Daul Cat Question

I would have to agree with you that dual cats would be better, but unfortunately it's not legal to convert your car from single to dual cats. The "hot" legal setup for your car would be to replace the stock cat with a high flow aftermarket cat, then buy an aftermarket cat-back exhaust system.

Gary

Maybee it is restrictive. after all there is some kind of filter inside the can. if only one side of the motor is running through it then that would be half the presure to force the gasses through the filters. Maybee it does need two banks of the engine to force the gass through at a stady flow. ? dunno I do agree with the Straw idea though. Why not do away with the Cats.

Regards Wombat.

Replace the 2-1/2" cat with a 3" one like I did. There's plenty of flow through the 3" unit. My pipes from the exhaust logs are 2-1/2" each side to the Y-pipe, then the 3" cat., then a Flowmaster 3" cat back exhaust. American Thunder is what Flowmaster calls it, I think. Maybe that's the system in my 68', either way you can upgrade the exhaust to handle it and won't have to worry about the constricted area that you'd have to run 2 pipes down. The last thing is that the system uses all of the original mounting points.

...Ron

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68'RS Camaro 88'Formula 00'GT Mustang

Take a look at the page below.

Find someone who can use all of the information about your engine and drive train and have them design the system that will work best with what you have. There is more to look at than just the cm3 of the pipe, you have to look into how well exhaust gasses will flow through those pipe with the least amount of restriction.

Most of the sites I've read have said that a 3.5" equals a dual 2.5" but the sites I was reading had vehicles that were talking about engines that exceeded 400 hp. I've put in a dual exhaust on an 83' Z28 and it was the most difficult fitting system that I've ever had to put in.

...Ron

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68'RS Camaro 88'Formula 00'GT Mustang

I installed a full dual exhaust with headers and dual cats onto an '84 T/A. The local inspection people said it was okay because a later model F-Body came from the factory with dual cats. Thankfully there was no sniffer test in the area because there was no way it would have ever passed. Sure, a later model came with duals, but the two 2 1/2" cats I installed couldn't have possibly gotten hot enough to light-off and clean the exhaust. Not to mention there just isn't enough room under the floor to fit all those parts. It used to scrape and bottom all the time.

My recommendation:

Edelbrock T.E.S. headers and Y-pipe. Stock H.O. 2x3 oval catalytic converter, or a high flow aftermarket 2

1/2" 3" Flowmaster cat back exhaust

That'll be 50 state legal, very high flow, and you can sleep well at night knowing the emissions won't kill any spotted owls or desert tortoises.

-rev

I would recommend replacing the cat with a high flow model at the same time. Making everything else flow better is a little bit of waste if you don't do the same with the cat.