Thanks mate that's very interesting and 325bhp from a 2280 wheel is good but I agree with what you say above regarding compressor wheel size but it goes to show what a stock turbine can achieve also.
More Science now which I like:-
I've measured the inside diameter of the exhaust housing of a stock K04-023 and its between 79.5mm and 80mm. The gasket is approx 83mm. We know how flow is restricted in its standard form with a standard turbine size such that gases exiting the turbine hit the lip of the exhaust housing and deflect out into the down pipe and away... Not great. Imagine now a standard aftermarket upgraded downpipe whether it be cupra r , s3 or TT, its 76mm OD which equates to aprrox 73mm ID. The turbine gases have an additional 3.5mm lip of restriction all the way around the down pipe flange in addition to those offered from the exhaust housing.
In its simplest form a solution for existing turbos would be have a new down pipe flange cut with a 80mm hole and a 88mm Pipe forming the DP welded over it. That way the oversized 88mm pipe will form an expansion chamber for the gases and if possible I would continue this for the whole DP if space allowed on the individual cars etc(4wd may be a prob). I'm liking the modern 5 inch 100cpi cats for this to mate too and a 3inch cat back zorst.
For new hybrids I would like to see the exhaust housing & DP flange milled at least an extra 3mm diameter overall (1.5mm across the circumference) on the turbo which would allow the stock gasket to fit perfectly. Consider you would now have an obstruction free diameter of 83mm to exit the turbine area as opposed to 73mm which we all have now. That's an increase in flow area of 29%. For ref the id of the 88mm DP tubing would be approx 85mm and I've checked that adequate clearance will still remain to fit a socket on each of the 3 nuts.
What do you think.
