ok guys...... can i put a dual catalytic converter system on my car with the stock manifold and y-pipe thats on it now, its not a TPI system but it has 2.5 inch exhaust right now, i'm going to need to replace it to pass emissions here in illinois........have tried doing a search on it already and have read a few posts on dual cats on cars..........will my car benefit from running dual cats on it at all??.....its a 305 V-8 L03 TBI.........any suggestions would help...thanks

 

Why would you want to run dual cats? for more restriction, or more for passing the E test?

 

Mark.................1st - well to get lower numbers for emissions here in Illinois would be top priority........2nd - after reading some posts on here with guys who have dual cat set ups stock on there cars i was wondering if it would benefit my car any????

 

Well, from my knowledge, and I may be wrong, having 2 cats, just adds to restriction, I think the only benefit of dual cats, was the factory setup, in which I assume the design of piping was better, creating better flow.

 

i think chitowncruiser is referring to the stock set up where they are side by side, therefore cutting the restriction to half

 

yes im refering to the ..stock.. set up that is found on Z-28s,Formula's and Trans ams with the dual catalytic converters on them..N10 is what i believe they were called.....is it possible to go from single cat to a dual with a TBI set up.....someone has got to know if it will work.......

 

Mark, get a clue! Dual cats are parallel, not serial.

Dual cats run a pipe from each exhaust manifold to each cat. After the cats they are y'd together. The factory system uses 2-1/4" pipes from the manifolds, 2-1/4" inlet cats, etc.

TBI uses 2" outlet manifolds, 2" downpipe, etc. The pipes are y'd together earlier than the dual cat system is. To do it properly, you should get TPI exhaust manifolds and have individual 2-1/4" pipes fabricated to the cats. Doing it with two 2" pipes would be better than the stock system, but more restrictive than the factory dual cat system.

You also need two A.I.R. pipes to the cats, as each one gets a feed from that system.

 

i heard that if it didnt come from the factory with 2 cats then its illegal to put 2 cats on. for cali at least

 

I read that same thing some place but I'm not sure if it only applies to certain states or not. Also, I don't think anybody is going to fail a person casue there cars originally came with 1 and now has 2. I think they're only going to check for a cat period.

 

I know here in Pa at least in my area (actually I think it may be federal) but tampering with or altering the emisons controls or systems on a car is illegal.

 

I just bought my '91 RS earlier last year and it has dual cats, in series. True the previous owner had custom exhaust made for the car, but that was only from the cats back. From reading in the repair manual and from other sites, the dual cats came from the factory to be less restrictive than the single cat cars. I guess the used two high flow cats to get through emissions rather than one more restrictive cat. So based on my car, I would say that you definitely could change over to dual cats on an LO3. And I don't know why it would be illegal in most states, seeing as you are still cutting emissions to meet there standards, except of course in Cali with their **** smog laws. Here in WI they don't even look under the hood or under the car, you can do anything you want as long as the car passes the sniffer on the dyno.

 

hey thats cool that ur car came with dual cats on it, but will i have to get TPI exhaust manifolds for it to work since most dual cat systems were with TPI cars???

 

You probably only need to find two cats that will fit and put them in. If you wanted to run them in parallel, then you would need to remove the y-pipe and make your own pipes from the manifolds to the cats. But if you wanted to use larger pipes then you might need the TPI manifold as was mentioned earlier. I wasn't aware that the TBI and TPI cars came with different sized exhaust manifolds, but I guess it makes sense. It kind of depends on what you choose to do.

 

Go to the online GM Performance Parts Catalog. Take a look at the 350 HO conversion package for third gen Camaros. When installed exactly as specified it is smog legal in all 50 states (even the People's Republic of California). The reason I mention it is because this package (a ZZ4, dual snorkel air cleaner, etc.) also came with a dual cat exhaust system. The factory dual cat exhaust system is still available from your friendly GM dealer.

 

went to that website but couldnt find the HO conversion package, do you have a part number for me to seach it with??

 

Go to the GM Performance Parts Online catalog (I think it is something like spoperformanceparts.com). Go to Crate Engines. It is the very top crate engine, p/n 10185077. It has been disco'd, but I talked to Scoggin-Dickey a few months ago and they still had one or two in stock. gmperformanceparts.com may also have the package.

The p/n for the dual cat "takedown" (that's what GM calls it) is 10185070.