doktor-t

My -86 with 32v engine has the same exhaust as the S4, ie dual 2,1/4" tubing. I found out that the stock exhaust was dead heavy and not an ideal thing for a sportscar.

I´m about to build a new exhaust for the car but cannot decide what way to go.

1# Dual 2,5" with X-pipe.
Pro: Good flow
Con: Not very lightweight

2# Dual 2,5" forming an Y-pipe and mate into a single 3" tubing.
Pro: Lightweight
Con: What about exhaustflow, is it enought?

3# Dual 2,5" forming an Y-pipe and mate into a singel 3,5" tubing.
Pro: Flow must be good
Con: ...


What would you choose? Pros and cons?


/Tobias, Sweden

Jadz928

I'm using #3. The only thing is 3.5" is less common in cars, more common in trucks. You will be limited on exhaust tip choices.
A 2.5" Y into a 3" single should be adequate flow for stock.

shmark

A 2.5" Y to a single 3" is something a lot of racers favor for lighter weight and flow characteristics. It's what I plan on doing for that reason, plus I just like the sound of the single a lot better, more of a higher pitch complex sound. You might get more power from a x-dual setup, not sure if I've seen a dyno comparison. A properly designed single can scavenge well too, but more development effort has been on the x-pipe.

Rick Carter

Single ve dual & pipe size

If you use a Y make sure it is similar to a Burn's Stainless. I have an exhaust by Tom Cloutier but I don't think he's making them now.

John Veninger

I like the Y to single 3.5"
Pros: weight savings and cool sound.
Con: can't say you have dual exhaust

Vlocity

I ran a merge collector into a single pipe for several years until I knew that the next step was a blower and then built a dual with an X pipe. There are plenty of threads that show the HP advantage of an X pipe over the Y pipe. If I was going to spend the money I guess that I would want the BEST no sacrifice setup so that I wouldn't have to visit this aspect again in a few years should I decide to make some other changes. A good X pipe is worth 20 - 25 HP or more. (Check the threads)

If you do decide to go with a Y pipe this is a good place to start. Put the Y in as close to the factory H placement as possible.

http://store.summitracing.com/partde...5&autoview=sku

You may notice that the tube is D in shape which will allow more flow along the bottom of the tube where the heavier gases tend to "settle".

What ever you do, use good quaility mufflers and mandrel bends.

Good luck.

Ken

John Veninger

http://www.performance928.com/cgi-bi...ss_parent=1128

Vlocity

John:

My memory had failed me.....I didn't recall that the two systems were that close. That would make the decision a lot easier if he plans to stay stock.

Regards,

Ken

doktor-t

What does OD mean that Ott refers to when talking tubing?

Vlocity

Outside diameter.

ID= Inside diameter

doktor-t

Ah! Good point

IcemanG17

It seems the Y pipe to a single 3.5" is popular with most of the racers...BUT I wonder if a single 3.5" system will flow enough for some of the really hot strokers.....I know Louie Ott and Tim Dey run dual 3" setups on thier above 500whp strokers....I'm pretty sure Joe Fan does too....not sure about Mark Andersons......

The general rule is this....the dual setups will give slightly more low end torque...& the single gives slighty more top end HP...but were talking small differences...

doktor-t

Due to OTT´S dynotesting it shows that the first diagram would be a good way to go. In my opinion it seems similar in design (exept for what muffler that was used) to the fourth dynotest. Right?

It might also be an really easy way to go if the Y-pipe is connected approximatly where the lambda/cats connect in the original exhaust setup.

I wouldn´t worry about exhausttips for the 3,5" pipes. It can be a good "design-it-yourself" task. Stainless sheetmetal i nice

/Tobias

John Veninger

That's why I run a 4" exhaust

doktor-t

So, either I choose dual 2,5" with an X or dual 2,5" merging into a singel 3,5" since it seems better with 3,5" than 3".

What about groundclerance when using 3,5" pipes? Any pics of a 3,5"?

/Tobias