlap a bit and increase the exhaust size, because then you're going for flow and cylinder pressure.