Here's my current situation.. I've got a 2.25 RSR Catback exhaust and I just bought the JDM DC header. I've read that most people say to get a carsound cat, but then, my 2.25 catback will still be restricting the flow. I guess my question is, how much of a difference will the carsound cat make and would just getting the donut and flange from jdmhondaparts be the cheapest way to get the header to bolt on my stock cat?

 

The sound difference is barely noticable. It will sound a little "smoother", but not any louder or quieter.

The cat is there only for emissions purposes. The muffler and resonator is the one that alters the sound (hence muffler and resonator). Hehe.

I have a test pipe on mine and I could barely tell the difference.

Some people say it sounds a little buzzy at high rpm's, but I have two friends who have the same thing and I couldn't tell the difference. It did smell a little worse at idle, but that's it.

 

I don't think the JDM header is a straight bolt on. It's longer and you'll have to modify the exhaust piping. Somebody correct me if I'm wrong?

 

The sound of it doesn't really bother me. My main concern is price. If a carsound cat isn't going to provide that much in terms of gain since I have a 2.25 piping for my exhaust, then I will just use my stock cat.

 

Yeah I don't think the header is a straight bolt on. It's supposed to be just like the JDM ITR header so if you have a GS-R which I don't know if you do, but anyways then you have to get a custom cat so it will fit properly.

 

I dont think he is referring to the sound differences but he is referring to the way the 2.5 to 2.5 (carsound)to 2.25 will affect his flow in comparison with 2.5 to stock cat to 2.25...in my opinion i had the same dilemma before...i just had a muffler shop make a flange for me...even w/ the carsound cat it will bottleneck at the end...getting the flange just causes the bottleneck a little bit earlier...just use a flange until u can get a 2.5 exhaust.( used in conjunction w/ cams and headwork)

 

You know what really ticks me off? I have a 2.25 exhaust and in order to do this properly I would have to buy another 2.5 exhaust. Thermal better have one or custom make one for me...

...Thermal

 

This mod is going to get way too expensive if i buy a new 2.5inch catback. So I guess the consensus is that if i'm not going to do the 2.5inch all the way, don't bother with the 2.5in carsound cat...