gruffalo

Hi,

In my search for the perfect exhaust system, I have yet to succeed.

My current setup has made the engine run smooth and strong, and the dreaded hesitation 1500 - 2000 rpm is gone.

But the resonance in the 2000 - 2500 range in unberable.

In my search for perfection I've come across adjustable aftermarket mufflers. (Porsche and Ferrari has adjustable OEM systems, we all know....).

http://aebtec.com/default.htm anybody familiar with this?
It costs (bloody) $600 !!!

Any others around? Or separate valves/butterflies for DIY?

hacker-pschorr

My 79 has MSDS headers into a Y pipe with an adjustable muffer in the place of the OEM. I almost never close it, but it is a nice option for 3am drives through the neighborhood.

gruffalo

what type of muffler have you got?

hacker-pschorr

Previous owner made it himself. I have a cable under the e-brake housing to adjust it.

Fabio421

Hacker.. is the muffler itself adjustable or does the cable close a bypass port similar to the way the old hot rods would do it?

hacker-pschorr

The cable closes a butterfly valve forcing the exhaust to enter a muffler chamber.

I just remembered there are pics of it here:

http://members.rennlist.com/pageauto/guess.htm

toofast928

c'on, your pullin my chain.

Garth S

Do you still have the OEM resonator installed? My '80 has a gutted cat, the mini OEM resonator ( like the S4 'GT' type), and a rear muffler ..... no resonances .. aka " resonator" = resonance terminator - it works, and next to zero backpressure.

hacker-pschorr

About what, the adjustable muffler? It's not pretty, but it works great and you cannot really tell its not the original unless your a 928 buff, visually at least.

MSDS header go straight into the muffler pictured - nothing else inbetween.

My 81 has the stock manifolds with the original CAT, nothing after that except empty pipe - sounds awesome and tame enough for street use.

Garth S

Sorry - meant to direct the question to Gruffalo, as he is experiencing the resonance: Anyway, your system 'sounds' to be resonance free.

hacker-pschorr

Video:

Here is the 79 with the muffler open:
https://rennlist.com/forums/showthre...ighlight=video

Here is the 81 (not the best quality, but you get the idea)
https://rennlist.com/forums/showthre...ighlight=video

gruffalo

I have a y section in to a single 3" in place of the front muffler, no cats. Then I have an OEM sized straight thru mid muffler, and the smallest rear muffler you've ever seen.

So basically 3" SS with mid- and somewhat rear muffler. By "straight thru" I mean there is a perforated 3" pipe straight thru the "can".

How would it change the situation to go to a larger rear muffler? Would that move the resonance to a lower frequency?

MM