black_gs99

Does anyone know how much power if any i would gain by removing the Cats and replacing them with high flow cats?

StockGS400

Well it depends on what other supporting mods you have. . . from your sig it says SRT and L-Tune so you might have the exhaust and intake. . . if you have those than hi-flow cats would make it better on high end but you still have the restrictive headers and y-pipe so it is really hard to say unless you actually do a dyno test

BoostAddct

There are many variables when it comes to adding high flow cats. Generally they will improve performance a little, but it is hard to say because different setups will yield different power. The best thing to do if cost really isnt a factor is to do the full exhaust including headers so the gases can flow smoothly out with no bottlenecks or extreme bends. Be careful with the diameter you choose though because if you go too big you will lose low end and it will be pretty loud. I believe they recommend 2.25" diameter exhaust, but don't quote me on that.

JBrady

The stock cats ARE high flow cats. No gain in replacing them and possibly a loss.

Lexmex

I don't know exactly how the GS system is, but having worked on my RX and seeing a few others at my track doing the same thing. One of the most hidden bottlenecks is an area between the main cat and the resonator (usually an O2 sensor sits in between the two). Despite having no precats and increasing the exhaust width to 2.5 inch on my Bank 1 (behind engine) and Bank 2 (rear manifolds) and having a twin 2.25 inch y-pipe after my resonator, the big enchilada was the area I previously described and I had to also increase that to 2.5 inches and use part of the existing O2 bung.

Otherwise felt like puffing my cheeks and not being able to let the air out. I was running 18.2 with ease at my track in the 1/4 mile, but now run consistent 18.0s once I opened this area up to 2.5 inch.

black_gs99

thanks guys for all the help.