According to Evolution Motorsports high flow cats are not worth the extra cost on our cars. I am debating doing high flow cats with my Sharkwerks exhaust. I am planning on installing the Cobb Accessport on my car with my Sharkwerks exhaust, but don't want to spent the extra 2k on high flow cats if they are really not needed. If you have already spent 2k on your high flow cats you may be a little biased in your opinion on this issue What is everyone's thoughts?

Here is the post I was referring to
https://www.6speedonline.com/forums/...ml#post4391281

 

GIAC stage 2 tune requires them.

It's not so much that they give such a boost by themselves but they are necessary to get the higher end tunes.

 

do you know the reasoning GIAC stage 2 requires them, but Cobb does not on their stage 2 accessport?

 

Cobb stage 2 clearly states that it require high flow cats and larger diameter piping in their map notes.

 

No cats.... if where you live doesn't require emission testing.

 

This was my conversation with Mitch from Cobb yesterday:


"I have 93 gas in MD, you don't see a problem running the stock cats with the increased boost and heat?"

"Nope the maps that come on the AP are made to be safe and reliable. If you custom tune you can make a bit more power, but the maps you flash on work very well.

Thanks Cody!

Mitch"

 

As you know, we use high flow cats where ever we can. On the 991 turbo, the car showed great improvement with them on our Supersport X-Pipe. As you can see in the dyno below a Supersport X-Pipe WITH cats we picked up +25 WHP and +31 ft/lbs at 4250 RPM which is very substantial gains. Although I do not have a dyno of high flow cats installed with a factory exhaust it does really open up the exhaust and give it a more aggressive tone.

If you want to maximize gains with any tune I recommend hardware first (headers and a full exhaust) and software after, this way you can really dial in the tune to specifically what that car has and where it can be improved. As shifter_ said most of the higher end tunes require what I recommended. Please let me know if you have any further questions!

 

Hey Cody,

If you are going with an aftermarket exhaust we do recommend high quality cats. With the amount of heat that the cats see you will want to be sure you use a good quality cat like HJS.

Sorry for any confusion.

Mitch

 

I doubt that. When you increase boost on a tune, you are increasing the temperature flowing through the stock cats. Therefore, any reputable tuner will tell you to run a high-performance cat to reduce exhaust temperature. It's simple physics.

 

+1 you need to bring down the temp/heat

 

Amen. Exactly on point. Stock cats will hurt performance on a big tune. You must got high flow cats or catless

 

We found much different behavior from the 991TT stock cats than we have on previous turbo models. We did not find huge power gains were had by going from stock to high flow cats, and our earliest test cars have not had any issues after 9-10 months of being beat on through half mile events, track days, and normal 911 Turbo daily usage. That being said, if we were to build a car we knew was going to be heavily tracked, we would recommend high flow cats for reliability until we get a better idea of how the stock ones will hold up long term.

 

Mitch already clarify that they recommend high quality cats...

 

High Quality cats? Or high flow cats?

 

High quality, high flow cats. HJS brand in the largest diameter you can fit is the only way to go. With cheaper cats, your best case is that they won't clean the exhaust and you won't be able to set the monitor (defeating half the purpose of even running cats these days with OBDII emissions), or worst case they melt down, come apart at full throttle and clog the exhaust, damaging the engine.

Generally if you're not paying at least $800-1000 for cats, they're not HJS or the exhaust company is pulling a fast one.