Thread: driving a transfer case from the output shaft

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Hi Gang,
We have a 24ft. aluminum Jet boat that was powered by a 8.1L gas engine and would like to use a Diesel instead of the gas.
The RPM of the diesel is a lot lower than the gas engine and the Hamilton Jet likes higher RPM. I think we could trade the diesel's torque for more RPM. The boat might not be as fast as a high RPM gas powered but might be a cheaper to run and less likely to catch on fire.

So we were thinking about using a 4X4 transfer case and sending the power from the engine into the "output" shaft and getting a 2 to 1 increase in "input" shaft speed when in the old low range.
Hooking the transfer case's old input shaft which would now be the new output to the Jet's input.

Anybody know how the transfer case is lubed? Is the chain drive to the front axle needed?
any thoughts
thanks
Hank

I'm not an expert on transfer cases but you might want to mention which transfer case you are intending to use. There are definitely differences.

The engine and transfer case are from a early 1990's GMC diesel 3/4 ton automatic pick up- not sure of the engine size yet.
We are hoping that the 8.1L gas bell housing has the same bolt pattern - I'll know when we pull them out.
I have been looking at the U tubes on how the transfer cases operate.
Just wondering if the transfer case can take the power bassackwards

The diesel will blow that thing up in no time. They aren't built to put power through them the wrong way. Find a proper gearbox.

thanks for the input
on our haywire ideas
Hank

Biggest problem is speed aka angular rotation. The bearings might not be rated to handle it. It would be interesting to se it attempted.

If you are planning on using a 6.2 than I can't believe it would blow up a transfer case without dumping a ton of money in it. They aren't power houses in stock form. The bell housing is the same as a sbc/bbc which should be the same as your 8.1. Have you looked into how you will affix flanges to the shafts on the tcase to install drive shafts or couplers yet? You might be able to get a drop box from SCS and you can change the gears out easily in those.

And no, you do not need the chain in the tcase for it to operate. Popular GM RH drop transfer cases are np208's and np241's.

thanks Ryan for the information
SCS has some interesting gear boxes
No we haven't figured our flanges yet

We are going to stick the turbo charged 6.5L GMC diesel in and see how it handles
It will not be as fast as when it was powered by the 8.1L
there might be a different Impeller for the water jet that is diesel powered
thanks for the replies
cheers
Hank

Take some pics and put them on here. I'm intrigued. I've been trying to find a suitable boat to dump a 5.9 cummins in for a while.

That diesel won't drive the impeller at the original RPM the 502 turned. Gearing it up will just power it down further.

Originally Posted by R Pope

That diesel won't drive the impeller at the original RPM the 502 turned. Gearing it up will just power it down further.

The 6.2 is governed at 4100-4300 depending on year etc. That can be increased with some tinkering too.

.

photo of where we salvaged the boat
We are going to stick the 6.2 lump in and see what happens
thanks
Hank

Crikey Hank; you wouldn't have pulled it out of there with your VW truck!

Whoa, that sure looks like it went for quite the ride! How bad was the boat once you got it out?