David,

2.5" sounds fine. The only NA car I know with a big exhaust is Norm with the 12 sec quarter mile. 3" I think might be too big, but I'm no exhaust expert. maybe 2.75? lol

zya
Yuichi
<a href=http://StrictlyZ.com>StrictlyZ store<a>
ZDriver.com



-Have you had your daily dose of Vitamin Z?-

 

The pressure differential & flow-characteristics across the turbine is what makes power in a turbo car, therefore a large system is desirable. But with a SC car, I'd expect that you still want to take into consideration the extra air that your car is consuming.

I'd be inclined to base the size on the boost level that you are running. Say, if it's any more than ~5psi go the 3". But you should do some pressure measurements on your current system & take it from there.

Ben
Adelaide,
South Australia.
'What's normally aspirated mean? I only speak turbo.'

 

This question can only be answered depending on the kind of hp you are extracting from your engine and what kind of muffler set up you plan on using. I've done alot of research on exhaust in choosing the best set up for my z. I'm currently running around 270hp at the flywheel and about 220 to the wheels with my high compression 2.8L z motor. You can check out my ride, its a pretty built street motor. I'm going with Borla on my z with 2.5 inch pipes. The only reason to use 3" pipes on a z is if you're running pretty high hp or if you're using a baffle style muffler such as the flowmaster. These baffles are more restrictive and therefore 3" pipes are used to compensate for this extra restrictiveness. Borla muffler's, with they're straight through, perforated interior design allow maximum flow with minimum pipe size. This max flow is the very definition of "backpressure" or the "scavaging effect". It is the velocity of the exhaust pulses through the system that aid in "scavaging" or extracting exhaust from the cylinders during the exhaust stroke. I spent alot of time on the phone speaking with a Borla representative who owns a z and showcases it every year during the Motorsport Auto Show. The common misconception is that "Bigger is Better" and this isn't the case. After speaking with Steve, he helped me realize that for my street application, that 3" pipes were just too big and would allow the exhaust to lose its velocity/energy. The key to hp is velocity and uninterupted flow. Borla was the #1 recommendation to me from the Z shops around Atlanta for its longevity b/c of its stainless steel construction, million mile warranty, and hp ratings.-Taylor

<P ID="edit"><FONT class="small"><EM>Edited by tyco1983 on 02/15/02 06:27 PM.</EM></FONT></P>

 

I have a stock 280zxTurbo. 2 1/2" for a N/A is fine. But concerning a turbo pushing say 12PSI boost no backpressure is the way to go. That's why I plan on fabbing my Downpipe and going with a 3" exaust with probably a borla muffler or a warlock (where you can remove a cap and go straight thru). This is not just me talking. I've read and E-mailed alot of other Z guys on other webs running 300 to 350 hp on their stock 280 zxTurbo engines and they really like their 3" and doesn't cost that much more if you fab it yourself buying from Jegs or J.C.Whitney for mandrell tubing. Just my 2 cents!

 

A 3" pipe is most likely a good application for 300-350hp, but "no backpressure" is never a way to go. You always want that scavenging effect to aid in the extraction of exhaust from the cylinders. The only application i've seen where no backpressure may be useful is in the 1000+ hp range on methanol dragsters that have 2 foot long pipes running off of the exhaust ports b/c of the sheer amount of air running through those HUGE engines.