I just got a chevy step van with a 4bt3.9 engine 1980 vintage.
runs good but SLOW!!! 55 mph is all i get out of it.I am making a small motorhome out of it and going to pull a 2 horse trailer.I need to pick up the speed and mabe a few more horsepower under the hood and not in the trailer.any ideas.The engine looks just like my 93 ram250 but 2 pistons missing.
HELP robert

 

im sure some pump mods could be done.
maybe a gear splitter overdrive unit.

 

the fuel pump lookes just like my 5.9 cummins but i think it has a speed gov. on it i haven't got a good look at it yet.I was a diesel mech in the army back in 66 to 68 in Nam but this one beats me.

 

It's a diesel, they all have governors. Nature of the beast.

You can probably get a few more mph out of 'er by backing the high idle screw out until it's just barely stopping the throttle lever. You don't want the pump internals stopping the lever, make sure it's stopping on the screw but just barely. High idle screw is the one that stops the throttle lever when youve got the accelerator matted. That might get you to 60 for free. The 3200 RPM gov. spring should get you up around 70 if the governor is set to the same RPM as the Dodges. Info on getting the spring and putting it in is in the "tech facts" section of the site.

Don't start messing around with adding more fuel (main fuel screw, fuel pin, star wheel, etc.) until you get a pyrometer on it, that poor little 4BT is working its guts out already, you could fry it real easy.

 

I am pretty curious about this rig and interested to hear how it turns out . . .

Does it have a manual or auto tranny? and what rear axle ratio? Is it aftercooled? (I don't think that they are).

I think that you will have to add an aftercooler and new turbo (maybe an HY with the 9cm housing?) to get the kind of performance that you are looking for, and you will probably have to swap to an overdrive transmission . . .

Can you post more specs for the truck?

 

i'll do my best to get all the info on the little engine but for now it has a little 3 spd auto trans.in a 1 ton body.I maybe asking it to do too much for its size.it's very good on fuel but what do u want out of a 4 banger i think its got 370 gears in the rear but not real sure

 

How much did you pay for the van?? The tranny that's behind it is a turbo 400. I would think that with a few mods your "little" motor could easily be at about 250hp. And still get great fuel milage.. I'm gonna put one into a 41 WC... someday