Internal exhaust mod
 

As I mentioned in the Crios Mod thread, I had an idea on how to modify the stock muffler for more sound without any visible traces on the outside. Now it's done!

The idea was to do it like this:
http://986forum.com/forums/uploads02...1467036314.jpg

Make an opening on top of the muffler, right where the exhaust inlet is, drill a hole straight through the inlet pipe so the exhaust gasses can take a shortcut to the pipe that leads straight to the outlet.

I bought a second hand muffler for virtually no money at all (like $60) and paid a skilled welder and metalworker less than $100 to get the work professionally done.

On to the pictures:
http://986forum.com/forums/uploads02...1511252139.jpg
The holes were marked...

http://986forum.com/forums/uploads02...1511252173.jpg
...and cut.

http://986forum.com/forums/uploads02...1511252214.jpg
I chose a 12mm diameter for the holes. They go straight through the inlet pipes, so there's two holes in each pipe.

http://986forum.com/forums/uploads02...1511252286.jpg
If you look closely, you can see where the outlet pipe is. (top left corner)

http://986forum.com/forums/uploads02...1511252334.jpg
All welded up! He could have made it better looking, but since it's on the top side of the muffler, it won't be visible. Making it prettier would have taken more time, which would increase the cost. I'm happy with it.

The next step is to clean up the muffler, perhaps paint it with some heat resistant paint and polish the exhaust tip.

During the winter I'll see if I can mount it on the car, which is currently 400 miles away, and see how much of a difference it makes.

How do you like the sound? I made my holes much bigger than that and still feel it could be a bit louder.

I don't know. As I mentioned in the post, the car is 400 miles away, so it's not mounted yet. I will make sure to record the sound before and after, though. Updates will come, perhaps as soon as in April. :D

Edit: Considering your experience, I think I'll get in touch with the welder again to have the holes redrilled to 20mm instead.

Well, the welder screwed up his math and instead of increasing the diameter of the 12mm holes, he added an 8mm hole on each side. Beacuse 12+8=20, right? :P
Anyway, I decided to give it a shot and install it anyway. Here's the result.

https://www.youtube.com/watch?v=Q4-6uec4U_E

I quite like it. It's a bit louder, but not anywhere near obnoxious. And considering that the wife will drive it 300 miles on thursday, that's probably a good thing.

If I still want more, I can always add a couple of Crios holes as well. ;)

I like this idea. I have a spare muffler I'm going to try this on. I'm planning on going way bigger though. At least 1 1/2 inch holes. :eek:

Nice :cool:

Still loving mine. It's just about the perfect exhaust: nice idle growl, loud (but not too loud) at higher rpm and no drone. :)

You went with 1 inch holes correct?

I went through both sides of the pipe with a 1" bit, so two 1" holes for each inlet pipe. The area of a 1" hole is 0.79" sq., so I have 1.58" sq. on each side of the muffler.
For reference, a 1.5" bypass pipe has a cross sectional area of 1.77" sq., so I'm fairly close to a 1.5" pipe. ;)
A 2" bypass pipe would be 3.14" sq.

Though I do love it, if I did it again, I'd do a third 1" hole on each inlet. I wouldn't mind just a tad bit more. :D

After having driven it for a bit, I realized that I want it a bit louder. I think I'm going to do the Crios mod as well.

It's not what I had originally planned, but since the welder screwed up the measurements and the muffler is mounted on the car, I think it's a reasonable solution.

Am I missing something, why cut into the box, why not drill straight through? It's not like you could miss the pipe internally.

Either way, you'll have a hole that needs a plate welded on. Cutting a larger hole would certainly make the work a bit easier.

You're not going to drill through the body and pipe in one pass, anyway. You have to drill or cut a large hole through the body, then center punch the pipe so the drill bit doesn't just slip off of it.

http://986forum.com/forums/uploads02...1529883277.jpg
Would it make sense to make the cutout on the bottom of the muffler and only make a hole on the bottom side of the inlet pipe? I ask because the outlet is below the inlet pipe. So if you only made a hole on the bottom near the outlet, it would seem more sound would make it to the outlet. Maybe it doesn't matter either, not sure about it. What do you guys think? To be clear, blue line on left side is inlet and the red line below it is the outlet to the tip on the left side.

I really don't think it would matter. I went clean through the inlet, so there are holes on top and bottom, anyway.
The benefit of doing it from the top is that it looks 100% stock since the welded on plates are hidden up top.

Side note: I went through a short tunnel the other day...holy balls! It's sounds beastly! :cool:
I'm going to have someone do a video of a drive by soon.

BTW, I made my holes larger.
To avoid grinding down the welds to open mine back up, I took the muffler off (I'm a pro at this, now :D) and used a piece of steel bar to make my holes oblong by going through the muffler inlet. I sharpened the tip of the bar to a chisel point, then used a 5lb sledge to hit the hole edge on with the chisel.

Rough estimate is that it's equivalent to three or four 1" holes per side, now. Sound is great and I'm satisfied now. :)

Yeah I was definitely planning on making my holes bigger than one inch. I'm glad you tried it first :p It's too bad a 90 degree drill wouldn't fit into the inlet pipe. That way you wouldn't have to cut into the muffler shell at all. Although it may be possible to fit a sharpened bar with a 90 into the pipe. Then you could wack it with a hammer. HMMMM

It was only because I wanted the muffler to look completely stock from the outside. ;)

Guys, is the internal modification ANY different in sound then adding the external pipes like others have done? I too do not like the look of added pipes welded on and prefer the stock look but I can't help but think by diverting some of the exhaust prior to entering the muffler you would get a slightly beefier sound using external pipes. Otherwise why would places like Fister or even Pedro's Exhaust not use the easier route just to drill out the pipe.

Thoughts?

Here's a video...you must listen with good headphones or you'll miss all of the low rumble.
Sorry for the wind and interstate noise.

https://youtu.be/qzBn-q5h25o


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Any drone with this?

Drone? The ear-splitting, make your head ring/hurt, resonance?
I'd say no. It's definitely louder in the cabin, but nothing that bothers myself or my wife when cruising around town or on the highway.

I know 90% of the drone on my Circuit works exhaust is from leaks. The 2 bolt clamps up near the cats will leak if I don't tighten the hell out of them. The ones closer to the muffler leak even worse. I even bought new clamps and they still leak. I'm positive that the muffler pipe diameter is a touch less than the stock muffler due to thinner metal. No matter how far I shove the C pipe in or tighten the clamp it still leaks. So i'm just going to mod my stock muffler, buy new 2 bolt clamps and be done with it.

I know you say you're done with it, but have you tried something like packing fiberglass cloth in the gap before tightening?

Well I thought of placing something in there to take up the extra space....but I actually just cut into my stock muffler at work. Right now i'm at a 1/2 inch hole all the way thru the pipe. I have to run to the store and get a bigger drill bit. I'm thinking going with 2 one inch holes all the way thru the pipe.

Progress so far.

http://986forum.com/forums/uploads02...1530140986.jpg

http://986forum.com/forums/uploads02...1530141003.jpg

http://986forum.com/forums/uploads02...1530141020.jpg

Both of the holes on top are 3/4 of an inch. The holes on the bottom of the pipes are 1/2 inch on one and a little more on the other maybe 5/8. I had to make the bottom holes smaller so to not drill thru the bottom of the muffler with this bit set up. :eek:

Looking forward to your results, Tommy! :cool:

I got it welded back up last night. It doesn't look pretty, but it should work ok. I think i'm going to use a chisel to make the bottom holes into one larger one before I put it back on the car. Kinda like Particlewave style :cool:

OK I put the modded stock muffler back on the car. I still have a wicked exhaust leak at one of the 2 bolt clamps near the cat. So how does it sound? I think it sounds like a proper sports car now. The difference from stock inside the car is subtle. It is a little louder but you can still hear the intake. It has a much raspier tone then the twin can Circuit Works muffler. When at WOT you can really hear it once it hits the 5,000 RPM Variocam crossover point.

Outside of the car is another story, under a bridge or in a tunnel it screams. I had my wife rev it up in the driveway, it sounds awesome from outside the car. It has a throaty almost metallic sound to it. It sounds a lot like the FVD sound version muffler IMHO.

Even with the exhaust leak there is no drone in the car. With less of a leak the twin can muffler was headache inducing. I've ordered 2 new OEM Porsche clamps from our sponsor. When they come in I will take it all back apart, make the holes a little bigger and button it up.

If you don't mind the weight of the stock muffler and don't want to spend $1500 for the FVD muffler, then this is the way to go. I honestly think this sounds much better than the twin can mufflers. The tone of the twin can mufflers is a little deeper than i prefer and it's always kinda loud. The modded muffler is pretty tame during normal driving and under 5,000 RPM, but when you get on the throttle it sings. It even has a little burble on over run sometimes. I'll try to post a sound clip when I get the new clamps.

All this was done on a 2000 S muffler. It has two 0.75" holes in each top of the pipe, two 0.50" holes on the bottom. I used a chisel to open the pipe between the holes on the top and bottom of each pipe. It also has a Crios mod with 0.75" holes I did before.

Question (maybe a dumb one at that) does the Crios mod or one like you are doing affect passing CA smog?

The muffler only affects sound, not emissions, so I don't see why it would.

No I don't see how it could. It doesn't affect or alter any of the emissions equipment on the car. Plus the car will look stock, just a few hidden holes in the muffler :D

cool...thanks....time to bust out the punch then!

Nice, right? :cool:

I took the car on a 2 hour round trip yesterday. Cruising at around 3000rpm on the highway, the sound inside the cabin was just fine...a low rumble that was not at all bothersome.

As soon as you pass under a bridge or through a tunnel, especially at higher rpms, sound is intoxicating! :D

Yeah I agree. The little 2.5 sounds raspy...kinda like a mini GT3.

Drone is caused by fitting a muffler that weighs significantly less than the OE muffler. Unlike most cars, the Boxster muffler is suspended by the same mounts as the motor and transmission, and they are simply "tuned" to the original weight.

I'd be fairly certain a little gutting of an OE muffler won't make much difference in terms of weight.

Another pretty easy was to improve the sound of an early 2.7 or 3.2 is to fit a 2003-4 OE muffler.

Bolts right on, sounds way better, interchangeable tips.

No, Kent.
Drone is caused by lack of a phase chamber or crossover pipe where opposing pressure waves can cancel each other out. Weight has nothing to do with it.
Also, the '03 sitting in my driveway right now sounds an awful lot like my stock 2.5 did before the muffler bypass. :confused:

There's no comparing stock to the internal bypass. ;)


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My exhaust system is 17 lighter than stock and I have no drone. My muffler does have a crossover pipe though.

I spoke with a guy at a local muffler shop about this yesterday. I'm going to get it done next week. Can't wait!

I'm sure you'll love it ;)

Just make sure you get at least three, if not four 1" holes on each side (or equivalent).

so here's my cheap chinese muffler that drones like crazy at 2500-3000rpm but otherwise sounds pure bred and high strung.
how would one add a cross over pipe to reduce drone and would it even work?

add a small pipe connecting the two exhaust tips which is downstream from said muffler? or maybe a straight pipe connecting each muffler together?

http://986forum.com/forums/uploads02...1561692208.jpg