Cat back exhaust information on LC's; ecu compensation ?

[cclngthr]

I was mocking up a catback exhaust system for my 2001 Accent GL and found a tidbit that can hamper the installation if anyone is considering a dual exhaust setup; which I was planning on doing.

The emission canister, which is located in the rear of the car where a left muffler would go happens to be in that location, instead of under the hood of most cars.

http://www.hmaservice.com/webtech/ii...102#_394878102

I also asked several shops about backpressure of the Alpha engine and got conflicting results. One shop told me these engines like some backpressure, saying the engine was similar to the Mitsubishi engine; which I informed him that is not true, the alpha engine is different than the earlier model Hyundai motors. The second shop told me the bottleneck is the cat, and could be swapped for a high flow unit since his information told him the alpha engine doesn't need the backpressure the other shop described (although I think it does, it is not as great as some think). I also got conflicting reports of the particular size of the pipe needed. One said 2 inch, and the other told me a true 2.25 inch from the engine back is the appropriate size. (It appears nobody has any evidence on a standardized size of pipe). Dealers tell me that changing the exhaust from the cat forward may void the warranty and want a stock sized exhaust. However, performance wise, especially with turbos, supercharging, nos and other high performance engine work, the less restrictions you place on the engine, the better you are in getting the engine to run right.

However, I still need information on the ecu's ability to compensate for a high flowing intake and exhaust setups in order for the engine to run without sending fault codes. Any ideas?

[Edited by cclngthr on Jun 3, 2003 7:28 PM]

[skierd]

I think you're thinking way way WAY too hard about this, lol. A 2" to 2.25" exhuast is best for our displacement and redline. We, nor any other car, do not need backpressure. Backpressure is EVIL, and cars 'needing backpressure' is a myth due to, from what I can tell, the better scavenging of smaller pipes at low rpms. Unfortunately, the small pipes will also get choked with exhaust at higher rpms and WOT. To make more power overall, you'll need something bigger than stock thats big enough to flow up top without losing too much down low. Usually its an apparent drop in low end torque due to the majority of the power gain being concetrated up high. If there is a drop in low end grunt, it can usually be tuned out with an safc or the like.

Just a little experience: the KORE exhuast is something funky at like 2-1/8" in diameter according to Dan, but I can feel the car breathing MUCH better throughout the powerband. The car just responds quicker at all engine speeds. More so above 4000rpms, through thats where the intake starts working really well too.

As far as compensating for a free flow intake and exhuast... mine's had no problems so far aside from a funky cold start issue that just started up recently. It would be better if I could tune it, but the car runs fine as it is.

[cclngthr]

Originally posted by skierd
[body]
I think you're thinking way way WAY too hard about this, lol. A 2" to 2.25" exhuast is best for our displacement and redline. We, nor any other car, do not need backpressure. Backpressure is EVIL, and cars 'needing backpressure' is a myth due to, from what I can tell, the better scavenging of smaller pipes at low rpms. Unfortunately, the small pipes will also get choked with exhaust at higher rpms and WOT. To make more power overall, you'll need something bigger than stock thats big enough to flow up top without losing too much down low. Usually its an apparent drop in low end torque due to the majority of the power gain being concetrated up high. If there is a drop in low end grunt, it can usually be tuned out with an safc or the like.

Just a little experience: the KORE exhuast is something funky at like 2-1/8" in diameter according to Dan, but I can feel the car breathing MUCH better throughout the powerband. The car just responds quicker at all engine speeds. More so above 4000rpms, through thats where the intake starts working really well too.

As far as compensating for a free flow intake and exhuast... mine's had no problems so far aside from a funky cold start issue that just started up recently. It would be better if I could tune it, but the car runs fine as it is.
[/body]

So far, I've heard many conflicting stories about the issue (It probably is discussed too much at times) and I also tend to be very particular in how things should work (perfectionism), both here and who I have contacts with. It seems few people can give a common answer, or even a similar answer from what I personally have heard.

The engines I've built had high flow exhausts and worked great, however, most of these were v6's and v8's, which are different than the 4 cyls (which I've done a few on, but stock ones).