Diesel conversion for a 1970s GMC RV
 

Hey folks,

First time poster here, long time forum member at the VW TDI club forums. They can't help me with this one though. =)

I'm totally obsessed with the mid-70s GMC RVs. The only fatal flaw is that they never came in diesel! I know, right? GMC motorhome - Wikipedia, the free encyclopedia

They seem to be loosely based on the Oldsmobile Toronado chassis and use the Toronado/Eldorado Turbohydramatic 425 automatic transmission.

Would it be possible to drop a Cummins turbo diesel into this rig? What exactly would that take to install?

If not a Cummins then what else? I am fond of the TDI motors but stock HP on the GMC RV looks like it was around 150+ and my TDI puts out only 90. =) I do have a Chevy PD van with an detroit diesel V8 but I think it's crap. =)

Keep in mind the Olds 455s put out over 400ft/lbs. Some careful measuring will be needed, the 4BT cummins is a fairly long motor (~31" long overall).

Is the a handy reference chart somewhere for Cummins motors and their sizes?

The 6BT is 36" long... plus whatever you add on for adapter or flywheel housing.

"adapter or flywheel housing."

It seems like there's a number of stock adaptors. Is there a list anywhere of adaptors and housings?

Otherwise... does it sound like I will be fabricating my own for this RV?

I am aware of adapters for Chevy, smallblock Ford, whatever Dodge used, and SAE types (i.e. round from medium-duty trucks).

One of my previous employers had a motorhome like yours. I have a pretty good memory of how they're put together. Basically the torsion-bar setup from the '70's Toro/Eldo platform. I would stick with a GM engine for size, weight, and not destroying the drive system. Chevy engines can be adapted to the Olds pattern with a simple steel plate (4 of the 6 holes are the same). A turbo 6.2/6.5 diesel should do okay with the 3.07 final drive.

If you really want to Cummins it, you could run a 4wd trans and t-case with a Dana 60 front axle. Some aftermarket companies build these for some bus and box truck applications where a low floor is desired. Just thinking outside the box ;)

Cab Chassis |

u2slow, thanks for the info. I like your thinking outside the box, that's an interesting tangent, that maybe the trans can be replaced as well.

I own a 1993 NA 6.2 in a Chevy P30 van and I can't say I'm very impressed. It does not seem nearly as well-engineered as my 1996 TDI for instance. I've never owned a Cummins but I hear they are bomb-proof in terms of reliability and power-to-weight. Is this just a myth? Is the turbo 6.2 really comparable to a Cummins?

I feel confident I could handle a conversion if it's a matter of buying available adaptors. I'm not sure how up I am for fabbing my own adaptor plates. Engine mounts I can manage, maybe. =) Fabbing though is a whole new world to me.

A 6.2/6.5 doesn't hold a candle to a 6BT. I'm really only suggesting it as a means of keeping the Toro/Eldo suspension & drivetrain intact.

If I was intent on a Cummins fwd situation, I would probably use a Dana 60 (spring-under & airbags?), trans of your choice (think OD trans), and a NP205.

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I remembered there's CV-jointed axles for the Dana 60 available from a company called RCV.