[CarDesinr]

This is my 1991 GMC Sierra that I complete a Cummins 4BT swap, about 18 months ago. I used a 47RH transmission and modified the standard drive shaft, shortening the front section before the carrier bearing and adding the correct input spline. After having driven it for the past 18 months, I wanted to make some changes.



1: The turbo is a Holset H1C with a 16 cm exhaust housing and feels laggy and doesn't come on up on boost till the top of the rev range. I heard they made smaller housings but have not been able to find one yet. Any links would help.



2: The 47RH feels like it shifts too early within the rev range and I have to shift it on the column to get any power out of it. The fluid level is fine so I wanted to know if this was normal.

Here are the drivetrain brackets.




Here is how the engine fit.



And Marty thought it was MAAAAAAAAADDDD....

 

[Moochoff]

The hx35's wastegated 12cm exhaust housing is compatible and helps quite a bit with total boost, spool, and egt's. No doubt the factory h1c sucks! Hx30/6cm would probably be a better upgrade for your time though......

And adjust your 47rh's tv cable back a little. 1,2,3 shifts are controlled there. And OD-TC are obviously electronically grounded.

Looks great! Have any vibrations with the shaft?

 

[CarDesinr]

No vibrations at all. I took it to a shop in my town and they did a great job. They just had to shorten the front half about 3 inches and put the splines I got with the 74rh. I have a switch on the dash board for overdrive. For the turbo, are you suggesting that I should replace the h1c with the hx30?

 

[Moochoff]

I originally swapped in a 12cm housing with more fuel. it was ok in my old 98 ext cab 1500, but I still wanted more. I was making around 22psi with egt over 1200 on a WOT run

I would compare the 40mm h1c/12cm, fuel turned up with an intercooler to a 5.7 TBI truck...

I now have the hx30 going into my jeep, just from the charts and posted numbers it looks like there is no comparison. The reason I say hx30 would be worth the time is- I had to rework my down pipe going from the 16cm housing(clamp on ring) where the 12cm used the bolt on plate behind the wastegate

 

[CarDesinr]

Ill have to figure out which one I like more because there is also a C2500 on a 1500 stretched extended cab frame, crew cab, short bed with a 6BT in the works. Does anyone know if the H1C lags just as much on the 6BT?

 

[char1355]

Depending on which 6bt you have, they came with a larger H1C. It was a fair turbo on those but the WH1C or HX35W was far better. The H1C has a large non gated turbine housing to help keep EGT in check. Makes it a bit slow on spool up. You've already seen that on the 4bt. The WH1C and HX35W were found on the '94-02 Dodges. Some of the 24 valve models also used the HY35W but the HX35W came on the higher hp models. Another popular option is using a HE351cw from the 5.9 common rail engines. The Dodge guys seem to like that one. It has an electronic waste gate control, but they make a plug to convert it to manual.