Please don't ream me for this question...
Please don't ream me for this question... Hi all, I have been researching all the posts and old posts of this. I am going to run a true dual x-pipe into sweet thunders dumped set-up, with stock manifolds and high flow cats. Originally i was going to go with 2.5" since this car won't see any engine internals change, now my question. Will a 3" inch system be louder than the 2.5"?? I ask because I am going to run cats, just need to know if the that .5" with cats makes a sound difference. Thanks for taking the time to read.
00 WS6 waiting for lid and smooth bellows to come in, and duals.........
00 WS6 waiting for lid and smooth bellows to come in, and duals.........
it will be a bit louder but with cats and mufflers,l it will sound mellow when you want it but have all the performance ur ever gonna need being 3 inch. 2.5 is just not enough with extra cubes or a big cam which you might do in the future
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From: The South
You will get mixed responses to that, I think. A lot of people say they won't go into the engine, they will only do this and that and then stop.......and it just doesn't happen that way. Mod bug. 
There is not much difference at all between the two pipe sizes in sound...why are you running cats? I see no reason for cats on duals, they are already rasp free and aren't as loud as a Y-pipe setup. For example: my current exhaust is really no louder than stock plus loudmouth, which is what I had previously.....it just flows/sounds a HELLUVA lot better. 
Another thing to consider is that 3" off headers and into the X, then out of the X at 2.5" is capable of adequately supporting a fair bit of horsepower as the exhast gasses have cooled a little by the time they make it out of the X and you can actually help keep the velocity up with the narrower pipes in the bakc half of your exhaust setup.
There is not much difference at all between the two pipe sizes in sound...why are you running cats? I see no reason for cats on duals, they are already rasp free and aren't as loud as a Y-pipe setup. For example: my current exhaust is really no louder than stock plus loudmouth, which is what I had previously.....it just flows/sounds a HELLUVA lot better. Another thing to consider is that 3" off headers and into the X, then out of the X at 2.5" is capable of adequately supporting a fair bit of horsepower as the exhast gasses have cooled a little by the time they make it out of the X and you can actually help keep the velocity up with the narrower pipes in the bakc half of your exhaust setup.
Originally Posted by blkZ28spt
You will get mixed responses to that, I think. A lot of people say they won't go into the engine, they will only do this and that and then stop.......and it just doesn't happen that way. Mod bug. There is not much difference at all between the two pipe sizes in sound...why are you running cats? I see no reason for cats on duals, they are already rasp free and aren't as loud as a Y-pipe setup. For example: my current exhaust is really no louder than stock plus loudmouth, which is what I had previously.....it just flows/sounds a HELLUVA lot better. Another thing to consider is that 3" off headers and into the X, then out of the X at 2.5" is capable of adequately supporting a fair bit of horsepower as the exhast gasses have cooled a little by the time they make it out of the X and you can actually help keep the velocity up with the narrower pipes in the bakc half of your exhaust setup.
There is not much difference at all between the two pipe sizes in sound...why are you running cats? I see no reason for cats on duals, they are already rasp free and aren't as loud as a Y-pipe setup. For example: my current exhaust is really no louder than stock plus loudmouth, which is what I had previously.....it just flows/sounds a HELLUVA lot better. Another thing to consider is that 3" off headers and into the X, then out of the X at 2.5" is capable of adequately supporting a fair bit of horsepower as the exhast gasses have cooled a little by the time they make it out of the X and you can actually help keep the velocity up with the narrower pipes in the bakc half of your exhaust setup.Sorry for this taking so long, just wanted you to know where I am coming from. Thanks for the help.
i guess i just dont want to ruin this car, with all kinds of mods
Hard to explan what i meant, mods dont ruin the car, just not what I want to do with the car.
Last edited by psykoTa; Sep 4, 2004 at 10:50 PM.
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From: The South
Originally Posted by psykoTa
Ok, this is the first NICE car i have ever owned, all others I was always bendin wrenches on(69 chevelle,85 TA, 89 TA) which I had no problem modding them. But now I really want to keep this one mostly stock, especially since it just rocks the way it is. However, there are some mods that are good and i like,and are easily returned to stock....lid, bellows, exhaust...and I know that these mods will not affect the computer. Such as headers causing the car to run leaner. also that is why I want to run cats, Ive read about EFI cars require some amount of backpressure to run correctly, and I dont want any funky smells since there are no cats, been smelling like exhaust from other cars for long enough. I really dont want to get into tuning or anything internal(engine). Right now I justwant this bada$$ car to sound just that. Ive gotta go to and from everywhere in this car so mileage and whether or not the car is running lean or rich, is very important to me. i guess i just dont want to ruin this car, with all knds of mods because I am not looking for that extra tenth. Back to the exhaust: will where the cats sit, make a dif.?? I dont know much about exhaust flow, so if the high flow cats are right on the end of the manifold, will that be louder than if they were further down the pipes?
Sorry for this taking so long, just wanted you to know where I am coming from. Thanks for the help.
Sorry for this taking so long, just wanted you to know where I am coming from. Thanks for the help.
A few things: most people run rich with headers on these, not lean. A simple dyno tune can fix your air to fuel ratio, etc after mods and make the car run even more efficiently than it did before. I've seen cammed LS1's get 30+ mpg on the highway. A tenth gain? Bigger mods on an LS1 gain more than a tenth
You do NOT nead backpressure. In reality, and I am almost certain on this, any backpressure at all is bad, that is a misconception that you need it. What you lose with larger diameter is exhasut gas velocity. The additional inertia of the larger volume of gasses to be dispelled from the exhaust can cause a slight loss of low end as the velocity builds, but you should get it back on the top end when the added inertia is on your side once moving. I do see where you are coming from, though.
Originally Posted by blkZ28spt
I just realized something........are you doing duals on stock manifolds???
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From: The South
I would personally recomend you get a good set of LT headers and do the duals off of those. You might want to keep the idea of cats to help with exhasut fumes/smell as dumps under the car can sometimes get smelly. I assume you are getting dumps, anyway, since almost everybody does due to the $$$. Yes, LT's to duals with a good dyno tune will run very efficiently. Grab all the bolt ons you plan to do for now and can afford (headers, duals, lid, CAI, ported TB, crank underdrive pulley, LS6/LSX/LS2 intake, etc etc are your most obvious choices) and then have it tuned. It should run very efficiently.......and/or very quickly......which of those two depends mostly on your right foot. 
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Originally Posted by blkZ28spt
I would personally recomend you get a good set of LT headers and do the duals off of those. You might want to keep the idea of cats to help with exhasut fumes/smell as dumps under the car can sometimes get smelly. I assume you are getting dumps, anyway, since almost everybody does due to the $$$. Yes, LT's to duals with a good dyno tune will run very efficiently. Grab all the bolt ons you plan to do for now and can afford (headers, duals, lid, CAI, ported TB, crank underdrive pulley, LS6/LSX/LS2 intake, etc etc are your most obvious choices) and then have it tuned. It should run very efficiently.......and/or very quickly......which of those two depends mostly on your right foot.
The dyno run, do they tune on a single run?? or several?? do they measure hp in the same run as well?? And where?? Im in VA. Thanks for clearing up the ???? I'm sure Ill have more for all the gurus in here...... 
LT's are sounding better now, really would like to keep cats, not sure if the rear O2's would like high flow cats??
Man, a lot for me to think about...The way GM designed the car works, its factory, its a complete system, when you change soemthing in that system something else changes and not just that one area, so then you have to correct for that change and so on. Just tryin to avoid problems down the road.
Does anyone else have any input??
I'm running 2.5" Sweet Thunders with Pacesetter LT's.. The exhaust sounds insayne ( now that I've fixed my electrical problem). As for the size of the Sweet-Thunders. I think that even if you go with a 3" inlet/outlet, you still only get a 2.5" core.
As for how loud, I don't think these things can get any much louder.
2.5 or 3.0 should have about the same tone and loudness.
As for how loud, I don't think these things can get any much louder.
2.5 or 3.0 should have about the same tone and loudness.
Thanks all for the help. After more research I am going to go with GMMG, 
Better for me now, as it has the sound and I don't have to go with headers and all that right away. Later I will add TSP's catted Y, and maybe some LT's or macs. Ok, well thanks guys.
Better for me now, as it has the sound and I don't have to go with headers and all that right away. Later I will add TSP's catted Y, and maybe some LT's or macs. Ok, well thanks guys. 
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Originally Posted by psykoTa
Thanks all for the help. After more research I am going to go with GMMG, Better for me now, as it has the sound and I don't have to go with headers and all that right away. Later I will add TSP's catted Y, and maybe some LT's or macs. Ok, well thanks guys.
Better for me now, as it has the sound and I don't have to go with headers and all that right away. Later I will add TSP's catted Y, and maybe some LT's or macs. Ok, well thanks guys.