Muffler options for an M491 with a 3.6

Tremelune · 05:34 AM

I am in the process of acquiring a monstrous beast that sounds like Smaug pillaging Lake-town. The sound is invigorating, but it is way, way too loud for the street. I am not a fan of loud exhausts. I'm hoping to get it as quiet as possible.

The car is an '84 M491 with the motor out of a '95 993. I am told the headers are from an '83 and they still have the heat exchangers (which I want to keep). The motor is otherwise stock. From what I've read about 3.6 swaps, you can't just put a stock muffler on...or was that headers?

I'm having trouble knowing where to start my research. Ideally, I'd like the car to be as quiet as stock without losing any power or messing up the air/fuel mixture, but I'm guessing that has more to do with headers than the can, correct? Anyway, if anyone has experience with 3.2 -> 3.6 swap exhaust options, I'm all ears...

Is this something I need to have made custom or can I just buy any factory 993 can and bolt it on?

arrivederci · 07-14-2014, 05:35 PM

I haven't heard of anyone using heat exchangers from an SC. That doesn't add up to me. Any chance you can take a pic of what is there?

Tremelune · 07-14-2014, 05:44 PM

I'll see what I can do. It's possible the headers are stock from the 3.2 and I misunderstood. They look OEM to me.

johnsjmc · 07-14-2014, 05:48 PM

Often the 993 HEs are used and then a 2 in 2 out crossflow muffler (Magnaflow) and a couple of small resonators are added. To keep it quiet you could cap one of the 2 outlets and use a 2 1/2 muffler.or better power a 2 1/4 muffler with both outlets open. Timmons used to sell a unit called a "happy crab"which is expensive but looks like what I am suggesting.
If extremely loud someone might have used the 993 catalytic convertor as a final muffler after the HEs.
SC parts will fit but are very small diameter and will restrict flow and power considerably.3.2 Carrera exhaust would be the same as a SC but slightly bigger.

Elombard · 07-14-2014, 05:50 PM

nope the 3.6 exhaust is totally different than the earlier cars.

Tremelune · 07-14-2014, 05:52 PM

Perhaps I heard "83" instead of "993"...Bah, sorry for the lack of info, I'm not yet in possession of the car. I was just hoping to get my ducks lined up.

clutch-monkey · 07-14-2014, 06:01 PM

i used the fabspeed system and extended the tips an inch or so to exit out of the valence.

Elombard · 07-14-2014, 06:29 PM

Have you looked at the options that Instant G sells? He has nice options. Not cheap. I think to get OEM quiet you will have to sacrifice some power/response and add quite a bit of weight to the back. There is some threads on this with a lot of good ideas and things that have been tried.

Tremelune · 06:58 PM

I'll take a look, thanks. If I can keep the headers that are on there, I would really like to. The car is anything but down on power. I do like my quick throttle response, though...

One thing I do not need is a catalytic converter. Perhaps I can look into a "pre" muffler if I can't find a light muffler that's quiet enough.

arrivederci · 07-14-2014, 07:06 PM

Do you need heat?

Tremelune · 07-14-2014, 07:24 PM

Yes, heat is a must. Defrost would be lovely, too. One day I even dream of good AC, but that's a ways down the list...

Elombard · 07-15-2014, 02:12 AM

There just is not a heck of a lot of room back there. cats help keep it quiet, does it have cats?

Tremelune · 07-26-2014, 04:12 PM

I have the car, but it's difficult to get under there to see what I have:

Elombard · 05:35 PM

You might try wrapping that bad boy with header wrap and if the muffler is open inside cap off one more of the outlet pipes and see what you think. I wonder what brand muffler it is. Looks the business!

Oh love the cat - not cats on that muffler set up though. Yeah I think Instant G makes a bolt on solution for the 993 Heat exchangers. I think those are OEM Bischoff heat exchangers there called and FWIW the heat is not hooked up.

Tremelune · 07-26-2014, 05:32 PM

It's not loud-loud-loud (it's quiet enough for Lime Rock), but it's way louder than I'd like in the neighborhood. I kinda wonder what it sounds like with those baffles removed, though...Must be pretty nasty.

Tremelune · 10-29-2014, 08:43 PM

From this 3.6 swap FAQ:

IG's 3.6 Liter Conversion FAQs

It looks like these are my options for a 1995 motor with heat exchangers and a 915:

- 3.2 headers, which are 1 5/8". Stock diameter for a 3.6, but restrictive.
- 993 headers, which are also 1 5/8". I'm pretty sure these are what are currently on the car.
- B&B headers with exchangers and a 1 3/4" or 1 7/8". A cool $2,000.

Some better photos:

Tremelune · 10-29-2014, 08:44 PM

If I'm not mistaken, it looks like I just need to find a way to get a quiet muffler attached to this thing and that will work. There are no cats, no space, and the thing is loud as hell.

Considering I have no way to fabricate anything, what would my next step be? Take some measurements? Research mufflers that might fit and have a muffler shop make it work? Ideally, I would like to get this car as quiet as possible while minimizing power loss.

Do I have to worry about air/fuel accommodations, or will the 993 injection system automagically compensate for modest exhaust changes?

Tremelune · 10-29-2014, 08:46 PM

Final addendum...There is not a lot of space for heating ducts...Has anyone actually gotten heat to work well in a 3.2/930 that had a 993 motor in it?

johnsjmc · 10-30-2014, 03:12 AM

Quote:

Originally Posted by Tremelune

Final addendum...There is not a lot of space for heating ducts...Has anyone actually gotten heat to work well in a 3.2/930 that had a 993 motor in it?

Yes. I used the 993 stock cast aluminum heat crossover and connected to my 1980 SC heating system . I removed the rear booster fan for space but everything worked just fine above idle. I even retained the AC. I used some orange high temp heater hose similar to original which I sourced from the small aircraft (Cessna) industry.

Bill Verburg · Bill Verburg's Garage

You have stock 993 headers plumbed into some sort of aftermarket muffler and no heat is currently hooked up(at least on the right side, can't see the left)

To use those headers and have heat ducts must be run from the header hets ou to the chassis heat in

It takes some welding skills to connect those header to a reasonably quiet muffler

here's one that is nicely done, you can see the left side heat duct(orange) in the background, I believe the muffler is a Monty, but a Dansk or oe 2 in banana would work too

Alternatively, ditch the oe 993 headers and purchase some aftermarket headers w/ heat shrouds

I used some custom B&B on my 993 t/p, they have 964 heat in and 911 heat out, it uses 964 heat crossover(just to the left of the Flowmaster(loud) muffler