Engine swap?

[newbe351]

I recently purchased a 66 GMC with a rebuilt 351 V6. The thing is strong as all get out, but it only gets 8 mpg. What would it take to swap it out for a 283? It's my understanding that this year of GMC won't take a Chevy engine without some fairly serious modifications.

Thanks

[60-66 Nut]

Hello 351, welcome to the board. Yes, there are a number of parts that need to be swaped to put in a Chevy V8, starting with the engine brackets. If you have a standard trans, the trans will work but you'll need the V8 bell housing and all the clutch linkage is also different from the pedal down. If you have an automatic trans(I've never seen one but have heard the V6's were available with the powerglide)the trans will have to be replaced also. If you like the V6, an easier way might be to try a taller rear end. I've heard of people putting 3.08 or even 2.73 gears behind those old engines and picking up a couple miles to the gallon while barely even noticing a difference in power. A better carb might help too, there are several carb upgrades for those engines. It all depends on what you want it for. While they don't make great hot rod engines, they are very strong and dependable but parts might be getting hard to find for them. Good luck whatever you decide.

60-66 Nut

[newbe351]

Thanks 60-66,

Yeah, I have the 4-speed manual and 3.54:1 rear end. After some more thought, I think I'll try to swap out the rear end to the 3.07 before I drop any serious money for an engine swap. The truck is really straight and I would like to keep it close to stock if I can. It has some serious low-end power. Don't know if 2.73 gears are an option in this year truck, but the 3.07's might buy me a mpg or two.

Thanks again

[60-66 Nut]

The 4spd should work nice with a tall gear, the granny low could compensate for the higher ratio. It would be like having an overdrive. I think the GMC's all had rear leaf springs(unlike most of the Chevys which had the coil spring rear suspension)so that should make it a little easier to find a rear end to fit. I have a 66 GMC parts truck, the rear end under it is supposed to be out of a 79' Chevy four wheel drive, and other than being wider from wheel to wheel it seems to fit perfect. And being from a four wheel drive it still has the 6 lug hubs. The hard part would be finding a four by four with the tall gears. My brother had a 78' Chevy 4 by 4 with 3.08 gears, but I don't know how common they were.

60-66 Nut

[kamikazegmc]

if u want to know more about ur truck u should check out the link in my signature it will help with alot of things