Louie928

Number 1. The single 3" is about 2.875" ID and it doesn't have as much area as your stock dual pipe system. Yes, the duals weigh more and will be more expensive, but the weight savings of the single cost more torque than the savings in weight gain in performance. A single 3.5" is difficult to muffle adequately and it seems to flow too well and costs mid range torque as compared to the dual 2.5" (2.375" ID).

Check the dyno charts in the link provided by Rick Carter. That tells the story.

BC

Thanks Louie. Thats what I was looking for - the comment you have made here. "Difficult to muffle inadequately, means too loud to me. Is that what you mean?

Louie928

Hi Brendan,
That's what I meant. Check the offerings of the 3.5" mufflers and then see where they will fit. One muffler won't be adequate. You can put one behind the Y and in front of the transmission. It's really hard to put a 3.5" muffler beside the tranny unless it's quite short. The inlet angle there makes things really tight with the big tubing. You can put another muffler in the rear.

Louie928

If you prefer the torque loss of the single 3.5" system, I'd suggest using a "Y" merge collector right up front with the 2.5" inlets of the "Y" connected right to the exhaust manifolds. I have seen an X pipe with 2.5" outlets connected to a "Y" merge going into a single 3.5" or 3". That just complicates things.

When I did these exhaust tests I had an X pipe with nothing behind it. I had a good "Y" merge pipe (one Tom Cloutier made) with nothing behind that. There was no noticeable difference between them. The dual 2.5" X pipe, and the "Y" merge (two 2.5" inlets and merging into a 3.5" outlet was the same. Next step was to connect an exhaust system to go out the rear. Adding the dual 2.5" pipes with 2.5" straight through Bullet brand mufflers showed a torque increase from below 3000 to about 4500 rpm as compared to no rear exhaust. Top end was the same. Next was to put on a 3.5" rear exhaust connected to the "Y" merge and try that. The 3.5" rear exhaust showed no change from having no rear exhaust at all. That is less torque from 3000 to 4500 than the X pipe with 2.5" duals. True, it isn't much of a difference, but a series of small improvemente adds up.

IcemanG17

John
Exactly what I was looking for!!!! So a single 3.5 flows about the same as a dual 2.5.....so a single 4 flows about the same as a dual 3" I guess......that should be enough!!!

IcemanG17

My thoughts on exhausts kinda work like this.....for a race shark.....where noise isn't as much of a concern....i would go with a 3.5" single system for a stockish motor...bumped to 4" for a stroker

On a street 928.....dual 2.5" is plenty for stockish motors....dual 3" for S/C-strokers....

Landseer

Am expecting delivery of rest of parts this week to try 2.25 dual on a 16V.
No science. So I can say I have duals.

Seems like there are real advantages for single, though.

FBIII

On a euro S with MSDS headers having a 3 inch collector could you run 3" into 3" cats into a y pipe and then 3.5 after the Y? My thinking was to run as large a cat as possible to minimize its affect and to also add a small amount of muffling.

doktor-t

Okey guys, I´m convinced. I will go with the dual 2,5" with an X to be on the safe side so to speak. I´ll try to use one dual muffler at the rear to get the tones down but still retain a good roar

Thanks for your inputs and opinions.

/Tobias, Sweden

LostInSpace

I've been thinking about a dual 2.5 system as well and was wondering how the 2.5 inch tubes mate up to the exhaust manifold, i.e. what is the internal diameter of the manifold?

largecar379

I prefer my set-up, but would have gone to this if not for the sidepipes:

headers into crossover

crossover into 3 inch pipe (duals)

CATs if required (duals,3 inch in/3 inch out)

Flowmaster mufflers (duals, 3 inch in/3 inch out)

twin 3 inch pipes out the rear

for a street car you should not really need to worry about the weight, but if for a race car--who needs CATs and mufflers?


--Russ

Drewster67

MSDS headers into straight pipes that merge into 1 3" pipe that have a 2 chamber 40 series flowmaster at the end.

http://youtube.com/watch?v=uTI6-YV-fCU