Exhaust pipe diameter past the collector?

[TwistedD85]

I know the SHO relies on backpressure to give it more low end umph. But for a totally N/A engine, built to the gills, unrestricted intake, big cams, adjustable sprockets, catless 2.25" y-pipe, headers, valve work, ect. What do you think would be the proper exhaust diameter past the collector? Just bored and figured I might as well balance the bad thoughts of my possibly dying alternator thread with something fun to think about :wave:

 

[Sho Amo]

probably 2.5 i think 3in is a waste. i know alot of small block v8 guys that wouldnt even touch a 3in catback.

my ideal system would be a 2.5in system all the way back with a huge resonator and only 1 magnaflow muffler. the muffler would be mounted before the axle and there would still be two exits in the rear.

 

[SHOtime2511]

needing back pressure is a myth,velocity and flow are key.
read this http://www.miata.net/garage/KnowYourCar/S4_Back.html
im running a 3 inch catback now but it was built for turbo setup that is in the works.
ive noticed no low end loss in power.
IMO the best thing you can do for your exhaust is to get rid of the collector on that Y and replace it with a better merge.

 

[TwistedD85]

Hm, sounds interesting enough. That's one of the three things on cars I'm clueless about, the science of exhausts, the intricacies of suspension settings and the purely electrical side of wiring, the physical stuff I can do easy. A to B makes electricity go, but I don't know how well, kind of like exhaust I guess.

 

[93rev2sev]

For NA, 2.5 in mandrel bends will be just about right.

 

[NovaSS]

for a STOCK SHO .... factory manifolds into 2.25 mandrel bends into free flowing dual cats, then a merge style Y into 2.5 pipe running into a resonator ( long glass pack muffler ) into the single muffler of your choice

 

[K-Dawg]

for a STOCK SHO .... factory manifolds into 2.25 mandrel bends into free flowing dual cats, then a merge style Y into 2.5 pipe running into a resonator ( long glass pack muffler ) into the single muffler of your choice

That's what I'm going to be running on my otherwise stock 3.0. Cats, full mandrel bends, and Magnaflow resonator/muffler.

 

[illSHOyou]

I know the SHO relies on backpressure to give it more low end umph. But for a totally N/A engine, built to the gills, unrestricted intake, big cams, adjustable sprockets, catless 2.25" y-pipe, headers, valve work, ect. What do you think would be the proper exhaust diameter past the collector? Just bored and figured I might as well balance the bad thoughts of my possibly dying alternator thread with something fun to think about :wave:

2" dual from the stock exhaust manifold, big cams, and worked over intake manfiold. 2.25" dual if you go really exotic, like almost 9,000 rpm. The outlet of the stock manifold is 1 15/16" so 2" becomes a natural choice if you decide to take the dual exhaust route, and maintain the highest exhaust velocity.

I don't think there is really much to gain with staying with the y-pipe setup, the difference between 2.5 inch and 3 inch after the y-pipe is really a coin toss. If you cant improve the velocity in the first 4 feet of the system it doesn't really matter. When designing a exhaust system you want your restrictions at the end of the system where it is less detrimental to the engine. If your going for streetability stick with the stock y-pipe and good bottom, if you decide to race move onto a better design system than the factory y-pipe.

Thats my opinion...

 

[jthod]

For NA, 2.5 in mandrel bends will be just about right.

I know...

http://www.shoforum.com/showthread.php?t=96832

sounds like poo right now, but damn does it pull!

 

[Phoenix]

2.5 or 3"

3" here and I love it. No idea if there's any loss/gains between the 2.5 and the 3" , never heard of anyone that had the proof of any loss/gains on both setups.

 

[K-Dawg]

If your going for streetability stick with the stock y-pipe and good bottom

I don't think so, Tim.

 

[illSHOyou]

I don't think so, Tim.

R i g h t ......

 

[K-Dawg]

Have you ever seen the stock MTX Y-pipe?