I'm about to build a custom exhaust for my autocross car. The car is a 98 Civic DX hatch and the motor has been "converted" to a Y8 (intake mani, head, ecu, tranny, etc.). In the near future, I'll be swapping in a set of Z6 pistons to bump up the C/R to a respectable level, along with a cam (maybe) and I'd like an exhuast that can accomodate these upgrades, as well as producing good performance in it's current state. There's a wealth of exhaust info on the DOHC's, but it's tough to find much on the SOHC's. At this point, I'm thinking toward 2". Would that be suitable, or should I go larger? Smaller?

Since the purpose is for autox, I'm primarily intersted in power from 4000-6500 rpm's. This sounds a little higher than some folks think is applicable for autox, but it can be done. Fact is Hondas just aren't competitive at low rpm's. ;-) Thanks for the advice!

 

go 2 1/4 thats what most of the aftermarket ones are. But the pistons will put you into mod, so if you want to be competitive leave the internals alone.

 

Biggest improvements have been noticed using a 2.5" exhaust.

 

I think you'll a lot of midrange with 2.5", 2.25" is probally best. And the pistons won't put you in mod, it will put you in street prep (which you'd already be in). I believe you can use any equipment from the same model car or any year (I'm pretty sure).

 

im not sure about autocross but 2.25 is what i use and alot of other people use in drag racing

steve

 

i have a turbo on a d16y8 running 2.5 inch exhaust no muffler just a cat and it gargels when i shift. you know the sound a car makes when it has no back pressure. i say go with the 2.25 max

 

The head and tranny swap put me in SM (street mod), and under SM rules it's legal to modify engine and tranny internals as well (unlike street prepared).

SP allows exhaust, fuel delivery, and engine management mods only. No gearing (LSD and flywheel are ok though) or internal changes like cams, head work, pistons, etc. Port matching of heads to intake/exhaust manifolds is allowed, as well as balancing/blueprinting, but that's as far "into" the motor as you're allowed to go.

I messed around in FSP for about 3 years, but finally got sick of trying to make a competitive FSP car with the ridiculous D16Y7 gearing. In SM, there are a couple of schools of thought concerning Hondas and their ability to compete. Some say you gotta do a DOHC swap, and others say the SOHC is a better choice because it can be "built" to put out as much HP as you need, while still being lighter than a DOHC. Weight is *THE MOST* important variable in the world of autox (and the most overlooked...), thus I subscribe to the SOHC theory... With that in mind, why don't I just do a short pipe and a turn-down? Well I still have to drive this thing to work...

Wow, 2.5 inch? That seems huge for a N.A. 1.6L. So 2.25 is the most popular? I guess I'll have to go a little larger than I had planned. The reason I'm concerned with the 2.25-2.5 inch piping is because most of the performance data has been obtained using the higher revving DOHC motors. Thanks again for the help.