connected to the stock LS2 exhaust?

Did you replace the stock cats with a high-flow cat?

What does it sound like? HP gain ?

I've spent days looking over the past exhaust threads and haven't seen this combination

My answer will not be the best I'm sure but I will take a crack at it.

If your going to put Headers in the Cats will need to be moved. If you decide to keep your stock exhaust then you will proabably need to cut it up to throw in some High flow Cats.

This could all be done but a welder will probably be required. Do you plan to take it to an exhaust shop or will you be doing it yourself?

Headers ... connected to the stock LS2 exhaust ... Why? :confused:

^^ Good question.

That is why there are no threads of anyone doing this.

Not a good idea in that it is pointless.

^^ Well now that was to the point.

According the engine builders that I have talked to (MTI and HPE) the restrictions on the stock CTS-V exhaust (in order from highest to lowest effect) are: (1) the stock cats; (2) the stock manifolds; (3) the front resonator; and then (4) the rear mufflers. Accordingly, they indicate that you can install headers, high flow cats, and an X pipe (instead of the resonator) and get most of the benefit even if you keep the stock mufflers. This is presumably because the exhaust gases have cooled and contracted considerably by the time they reach the mufflers at the rear of the car. The point in doing this would be to get most of the horsepower benefit with much less noise.

A customer of mine has B&B headers/cats with the stock exhaust and he thinks it is way too loud.

interesting, do you think it's louder then the B&B exhaust?

A customer of mine has B&B headers/cats with the stock exhaust and he thinks it is way too loud.IMHO, replacing the stock cats with hi-flo cats has the most pronounced effect on decibel levels.

... restrictions on the stock CTS-V exhaust (in order from highest to lowest effect) are: (1) the stock cats; (2) the stock manifolds; (3) the front resonator; and then (4) the rear mufflers. Accordingly, they indicate that you can install headers, high flow cats, and an X pipe (instead of the resonator) and get most of the benefit even if you keep the stock mufflers. ... The point in doing this would be to get most of the horsepower benefit with much less noise.I agree with the order you have, but if the rear mufflers have the least effect, why would keeping them produce the least noise? I know, I know ... it's late. :coffee:

IMHO, replacing the stock cats with hi-flo cats has the most pronounced effect on decibel levels.

I agree with the order you have, but if the rear mufflers have the least effect, why would keeping them produce the least noise? I know, I know ... it's late. :coffee:

Keeping the stock mufflers presumably makes less noise than substituting the replacement mufflers that come with the cat-back systems e.g. Corsa, B&B, Magnaflow, Borla, etc. Stated differently, if all you did was to cut off the stock mufflers and replace them with the muffler component of those cat-back systems, they would all be louder than stock, but the horsepower difference would be small.

Also, except for the B&B 3-inch cat-back system, the others are 2.5 inch systems which are no larger than the stock.

Finally, as Rick indicated above keeping the stock mufflers in conjunction with high flow cats and headers does not keep the car as quiet as stone stock.

I suggest you talk with people who have actually installed headers with the stock exhaust system. Also, talk directly with header mfg such as Kooks, Katech, LG and TPIS.
While I do not have an LS2, I have an LS6 with TPIS headers and bone stock exhaust system aft of the cats. I used TPIS's cats as the factory cats are too large to be relocated at the end of the headers. There was some minor welding to join up with the stock exhaust, but it was not expensive.
The stock exhaust system is quite efficient plus it is quiet. With just the headers, the sound is almost stock. My wife did not notice the change. There is no droning, etc.
Horsepower gains with replacing just the exhaust with a aftermarket exhaust are not nearly as great as the gain to be achieved from headers. I haven't dynoed my CTS-V, but TPIS said (my recall) is their headers gained somewhere between 18 and 25 rwhp. Typically, what I have seen on this forum (I am sure to be corrected if I am wrong) from just exhaust is in the vicinity of 10-15 rwhp, with more hp achieved with louder systems.
Aftermarket exhaust suppliers have had problems eliminating a nasty drone at highway cruise speeds. Yes, I know some of you love this drone, but I don't. GM spent a lot of engineering time eliminating the drone in the stock exhaust. My understanding is that Corsa is the only aftermarket mfg which has successfully eliminated drone.

^^ Nice write up but what were your gains?

According the engine builders that I have talked to (MTI and HPE) the restrictions on the stock CTS-V exhaust (in order from highest to lowest effect) are: (1) the stock cats; (2) the stock manifolds; (3) the front resonator; and then (4) the rear mufflers. Accordingly, they indicate that you can install headers, high flow cats, and an X pipe (instead of the resonator) and get most of the benefit even if you keep the stock mufflers. This is presumably because the exhaust gases have cooled and contracted considerably by the time they reach the mufflers at the rear of the car. The point in doing this would be to get most of the horsepower benefit with much less noise.


This is what I was thinking. If the cats are the big blockage, replace them along with headers for the biggest HP bang for the buck.

I don't like the sound of the header,high flow cat, cat-back systems I have heard.

anyone else tried it?

I think that any header mfg will tell you that the cats are not a big restriction. The reason the cats are replaced with headers is simply there is no room for the large factory cats.

I think that any header mfg will tell you that the cats are not a big restriction. The reason the cats are replaced with headers is simply there is no room for the large factory cats.

I have not talked to the header makers, but both MTI and HPE (engine builders specializing in LS motors) in Houston have said that if I am not willing to discard the stock cats in favor of high flow cats I should not bother with headers because the stock cats are too restrictive. I do not have an independent opinion on this, and I am just reporting what I have been told.

:food-snacking:

I think you should leave the exhaust 100% stock and get a Maggie :lildevil:
It will make more power and be quieter than any header/cat/exhaust combo.
Well that was my plan for my 1st V that never materialized. :banghead:

If you can't feel the Maggie, I encourage you to try Darkmans idea.
Headers, High Flow Cats, X-Pipe (in place of stock resonator) & Stock Rear Mufflers.
I bet that would be perfect.
If it ends up bieng loud, you can always add dual resonators.

I'll tell you Headers, High Flow Cats & Corsa is real loud but miraculously, it does not drone on the highway.

Right now my exhaust man is trying to talk me into Flowmaster Delta 40 mufflers, to quiet down my Corsa.
I'm tempted to give it a try.
I doubt it could be any louder, although it might drone.