88 S4 Auto

Im considering going large single after the dual cats.


Will be:
X pipe
Dual cats
Y to a single 3"
Muffler to be determined (im down to a few choices)
Dual outlet (or dual look like the RMB).
SS of course.



Single 3 has more flow area than the stock dual..by a shade..


Thoughts?

Probably drop 30lbs off the stock system as well.

 

Do you plan to remove that for smog inspection here in CA, or hope they don't notice :-)

 

Just passed with it 2 weeks ago.





Know Thy Smog Shop.

 

I hear you, I do - I paid my guy $100 for an hour on his dyno/test rig to tweak my 86 with Porkens Blink'r, before we tested it.

 

For sound the best option is an RMB..it also saves a bit of weight..... For power the best option is an X pipe with no cats..... but this is a bit on the loud side with an RMB....I ran Sharky this way for a while and it was more of a raspy sound that the classic burble....it did feel more powerful, but I never dyno'd it to find out for sure....

 

Thats what I have now.

X pipe
Dual cats
89 exhaust
RMB


Too loud...too heavy.

 

Jeff, with stock S4 cam's, I don't think there is much (if any) horsepower advantage to a 3" single vs. stock duals. If the primary issue is sound, then try some different mufflers in place of the stock resonators on either side of the tranny, with the RMB. The factory resonators are empty cans with a perforated thru-pipe, and don't do much muffling. Earlier cars had larger resonators, which are slightly quieter-- but still too loud, in my view, with an X-pipe plus RMB.

If you recall our cars at T'Hill, the S4 has an x-pipe with hi-flow cats, large stock resonators, and a "gutted" stock rear muffler. Acceptable, not great.
The GT has headers, x-pipe, and a 2.5" dual exhaust with a pair of "Bullet" brand mid-muffers, no rear muffler. And GT cams, that makes a difference in sound (and power). IMO it sounds great-- relatively quiet idling and under very light load, without attracting unwanted attention, yet speaks with authority when you stand on it.

 

Ya..im looking at a couple of 3 chamber mufflers, and a third option...but large single will be a smoother sound for me as well.

 

Jim, What do you mean by "gutted" rear muffler? What was your process?

 

1) band saw
2) tig welder


That'd be my guess.

 

Jeff
Take a serious listen to Seans racer...its 928intl Headers, into custom mandrel bent stainless exhaust with two stainless sebring mufflers out back.....very nice...but kinda heavy since its stainless...

If you are building a system I think a single 3.5" is about perfect....lighter than duals and gives you enough "room" to increase HP later if you want...

The Estate has the wonderful combo of a 85-6 headers into a missing cat (I like to call it Y pipe) then into the stock 84 2.5" single system with a magnaflow out back....its too quiet really...probably could dump the magnaflow.....

Since you will have to smog every other year I would leave the headers and build from there....its much easier to remove an exhaust in pieces than pull headers..which can be a PITA

 

3" is fine for my plans...headers, nah..then Id need cams, and I dont wanna.


If I wanna corvette, i'll buy one...in fact, I did that once. Didnt like the cost of tyres.


This is a peachy 928...as is.

 

I'm VERY happy with the kit I bought from Roger. Here you can see the new laying on top of the old. Shed at least 30-40 lbs from stock.

 

I'm running a large (3 or 3.5" can't remember) single exhaust on my '87. Borla muffler and resonator after dual hi-flow cats installed by PO. I believe its an early Devek system. Car has a wonderful deep, smooth sound. Unlike any 928 I have heard. A bit loud and drones a tad on the freeway though. I wouldn't have installed it myself but don't feel the need to pull it off either.

 

I have an 84 that uses a 85 stock cat (dual out) into a single pipe system.
I had a muffler shop build a Y-adapter that fit onto the exit of a 32V factory cat.
Then, they sliced the 4-bolt flange off the inlet of an 84 single pipe cat-back.
Welded the single pipe system to the exit of the Y.
This was done to economize and stay compliant.
Can't find the pictures. Simple conversion though! You could do it !!!. Just use a custom Y with a bigger outlet than I used.
Then you can select light tubing for the pipes.




Since we are archiving exhaust pictures on this thread ----
Separately, here's the MSDS / twin dynaflow / Spintech with an oval Magnaflow tip. Pipes are 3 1/4 OD.
This system has a Y that is "big" both inlet and outlet.
The pipes are very heavy on this particular system -- could be much lighter
(The MSDS are 3mm smaller in diameter at the heads than the 85/6 tubular headers (similar to 87-on also)).