Exhausts myths and truths.

[Myssan]

I have a 2" exhaust and a cat on my S14 SR running stock ~8 psi. I figure unless IM gonna run more boost or a bigger turbo the exhaust I have shouldnt give me any turbo lag problems I dont think. Its nice and quiet now and I could spend the $500+ dollars on other things besides a 3 inch cat-back. Now truthfully...will I really see any real performance gain if I upgrade?

[uiuc240]

Originally Posted by Myssan

I have a 2" exhaust and a cat on my S14 SR running stock ~8 psi. I figure unless IM gonna run more boost or a bigger turbo the exhaust I have shouldnt give me any turbo lag problems I dont think. Its nice and quiet now and I could spend the $500+ dollars on other things besides a 3 inch cat-back. Now truthfully...will I really see any real performance gain if I upgrade?

Yes. Your turbo will spool faster and smoother, meaning you will get more power in the midrange. Sometimes, a larger exhaust even allows you to make a bit more boost...

Eric

[andrave]

from a 2" with factory cat? defintely a big increase, from the dyno charts I'd say up to 20 hp is possible, depending on what you upgrade to...
and like the above post, faster spool up too.

[Jeff240sx]

Originally Posted by andrave

from a 2" with factory cat? defintely a big increase, from the dyno charts I'd say up to 20 hp is possible, depending on what you upgrade to...
and like the above post, faster spool up too.

Alex on Fresh Alloy ran a 3" turbo exhaust on a 180k miles NA KA motor with simply an air intake. He gained 14 horsepower and 9 ft/lbs of torque. At some points, gains of up to 20 rwhp. Not a loss in torque from the sizeing anywhere. He just said its loud. But for dispelling myths, this is a whale! ADD A 3" EXHAUST TO YOUR STOCK KA FOR 15 HORSEPOWER!
-Jeff

[andrave]

its not a stock ka, its an SR...
I'm confused as to what the heck you are talking about, dispelling myths? if he made 20 hp it would seem to me that he wouldn't be dispelling a myth (20hp on stock ka) but rather confirming one...

[Jeff240sx]

Originally Posted by andrave

its not a stock ka, its an SR...
I'm confused as to what the heck you are talking about, dispelling myths? if he made 20 hp it would seem to me that he wouldn't be dispelling a myth (20hp on stock ka) but rather confirming one...

The myth pertains to this guy's problem about 2" exhaust on a SR. He doesn't know whether to go bigger, ect.
MYTH: Big exhausts on small NA engines lose torque. Myth busted.
-Jeff

[Myssan]

it might be a little bigger than 2". I couldnt measure the I.D. of the pipe to be sure. The KA had a header and a HKS super dragger muffler. The only section that might be restrictive is the cat and the portion where the Im assuming the resonator used be. (a peice of pipe was welded there)

[mellojoe]

You don't need a huge exhaust to make good power. Get rid of the cat and the restrictive muffler and you will be OK. Those are probably the two most restrictive points in the exhaust system.

Then, go get some piping that doesn't have crush bends. Those are incredibly restrictive, too.

A good exhaust system is mandrell bent (no crushes) and a free flowing muffler and a less-restrictive catalytic converter (or no cat.).

Size really isn't an issue unless you are going with a big turbo and start moving massive amounts of air.

[tommy_thrash]

What do you think a A'pexi GT spec exaust would do to a semi stock S13 with a SR20det that has a few upgrades, about 250hp?

[uiuc240]

Originally Posted by tommy_thrash

What do you think a A'pexi GT spec exaust would do to a semi stock S13 with a SR20det that has a few upgrades, about 250hp?

No. Not without a LOT of boost. You might see somewhere close to that with about 17 psi on the stock turbo...but I doubt it. More likely with a T28 set to about 14-15 psi.

You were talking about RWHP right? Or where you talking about power at the flywheel? My car is pushing 11.5 psi right now with a full 3" exhaust, and I'd guess it's making around 210-220 at the wheels. On a cold day.

Eric

[tommy_thrash]

Well im thinking I will have almost 250hp with everything I have done not including the exaust. I was just wondering if it would hurt to have a 95mm exaust on a car with only that much power. I was told that it would hurt my lower end.

[kandyflip445]

It's a stock KA, jeff was right.

"This dyno confirms what SCC found in 1999 when they made a whoppin' 15RWHP with the Apex'i N1 exhaust on a S14... that turbo-sized exhaust systems really make a huge amount of power on the KA. There were NO losses throughout the entire powerband; from 5000-7000RPM there were 10-15RWHP gains! This confirms the notion that the KA needs to improve its breathing in order to make power... almost an exaggeration of that notion!"

That is from his post.

[tsunami0ne]

Originally Posted by kandyflip445

It's a stock KA, jeff was right.

"This dyno confirms what SCC found in 1999 when they made a whoppin' 15RWHP with the Apex'i N1 exhaust on a S14... that turbo-sized exhaust systems really make a huge amount of power on the KA. There were NO losses throughout the entire powerband; from 5000-7000RPM there were 10-15RWHP gains! This confirms the notion that the KA needs to improve its breathing in order to make power... almost an exaggeration of that notion!"

That is from his post.

I'd like to say as a DOHC KA owner, that from my experience, putting on a 65mm HKS Hiper Exhaust on my '95 has given me no "clear" power gains. I cannot feel it at all, even in the high end. Same thing with an intake. I have an AEM short ram and now my car actually feels slower because the damn car gets so loud when I step on the gas like usual.

[driftmayhem]

No gain with intake and exhaust.. huh... push the gas all the way down...lol.. When I first got my 1995 I did a 2 1/2 straight to a jic titanium muffler that I got for my b-day from my fiance and I installed a injen intake and it made a huge difference but this was a while back when I first got it now im running a 125 shot NX and its f..f..f..fast.... WWWEEEEEEEE....lmao.. bottle's are for baby's? then im an infant.

[Maeda]

Corkey Bell says something like

The best exhaust for a turbo charged system is none at all.

The less restrictive the better for forced induction! Slap on that fart can and let the BOV wail =D

[RedlineRacer]

You really can't tell the difference in power in crush bent (not the factory accordian style) and mandrel bent unless you are putting down some serious power. Also, if you do very slight bends (like 5 degrees) with crush bending, its really hard to tell that it is not a mandrel bend.

[HiPSI]

Originally Posted by tommy_thrash

Well im thinking I will have almost 250hp with everything I have done not including the exaust. I was just wondering if it would hurt to have a 95mm exaust on a car with only that much power. I was told that it would hurt my lower end.

it will only help on a turbo car. turbo engines get their backpressure from the turbine itself, negating the need for a special sized exhaust to gain backpressure.

[LanceS13]

backpressure...blah.
It's all about exhaust gas velocity and scavenging. An n/a motor needs it. Exhaust negative pressure pulse spacing and speed are used to draw exhaust gases out of the combustion chamber(s)...this is normally optimized for a certain (relatively small) rpm range. A turbo motor doesn't need this b/c the pressurized intake charge pushes all of the exhaust out. The less restriction after the turbo, the easier exhaust can travel through it, the easier exhaust leaves the combustion chamber, the easier the intake charge enters the combustion chamber,..., the more power you make...gains throughout the power band (theoretically).

[Brolewigi]

on my turbo Integra, getting rid of the cat and getting a larger exhaust made a huge improvement. Since Hondas do not make that much back pressure you could possibly loose power with a bigger exhaust. Since the nissan has a bigger displacement than the honda engine the back pressure is larger. A larger exhaust would be benificial towards your setup. A 2.5-3" exhaust is where you should be looking at getting. that smaller diameter size piping could choke your engine. Sometimes I have backfires because my engine is choking. But my turbo is LARGE and my piping is small (2.5"), my turbo spools at 3500rpm and hits full boost at 4000rpm.

[phatsx]

Just get apexi GT-Spec and be done with it. One, you will never have an exhaust thats piping is too small, people will shit their pants when they see how big it is and three, it's not really any more expensive than any other good exhaust system out there.

[Myssan]

Cool. My original reason for posting this question is a friend of mine who happens to be really knowledgeable and an expert on this type of stuff thinks I'll be fine until I upgrade to a bigger turbo. But everyone else is saying it makes a huge improvement. I trust his judgement but I think Im gonna have to get a bigger exhaust regardless. What everyone here is saying is in accord with what Ive been thinking all along.

[HiPSI]

here's another way to look at it... turbos spin because exhaust gases go through the fins of the turbine wheel. they move that direction because anything that's in a pressurized system will always try to take the path of least resistance. 2" exhaust = a good bit more resistance than 3" exhaust, and decreased resistance on the exhaust side of the turbo means you would gain in spool time (thus beginning to make power earlier increasing your overall power curve). you'd also see some gains on the top end when your car really needs to get rid of the exhaust gases as quickly as possible.

[tommy_thrash]

Well I thought that was the case, I was just told by the place I was ordering from that it would be to big. I guess they thought I just had a KA. Thanks for the advice!

[Brolewigi]

A wise man once said. "It's like blowing on the top of a pop bottle, if you blow too soft, nothing. Too hard nothing. But if you get a larger pop bottle you can blow harder to get the sound." Just a little methaphor.

[s13conv]

So if I put my 3" catback on before I'm turbocharged, it may actually pick up power on my KA?
The reason I ask is because my OEM muffler has two big holes in it and I have 3" URAS cat-back in my basement.

[West]

Originally Posted by Jeff240sx

Alex on Fresh Alloy ran a 3" turbo exhaust on a 180k miles NA KA motor with simply an air intake. He gained 14 horsepower and 9 ft/lbs of torque. At some points, gains of up to 20 rwhp. Not a loss in torque from the sizeing anywhere. He just said its loud. But for dispelling myths, this is a whale! ADD A 3" EXHAUST TO YOUR STOCK KA FOR 15 HORSEPOWER!
-Jeff

Sure it was a Stock KA? IIRC Alex had just about every bolt on there is. Or im thinking of another Alex.

I plan to get the RSR Ex-Mag 3" and run it NA until I get my turbo. Its suppose to be a quiet exhaust, so I will see. I hate loud exhaust to begin with.

If your exhaust isn't big enough then you are creating unwanted backpressure on your compressor, causing turbulence. Your turbo wont spool as efficiently.

Bottom line, backpressure is our enemy. On NA cars there is a happy medium. IMO you wont notice the loss of low end torque if you run a 3" exhaust on your NA KA.

[ratm]

This is the thread off of Freshalloy http://forums.freshalloy.com/ubbthre...b=5&o=&fpart=1.