968 muffler replacement ideas

[968rsr]

My muffler is making a rattling noise and needs to be replaced.

It has the factory muffler with two pipes going in and one going out to the exhaust tip.

Has anyone replaced it with a single inlet pipe set up? I'm not into welding but can use a reciprocating saw or hack saw and pipe expander if this will work. Let me know. Thanks

[flash968]

unlike any other engine i have ever dealt with, the 968 is extremely touchy about exhaust changes. to date, with over 20 systems tested, all but one have resulted in torque loss. i would be very careful about what i chose.

you should be able to pick up a used stock muffler very easily. expanding the end of the pipes would then be easy, and you could slip it on and clamp it.

[speedysprocket]

On the topic of 968 exhaust, will I be losing some using my 944 exhaust with Dansk muffler on my 968 engine..?

[flash968]

i would need more information (i.e. tube size, merge points, muffler design, cat, etc)

the dual resonant intake, unique to the 968, coupled with the variocam, create a situation where pulse timing is very critical. opening up the exhaust results in midrange and low end torque loss. restricting it results in upper range horsepower loss. cat removal turns everything to crap. that is going to be the big one. the 968 engine likes the 968 exhaust, and particularly the 968 cat. i've tested the aftermarket cats, and none of them work well. all of them messed with the O2 sensor readings, and all of them resulted in low range loss, mid range loss, or both. of all of the systems out there, and all of the other mufflers and resonator and tubes tried, only one managed to not lose anything, and it fits goofy. none of them gained anything without losing somewhere else. i personally spent $11k trying and testing various things, with no real success.

this gets really messy if you are in california. an engine swap means that you are now required to have whatever the engine came with, not what the car came with.

[speedysprocket]

Well it's the 87 S exhaust. Cat insides fell apart a long time ago, so it's currently empty. And since the car no longer needs to go through emissions, I was planning to do a straight pipe in place of the cat at some point. The tail pipe/muffler assembly seems to be pretty close to a stock replacement for the 944, except it's stainless. I think that exhaust is all 2 1/4" tubing, single tube... I do have an after market clamp in cat used for the car's last ever emissions test if it would help...

[flash968]

the 968 engine does not run right without the 968 cat. been there - done and tested that. the O2 sensor gets bad readings, due to the accelerated flow, and goofs up the mixture as a result. there is also a fairly large torque loss below 3500.

as for tubing size, a 2.25" tube is too small for the 968. even 2.5" is a bit on the small side, if you wanted all of the upper end available, but 3" is way too big. the key to any tubing though is to have it mandrel bent, and not press bent. press bending creates resistance and turbulence.

porsche went to great lengths to design the 968 exhaust. there is quite a bit of info out there about it. it's not nearly as simple as with other engines, very different than the S2, and very touchy about changes. things that work on every other car, just don't work on the 968. it has really been a pain in the butt. i've thrown away a LOT of money trying to figure things out.

if i had to guess, using the 944 exhaust, with no cat, will cost you about 10hp over 5krpm, and about 15 lb/ft below 3500.

if i had to build my own, for a street car, assuming you can't find a 968 cat, i would find the biggest aftermarket cat i could find, to slow things down as much as possible, run a 2.5" mandrel bent pipe, and use a 2.5" perforated (not louvered) resonator up front, with a 2.5" in and out reverse flow muffler in the rear. that will be your best compromise for flow, sound, and power.

[968rsr]

Thanks for all the great information.

I didn't realize the 968 was so touchy with the exhaust system, I guess I'll be looking for a used factory 968 muffler or 968 cat back.

Thanks again.

[flash968]

yeah - i never would have suspected it either. it was only after spending a lot of time and money, and actually conducting tests, that i figured out what was going on. made me a bit nutty at the time.

now that i am putting out about 350hp, i am back at it all over again - ugh

[Gawernator]

And to think Flash could have just gotten an epic 911 for that money, hehe

[v2rocket_aka944]

flash, any recommendations for a decent perforated resonator, without breaking the bank?

[flash968]

i've been using the magnaflow resonator up front. the fiberglass burns out after a couple of years, but it works pretty well until then. they make a few different lengths.

[v2rocket_aka944]

how did the FG burn out?!
does the unit still quiet effectively without the FG?

[flash968]

fiberglass burns out of any muffler or resonator that uses it. it's the nature of the beast. that's why a lot of companies are going to ceramic.

the sound deadening effectiveness of any fiberglass muffler or resonator decreases as the packing burns out, though the performance is far less affected. it is a slow gradual process, and how you drive, and the heat generated, play large roles in the rate. the good news is that they usually rust out on the inside at about the same rate (yes, even stainless ones), so you are going to be in there replacing it anyway

[v2rocket_aka944]

The 944 muffler is a FG-packed piece too...I wonder if they've lost their effectiveness over time?

How long would you say a fair "life-cycle" is for one such Magnaflow resonator? 5 years?

[flash968]

mufflers last longer than resonators. heat is the cuplrit here. mufflers are farther away from the heat. temps drop dramatically the farther away you get.

how long they last depends largely on how the car is driven. run it hard, exhaust temps go up, and lifespan goes down. just cruise around and it will last a lot longer. i've burned them out in 2 years, and had them last 6 or 7. it really depended on the driving.