Thank you very much, I decided I can't wait til Saturday, I'm doing it today instead. That way I'll be all set to take the car our for a nice drive on Saturday. In California we are in drought conditions and the temp has been running consistently in the low 70s, perfect topdown weather conditions.
I'll let you know how it goes.

Thanks guys

In the extreme, opening up the bleed holes in chamber 1 and 5 would effectively give you a free flow system. You would however have to remove the box to get to the ends, or cut holes in the casing.

I am not sure that the mixing of gases causes the resonance. I have just removed a Toyo free flow exhaust from my car due to the resonance (it was so bad my wife refused to travel in it) and there the two pipes and silencer boxes are completely separate ie there is no mixing of exhaust gas from left and right cylinders. I have had resonance before with stainless steel boxes and think it must be something to do with the vibration of the casing. I don't believe that modifying the std box will ever give you resonance, but then that's just my view.

I would have thought it was quite the opposite.
By design the stock exhaust seems to be designed to ensure the gasses from left and right collide, and therefore, equalize, and therefore not drone.

Where as the after market toyo had no such feature and hence drone?
Who knows?
Jake must have studied this at length...maybe he will chime in?

This is just speculation based on what I see; the equalization chambers should help prevent drone by introducing the opposing exhausts to each other, canceling out a lot of noise since they should be somewhat in phase with each other.
Obviously, exhaust gasses are a push-push system (as opposed to push-pull of sound waves), but I think phase canceling would still apply to a point.

In other words, the more equalization chambers that you bypass, the more annoying drone you will get. I think this mod (allowing some bypass of chamber 3) is about as far as the stock muffler can go without getting drone/resonance.

Son of a Bee-atch, I have a 01 Base and the exhaust tip seems to be welded into place, thus unable to remove. Now I can seem to have enough reach with my drill bits to actually make contact with the surface I need to drill. Am I missing something or just a tard?

Start the hole with a long screwdriver or punch first. Then the drill bit will have something to bite into. A couple of semi hard wacks on the end of the screwdriver or punch will do the trick. I tried to just drill at first, but the angle of the pipe would cause the the bit to slip. I didn't have to take the chrome exaust tip off. I hope this helps.

Same here...I used the sharpened 10" long bolt hole alignment tool as a punch (posted on the previous page) with my welded on tip. The punch is a must with welded on tips because of the angle and depth.

I'll give it a go, but not sure if bit will reach in there deep enough. I'll keep you updated. Thanks

I went on an upward angle and found it much easier.

As you can see, the 10" punch was more than long enough.

EDIT: my holes are 7/16", not 9/16". Definitely going to go a bit bigger before spring ;)

Last stage of the test complete. I had 15mm holes and it sounded OK - quite raspy though. I increased the size to 20mm and then to 25mm. Big difference. At 15mm you could hear it at idle and a little over that. At 25mm you hear all the time. Much deeper sound and louder.

I have updated my video (apologies for the sound of rain in the background in the last 2 tests) but I think the camera toned the sound down so if you listen to all 5 x recordings they sound the same loudness. In fact, the last one is at least twice as loud as the first.

Porsche Boxster 986 Crios Mod 2 - YouTube

Great comparison video chipmunk. The sound at idle and at lower revs is noticeable but there seems to be little difference at wider throttle openings and higher revs. Of course there is no load. Do you notice much difference when in the road at higher revs and wider throttle opening?

Now someone needs to get the angle and get 2 1" holes (25mm) in that middle pipe. :) If my car wasn't behind 2 ft. of snow I would do it.

I took my car down the motorway this morning to give it a proper test at different engine speeds and load conditions. The best way I can describe it is it's like a tame lion. It roars but doesn't necessarily follow through. When I had the Toyosports exhaust on I got a spine tingling racing car roar whenever I took the revs over 5000 rpm. You don't get that with this mod - you get the same type sound but in a much more subdued form. In fact I would describe my exhaust now as how I would expect a sports car exhaust to sound as standard - throaty but within acceptable norms.

What I will say is that there is a significant difference between 15mm and 25mm. At 15mm it's a bit raspy and you don't notice much difference except at idle. At 25mm it's much deeper (more like the sound of the SS free-flow systems) and has a nice purr to it at low and middle ranges, with just enough at high revs to let you know it's there.

Interestingly, while there is no resonance as such, there is a definite peak in sound volume in the car at 2800rpm. I have a feeling that if you went bigger than 25mm holes that you might end up back with the resonance issue, without the performance benefits of the free-flow system. This makes me wonder whether the resonance is more related to intensity of sound causing the car to vibrate, rather than the design of the exhaust - I'd be interested to hear whether anyone that has fitted one of the more expensive performance exhausts also has the resonance problem. My advise therefore to anyone thinking of trying this mod is - go to a max of 1 inch / 25mm. Bigger than that and you may regret it.

Update on my last post. I took my car for a long drive on Sunday and unfortunately, when under load on a slow incline, there is a drone. Certainly not as extreme as with the performance exhaust however a drone none the less.

My advice to anyone that is planning on doing this mod is stop at 15mm - possibly go to 18 or 20mm but 25mm is maybe too far.

Unfortunately in my enthusiasm I went from 15mm to 25mm without road testing so I can't say whether a middle point might have been better. What I can say is that I am now about to change my exhaust for the third time. Anyone passing through Kent this weekend is welcome to stop by and offer their moral support ;)

Really? Drone? What other exhausts have you had on the car? I have had many and yes there is a tone/sound (you can hear the exhaust) but not drone. I'm just curious as to what you are comparing it too.

:) well - I'm certainly not any expert on exhausts however my comparison is the Toyosport stainless system that I had on before. Currently, the exhaust sound is fine but at 2500 to 2800 it becomes more acute - what I would call a low grade drone. When the holes were 15mm this was hardly noticeable however now I have taken them to 25mm is has become annoying. Certainly not extreme like before however I guess it depends how fussy you are ;) It may also vary between different cars / engines / models / etc.

http://986forum.com/forums/uploads01...1390946893.jpg

That's too bad, but at least we know that there is a limit. Someone had to find out the hard way :(
Thanks for all your hard work and dedication.

I have 1" holes. You hear the exhaust but not drone in my case.

Okay you have all convinced me, NOT! Since I have been having trouble getting the bit to bite anyway and now I am hearing conflict on drone, nothing special in sound (from the sound bites I seen posted, I can't really hear much of a difference, maybe none at all), I'm leaving it stock and going to enjoy it as it was engineered by Porsche. Thanks for the thoughts and guidance but I'm standing pat, if I want more sound or different sound I'll put in a Borla or Magnaflo or something like that.

It's always difficult with something like this as the definition of what is or isn't a drone is often a matter of opinion. Also, my car will make any increased noise at the 2500-2800 range more noticeable as it's a tiptronic and likes to keep the revs there when doing 50mph (the speed limit on a lot of our roads). As I have said, the drone is fairly marginal (certainly not like before) so quite possibly what I hear as a drone JAAY may think is just increased exhaust noise. You really need to experience it yourself.

What I can say though is that there is a significant increased volume from the exhaust overall - the video clips don't show this as I think the camera has automatically adjusted the volume. With the smaller holes I could only hear the increased exhaust note at idle but now I can hear it reflecting off buildings as I drive through town, so a big improvement there. The sound is also much better in that it's not a raspy sound (a bit like a hole in your silencer - which of course is what it is :D) but a deep sporty sound. I just think (for me) I should have stopped a little sooner however others may think it's absolutely fine - especially if you drive a manual and don't spend much time in the 2500 - 2800 range.

While this doesn't help anyone in the US, anyone close by to Kent in the UK is welcome to stop by and hear what it sounds like. A second opinion might be useful.

The automatic would definitely make a difference and also I have hight flow cats, headers and a totally different motor. None the less great job documenting all of this!:cheers:

Changing the manifolds does make a difference. I remember EDC saying that the drone decreased appreciably when he installed free flow manifolds.

Just curious - with that configuration, would a high end performance exhaust not be better than modifying the std muffler? Or do all performance exhausts suffer from the same drone problem? :cool:

I have had many exhausts and they all had drone that was deafening. The stock muffler had made the most power in conjunction with some cheap headers and good high flow catalytic converters.

Interesting - I did wonder about that. I originally thought that the drone was related to the design of the exhaust system and the materials it's made from. I have now come to the conclusion that the car - location of the engine, seating compartment, etc are susceptible to reverberation from the exhaust sound i.e. it doesn't matter what system you use - when the exhaust noise reaches a certain level you get the drone. This seems to be in line with your experience as well. Maybe this is why the Boxster exhaust is so quiet in std form...

My thoughts exactly. It is what it is and there is nothing we can do about it.

I just put my long tube headers on and with the 1" holes yes there is tiny bit of drone, nothing like an aftermarket exhaust at all. I had no drone with my shorter headers.

I just drilled 3/8 holes in my tail pipe and couldn't tell the difference. My factory exhaust has always sounded like a Honda Civic from the driver's seat. Are my CATs plugged?

3/8 will be fairly quiet, however you should hear it when you start and at idle. You need to go a bit bigger to get an overall increase in sound. Just be careful going too big. Read the previous reports that I have given regarding the drone you may get at 1".

JDLMODELT, comments like yours have made me stop considering drilling anything into my exhaust. The exhaust sound is important to me, but in reality just a ego/notice me kind of thing, at least for me. I actually don't need the ego stroke to love my Porsche. To each his own. However if I come across a real nice exhaust system that is going cheap, then I will be stroking my ego immediately.

My observations in all of this are that Porsche must have designed a quiet exhaust for a reason - as JAAY has pointed out, all his previous after market exhausts have droned. Also, randomly drilling holes in things is generally not a good idea and once done there is no turning back.

Excellent comparisons. I liked the throaty sound at 25mm. However, from some of your newer posts, you indicate 25mm is too much volume.

No, the volume is fine - not loud, more like a background purr that you can hear through the rev range. When you open it up it's almost a little disappointing as you don't get the corresponding increase in exhaust note - primary because the higher the engine speed, the more exhaust gas passes along the original route, rather than out the drilled holes.

My only concern was the introduction of a little drone at 2800rpm - nothing like aftermarket exhaust however something to consider. On the flip side, the exhaust sounds like you would expect a sports car to sound.

I will put together a "driving video" when the weather warms up a little. It's a bit too cold at the moment to put the roof down!

So based on this thread I drilled my muffler. Sounds a little better, but will be returning to stock. There's a slight "hum/drone" that is a bit annoying. May be I drilled holes too big?

Here is stock:
https://www.youtube.com/watch?v=h03dShxx1Xk

Drilled:
https://www.youtube.com/watch?v=fah0Jx_BQ08

How big did you go?

I'll try to dig out a photo I took whilst cutting Into a 2003 .
They're different .
I modified mine into a "permanently open Pse" inside the muffler , then welded it closed again .

I have a 2003 so definitely interested in any photos you have. Drilled sounds so much better but you need to be prepared for a small amount of drone.

I thinki Drilled mine as well in case it was needed later ....
I'll have a look later , but I think I remember drilling a pilot around 1/4" while it was easy and off the car with the tips removed :)
But basically on a 2003 the chamber layout and gas flow is different ...

My idea was to follow what porsche did with the Pse which to all intents was a modded stock muffler , as they all ready took care of engineering out the drone ;)

yes yes i know this is an old thread but Im considering drilling the holes in my 97 base. I live in California so does anyone know if this would effect the smog at all? I'm thinking i want to go with 3/4" holes to avoid the drone but still have a noticeable difference. If its still too quiet ill drill it out some more. I'm sure it cant drone worse than my 87 944.

I'd go half inch and then increase from there. 1 inch provided a nice deep tone but there is a little drone (more noticeable on steep inclines). It is also noisy inside when driving at speed. I have just put a std box back on and it's nice to be able to hear my music again without turning it right up.

ill just leave this here https://www.youtube.com/watch?v=wHRZ6_C6VZw

But in all seriousness I plan to do the mod when I pick up my car (a week -_-) I just hope it wont effect the ability to pass smog