9t4lt4z28

So I got my 355 LE2 engine setup back in my car and running. I have LT's with 3" y pipe (no cats) into 3" over the axle into a single in, dual out flowmaster that routes out the back (like the magnaflow setup where the passenger side pipe does a 180 right out of the muffler then to the passenger side). Anyways, I'm wanting to quiet it down a bit and I know that it's not going to be real quiet with the motor mods I have.

So my options right now are:
1)keep it same 3" setup maybe add cats to the y pipe and swap out the muffler.
2)switch to the hooker blackheart 2.5" true dual setup and possibly add cats
3)keep 3" y pipe and merge into a 3.5" over axle pipe into a single in/out muffler and dump it out the back on driver's side.

How much will cats quiet it down? Whats the HP rating for single 3" vs single 3.5" vs dual 2.5" ? I'm not too worried about a lil HP loss with the dual 2.5" instead of 3 or 3.5" single setup, but I'd love to lose the rasp and quiet it down some. What are some good flowing but quiet mufflers that ya'll are using?

Injuneer

I ran the Mufflex 4" catback with the Flowmaster race series single in/single out. Had a 3" CarSound cat in each branch of the Y-pipe. Not bad, but the usual overpowering Flowmaster drone at 2,500 RPM. The cats were flanged so they could be dropped out to run leaded fuel at the track, and replaced with 3" Borla XR1 mufflers. The Flowmaster/XR1 setup was actually quieter than the cats.

Still louder than I wanted. Mufflex offers a SpinTech single in/dual out muffler in place of the Flow. The owner of Mufflex had a modified LS1 4th Gen, and took me for a ride. The SpinTech was a lot quieter. He also indicated he had run both the Flow and the SpinTech at the track, and there was no significant difference in performance.

Mufflex offers both 3-1/2" and 4" cat backs.

JakeRobb

Let's talk a bit about what's wrong with how it sounds now.

Is it too loud?
Is it too boomy?
Is it too raspy?
Is it too drone-y?

Also, do you want it quieter from inside the car, outside, or both?

If you want to get rid of boom or drone, I'd suggest a tuned noise-canceling muffler system like Corsa. Pricey, but worth it. Here's what mine sounds like (LS1, stock manifolds, Y-pipe, and cats; Corsa cat-back system):


If you want to get rid of rasp, putting cats back on is one way to do that, but you can also do it with muffler choice. I don't have any useful firsthand recommendations here because my cats are still on, so probably pay attention to Fred's SpinTech recommendation above if you want to go this route.

If you want things to be quieter from the driver's seat, you might consider adding some sound deadening materials to the interior -- the rear wheel wells, the floor pans, the doors, etc. Pull up the carpets, lay on some adhesive deadening panels (e.g. Dynamat, but there's some roofing material you can get at Home Depot that's basically the same stuff for much cheaper), and put the carpets back down. If you want to go all out, you can have spray-in bedliner (or a purpose-made product like Lizard Skin) sprayed on the underbody, but this is a lot of work because you have to remove or mask everything under there first. The benefit of this option is that it makes things quieter for you, inside the car, without any chance of affecting your car from a horsepower standpoint (although you are adding weight, so take that into account).

Not Dave

My car runs stock exhaust from the manifolds to the Y pipe with dual cats. I did have a Hooker AeroChamber muffler installed and it's not bad at all. It's a nice low rumble, does have a slight drone but not at cruising speeds, it's only on easy acceleration.

Having LT headers and no cats will increase the sound output.

A pickup truck I had had a Flowmaster muffler and it was rather loud and droning. Getting a spray in bedliner did reduce the noise significantly so some sort of sound deadening will help as JakeRobb stated.

Dave C. '97 Z28

I run a Dynomax crossflow muffler (3" single in- dual 2'5" out). It doesn't restrict flow too much and produces a nice rumble but not loud and raspy. I suspect the internal fiberglass packing helps in this regard. I used to run a Hooker Aero Chamber and the Dynomax is much more quiet, but still sounds good.

-Dave

'97 Z28, 6MT, LT-1 Hot Cam, Pace setter long tube headers, custom 3" y-pipe, Ported & polished heads, Baer Track kit brakes, 1LE stabilizers, Eibach Pro-Kit, yadda yadda...

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