Thoughts on a dual exhaust with cats

[MaineShark]

I need a new exhaust, so I'm thinking of having one made with dual cats (just in case we get smog inspections, I don't want to have to install a new exhaust again in a few years).

Here are my thoughts:

2-1/2" pipes back to the two high-flow cats. 1-3/4" crossover just behind the transmission crossmember (cats right after that). Out the back of the cats, 2-1/4" pipes going back to the mufflers.

I figure the cats should provide enough back pressure to keep my low-end torque, while the 2-1/2" pipe seems like it should work better with the crossover (more room for pulses to move). Also, I believe most commercial headers have 2-1/2" collector outlests (right?), which means I can add headers later with less trouble. I dropped the diameter to 2-1/4" after the cats to keep the velocity up, with the lower pressure.

Any thoughts? I've never really designed an exhaust system before, so I'm not married to this idea. I've just been batting it around a bit in my head.

Joe

 

[Eric]

Joe,

Check out this thread. Bobchad did something very similar only it's a Flowmaster system. There is a sound clip of it and it's pretty nice.

 

[Bob Chadwick]

Still really happy with it.

 

[Derster]

Depends on emissions regulations! If they plan to sniff test only you may be ok. But if a visual inspection is required they may still see it as a modified system and deem it illegal. You may want to just build your new system for performance and retain your original incase you need it for testing. It would not be that hard to transfer it over if you needed to.

Steve

 

[Stallion]

When you talk about exaust, do you mean headers? What are "cats"? I'm afraid I'm not familiar with that terminology.

Just another quick question, what do you think about side pipes? In my book by Richard Newton, he showed having side pipes in some Vettes. Says they sound nice! I'm sure they do. Would they pass emissions? Even if they're originally on the Vette?

Sounds like we have to be careful with modification on Vettes, huh? If he didn't pass the test, I guess he would have to pop his stock setup back in.

Thanks!

TR

 

[Eric]

When you talk about exaust, do you mean headers? What are "cats"? I'm afraid I'm not familiar with that terminology.
...
TR

Cats are catalytic converters, an emissions control device that is part of the exhaust system.

Exhaust can mean anything the car has between the heads and the tailpipe. That can be pipes, headers, exhaust manifolds, mufflers, cats, pre-cats.

- Eric

 

[Stallion]

Okay, thanks! I've heard of catalytic converters, but I didn't know that's what you were referring to when you guys said "cats". There's quite a few abbreviations going on this site, but I think I've got most of them down now.

Thanks again!

TR

 

[MaineShark]

Guess I should have also mentioned that the original no logner exists. The car currently has an aftermarket dual-exhaust on it, which has major rust problems.

I think I will just skip the cats, and I can always add them later if needed. Technically, this won't be the original configuration, but I doubt any inspection station has a clue whether the car was supposed to have any cats, or one cat, or two, so I think I will be safe.

Next question is: 2-1/4" or 2-1/2"? I want to keep the low end strong, but I don't want to kill the top end, either.

Also, does the 1-3/4" crossover diameter sound correct?

Joe

 

[Bob Chadwick]

I went with 2 1/4 on the recommendation of the shop and Flowmaster. My crossover is the same size, I think.

Bob

 

[RLP]

I know of a 80 Corvette that has the stock cat and no mufflers. Two pipes out the back and no mufflers. The setup sounds good and not overly loud.
A muffler is not required for inspection in Texas.

 

[born2saw]

I was thinking of getting a stock 1974 exhaust system and having my local muffler guy cut in 2 high flow cats (or I might just skip the cats--no inspections in Indiana right now). My current exhaust is stock & from the cat back is in real good shape but pretty poor up front (could be the original cat from the looks of it). To save a few $$ I might see if I can use my current mufflers with the stock 1974 exhaust pipes.

Anyone with a 75 tried this? Or should I just pay the bucks to a good exhaust guy and have them build a custom set. I would like a little more aggressive sound, but I'm not willing to make any major performance mods to this car as it is currently 100% stock L48 (wimpy) motor (OK I will probably get a K & N filter too).

Some day I'm going to buy a "project" vette to build up, but right now...

 

[Stallion]

"Some day I'm going to buy a "project" vette to build up, but right now..."

Yes, I think that would be very interesting, fun, and rewarding. I will do this for my 2nd or 3rd Vette when I have a lot of experience and time and money. That would be really good. What did you have in mind exactly? Just curious...

 

[born2saw]

What did you have in mind exactly? Just curious...

Rescue a near basket case C3, crate motor or transplant a late C4 drive train (a nice street drivable drive train with enough speed to choke a Nissan), upgrade suspension, upgraded HD rearend with a high 3's ratio, upgrade brakes, chambered exhaust (maybe), killer stereo, custom seats, roll bars, nice chrome aftermarket 16" wheels, semi-custom paint job.

You know, spend way more money than I can ever hope to get out if I sell (and enough to make my wife say I'm crazy), and go out to see how fast I can destroy $150 apiece tires while waking the neighbors at night!!

Of course to afford this, I have to sell my '75, which I'm still having way more fun in than ought to be legal. And is too original (for my taste) to modify.

 

[Stallion]

Ooh, that sounds nice to do. Like you said, a project like that would just be an absolute money pit. But...it would be fun!

That's a beautiful '75. I don't think I would ever sell that car in my life (unless you're selling it to a guy named "Stallion" ). I see what you mean.