It will depend on what 600 turbos...... A split design downpipe will normally make more overall power over a open downpipe. A expansion split design downpipe will make HUGE power over either of the other options. The Turbo is driven by the difference in temperature and pressure of the two sides of the turbine blade. The gas is hot and still expanding coming out of the turbo and needs lots of room, but it needs to be controlled to keep from causing turbulence and inducing even more back pressure from the turbulence. This is why expanding the pipe coming off the turbo works so well......It actually just about creates a vacuum pulling the exhaust out and creates a cooler area the hot exhaust looks for :-) Separating the wastegate and bringing it back in smoothly also keeps from causing turbulence and keeps velocity high. These are basic principals that will allow any internal wastegate turbo to work more efficiently. Two different companies are selling 600 turbos and they are very different. JWT has a 600 turbo that uses a stock 4 bolt exhaust housing and they stuff a exhaust wheel in this turbo that is larger than the flange area. The problem is the 4 bolt split down was designed for a normal 4 bolt opening like a stock turbo or JWT sport 500 turbo. The turbine pipe on the 4 bolt split downpipes is 1 3/4" to work best with stock and 4 bolt sport 500 turbos. You always want to make gradual changes in exhaust size to keep from inducing turbulence. The issue with the 4 bolt 600 turbo is that the exhaust wheel is larger than 1 3/4" and you would restrict exhaust flow with a normal 4 bolt split downpipe. Also on the market are 5 bolt 600 turbos and the standard pipe size of the turbine pipe on 5 bolt split downpipes is 2 inch and that works fine. For the 5 bolt turbos the standard 5 bolt set up works perfect for turbos as large as 700 turbos. For 5 bolt turbo that have larger wheels than 2 inch like 2871 turbos or 3071 turbos we do make a custom flange and separator and we use a 2 1/4" starting turbine pipe and expand to 3 inch. I just had some custom flanges and seperators made for the 4 bolt downpipes that allow a 2 inch starting turbine pipe on the downpipe. So soon I will have available special super splits and expansion 4 bolt downpipes that will be made special for 4 bolt 600 turbos :-) The reason I never made 4 bolt downpipes with a larger opening was because I always felt better turbo choices were available and I steered people to purchasing better choice turbos. A few people make 4 bolt turbos still that carve out part of the gasket area of the turbo to fit larger wheels. Because a number of people have asked and people keep making 4 bolt turbos with huge exhaust wheels I figured I would go ahead and make a downpipe to make this work correctly.
