Subaru WRX Forum banner
1 - 5 of 5 Posts

·
Registered
Joined
·
167 Posts
Discussion Starter · #1 ·
i have a catback installed right now with a high-flow cat and 3" piping. I'm planning on getting my uppipe/downpipe any day now but was wondering if i should remove the high-flow cat as well or just leave it.

do high-flow cats restrict the car's power much? do they keep the noise level down any? what should i expect if i switched to a catless midpipe once i got the up+downpipe in.

i also have a silencer for my exhaust if sound would get too loud, though i dont like to use it usually cuz it totally restricts the exhaust and the car runs like crap
 

·
Registered
Joined
·
103 Posts
So many conflicting ideas on this

you'll hear some people say that any cat is a performance killer, and others say a 3" hi-flo in the center position won't cost much more than 3-5 hp. I don't know yet, but I plan on getting my unichip retuned in January and I will try swapping out the hi-flo cat and stock muffler (I have a TXS stealthback) with the catless racepipe and a 2.5" straight thru Magnaflow in a direct comparison of which makes more power and by how much. I wonder, at 230 whp how much difference will no cat and a freeflow backbox make vs. a hi-flo and the stock can? Hmmmm...
 

·
Registered User
Joined
·
1,911 Posts
Well a few key notes here. A "high flow cat" will always hurt performance on a turbo car. That's a given. Now how much depends on your state of tune. On a mild car with stock turbo, you'll probably only lose 5 hp or so but on higher HP cars, I've seen loses of 30+ HP. High flow is subjective. The flow of these so called high flow units is the same as stock per given size. They all use the same honeycomb cat material. The only true high flow cats are the metal cats which are prohibitively expensive. Now you wil get some improved flow just from it's diameter but what you will notice between this and a cat free system is that the cat free system can hold power after it's peak HP point much better as well as give you better response and low end power. So although the peak number may be only 5 HP, the shape of the curve on the cat free system is always better overall. Remember, that area under the curve is better than a peak number. HTH
 

·
Registered
Joined
·
1,895 Posts
In my semi-stock/bpu WRX switching from a TurboXS high-flow cat section to their "race pipe" didn't make ANY difference in the performance of my car. The exhaust note got a little more "burbly" - but no change in my e.t./mph at the local 1/4 mile track.

I don't have any experience with larger turbos (hopefully I will in a couple of weeks!) and higher horsepower applications so YMMV.
 
1 - 5 of 5 Posts
Top