2.5" exhaust question - Honda Prelude Forum

Dotay · 11-15-2006, 03:42 PM

I will be putting a 2.5" custom exhaust (vibrant sleeper straight through black muffler) on my Civic (92 Si hatch)in preparation of a turbo in the spring. I would like to go ahead and put it on now since the exhaust that's on there currently has a hole right before the resonator and is annoyingly loud. My question is will the flange for the 2.5" exhaust mate up with the flange on the stock cat? Any worry about leaks due to the size difference? I pretty sure people put 2.5" exhausts on stock cats on Preludes and I just wanted to see if there was anything special I needed to do.

TIA.

petern101 · 11-15-2006, 04:49 PM

i'm pretty sure it won't fit. but if you are getting all that stuff.......why not get a 2.5 cat?

Dotay · 11-15-2006, 07:07 PM

Quote:

Originally Posted by petern101

i'm pretty sure it won't fit. but if you are getting all that stuff.......why not get a 2.5 cat?

Well, I've already got my mini-ram manifold and my 2.5" DP and I'm planning on going with a 2.5 test pipe but I'm not exactly sure where the DP is going to line up so I don't want to buy something that won't fit when I get around to doing the rest of the setup in the spring. Also, wouldn't I have the same problem at the header end if I went with a 2.5" cat/test pipe?

petern101 · 11-15-2006, 08:00 PM

^yes. i'm surprised no one else has chimed in. there are plenty of ppl running this type of setup (but not to my knowledge with a stock cat). you probably will run into problems hooking up a stock cat to a 2.5 inch setup. when i hooked in the 2.36 inch rsr to the stock cat.........there wasn't much room for a bigger diameter. (but i could be wrong)

i guess you'll just have to wait and see. but why not stick with the test pipe (unless you haven't bought it yet)? if the hole is bothering you, just go to an exhaust shop, should cost ~20 bux or less to patch it up (mine was free, megan header with a 1 cubic inch hole)

IgnacioLT · 11-15-2006, 09:26 PM

I am pretty sure my exhaust is 2.5" and bolted up to my stock cat just fine. Yup just looked it up.

preludex2 · 11-15-2006, 11:18 PM

You should be able to bolt up the 2.5" exhaust to your stock cat by simply "slotting" the holes a small amount on the cat flange. In other words, "drill" them out or slot them to match the larger diameter pattern of the 2.5" exhaust flange.

marcucci · 11-16-2006, 08:44 AM

2" to 2.5" 3-bolt triangular flanges usually all use the same bolt pattern. I've had good luck with JC Whitney, Jegs, and Summit flanges all using this same pattern (which is almost identical to Honda's).

I would recommend a 3" system unless you are only going to be a 5 or 6 psi or less of boost. 7 psi plus and a 3" system is preferable to cut losses.

A 3" flange I think uses a larger pattern. 4" even larger still.

Dotay · 11-16-2006, 02:12 PM

Quote:

Originally Posted by marcucci

2" to 2.5" 3-bolt triangular flanges usually all use the same bolt pattern. I've had good luck with JC Whitney, Jegs, and Summit flanges all using this same pattern (which is almost identical to Honda's).

This is very good news. Thanks for the info.

Quote:

Originally Posted by marcucci

I would recommend a 3" system unless you are only going to be a 5 or 6 psi or less of boost. 7 psi plus and a 3" system is preferable to cut losses.

I'm only really shooting for ~200whp since I'm using a 14b. This would put the 14b at around 12-15 psi and from what I've read the 2.5" exhaust would be fine for this HP setup. I've already got the 2.5" DP and 2.5" muffler so I'll just go with what I've got for now and if I end up switching to a different turbo and pushing more power I'll probably sell the 2.5" setup and switch to a 3" at that time. I'm really shooting for reliable (relatively speaking) setup so I'm not planning on getting too crazy. I do appreciate the info though.