I asked a similar question. The basic information that I was given involved finding how much airflow you need, boost pressure, and pressure ratio. Then you need to find the turbo compressor MAP and plot the lines to see if the turbo is in the efficiency range.
Take the desired horsepower (crank, no RW) and times that number by the desired AF ratio (a good number for diesels is 25:1) and then take the Brake Specific Horsepower Consumption of the engine. For a Cummins, the BSHP is .35 pounds per hour. Divide that number by 60 to get the lb/min of Air Flow needed.
(Desired HP) * (AF Ratio) * BSHP/60 = LB/Min Air
For example, 450hp * 25 * .35/60 = 65.625 LB/Min air flow.
A VERY GENERAL assumption would say that for 66 lb/min air flow you would want a 64-66mm inducer. Should put you in the area.
If you want to find out the pressure ratio, it gets a bit more complicated.
LB/Min Air Flow * 639.6(constant) * (460(constant) * (intake temp - APPROXIMATION (unless you are rich and have the tools.. then please share the info.
)
Divided By:
(.)Engine efficiency * RPM/2 * Engine Displacement
OR:
66(Air Flow) * 639.6 * (460 + 130) Divided By .92 (about a 24v efficiency, the new common rails are a bit higher) * 3200/2 * 359C.I. (don't let dodge lie to you on the engine size!
)
= 47.13PSI ABSOLUTE manifold pressure for desired airflow. Take away atmospheric pressure (14.7 at sea level) to get 32.43
So, to get roughly 450 HP at the crank ASSUMING engine efficiency of .92 (which is close) and ASSUMING air charge temp with a decent AF ratio of 25:1 you would need to be reading 32.43psi on the boost gauge.
You can loose about 2psi in the tubing, so figure 35psi on the gauge to get really accurate. Which is needed.
To find the pressure ratio, take absolute manifold pressure + 2psi lost in tube divided by atmospheric pressure.
(47.13 + 2) / 14.7
Pressure ratio (at sea level) is approximately 3.34:1
Plot your LB/Min air flow with pressure ratio on the turbo map and see if you have a winner.
Rinse, Wash, and Repeat.
Seems to me that a good turbo for around his HP would be any number of the 66/14 turbos offered.. I myself will be going with an S300 variant in a 64/14 trim. According to the plots, I might get a not so desirable AF ratio in some of the RPM ranges, but as long as you can keep it above about 18:1 then things are “bend the pyro back around to 0” hot.. So I’m told.
I’ve picked this all up in about a day of research, so there is a high possibility an expert may come in and blow everything I’ve just said out of the water.. So take your Internet information with a grain of salt.
Injectors? Bigger = More Gooder if you have the Air Flow. See Above.