$100 Muffler Mod 1 in 2 out + Sound & HP

[jhubs]

Several people have emailed me and asked how I made the modification to my stock muffler 1 in 1 out, to a 1 in 2 out. So, I’ll post it here for everyone.

If you don’t want to spend a lot of money on SSI’s or M&K, but want better sound from your 911 and 4-5 more HP, you might want to consider this simple modification to your 1-in-1-out stock muffler.
And, it is very inexpensive! It's like going from one speaker on your sound system to 2 speakers with larger woofers. The sound will be lower and louder. My neighbor, Jim, did this last year to his 88 911, he gets all the credit/blame here!



If you don't want to cut a hole in your rear (the cars) you could add the second hole in the right side of the muffler and have the pipe installed and turned down. you will not see it, but will hear it.

I made a cardboard pattern of the hole in the valance on the driver's side. Then turned the pattern over and measured and transferred the pattern to the Passenger side valance. I marked it with a sharpie and cut it out with a round diamond blade/wheel on my Dremel tool. The blades are cheap at Harbor freight. It took about 1/2 hour, and two blades, as I went slow and was careful not to slip and damage my fender. I finished the cut out with a 1/2" grinding wheel on the Dremel and painted on a reddish primer with a sm. brush.

I took my 911 to the muffler shop. He took the muffler off as he did not want to cut and weld in such a tight spot and damage any oil lines etc.
He cut a hole in the end of the muffler the proper diameter I requested and then cut and bent a pipe to fit. He then tacked welded the tail pipe on and remounted the muffler to check the angles of the pipe in relation to the hole in the valance and if it looked the same as the driver's side pipe. He adjusted it and welded it on. Then he welded the SS tips on.

I got the SS polished tips on ebay for $9.99 each + $9 for shipping. Just type in... 3" Stainless Steel Chrome Exhaust Muffler Tip EX-1001, then have the muffler guy cut the 3 bolts off the SS tip and weld them on. They are rolled ends and angled.

Total charge was $67 for muffler work + $29 for the tips = $96

The new sound of the two pipes is incredible...very low and throaty... stereo like. Not loud and annoying, but really sporty, but not obnoxious. I have WebCam 20/21 High Performance Cams and that makes the sound a little lower and louder from the start. But, my neighbor has stock Cams and he did the same modification, 1 in 2 out, and his 88 911 3.2 sounds perfect!

Right side new pipe and tip.



Oh, I should mention that I put in a "Sport Muffler" Steve Wong Chip, but that does not change the sound, just enhances lower end RPM torque.

I am definitely no expert and I'm sure it is possible to find data that will support any theory regarding HP and mufflers.
But, in Bruce Anderson's book, EXCELLENCE Technical Notes, page 46, on Exhaust Systems, he states that his Dyno test data showed an increase in HP, with different engines and different muffler configurations, from 4.6% to as much as 10.5%. Some of these %'s were at peak power and some at 3500 RPM.
What really surprised me is that his data showed, that by simply adding a second pipe to a stock muffler on an 88 3.2 Carrera, an increase in HP at peak of 5.75%, and that's 11 HP!

Actually it is really more like 3Hp @ 5500RPM and 6 HP @ 6900RPM. Ok, I'm happy...I'll take better sound and +5HP for $100 !

...right foot all the way down... and Good luck. jhubs

[81 911 SC]

Excellent write up. The muffler looks very nice.

[Al S]

What size hole did you go with, and do you get any resonance or droning at freeway speeds?

Thx

Al S

[jhubs]

The hole was for a 1 1/2" (38mm) pipe/ outside diameter, inside diameter of pipe for hole was 1 1/4" (32mm)... the hole was probably 1 1/2" as the pipe was inserted into the hole and then welded.

You could weld on a short 1" pipe and then a 3 bolt muffler bracket and bolt on the pipe and tip or a cover plate to cover the hole if you want to block the sound for some reason...? I don't weld, so I skipped over that idea.

No resonance or dorming at high speeds that I noticed...had it up to 120...sounds great.
J

[mthomas58]

This is just what I didn't need to see!

Nice work!

[SCWDP911]

sub'd

[jhubs]

Mark, WHY?

v8_ranch, I love your Ruby Red!!!

[SCWDP911]

Originally posted by jhubs
Mark, WHY?

v8_ranch, I love your Ruby Red!!!

Thanks! If only I had some Fuchs...

Nice thread, Jerry. thinking about trying this when I install my M&K 1in 1out next week. Then swap back to see the difference. One thing about exhaust notes, they tend to be "beauty in the eye of the beholders"

[mthomas58]

Jerry, half kidding - I don't really NEED any additions to my projects list.....but always looking for ideas. Sure like the balanced look of two out.

Again, nicely done!

[yngwie1]

sub'd

[jhubs]

v8_ranch,
pm me and maybe I can help you out.

J

[Tim Hancock]

For those contemplating this, I did this also, but made the new 2nd outlet a bolt on affair to allow me to install a block-off or restrictor plate in it for long trips etc.

Here is a link for reference showing and detailing how I did mine. It sounds better (to me anyhow) than stock, but it is not as sporty sounding as Ben's mufflers. DIY stock muffler mod, 1 out to 2 out, SC

My SC sounds kind of like a muscle car at idle, and sounds "OK" when you get on it. My mod was worth the effort, but after hearing some recnt sound files of Ben's, I think I will have to upgrade to one of his one of these days.

[munsonbw]

While on the topic of muffler modifications, anyone ever try to make a 2-in, 2-out? This probably more work than its worth, but I will be adding early HEs to my SC and will have a useless muffler. Add time and a welder... sounds like a project. I found a diagram of an early muffler, but nothing on the SC vintage 1-in, 1-out.

Comments????

[jhubs]

Tim,

Thanks for the addition to the thread! What is the distance from the muffler body to the welded on flange?

J

[jhubs]

Tim,
This is the distance I'm interested in, in this photo of your post.



It looks like around an inch?

J

[Tim Hancock]

About 5/8" from the back of the 3/8" flange to the muffler body Jerry (the short section of tubing was probably a bit longer so that it protrude slightly into the odd shaped hole sawed opening).

My flanges were just made from some 3/8 steel I happened to have on hand. They are a bit heavy, but I wanted plenty of thread in the tapped section so I did not have to use nuts (easier to quickly remove the anti-seized bolts with a socket on an extension while simply laying on the ground next to the car).

I only ran a restricter plate (made from 16ga sheet metal) one time when my wife rode 6 hours or so with me to the Hershey swap meet last year. It is really not all THAT loud even with the full opening.

Nice looking car by the way and I like your high quality looking tips!

[jhubs]

Tim,
The sound of my 911 really is quite cool! It is louder and lower than the factory 1 out. Maybe the Cams have something to do with it being a little louder than you described yours.

I would like to design something (other than a cap on the end of the tip) that I could put inside the pipe and turn or rotate from the outside to close it off or turn it back on (you know, the wife thing on long trips).

Oh, what did you paint your muffler with?

jubs

[jhubs]

Thanks Dan! I'll work on the Adjustable Tailpipe Noise Apparatus....

[jtratza]

I did the same after a rebuild that included a set of 964 grind cams. Very loud without the cat but I like it. Sometimes to me it sounds like nothing more than a hole in the muffler...which it is. Next step is a lighter muffler since the stock one still weighs some 30 lbs and is probably just as loud as an aftermarket job.

[Tim Hancock]

Originally posted by jhubs
Tim,
The sound of my 911 really is quite cool! It is louder and lower than the factory 1 out. Maybe the Cams have something to do with it being a little louder than you described yours.

I would like to design something (other than a cap on the end of the tip) that I could put inside the pipe and turn or rotate from the outside to close it off or turn it back on (you know, the wife thing on long trips).

Oh, what did you paint your muffler with?

jubs

Don't get me wrong, it is definitely louder than stock, but it just is a tad too musclecar loud sounding. I like it better than the stock sound, but after hearing some recent sound clips of the M&K, I find myself thinking about buying one at some point. For the record, I had the cams reground to Elgin's "Sport SC" grind when I rebuilt my engine.

I forgot to mention I also modified my pretty much blown out cat by cutting it apart and modifying it internally to more of a cat bypass type configuration. This probably also alters my particular car's sound. DIY cat mod experiment

After revisiting this cat mod post, I am thinking I need to redo this someday when I get some free time as I don't like how the mini chamber in the cat transfers to the single perforated tube. Too many projects and hobbies, not enough time!

I don't recall the brand, but I just used some kind of high temp paint readily available at Auto supply stores. After nearly two years of use and maybe 10-15k miles rain or shine, it has held up "OK", but there are probably better solutions available for finish coating.