by KTA » Wed Oct 15, 2014 12:53 pm
What kind of hp is BC dynoing? I made about 480rwhp and 1100ft-lb multiple times with a 62-71 .80 turbo and a 12mm pump. I still have a stock cam too but had done a bunch of head work. It burned clean at that level once boost came on so I thin the 62mm is fine, maybe even a bit smaller would be better. I think cooler air and a cam that drove the turbo harder would have maybe been enough to break 500, I don't know really that a lot of hp could be gained as the fuel just isn't there, but the torque could easily be increased which of course would result in more hp, just not more peak hp, and of course a better driving truck. For a 12mm pump truck you don't need a ton of air, just more cool air and early in the rpms. I think the best way to do that is to have your low pressure turbo with a mid sized compressor, probably a 68-71mm with a big turbine and a very loose exhaust housing. the loose housing and big turbo makes the back pressure on your high pressure turbo virtually none so you can get it spooled fast, once you get the little one started it will kick the big one in the butt and get it going for when you need it on the top. It is counterintuitive to spoolup, but I have seen it work. If I redo my twins I will be doing something similar as opposed to the tight housings and wastegates I run now.
Fleet of Junk: 1989 D350 627rwhp 1300 tq B-1/Hx60 twins, KTA pump/injectors, ported head, BIG fuel supply. 13.75@ 109.5mph 1/4: 1992 W350 Cab-chasis, 1993 W350 ext cab cust.370 inj Hx40/16cm 290rwhp hydroboost brakes,1984 D350 crew-cab another project.