Cats with Superchargers
 

So I have been looking into what to do with my Cat situation on a high horsepower supercharger setup. I hope to make around 14psi some day and have been investigating what this means for cats.

I have read numerous articles which are mostly contradictory and/or non inclusive.

GTM says that you will make more power with stock cats.

Stillen says you will make more PSI with stock cats.

You definitely see more PSI with backpressure but I would rather make more power than psi anyway. I have read where you can make more whp with test pipes vs catted pipes. However, GTM says you will still make more to the wheels with stock cats over anything else.

I have read articles where guys, mostly mustang owners, have went for high HP from centri sc'ers and have clogged their exhaust with the cat guts. But this seems to be happening on cars with 600+whp.

Currently I have Berk HFC's. I prefer cats for the sound and smell. I do have a Fast Intentions cat back with 18" resonators. It sounds good but honestly I liked the sound better with stock cats as I drive into work with this car a lot and a raspy loud car at 6:30am is not very fun and gets old quick. This is why I would not be able to go with straight test pipes. My neighbors would also hate me. But, I would do what is best for my cars safety. I would hate to plug up my exhaust and risk catastrophic failure with a cat that went bad and melted.

I have also heard that stock cats will hold up better in this situation than aftermarket HFC's. So if I will truly make more power and my oem cats will hold up I'd go that route. If I need to I will find some dual resonated test pipes, but would rather not. Not even sure these would offer any benefits over my already resonated FI exhaust with the 18"ers in them.

I plan to run E85 if this matters as I know you get slightly cooler EGT's with it.

Any input would be appreciated.

You could look into getting some oem cats off of one of these new muscle cars. Mustang, Corvette, Dodge SRT. There already made for big power just have them cut and welded to fit. Just an idea, maybe i don't know what I'm taking about.

Measure your EGT's with the supercharger at 10 psi boost and it will tell you what you catalytic converter will survive and which one wont. E85 fuel will help keep the EGT temp down.

That's a possibility. Easier than dealing with a plugged system and avoiding that whole issue. Thanks.

Oh and why did you let an 82 year old woman drive your 350? ;)

Hope that wasn't too early.....

Oh snap! No way she ran into me with her old beater that was already wrecked. Her ins company paid up good though! Hence my 370

Who considers torque app with OBD reliable to measure this? It displays this but not sure its accurate.

The app should be extremely reliable - it just grabs values from the various modules on the CAN bus.

Sensors measure things. Where are they on the exhaust?

I know. :tup:

I've also got the Berk HFC's, basically no one has tested both with higher than normal 8-9psi from the kit, if you are going to pickup some standard ones, maybe wait till you have completed the build and see what the difference is once you hit the higher boost levels. What's the chances of test pipes/HFC's out performing with higher boost levels?

They will definitely outperform stock cats in my opinion. I mean, how can a more restrictive exhaust offer benefits in any way? An engine is a giant air pump, so the more air in, the more air needs to come out. The faster that can happen, then more power is made. The only benefit of stock cats should be the decibel level and smell control. But, GTM states this to be different. If I could ever get ahold of one of the guys over there I would ask how that all works, but good luck with that.

From what I've read on here before, the reason stock cats perform better has to do with the performance curve of the supercharger itself. With an exhaust that is too free flowing the SC can't create the pressure it otherwise would. I'm sure valve overlap, etc. also plays a role in this.
YMMV

With SC it has to do with exhaust pressure and our VVEL system.
It seems VVEL and GTM/Stillen SC on 8 or less PSI benefit from a stock cat as it holds the exhaust pressure just a bit longer. Now with VVEL control you could possibly achieve this through tuning and then open up the exhaust with TP so you have a true free flow exhaust but the exhaust cam is able to hold a bit longer for the needed pressure.

Now this is all with 8PSI or less, as you bumpt that PSI up I am unsure what VVEL will do and how stock cat versus TP will behave differently. I do know that aftermarket HFC do not work well with any system as they will break down faster & it will clog the pipe.

Thanks for the input guys. So do you think stock cats will be ok for 11psi? How long do you see them holding up if not?

Honestly cannot say, I destroyed a stock cat at 8PSI after about 30k miles.
The added heated will destroy them faster but at what rate will depend on how much you drive, how hard you drive, etc.