Well, actually a hi-flow cat has the potential to do alot. Think of it this way, if you port and polish your head and add a BBTB to a naturally aspirated car, you might see small gains but the reason most people do these things is to prepare the engine to flow higher volumes of air with less restriction. Add a SC or a turbo to the same engine and thats when you will fully benefit the port/polish, BBTB, etc.

So on the flip side, adding a hi-flow cat(along with a cat-back or a custom exhaust to those who perfer it tongue.gif ) will minimize restriction and maximize exhaust flow. Add a SC or turbo along this setup and your car will see big gains(personally i still think a cat-back gives the better sound wink )

Ever hear about people w/ turbo cars gaining 30HP from just intake, downpipe and a muffler? most n/a cars see maybe 9hp-14hp (well downpipes don't apply to n/a cars duh smile.gif )

 

So, Koreandude, I am planning on purchasing the KORE setup and SR 4-1 Headers in the near future. What should I definitely consider when getting these installed or buying an exhaust system? I want to add a SC, when it actually works, (AKA Alpine... a-hem!) in the future. Hoiw can I get the best gains from it? What other things should be upgraded to further the catback setup?
Sorry for so many questions. I'd just like to hear a descriptive layout of this.

 

Well, now you're giving more info.

If you are seriously planning on running boost in the relatively near future, dont bother with a n/a exhuast. Wait untill you have the supercharger, then run a 3" exhuast. As for what to do with the header... I dunno. I dont know of any headers that are designed for our cars (or many others eiter) that are designed for a car running a supercharger i.e. large enough runners to get the volume of exhuast thats being produced out of the engine without backing up and causin reversion (where the exhuast gas gets back into the cylinder because backpressure is shoving it back in, causing combustion temps to soar and a less efficient burn (re: detonation/power loss)).

I could be making something out of nothing though, as most headers have runners that match the size of the stock exhuast ports.

As for the cat-back, the KORE cat-back is designed to bolt up to the stock exhuast manifold at the end of the first catalytic converter. If you get the SR headers, you'll have to hack up the KORE cat-back to fit the flex pipe and hi-flow cat after the header. Also, i'm 90% sure the KORE cat-back is 2.25" diameter: too small for boost.

Here's what I would do if you are serious about superchargin your tibby:

SR/HVE/KORE 4-1 header, hi-flow cat, and a custom 2.5" mandrel bent cat-back using a dynomax ultra flow muffler and thrush glasspack. This setup will be a lil big for running n/a, and a little small for boost, but should do both jobs well enough and save you from getting 2 exhuasts (one for now, one for after you're supercharged).

 

Oh, and the High flow cat is a must. Our cars run rich enough to clog our stock unit pretty quickly, and the stock unit is a puny 2" diameter. The OEM cat will just be a roadblock to power.

I'll come up and break your kneecaps if you dont put a hi-flow cat on though. wink They dont really affect power, and when they do its 1-2 hp. 1-2hp aint worth polluting the air horribly.

 

Skierd has many good points. If you are running a power adder in the near future, a cat-back may not be able to excavate the exhaust gases enough since most of these systems were designed for an N/A setup (2.25" is the usual mandate). I've read many articles that say when running boost you can never have to large of an exhaust but that's dependent on boost. I think the 3" is a wise choice. Just make sure you get the turbo/super c. first, THEN the 3" exhaust. 2.5" is up to you. Just remember, not enough back pressure and you'll screw up the dynamics of exhaust excavation and all the physics involved. Just make sure you get those curves in your exhaust mandrel bent!! wink Hi-flow cat IS A MUST!! And the header? Most headers (at least the SR) are exhasut port matched at the flange with equal length (or close enough) runners for maximum effeciency. Typically a 4-1 design will deliver peak power higher up in the RPM range whereas a 4-2-1 will deliver better low end and less top end. Most people say if you have a 5-speed go with a 4-1 but i think it's all about tunning.

I have a 5-speed and a 4-2-1 but i plan on getting some RPW stage 2 cams to shift my power band further north. Hopefully with the 421 header/cams combined, i'll have a wider power band and a pretty decent top end. That AND a Supercharger, now your talking. SC's love N/A cams unlike turbos since the exhaust gases (from boost) aren't getting sucked back due to overlap from the N/A cams. Anyhow i talk to much and tried not to go into too much detail. hope we helped ya out.

[ August 07, 2002, 01:35 PM: Message edited by: Koreandude ]

 

Not entirely correct... The biggest concern with the exhuast is to keep exhuast velocity, and hence exhuast temperature, as high as possible. The hot, high speed exhuast will act like a vacuum, aiding in scavaging the cylinder. Larger pipes flow more than smaller pipes obviously, but allow the exhuast to cool more and loose speed, "clogging" the exhuast with exhuast gases causing power loss.

The perfect exhuast balances the need for flow with the need to retain temperature/velocity. For naturally aspirated 2.0L motors that only rev to 6500rpm (re: the beta) 2.25-2.5" happens to be that ideal middle ground.

I'm not too sure what you said about n/a cams and superchargers is true either... but turbo's are my bag so i'll let someone else handle that one. I would still think you wouldnt want lots of overlap, no matter how you're making boost.

 

sorry i guess i was a little confused on exhaust scavenging and back pressure, however i do know that N/A cams work well with superchargers. Random had explained it to me not to long ago. Skeird, since your the turbo expert, you should know why n/a cams are crap for turbo cars 'cause of the exhaust reverting back into the head from the overlap on the cams but ask Random if your curious enough about the s/c w/cams