I'm in the process of making a collector/down pipe to go with the standard GT1546S as I personally think this part is quite restrictive. I am getting the flange laser cut out of 10mm stainless and I asked for 2 to be made so it's yours if you want it...
Personally I'm going to use a 60mm 90 bend, ovalised slightly with another bit welded on to account for the extra long oval shape. I'm then going to weld this to a 2.5" v band flange and then go 2.5" the rest of the way out. (I'm using 60mm because I had a bit laying around and it seems to fit well, 2.5" is 63.5mm).
The standard outlet from the turbo has an ID of approx 48mm (and also quarter of the pipe is indented inside) so with something around 60mm you're getting an increase in flow area (ignoring boundary layers) of 56%. Quite a big difference really. I'll update once I've tested.
Personally I'm going to use a 60mm 90 bend, ovalised slightly with another bit welded on to account for the extra long oval shape. I'm then going to weld this to a 2.5" v band flange and then go 2.5" the rest of the way out. (I'm using 60mm because I had a bit laying around and it seems to fit well, 2.5" is 63.5mm).
The standard outlet from the turbo has an ID of approx 48mm (and also quarter of the pipe is indented inside) so with something around 60mm you're getting an increase in flow area (ignoring boundary layers) of 56%. Quite a big difference really. I'll update once I've tested.