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.