Ok, I've read a number of posts regarding the issue of backpressure, and it's been bugging me that so many people don't have the right info about it. Contrary to popular belief, backpressure is bad, on any engine, forced induction or naturally aspirated, period. No if's, and's, or but's about it, it's bad. Where people get confused is that, depending on the engine, a smaller exhaust may be better than a bigger one. This does not mean said smaller exhaust is creating backpressure, it simply means that beyond a certain point, the bigger exhaust does not flow fast enough and the engine loses low end power. For example, generally on a 4 cyl. n/a motor, you wouldn't want an exhaust bigger than 2.25" (personally, I like 2", but that's just me), now I'm sure there are exceptions to this, but I'm being general. The 2.25" exhaust system gives optimum flow in that it maximizes exhaust gas speed and minimizes backpressure, if you went larger than that (say 3") then the speed would be sacrificed, hurting low end performance. Keep in mind that you can have backpressure near zero without a 3" exhaust (depending on the motor). In turbo setups, since there is more exhaust gas flowing, a larger daimeter is called for, but the same principal is in effect.

For more reading, go here:
http://www.clubprotege.com/forum/sho...t=backpressure

 

I agree with your post, although I would say that the ideal size of an NA 4 cylinder exhaust varies with the displacement of the motor. 2.25" works GREAT on EJ25s, and 2.5" is good too. On a ~2.0 liter motor, 2" is probably best.

 

Like I said it varies, and I was being general, I have a 1.8L inline 4, and 2" is about the limit for my motor.

 

This is a message that so few n/a engine drivers get. I see so many Civics, Integras, Preludes and CRXs in my area with big 4" exhaust on them but otherwise stock engines under the hood; you can always spot them, because they spend nearly a minute in first gear (bbbrrrRRRRRRRRRRRRRRRRRR) and what seems like forever in second gear, having let all of the power and torque out of their engine, not to mention subverting the VTEC timing on the decent Civics. Ah, the price some pay for a little bling (and no, I don't mean the exhaust and muffler, which they paid $49 for at Pep Boys).

I'll see if I can get a picture for you of the '92 prelude with 4" DUAL exhaust that parks in the lot next to mine. I think I could beat him with a Segway!

 

hahaha, that's clutch. Should this be a sticky for easy reference when someone is blatantly wrong?

 

I will add it to the Threads of Note Sticky.

 

You should have moved it over here to the NA forum first... although, I should have caught it too the first time.

 

well it's not just n/a, that's the thing, it applies to turbo and n/a. I used n/a as an example because that's what I'm more familiar with. Turbo just uses bigger piping, but you could still go too big.

 

Or you could talk to the owner. . . who, depending on the person, may or may not know what the hell they're talking about, lol

 

There's no shame in looking under someone else's car. It isn't quite as personal as when dogs sniff each others' behinds.

The Liberty rules. My brother's Loyale (identical, different year?) is still kicking at 196k.

 

All I know is that if you're getting an exhaust for any japanese cars, JDM exhaust is always a good match. Not, the $49 dollar ones that you get from pep boys like people say.

 

Problem is if you're doing full exhaust JDM is for RHD vehicles, which on some cars can lead to problems. If it were me, I'd rather just have a kit or custom SS mandrel bent and piece together my own kit.

 

are you saying that if teh exhaust is to big for the N/A engine to handle then it will cause the backpressure. I have a 2.5 and have an intake and apexi exhaust with 3 inches and for some reason my car starts to misfire but i checked the gaps on them and they seemed fine, do you think that all the back preassure causes that misfire to occur cause it only does it when i am at 4krpm in second or on the highway in 5th gear if i smash teh gas.
im new to the forums btw thanx guys.

 

No, he was saying that a certain amount of backpressure is good. But if your car still has stock headers and the stock cats, then the catback doesn't do anything but make noise really. What year is your car and what intake do you have? That's the more likely culprit, barring a mechanical issue like bad wires or coils.