Hey guys, it’s been a bit since I’ve posted, but I wanted to ask your for your opinions. I’m currently running shorty headers, off-road y-pipe, and Flowmaster after. Had it this way for years. I want to quiet it down some and quell that rich, nasty exhaust smell. A few of buddies recommended putting a high flow cat back on the car to help with the smell, which might also help quiet it down some. I think if I did that I’d need 3” inlets, right? I could’ve sworn my Flowmaster cat-back system was 3” in, but 2.5” out. (I haven’t peaked under the car in a while.)

I don’t have emissions to worry about where I live. I guess maybe I’m just getting old. lol

Any recommendations on a converter without spending a small fortune?

Thank you!

 

Do you want to use a single cat after the Y-pipe or dual cats in the Y-pipe branches?

 

Preferably a single cat setup, I think, shortly after where the Y pipe comes together. I would just like to keep my options open with the cat-back system in case I want move away from the Flowmaster.

 

Depends on what kind of HP you’re making. Single cat (only factory installed through 1995 model year) can be restrictive with any significant HP upgrades. I ran a 3” CarSound cat on each branch of a custom Y-Pipe into a 4” Mufflex catback w/ a Flowmaster Race Series cross-flow muffler (single in/single out). The Flowmaster still had an annoying loud drone at 2,500 RPM. When I was at the Mufflex shop, the owner took me out in his LS Camaro. He had a 4” system with a SpinTech single in/dual out muffler, and no resonance. Had a “good” power sound, without being annoyingly loud.

When running at the track (leaded VP fuels C16) the flanged cats were dropped out and replaced w/ Borla XR-1 race mufflers. Even adding those was barely enough to meet the local track’s noise restriction - 90 dB @ 100-ft under max power.

If your Flowmaster (American Thunder?) catback bolts to the Y-Pipe now, if you add a cat in the intermediate pipe it would seem you have to cut the intermediate pipe. Or is the straight section of the combined Y-Pipe long enough to be cut down to allow the cat to be installed there?

As far as HP issues, many years ago when Lingenfelter was selling a 400 HP 383ci LT1 package (49-state emissions certified) they claimed the single cat cost about 5 HP.

 

The car primarily has bolt-ons. No significant engine upgrades. Headers, CAI, Off-road y-pipe, 3.73 gears. Might do a cam at some point, but I want it sound better as-is first. Yes, she has the Flowmaster American Thunder cat back. Loved the sound of it on stock manifolds. Hate it with headers….lol

I’ve never heard a bad word about SpinTechs. People seem to really like them.

Not too worried about a minimal loss in power. I think there’s enough room in the intermediate pipe for it. My y-pipe is thick stainless. I’d rather not break into that twice. So I’m thinking the single cat is the way. I think my intermediate is 3” steel. Whatever that American thunder one is. It’s definitely 2.5” on the outlets. Do you have budget-friendly one you’d recommend? Those damn cats are not cheap.

 

Why is the diameter of the American Thunder outlets important? Are you looking to replace the muffler?

Also need more info on the “nasty exhaust smell”. Has it always been bad, or is this something recent?

 

The nasty smell started after I took off the stock cats. It’s been that way for years. It just bothers me more than it used to.

I started looking at cat prices online and that’s when I started noticing the outlets were sometimes different, and sold as ‘right’ and ‘left’. Being that I wouldn’t be buying a ‘stock replacement’ cat, I figured the size was bigger. Pretty sure my stock exhaust wasn’t 3”, but it’s been so long since I’ve replaced it, I can’t remember. So, what I’m wondering about is the intermediate pipe diameter where a single cat setup would go. (Hopefully.) My 02 sensors in the headers are fine, and the rears were programmed.