I've got a HKS Downpipe (2.65") and a JIC catback (3" that tapers down to meet the stock cat).

What high flow cat options do I have? Will any of the 3" highflows work, or do I have to get the UR 2.5" high flow?

 

The HKS DP will work with 3inch UR cat and 3inch exhaust. I had the 3 inch cat with stock dp for few weeks until my 75mm downpipe came in

 

Thanks. I am just worried about fitment with my catback, because I think it tapers down to 2.5" or 2.75" or something around there..

 

I have the HKS DP and the 30th catback, which also necks down.
I was able to bolt on the 3" UR cat with no problems.
The only "downside" of this is that when the exhaust leaves the cat it immediately
hits that smaller opening.
This will create some unwanted back pressure, which may cost some HP.
I don't care much. It still looks great. And the UR cat gets rid of the cat restriction at least.

 

i dont unserstand why anyone would buy a catback that might as well be the same as stock cuz it tapers down or a downpipe that is 0.15 inches bigger than stock? To me thats a huge waste of money. Why not just go with all around 3 inches?

 

The highflow cat from UR is not restrictive it twice as small as the stock cat and you can see throught the cat openings. It will made a big difference in my car which also has the hipower exhaust. Even if the opening don't match perfectly you will still see a change.

I will have my car on the DYNO in may during dyno day and will post the results.

 

Can't speak for others, but in my case, I usually don't drive around with my engine
over 5000rpms where a 3" has an effect.

But I do drive from idle to 5k all the time, where I'd like better low and mid range power.
This has been discussed here many times, where you actually lose a little down low with 3".

No doubt, if I was concerned about squeezing every inch of HP out of the car I'd go 3" all the way.

As for wasting money, I don't think it's much different than the guy who spends on $200 cam gears
and leaves them at zero, or the guy who buys CF this and CF that.
To each his own. That's what makes each car unique.

Anyway, I just wanted to answer the guys question, that they will bolt up fine.

 

The HKS downpipe may only be "0.15" inches bigger than stock but it is hardly crushed and bent like the stock one. The HKS downpipe is a great piece and quite possibly has the thickest flanges I have ever seen. I remember seeing some dynos where the 2.65/2.75" gained more torque but loss some hp in the upper end vs the 3". I'll take the extra torque.

 

Cool, thanks! I'll look into picking up a UR highflow cat soon then..

 

You can find them from most vendors on here for around $150.
No doubt worth the money.

 

Hm... I just read up. Does the UR cat pass emissions? I heard that high flow cats will usually fail..?