DIY Exhaust Mod – Gain of 10+ HP!!!

[EssexPorsche]

Guys,
I'm sure it sounds different, possibly better than stock. But i don't see that you are bypassing any chambers at all.
I think the flow of the arrows is wrong on that picture.
Starting on the left (red arrow) the gasses enter here. They collect and equalize in the second chamber (when counting from left to right). When the pressure is sufficient, they progress - still from left to right - to the fifth chamber on the far right.
The final journey is from the collection chamber on the far right round the curved pipe and out.
Yes, there is some over-spill equalization in the center chamber but its not the primary route as gases in there eventually get pushed back to the left or right.
So why would you want to drill a hole in the pipe which is actually helping the exhaust gasses out (i.e.) the curved pipe. Surely doing this hinders the flow of the gas by allowing it to escape into the center chamber and hence hinder the expulsion.
Well.....that's how i see it anyway. ha ha. But if you like the sound....fair enough.

[particlewave]

Originally Posted by EssexPorsche

Guys,
I'm sure it sounds different, possibly better than stock. But i don't see that you are bypassing any chambers at all.

That's essentially correct. However, you are allowing some of the exhaust gas to bypass all but chamber 3 and go directly out the exit. This is similar to the Porsche sport exhaust, except that the amount of flow through the drilled holes is restricted by the flow through the baffle in chamber 3.

[particlewave]

This one is a bit clearer

[chipmunk]

I did look when my box was off but didn't pay that much attention. I am pretty sure though that the inlet pipe (from the left and rights sides) goes right through i.e. no blockages - maybe someone with a box off can confirm this.

If so, then by drilling a hole on the bend you are allowing gas that diffuses out in the middle chamber to exit directly, rather than first being routed to the 5th chamber and then out. Wouldn't make a huge difference to anything but enough to change the exhaust note.

[particlewave]

The arrow diagram posted earlier in this thread is incorrect and misleading. This is what's happening:

A) Following the left side (yellow), exhaust enters chamber 2 (with slight bleed off to chamber 1 for mixing with right side (red) exhaust through small holes in inlet pipe). From chamber 2, it is split and goes to chamber 5 and center chamber 3 where it is mixed with the right side (red) exhaust and dumped back into chambers 2 and 4.

B) From chamber 2, exhaust goes to chamber 5. In chamber 5, exhaust is again mixed with right side (red) exhaust, but to a lesser degree than the center chamber (see small holes in inlet pipe).

C) Chamber 5 exits directly to exhaust tip


So, by drilling holes in the exit pipe, you are creating flow from the center mixing chamber directly to exit, essentially creating a small bypass directly from inlet to exit with only the center chamber pipe working as a slight flow restrictor/baffle (similar to the PSE, IIRC...except that the PSE uses an exterior pipe to do the same thing).

[nieuwhzn]

So what would happen if the slight bleed holes in chamber 1 and chamber 5 get opened up more? In first order this will let more of the primary exhaust go straight out of the tail pipes. This is almost the same as the exhaust bypass pipes on the PSE. The big difference is that more of the primary exhaust left (yellow) is going to 'hit' the primary exhaust from the right (red). This could lead to these two exhaust sources starting to 'beat' against each other, i.e. drone.

Originally Posted by particlewave

The arrow diagram posted earlier in this thread is incorrect and misleading. This is what's happening:

A) Following the left side (yellow), exhaust enters chamber 2 (with slight bleed off to chamber 1 for mixing with right side (red) exhaust through small holes in inlet pipe). From chamber 2, it is split and goes to chamber 5 and center chamber 3 where it is mixed with the right side (red) exhaust and dumped back into chambers 2 and 4.

B) From chamber 2, exhaust goes to chamber 5. In chamber 5, exhaust is again mixed with right side (red) exhaust, but to a lesser degree than the center chamber (see small holes in inlet pipe).

C) Chamber 5 exits directly to exhaust tip


So, by drilling holes in the exit pipe, you are creating flow from the center mixing chamber directly to exit, essentially creating a small bypass directly from inlet to exit with only the center chamber pipe working as a slight flow restrictor/baffle (similar to the PSE, IIRC...except that the PSE uses an exterior pipe to do the same thing).

[chipmunk]

Originally Posted by nieuwhzn

So what would happen if the slight bleed holes in chamber 1 and chamber 5 get opened up more? In first order this will let more of the primary exhaust go straight out of the tail pipes. This is almost the same as the exhaust bypass pipes on the PSE. The big difference is that more of the primary exhaust left (yellow) is going to 'hit' the primary exhaust from the right (red). This could lead to these two exhaust sources starting to 'beat' against each other, i.e. drone.

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.

[EssexPorsche]

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?

[particlewave]

Here you can see the center chamber and baffle pipe more clearly. That pipe connects chambers 2 and 4 and diffuses into chamber 3.

[Ian c]

Originally Posted by particlewave

Here you can see the center chamber and baffle pipe more clearly. That pipe connects chambers 2 and 4 and diffuses into chamber 3.

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 .

[chipmunk]

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.

[Ian c]

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

[holtzy822]

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.

[particlewave]

And after drilling...

[chipmunk]

That makes sense. Nice diagram

[JAAY]

Let me know if your able to achieve the angle with a drill bit to get to that pipe. I haven't tried but I will once it's not 10degrees out.

[Slate 01]

I may have missed it, but I notice this mod addresses S models, it there a mod like this just for the 986 Base? My apologies if this was covered and I skipped over it
Thanks

[particlewave]

Not sure, but it worked on my '99 base; increased low growl and I swear the throttle response increased. Seems to rev up and drop back to idle a bit quicker.

[Slate 01]

PartWave and everyone else,
do I follow the same directions for drilling, I presume two holes, just like the S instructions?I've never really looked inside the tailpipe to see if the outlet consists of two holes, just like the S model.
You didn't notice any loss of power, low end or top end? And I presume no drone
Any downside to doing this modification? I've desnorkeled the 986 already but really didn't notice in appreciable sound change or performance change.

Thanks for the help

[particlewave]

I followed the instructions here and looking up my tailpipe, it looked the same as the pictures here.
If anything, I thought I felt a slight increase in power, but that was probably due to the fact that I love getting on the throttle even more now because of the awesome sound
Zero increase in drone and no annoying "coffee can muffler" ping/rattle. Excellent sound

I really noticed an increase in throttle response in the 3000-5500 rpm range. I have no regrets and even want to increase my holes from 9/16" to 3/4" or more.