There is one HUGE difference between the pulling tractors and a combine, other than the obvious, and that is the conditions. The pulling tractor only has to put out max power for maybe a minute. A combine has to do it for hours. This makes for a very different set of parts.
For starters:
1. Put a pyrometer in the exhaust manifold before the turbo. Make sure it stays under 1250 deg F under full load. This keeps things from melting. It also helps to know if you get an injector stuck open, or seem to have low power. A pyrometer is actually a pretty good power gauge. In general, more heat means you're using more fuel & making more power. I can't stress the pyrometer enough. Make sure you do it before anything else.
2. Turn up the pump. If that don't give you enough fuel, take it to a performance shop. Tell them exactly what you are trying to do, and any specifications you need it to meet (speed at which to make rated power).
3. If that still isn't enough, get the injectors worked on. Extrude honing the injectors 10% over-size can gain quite a bit of power. IIRC, a 5.9 in a pickup gained ~75-120hp from EH injectors. Otherwise get them overhauled & built larger.
3. Turbo. Since the combine really doesn't worry about acceleration, there isn't much need for multiple turbochargers. If you get the injectors & pump worked on, you'll probably be moving too much fuel for the stock 'charger. This will be shown by back-pressure in the exhaust manifold. I have no clue what size turbo to look for.
Stock, brand new, highest rated DT466E is 300HP, 860ft-lb, 2400rpm governor. VGT & HPCR electronic injection.
Scheid Diesel in Indiana should be able to put that motor where you want it. They are a very popular source for pulling trucks & tractors. Injectors, pumps, turbos, etc. They do it all.
