I need to know what is the best high flow cat available for the HKS Dowpipe 2.75?

Should I go with a 3 High Flow Cat or a 2.5 High Flow Cat?

The cat will be connected to my HKS Hi Power Cat Back Exhaust

Is it gonna hurt the performance if you go from a 2.75 downpipe to a 3 High Flow Cat?

So which is the right setup a 2.5 or a 3 High Flow Cat?

Thanks

 

Bump

 

If your HKS sytem is 75mm or 3" I would go with the 3" high flow cat, that way you will be going from a little under 3" with the HKS downpipe and then going 3" the rest of the way back. This is the set up I had and it worked great. I also thermal wrapped my HKS downpipe also. This will all help the thermal dynamics of the exhaust system flow alot easier and all the pipes will fit together better as well.

 

As you go back towards the rear of the car, you want to go bigger.. Don't "choke" your exhaust as it's trying to make it's way out of your car!

 

I am running an Ultimate Racing 3" high-flow cat with my HKS downpipe. It used to be connected to an Espelir exhaust, but I sold it.