DIY Exhaust Mod – Gain of 10+ HP!!!

[tommy583]

I did it. 98 base. 1/2 inch hole on each side. Sounds better for sure. No drone at all. I'm thinking of going bigger as well.

[Slate 01]

Thanks guys, I know what I'll be doing Saturday morning. Guess I'll go 3/4" and see what happens.

Also going to be applying VHT Nite Shades to my taillights as well. Should sound cool and look cool in the rear end by the end of this weekend

[particlewave]

One tip: I had a heck of a time with the drill bit side-slipping on me, so after fighting it for 10-15 minutes, I made this out of an old 10" long bolt hole alignment tool. You can get these at a hardware store for about $5.

Worked like a charm! A couple of light taps with a hammer to get it to bite into the curve, then a few good whacks to drive it through. Took all of 30 seconds per side. This makes drilling 10 times easier

Making the point offset to one side helps a ton with getting it to bite on an angle like in the pipe.
(My wonderful MSPaint work in the last pic is a bit deceptive as there aren't any "flat" spots accessible from the tailpipe. All you can see through the tailpipe is curve. )

[Slate 01]

So how long does the drill bit need to penetrate? I'm confused are we talking about just breaking thru the pipe or are we talking about 2 inches, 3 inches, 4 inches or deeper?

Thanks for the help

[particlewave]

Just break through the pipe, no further

[Slate 01]

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

[particlewave]

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.

[Slate 01]

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?

[tommy583]

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.

[particlewave]

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.

[Slate 01]

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

[particlewave]

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

[chipmunk]

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

[jdlmodelt]

Originally Posted by chipmunk

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

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

[chipmunk]

Originally Posted by jdlmodelt

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!

[edc]

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?

[JAAY]

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.

[jdlmodelt]

Originally Posted by JAAY

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 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?

[chipmunk]

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".

[chipmunk]

Originally Posted by edc

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?

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.