What kind of boost are you running right now? And how much do you plan on pushing with a smaller turbo? If it's 20 or under, the HX35 will be better, but that's still on the low side of the map for that charger. HX35's are a common turbo to use on tuner cars, but they are out of the map at low pressure ratios.
Look into an S200 or S300 based charger that the tuner guys use. With a strong map up to 22 psi. Something that was used on a high winding, 600+ hp V6 will supply plenty of air for a 4500 rpm IDI. If you're worried about restriction, you can always get a decent T3/T4 turbine housing on the S300 frame, instead of a smaller housing used on the tiny motors.
-yeah the garret we have is a t4 flange. we are just gonna kick around the idea of a hx casue we dont have a s200 or 300 laying around or the budget. mind you that we have two 6.9's and a 6.0 liter that are in the process of building.
We have only got 6-7 pounds of boost. our exhaust is tight and there is alot of rpm and fuel. it doesnt help that the exhaust housing is really large. i think if we had something smaller we could have better luck in lighting it.
and that truck has seen alot of torch work. We stacked 1200lbs on the truck and were still about 300 shy of 7500.