Can i run Roe SC with stock cats?

[vegasviper]

Or would they get too hot

 

[Sean Roe]

Hi Steve,
I wouldn't run stock cats on a stock car.
Too restrictive and too hot.
Regards,
Sean

 

[JimT 99RT]

I ran with 2.5" Roe oval cats, they are big truck style cats and are a tight fit and they get plenty hot, but look like they have good flow numbers. I have a Borla exhaust and had them welded in. I recently switched to 3" headers and removed the Roe 2.5” Cats and have been running with no cats, but it is just to damn loud. I had 3" slip pipes installed so I could put cats back in. Tonight I took my 3" slip pipes out and put in a pair of 3" RT Metal cats I got from JonB, they are smaller than the Roe units but are an easy fit, I had to cut them down to fit my application. The tuner that installed my slip pipes made them pretty short, so Roe style cats will no longer fit on my car in the slip pipe location, but the RT’s are small and seem to work fine. JonB states that the Metal RT cats flow around 528 CFM, while I seem to remember the no cats number is around 600CFM. I will have to get some time on the RT cats to see how they run and see if I like them.

 

[Joe Dozzo]

My .02 apply ONLY if you live in an emissions testing city / county / state...

I had a VERY difficult time making my 98 GTS / Roe SC w 7psi pulley and larger injectors with high-flow cats pass our local (Colorado) emissions test (really a dyno test with a "sniffer" stuck up the exhaust pipe - not a pretty sight!).

Had lots of very helpful suggestions from many sources - including Sean and Glenn (local Viper tech) - all to no avail.

Got close, including some "chemistry" experiments using ethanol, but no good. At least not with high-flow cats...

Put the stock cats back on - with no other changes - and passed with flying colors and WAAAYYY under the Hc, CO2 and Nox limits.

 

[VPRVENM97]

Joe,

Did you try taking the stock cats and cutting them in half then opening the ends to 3 inches? These modified stock cats pass strict CA emmissions (dyno with sniffer up the tailpipe) with no problems. Of course the Roe S/C itself would fail you immediately.

The exhaust note is similar to after market hiflow cats. They also run cooler then stock cats.

Stock cat

Modified stock cat

 

[Ron]

Joe,

How does the car run now that you have stock cats back on?

Dave,

How do you cut the cat bed without bending the corrigation and impeding the flow?

Thanks....

 

[IEATVETS]

Bottom line here......Listen to what Sean says. He knows his stuff. I would listen to him regarding your situation rather than anybody else. If he says don't run with them, then don't run them.

 

[VPRVENM97]

Dave,

How do you cut the cat bed without bending the corrigation and impeding the flow?

Thanks....

Ron, the stock cat is actually two cats welded end to end. There are two cat elements inside the unit with space in between them. That's probably why the stock cats are so restrictive and get so hot. When cutting down the middle of the cat, you're only cutting the casing.

 

[Ron]

Thanks Dave!

 

[Joe Dozzo]

Ron,

My car runs just fine with the Roe SC and stock cats back in. If I've "lost" a couple of HP out of 600+, I definitely don't feel it!

And I could have been more specific... I have stock cats, but they have been opened up to 3" on both ends - I guess that means they aren't "really" stock.

I should also say the sound is about the same... Not much difference (that I could tell) high-flow or stock cats... I have the 3" Borla 4 muffler system on my car with an equalizer just in front of the rear two mufflers (another excellent recommendation from Sean).

I am in line to try Sean's new heat shielding material, but I do not notice the sills are any hotter now than when I had the high-flow cats (both were/are too hot to hold on to - a pretty coarse measure, I know!).

 

[Ron]

Thanks very much Joe.

 

[FE 065]

If your emissions testing is only once a year, you could switch from OEM cats for testing and back to no cats for the rest of the year.