Exhaust question

Hi all,

I am working on my '93 Accord EX project/ track car and just finished putting in a new header (DC Sports 4-2-1). This car will only ever be used on track and I am debating if I should use the CAT.

At the moment, the exhaust just terminates at the end of the 2nd section of the 2 part header kit (where you would normally bolt on the old CAT/ muffler - excuse my lack of terminology, I am just starting to learn).

I realize this is probably not ideal. Some have told me the engine is not performing optimally without the back pressure created by the CAT/ remaining exhaust system. On the other hand, the car seems to run well at the moment. Without a dyno test, it is hard for me to asses.

What do you guys recommend? Should I install the remaining exhaust components? Should I buy a different exhaust geared towards track use? If so, any recommendations? My goal is to eke out as much extra power as I can.

Thanks a lot for the help, hopefully my question makes sense.

Kevin

If you're only ever racing it, and the rules don't require it, then I'd remove it to eliminate the possibility of a grass fire if you go off-track and stall.

You don't need backpressure. The disadvantages of a cat on a track car are weight and a slightly higher fire risk (as mentioned above).

If you can afford it, a custom exhaust is the best performance option, use straight-through mufflers if you're not running a straight pipe.

You could also put the original exhaust back on, maybe with a test pipe in place of the cat. That will work too.

Hi,

Thanks for the info! I think a custom exhaust would break the budget of this project - but do you think using a test pipe with the stock exhaust (or a low cost after market option) is better than what I a running now?

I think to use a test pipe I would have to cut out the cat from the system and then figure out a way to bolt the test pipe in place.

Any test pipe/ decent cat back (or test pipe back in this case) combos you guys recommend in the lower price ranges?

Thanks again!

Kevin

Check out mandrel-bends.com for exhaust bends and Summit Racing or Jegs for the straight parts, mufflers and hanger parts. You should be able to fashion something with a few clamps and bends to route the exhaust wherever it is convenient.

Ah, the old back pressure myth.

Backpressure is like constipation. Even "a little bit" isn't good for you.

IIRC you want the exhaust gas to have some flow velocity, hence why a 5" pipe on a NA civic is a bad idea (the gas has to flow faster through a 2.5" pipe to move the same volume in the same amount of time), but you don't want back pressure if you can help it. Someone correct me if i'm wrong.

You do want velocity but that doesn't mean you want any backpressure. What that means is that you don't want an oversized exhaust, and you want to avoid any step-ups in exhaust size (like going from a 2.5" downpipe output to a 3" catback). Also more insulation will help keep exhaust velocity up.

2.5" and 5.0" exhausts on a Civic might have almost the same backpressure but the 2.5" will have much more velocity.

In reply to Rufledt and GameboyRMH:

Yes and that's much more succinct than I could have tried to explain it. I see this idea floated around so often on another forum and I might borrow your phrasing to explain this in the future.

Found this out back with my first vehicle. 89 Jeep Comanche ended up with clogged cat took off the cat and pounded the ceramics out of it put it back on (because I was a broke 19 yr old at the time) and it ran better than before it clogged up.

Thanks for all the responses! It sounds like I should run with what I have - which is around 4" worth of exhaust tubing. I don't mind where it currently exits (just really loud). It sounds like if I wanted to go for extra credit, use a short test pipe that is the same inner diameter of the current tubbing just to help route the output further from where I am sitting.

Make sense or am I sort of missing a point?

Thanks again,

K.

Most rules state that the exhaust must exit behind the driver. I would at least make sure it exits to the side or rear, anywhere but under the car. Less chance of exhaust fumes being an issue with either smell or potential poisoning the occupant of the car. Some events and sanctioning bodies have a decibel limit so be aware of that.