Here are a few estimated operating curves. Each curve is identical. I know that my pressure ratio at full boost will be right around 2. Maybe a little above or below. I also know that my target rear wheel horsepower of 400 corresponds to 450+ crank horsepower, or 45+ lbm/min mass air flow.

Honestly, it looks like any of the above turbos will work just fine for my app.

The 71 is definitely running out of steam near the top and spends the least amount of time in the highest efficiency island.

The 76 Spends the most time in the highest efficiency island. Right in the meat of the powerband. This will correspond with lower intake temps due to less heat generation.

The 82 would also work just fine, but it is pretty obvious that it can provide a boatload more power than 450 crank hp. It is operating in its highest efficiency zone near the top of the power band.

I don't think there is any question that the 76 is the best option for this particular operating curve.

Now if I can just figure out the turbine maps...

Back for more later.

 

I've included the turbine maps for the GT35, GT30 and GT28. The compressor sides (the 71, 76, 82...GT30xx portion of the nomenclature) do not matter for these comparisons.

Interestingly, there exists a GT2876 turbo with the same compressor side that I have picked from the above posts but with a smaller turbine side for quicker spool.

Take a look at how these turbines perform by the mass flow rate at which they choke (or flatline). This indicates the level at which they cannot possibly flow more mass and the A/R must be changed or a wastegate must be used. If not, the engine will not be able to output any additional air and the power will drop off immensely while the pressure across the turbine goes WAY up.

Can anyone shed some light on the A/R and how we can interpret these maps?