The Stovebolt Site Forums The Parking Lot Tons 'o Fun Advice needed, GMC V6 engine

I have a '57 chevy 1-ton that I will be restoring as soon as I have time to work on it. It has a 235, 4 sp (SM420 I think)and 4.57 rear gears. I don't yet know if the engine is okay but it probably is. I also have a '66 GMC semi that was on my property when I bought it. It has a 478 V6. I've been contemplating the prospect of putting the V6 in the 3800. I don't have any idea if it will even fit. I've gotten some info from the 6066 GMC site about the engine and I'm thinking it needs to run at pretty low rpm's, maybe 1800 to 2000. Does anybody know if this engine will fit into a TF truck and connect to the SM420? What is a comfortable rpm for this engine to cruise at? Any other thoughts on the viabilty of this swap? Thanks in advance for any insight.

I can't speak to the fit and connect issues.

The GMC V-6's do not have a reputation for speed or economy. They don't turn fast and with 4.57 gears you'll be pretty limited in speed.

If you are going to do all teh work to put a new motor in I'd suggest something a little more versitile.

Check the info on the 6066gmcguy.org. If I remember correctly what I've read there, the 478 might use a different bellhousing than the other V6s, probably not a problem if replacing the whole drivetrain from the donor truck.

Without actually researching it... I think the 478, the 702, and the 638 use SAE #2 flywheel housings exclusively.

If that's the case then you can still use the SM420, but you'll be looking for a more than likely hard to find adapter clutch housing.
Would be better off switching to at least a 5 speed OD transmission, and a number of those come with SAE housings which makes that easier.

The 478 is probably not practical even if it does fit, but would be interesting.

Grigg

Here's a pic of a GMC v-6(probably a 305) in a '59 GMC Suburban for demonstration purposes. 6066gmcguy.org

The 478 will hold more then 2,000rpm . . . it'll cruise all day at 2,750rpm !


if you wanna save fuel it a the WRONG engine to use period !

Mike

The 478 V-6 is a Power House. It will be way more than you will need but, as mentioned, would be interesting.

I drove a 478 in a '62 GMC 6500 for 3 years.

BTW, do you have any pictures of the '66 Semi? I'm wondering if it is a Conventional Cab and what Series it would be.

Bill

There's a farmer next to my parent's place that has 1960-1962 GMC tandum axle trailer tower, with a 478M-V6, Spicer 7spd manual, 5.29 gear's and 10.00R20 T831 Firestone's.

say's it'll grunt around 35,000lbs all day long runs out to 70mph.

It's the only rust free dent free shiny farm truck around so it must be well cared for.

Every time i see it the truck is always pulling a trailer of some kind loaded rather heavy so it must have some power, i love listening to roll every time im in town its got duel 4" stack's sounds mean running through the gears . . .

Mike

You might be able to make it fit, but the engine weight will have your front suspension seriously overloaded. That's a BIG, HEAVY engine! You'll probably also have more torque available than the rear end and/or transmission will be comfortable handling. Add the fact that repair parts are scarce and expensive, and gas mileage sucks, and it's not a wise swap, IMHO.
Jerry

jfnar...Your '66 GMC tractor maybe good trading material (or an outright sale) which can give you the $$ for a more reasonable type of repower unit for your '57. There isn't a big demand for these heavy trucks but its worth a try. Try a post in the Stovebolt For Sale Forum, with lots of pics on webshots or something similar, and let us see what you've got.

Mike.... Would love to see some pics of that early 60s GMC tandem tractor you've mentioned, that's a rare truck indeed! And its still in operation??

James

We used to call the big v6 the "popping Johnny" of the trucking industry. Not much speed, not much fuel economy, but they last forever and the sound grows on you.

Here's a photo of the old GMC resting in peace in my woods.
http://i305.photobucket.com/albums/nn214/jfnar/1964%20chevy%20truck/DSCF1039.jpg
I've been able to use a few parts off of it on my '64 pickup, like the windshield and heater motor and a few knobs and fasteners. I have the 235 in my 1-ton running now and it hums along like a sewing machine. I expect I'll keep it as long as it will get me down the road. At one time I had some of the info on the old GMC that I'd gotten off the 6066GMC site but I've long since forgetten the specifics.

What you have is a B-Model GMC. The Series Emblems were on the doors on those trucks, but I don't see one on the drivers door in the picture. It will be in the first part of the VIN tho.

Was it a 5-Speed Trans and a 2-Speed Rear? I also notice the original type air horn on there. Does it have the all steel brake pedal with "Air Brake" on it?

Bill