I have been studying the turbo threads quite a bit. Everyone has different ideas. It seams to me that the turbo needs to match the operating RPM. The conversion I am working on is geared pretty high. I am running 2.56 gears in the rear axle in an attempt to operate the 4bt in an economical mode. Estimating my rear tire height at 28", I will run 60mph at 1855 rpm, 70 at 2150rpm, 80 at 2460 rpm. If I increase the rear tire height to 30" 70 mph is at 2008 rpm. The rpm will be slightly heigher than that quoted since I am using a GM automatic transmission and will not achieve full lock up of the converter. I don't know what the slippage is, Could it be as high as 5%?
From a previous post I clipped the following:
"I have tried several different turbos in my truck, hx30w9, hx35w12 24v, hy35w9, he351 04.5 and up HO dodge, hx30/hy35w9 and now run a (hx/hy35/)/hx30w9 turbo. I have a 01 hy35 compressor housing, wheel, cartrage, and a hx30 turbine wheel and turbine housing. The 24V hx35 and hy35 use the same compressor wheel. I went with this set up due to the fact my stock hx30w would overboost at the bottom and mid range and underboost at the top end. 10 psi at a level 55-60mph cruise. I could hit 29psi by 2000rpm but could not make any more then that. It felt like I was hitting a wall with it. The hy35 and hybrid seam to make about 20% more power then the hx30. The hx35 had bad compressor surge. The hy35 was a good mid range and top end turbo, but would underboost below 2200rpm. 1-2psi at 55-60 If i was pulling I would hit 26psi on a hill in 3rd but my egt's would run about 1300-1350. I would back out of it to hold 1200, but by that time i would be about 17psi and 75hp less. At 1600 I could only make about 7psi and no power. I needed a turbo with just a little more mid range. About 5psi more at 22-2400rpm, and a lot more bottom. The he351 gave me more upper to top end. Same fuel setting produced 32psi boost, but less bottom end boost. The hydrid I run now works nice, but under 1900rpm is subject to compressor surge. I have a steep hill I drive over every day. and at 1600rpm have a hard time pulling it with out getting surge. It comes in at 17psi at that speed. The higher the rpm the higher the surge limit. About 1900rpm it is no longer a problem."
From this information it would seem that the stock turbo would be the right choice for me. My top end would be what was considered mid range from this post. Will my EGT be high with this turbo/gear setup? More fuel would still help right? 4" exhaust can't hurt either, right? It's all new to me, but I'm studying hard!
Mine is typical and has the H1C stock. I guess these are all non waist gated. If that will do I will let it on. The exhaust housing looks faily small aleady, but I'm deffinately not qualified to make a comparison. If it isn't a 9 cm housing I may shop for one of those. If I can spend less and be happy with the performance that is good. If it is a real slug and I need to do the turbo upgrade then that is what will happen. I would like to figure out the hole turbo thing before I run the exhaust. That will determine if there are firewall modifications needed and possibly even motor location in the chassis.
I've put 9cm housings on the H1C and had a good all around turbo that went up to 28psi. Talk to Tims turbo thats where I got the 9cm from. The 12cm in some cases did just as good. On the compressor side I've used the large housing with small wheel that is most often what was used on the step vans or the early nonintercooled 5.9 dodge.