I am going to buy the hks 30th and turbo xs dp and wanted to know from people with experience if having the high flow cat is really worth it. I don't have to worry about smog until I move back home to cali in about a year so that is not an issue. I'm also going to buy the o2 housing piece asap.

 

yeah it's worth it,but If you want more power get the rally cat from RRE,it's the **** man.

 

Yes if you want to really open up the Airflow for more HP. I have around 310WHP with a Dynoflash. AL and many experts suggest a highflow cat. I spent $1200 for all my mods and I have 310whp. Without the cat I am loosing power. The cool part is you can still pass emissions with a highflow cat.

My mods

SP Downpipe 75mm
3" UltimateRacing highflow cat
Hi power Catback 75MM
Buschur MBC
KN drop in filter
Mail Flash

 

I have the HKS 30th with the HKS DP and the UR 3" cat.
Having the 3" cat over the stock definitely worth it.
The only "problem" with my setup, and yours too, it that the HKS 30th catback necks down
to about 2 5/8", or 65mm, where it bolts to the cat.
This makes it mate to the stock cat better. THe pipe is 75mm until the last 1/2" when it goes to 65mm.
When hooked to the 3" cat, like my system, you end up with a pinch point at the cat exit.
This will probably rob you of a few HP.
I'm not going to sweat it, but you could easily rework the cat end of the midpipe to
get it to 3" and remove the restriction.

BTW, the HKS has a great sound, not really any louder than stock.
It's just a little deeper at idle and WOT.
I love mine.

 

FWIW I would doubt highly if a "neckdown" of 10-15mm is going to net you any HP loss, especially so far back in the exhaust......

 

CEL ????

 

"A Must" is a relative thing. Works does not utilize a high flow cat with their turbo back system. It sounds like part of their argument for this is philosophical, but the gain is not huge. I've heard guestimates around 5hp? They say the stock cat flows pretty well as is, and they seem to have a good reputation. Just my 2 cents

 

Actually the stock cat does not flow well comapred to the high flow ones out there - the high flows and the test pipes flow nearly the same however.