It would seem that to get the best out the vg block a 3" system is the better option. Now, if your waste gate vents to atmosphere, your not forcing the useless(in respect to producing boost) air down your exhaust system. This is obviously great, less air to be pushed through, less resistance etc etc, is this a correct thought process? If it is then realistically ifyou do vent to the wastegate directly, would you make the same gains on a 2.5" system as your pushing less air down the system, ie less requirement of the exhaust to process air, so a smaller exhaust can do the same job. Now is that legal? because your venting air without a silencer etc, does this still stay within the mot regs?

And yeah I do think it sounds awesome lol.

If you're referring to Bird's thread, then yes, I would agree with you that there's no need to go to 3"

 

No idea if screamer pipes are considered legal or not

IMHO unless your pushing SERIOUS horsepower, a 2.5 ich system is more than sufficient.

The gas produced from 2 x 1.5 litre turbo engine just doesnt call for 3 inch bore pipework

If you're referring to Bird's thread, then yes, I would agree with you that there's no need to go to 3"

 

No idea if screamer pipes are considered legal or not

 

That sort of just came up at the right time, I've been doing a lot of reading recently, esp on the US forums. The gains they are getting from 3" exhaust systems and upgraded intercooler pipework even on stock turbo's is pretty impressive(but I don't need to tell you that you know better than I do), I'm looking at getting some gt525's and fully divorcing the waste gate, out to astrosphere like that to my mind would have the same gains as running a 3" system, Without having to source a new 3" system probably from the states at massive shipping rates because of the size bulk etc and without replacing the 2.5" system I've had for well not long.....the front pipes have been on there about 6 months lol.

Only just seen this, finally plugged the big air leak so done a sound video to try and see how it sounds outside the car

An open screamer pipe won't be venting on an MOT, so shouldn't be a fail in that regard. As for "road legal"... If you got caught with them venting at full boost, noise/air pollution will be the last thing on the Officer's mind.

 

You can always plumb it back into the system further down as opposed to a few inches from the turbine housing.

Stephen, I admire your thinking on this one, exactly the sort of technical musings I love on this forum. And Noz, you're probably dead right :lol: unless you're in first you are in bother aren't you.

An open screamer pipe won't be venting on an MOT, so shouldn't be a fail in that regard. As for "road legal"... If you got caught with them venting at full boost, noise/air pollution will be the last thing on the Officer's mind.

 

You can always plumb it back into the system further down as opposed to a few inches from the turbine housing.

 

I Agree here, no venting during a mot test so not relevant, another example of mot criteria and road laws differing.