I'm looking to make make my race car street legal. I have SLP A.I.R headers and a 3in Flowmaster set up installed by the past owner. Sounds fierce. I have the A.I.R. pump and plumbing, was looking at cats. I don't want to lose too much flow. What should I get? Honeycomb? Metal substrate? I was thinking I'd just put in a 3" universal slip fit in the stock location. Ant thoughts?

 

Guess not.

 

Im guessing your state or wherever you live requires a cat to be on the car?

Do you actually have to pass a sniffer test?

You need to figure out the technicalities on your local emission law requirements first than we could help answer your question better.

 

Yes Pa cat required and tailpipe sniffer test. Are these new convertors effective without increasing back pressure? Is it worth it performance wise to spend $250 on a super convertor or just buy one from Summit. Thanks for the reply.

 

Personally, mine come from AutoZone. 3" in and out for $65 with a lifetime guarantee.
Burned out a couple, but I know it was my own fault.
The new style honeycomb cats add very little back pressure, but any and everything adds some.

 

Thanks for the input Cflick, Does anyone know of a database that shows what cats flow what Cfm? Random does it for theirs. How much Cfm would I need for a 5.7? Thanks

 

Don't know of a database, which doesn't mean there isn't one.
How much CFM I can help you with.
What I did..... ( keeping it as simple as possible )
Assume 100% volumetric efficiency. ( not achievable on a normally aspirated engine )
Guestimate the highest RPM you expect the thing to work.
Divide that RPM by 2. ( 4 stroke engine ) Multiply by the displacement.
Do the proper conversions cubic centimeters to cubic feet, and such.
That's your max CFM intake.
Then, I went to a PHD chemist.
Assume stoich 14.7 AFR ( by weight ) normal combustion.
It gets REAL complicated at that point, but boils down to aproximately 3.
Multiply your intake CFM by 3, and that gives you roughly your total exhaust CFM, accounting for heat, expansion, and recombination of molecules into other gasses.
The actual number is something like 2.967 or some such, use 3.
Now, how much back pressure will you accept ? That gives you pipe size, muffler flow, etc.
It gave me true dual 3" exhaust for the 455 at 4000 RPM. ( or a single 4" )
Smaller will significantly choke the motor, bigger gets you very, very little.