Modifying early 911 muffler, Opinions needed Options

[dion9146]

Hey guys, thought I'd ask the 914 crowd for an opinion....I know, that can be dangerous.

Check out this thread I started over on the bird board. I'm looking for a nice, lower rumble using a stock early 2 in, 1 out muffler. I do not want to modify it like the early 2 out sport style, Yes, that's too loud for what I'm looking for. I'd like to stop setting off car alarms in my client's parking garage.....

So before I start cutting, I wanted to get your opinions on what and how much I should cut. (IMG:style_emoticons/default/sawzall-smiley.gif)

http://forums.pelicanparts.com/porsche-911...ons-wanted.html

Thanks,

Dion

[dion9146]

really, nothing from the 914 crowd?

[pcar916]

I have both cars and had an early 911 muffler in my 914/6 conversion with a modified 2.7L motor. It was a 2-in and 1-out version and far too restrictive. Here's a cutaway view of the internals of the early muffler. It's part of a description on how to convert one to an early muffler but will do for our purposes.



This Helmholtz resonator has several places to cut, but the only place I see to get lower db readings is in the upper chamber with the solid divider. Anywhere else you add a pipe is open to the inlets. That makes for an interesting problem since you don't really have a lot of space there. Hmmm....

If I were determined to make this project happen I would cut holes in the bottom of the solid divider (not a single one) and run them internally out of the bottom holes. It would look like a sport muffler but the internal pipes simply shunt off upstream from the original single outlet.

Alternatively you could use a new hole (like the one shown in the mod) in the side divider and run another tube out the end next to the existing pipe. If it were run along the existing one you would have a dual outlet from the same final chamber.

The internal welding would require cutting the bottom of the muffler body and rewelding it back into place after the mod is done. Dyno results will tell you if you've broken the code but it will be quieter than the sport muffler to be sure.

Prototype with a steel muffler and make the final copy as a stainless piece.

Good luck

[Joe Bob]

Gutting the muff, adding dual outlets as above BUT leaving the stock exit will allow you to cap the twin outlets. Quieter for around town but good for the twisties when ya wanna blast it.

OR just gut it as detailed with the single stock outlet.

BTW, I will have a dual in single out, stock 911 muff available soon.

[dion9146]

Thanks guys. If I put dual outlet on, I would probably never uncap them, so that's not an option. Besides, too many people are having issues with droning of the sport twin pipe config. I considered adding a twin tailpipe on the other side with a smaller diameter outlet, but that is plan B at the moment and something I can do after the fact.

I'm not overly concerned about added HP, and I don't think anything I do to the internals will screw with the FI based on what I've read. Besides, if my seat of the pants feel determines that I've robbed HP, then I take it back off and put the old one on. No big deal, and I'm not concerned enough to pay for dyno time, that's for sure.

I've attached a pic of what I'm thinking. The orange areas would be removed. Based on the airflow, and potential changes in pressure based on acceleration, etc., this gives the gases multiple routes to escape faster and with less restriction than the stock routing. Will it give me what I'm looking for? Hell, who knows, but I think it's a good compromise between the minor mod of doing nothing to completely gutting the muffler. The complete gutting probably sounds good, but has to be way too loud for what I'm after.

[Joe Bob]

I run a Supertrapp on the end of mine. It controls both back pressure and dB level.

[pcar916]

Based on the airflow, and potential changes in pressure based on acceleration, etc., this gives the gases multiple routes to escape faster and with less restriction than the stock routing. Will it give me what I'm looking for? Hell, who knows, but I think it's a good compromise between the minor mod of doing nothing to completely gutting the muffler. The complete gutting probably sounds good, but has to be way too loud for what I'm after.

Looks like a fun experiment. I'm thinking the transfer pipe cuts are redundant based on the solid divider cuts, but we're guessing here. The reason is that if the total area of the slots in the slotted pipe is bigger than the area transfer pipe inlets, the gas will try to return into the muffler (to the right) rather than exit the muffler. My guess is that this mod will make the muffler resonate less, so you'll lose some of that typical "throatiness". There will be lots of pressure "micro-climates" in that box that will move around and change based on RPM (exhaust pressure and pulse duration). That may not be a bad thing. Chaos is often our friend.

Let us know the sound you get from it! Looks cool! (IMG:style_emoticons/default/aktion035.gif)

[dion9146]

Good feedback Ron. But if you also look at the suggested mods to the solid divider cuts in the original article when installing the 2-out sport pipes into the lower chamber, it makes no sense at all. Why even modify the upper chamber when the exit is welded shut, and all of the exhaust pressure is entering AND exiting in the lower chamber?

That's why I got creative with the spraypaint brush. (IMG:style_emoticons/default/smile.gif)

[Eric_Shea]

Here's mine:

(IMG:http://www.914world.com/bbs2/uploads/post-2-1103132975.jpg)

I followed the instructions for the sport pipe mod. I listened to a car with this muffler before I did and, it really wasn't loud from the outside unless he was getting on it. Very streetable so, I decided to plug the original exit wound.

Some things to note (as I can remember them):

1. It was a bitch to cut through the skin(s). Multiple layers of steel wrapping. Not what I would call entirely fun so... be aware of this. A cutting torch may be better (IMG:style_emoticons/default/confused24.gif) The only problem I see there is, it;s hard to get a clean edge with a torch.

2. I did finally use a cutting torch for those pieces on the inside that needed to be removed or opened up. I don't see any other way to get at them frankly, unless you're opening up the entire muffler.

3. I used 2" pipe. You're local Midas or Mineke probably has a metal scrap dumpster on premises. The pimply kid behind the counter thought it was a cool project so he gleefully ran out to the dumpster and grabbed me a couple 10" sections and handed them over gratus.

[ArtechnikA]

When I did mine back in the day I just hacked into the upper chamber and cut out the half-bulkheads, then brazed it back together. Looked stock on the outside since the mods were in the top half. Definitely louder on the cam. More power? Nobody had real dynos in those days...

[dion9146]

3. I used 2" pipe. You're local Midas or Mineke probably has a metal scrap dumpster on premises. The pimply kid behind the counter thought it was a cool project so he gleefully ran out to the dumpster and grabbed me a couple 10" sections and handed them over gratus.

Eric,

Did you have any droning problems at speed on the highway? That seems to be the biggest complaint of the sport mufflers.

[dion9146]

When I did mine back in the day I just hacked into the upper chamber and cut out the half-bulkheads, then brazed it back together. Looked stock on the outside since the mods were in the top half. Definitely louder on the cam. More power? Nobody had real dynos in those days...

Thanks Rich. I'm assuming that would be 2 of my 4 orange spots above.

[pcar916]

Good feedback Ron. But if you also look at the suggested mods to the solid divider cuts in the original article when installing the 2-out sport pipes into the lower chamber, it makes no sense at all. Why even modify the upper chamber when the exit is welded shut, and all of the exhaust pressure is entering AND exiting in the lower chamber?

I agree until after a little totally theoretical noodlin', I figure they cut on stuff until either the back-pressure readings were matched to the carbs or, less likely, they were trying to keep the same approximate volume in the canister so the timber was what they were shooting for.

The later sounds more like Ferrari than Porsche, but a smaller cavity will definitely sound different. The original muffler resonated out lots of the pulses and kept drone to a minimum. The 2-out sport muffler definitely has a 4000 RPM drone in a 2.7L motor. I don't know about the current 3.6L. I have SuperTrapps now anyway so my 2-in 1-out has been in the attic for the last 11 years.

Frankly, the sport muffler on a 2.x Liter Porsche motor is one of my favorite sounds in the whole world. No matter what I do I'll never achieve it with this 3.6. I can't even experiment anymore. An auxilliary oil cooler is in between the pipes now.

The way you have it drawn may be the bomb. Be sure to let us know! (IMG:style_emoticons/default/driving.gif)

[Eric_Shea]

Did you have any droning problems at speed on the highway? That seems to be the biggest complaint of the sport mufflers.

It would have to be running for that... (IMG:style_emoticons/default/biggrin.gif)

Droning is a good thing. It helps you sleep. (IMG:style_emoticons/default/wink.gif)

Seriously, with the ZA should be at 3.5k at speed so, I'll probably be close to that issue if there is such on my 2.5

[r_towle]

I have a brand new Bursch muffler for an early 911 that I am bringing to Hershey if you want to use that...
The muffler is simple to cut off and replace and lots of different types.

Rich

[ArtechnikA]

When I did mine back in the day I just hacked into the upper chamber and cut out the half-bulkheads, then brazed it back together....

I'm assuming that would be 2 of my 4 orange spots above.

Not quite.
I left the center half-bulkhead in place and hacked at the two on the sides. I'm thinking now I couldn't have ripped out the whole thing with the limited tools and equipment I had at the time and probably just cut out the "aft" half or so.

I never noticed droning but as Eric has observed, 4000 rpm is ~90mph in top and one doesn't get to cruise there very much.

I had a Leistritz TPSM on the 911 (2,2E) and never noticed droning, but the 911 doesn't have the rear trunk over the exhaust to act as a resonator...

[dion9146]

I have a brand new Bursch muffler for an early 911 that I am bringing to Hershey if you want to use that...
The muffler is simple to cut off and replace and lots of different types.

Rich

That's what I have on there now, and that is an option potentially. I also don't like the way the Bursch hangs down below the rear valence which is another reason for the change.

I bought this one at Hershey 7 years ago. (IMG:style_emoticons/default/smile.gif)

Dion

[ChrisFoley]

You're looking for a muffler with a deep tone, not too loud, good ground clearance, no drone, and low backpressure for better performance right?
The Tangerine-6 meets all your criteria.

[dion9146]

Thanks Chris. Beautiful headers and muffler, but a little too rich for my budget at this time.

Maybe someday.

Dion

[dion9146]

OK, I was looking at it again last night. Call me sentimental, but I just can't bring myself to hacking apart the insides of a perfectly good early muffler. This thing is in such good shape, none of the metal is even starting to thin, anywhere.

So, I found this drawing on the bird board and I think it's what I'm going to do. Minor mods to the internals, add a second pipe on the right side, and start with a small hole then enlarge until I get the sound I want. I'll post a sound clip when I get it all done - hopefully this weekend.