As a bigger turbo is in the works I've been considering changing from my 2.75 inch exhaust to a full 3 inch setup. But I really like the look and sound of my current setup so I started looking for other options.
 
I came across this setup done by Texas_Ace that has an electric cutout added to the dp that can be opened and closed from inside the cabin. When open there are no restrictions so you can get the best possible flow, and its also super loud :D
 

 
The major downside I see with this is that you need to tune the car in the open position so it won't run as well when driving around with it closed which if you drive the car around town alot will be most of the time, not to mention it takes 5-8 secs to open and close which is a little slow.
 
Enter the boost actuated cutout which uses the actuator in place of the electric switch to open and close the valve. Its much faster and can controlled a few ways eg. by a boost controller just like you would a normal wastegate. It has a much quicker response time and once setup it will open automatically when you hit boost and can use the extra flow!
 

 
Has anyone done something like this in Aus? I'd be keen to hear anyones experiences even with non MR2 setups

Exactly what exhaust do you currently have? I simply changed the piping on my HKS 2.5" SuperDragger to 3". Fixed the restriction & sounds about the same.

I have the Greddy Power Extreme which I'd probably like to avoid modifying since as far as I'm aware there aren't too many around.
 
Atm I have a 3 inch Berk Dp going into the 2.75 inch PEX. I have another 3 inch dp lying around that I'm not using which I would use to experiment with if I do decide to try this!

Interesting device, but personally I wouldn't risk it for minimal gains. A 3" dump with 3" piping has proven to make over 300rwkw without the exhaust being the restriction.
 
If you are going to do it though, perhaps ECU that's responsive to changes (Haltech/Adaptronic etc) might be worth investigating so that it would automatically adjust the tune for you as you change the release.
 
I'd definitely say consider the implications if you ever get inspected by the defect police though!

Alot of people that have gone with these cutouts have used them have used ecu's like that. Some pretty interesting setups to using throttle position or cruise control buttons to open them!
 
The police certainly wouldn't like it but I think unless you blasted past them with it open they should never find it :) Definitely a risk though.
 
So you don't think 2.75 inch piping is going to be much more restrictive then 3 inch? 300kw is the goal of the build and I was under the impression the a full 3 inch system was best for that kind of power??
 
EDIT: Just realised you meant changing the b pipe to 3inch and retaining the muffler sections would flow enough for 300kw?
 
If thats the case that is what I'll probably go with, I want to keep the PEX but only if its not going to be restrictive!

These things leak and wear out in even low kay factory cars that do not see as much heat as a dump pipe does. Just another failure point. Plus you will get done by the fuzz eventually.

Steve_A
I have the Greddy Power Extreme which I'd probably like to avoid modifying since as far as I'm aware there aren't too many around.
 
Atm I have a 3 inch Berk Dp going into the 2.75 inch PEX. I have another 3 inch dp lying around that I'm not using which I would use to experiment with if I do decide to try this!

The main glory in that PEX would be the mufflers. I'd definetely recommend changing the mid piping (not the Y-pipe or mufflers) to make it 3inch from the turbo to the Y pipe. I don't regret for a second ditching the 2.5" mid pipe on my HKs SuperDragger.

It's ace in the hole is that it increases exhaust velocity, which reduces spool time. It's basic physics, that 15 years ago, I was shocked studying high school physics, hadn't been used before. It's now a cheap and effective way to improve efficiency of small capacity turbo engines without the complexity of variable vane geometry. The best control method is simply, vacuum; essentially a reverse waste gate.

If you want it to be quiet but without the restriction, there are loads of good muffler options I'd consider first.

I would bet that a regular 2.75 inch pipe would flow better than a 3 inch with a big ugly butterfly valve stuck in the middle of it anyway.
When stuff is getting as hot as dump pipes do I reckon less is more. Less welds, less bends, less joins and less mechanical bit and pieces.
P