engine swap

[1983shorty]

hey all , i am going to upgrade my 83 gmc 2 wd 1/2 ton shortbed from the straight six to a 350. getting a 81 monte carlo with a recently rebuilt 350 and 700r4 tranny. should be a pretty easy swap but i want to be on top of all the things i need to change before i start. i will be getting a new radiator regardless so thats no problem . probably will run headers so exhaust is pretty straightforward. i assume i will have to relocate the crossmember for the trans and possibly change the driveshaft length. currently have 350 trans. will i need new frame mounts for the 350 engine or will i be able to use the ones the six uses ? what about the wiring harness ? really looking forward to this ! its a southern truck with 73,000 original miles and aside from a hole in one cab corner is VERY solid.

[87 STEPPER]

To the board.

Yes the xmember will have to be relocated some of the others here have done this mod so they will be able to fill you in better on the exact details.

And driveshaft length will be an issue. but no big deal.

The frame mounts should work but you will want to use new engine mounts for a V8.

The wiring should be pretty simple both eng's are carbed and non computer controled and have ele ign so it should all be the same.

But you will have to get a bypass harness for the 700R4 so it will shift right since you dont have a computer telling it what to do.

You will also have to connect the TV cable on the trans that controls down shifts. so you may need to get the mount bracket for it again the guys that have swaped over to the 700R4 will be able to tell you about this better than me.

Theres instructions on www.73-87.com on how to properly adjust the TV cable.

Good luck and let us know how it works out

[beaterC10]

You will prolly need to change the radiator shroud and upper mounts to accomodate the v8 radiator. The wiring harness might also be an issue as far as fittment if you are swapping from the straight six to a v8, since th 6 is longer, won't have a q-jet with electric choke, and has senders in different locations.

If you don't already have the radiator you might check prices before you scrounge up the shroud and mounts. Last time I bought a radiator, the one for the trucks with A/C or HD cooling was $50-75 cheaper than the standard v8 radiator. The upper shroud and mounts are different between the standard v8 and A/C rad.

[1983shorty]

Originally Posted by beaterC10

You will prolly need to change the radiator shroud and upper mounts to accomodate the v8 radiator. The wiring harness might also be an issue as far as fittment if you are swapping from the straight six to a v8, since th 6 is longer, won't have a q-jet with electric choke, and has senders in different locations.

If you don't already have the radiator you might check prices before you scrounge up the shroud and mounts. Last time I bought a radiator, the one for the trucks with A/C or HD cooling was $50-75 cheaper than the standard v8 radiator. The upper shroud and mounts are different between the standard v8 and A/C rad.

maybe i can just reshape the six shroud with duct tape !! lol ill probably order a new shroud. the truck has air now ( not working ) . i may want to keep the air and fix it. maybe not if i cant use the existing setup with the correct brackets for the 350. i would imagine the lines would not work because the compressor would be in a different location. ill most likely install aftermarket guages.

[Russell]

Depending on the year of the truck, there is a chance that the driveshaft will be the correct length already

Other than that, everything appears to have been covered thus far

[benoit454]

Your transmission from the straight 6 will bolt right up the the 350 or any small block really. The flywheel.flexplate should too. We swapped our 76 straight 6 to a 350. Used the factory straight 6 3 speed tranny, already had a big radiator. Gotta get a new throttle cable unless you can loop your straight 6 cable and make it work, tranny kick down is too long as well so you'd need a loop or shorter v8 one. Frame mounts are the exact same and in the exact same location for both engine no moving needed, only needed are the clamshell style smallblock motor mounts that bolt to the motor.

I can't think of anything else, most of the harness hooks right up since you only have like distributor, alternator, and starter wires, they wil be long but you can cut them or tie them out of the way and leave them long, if you cut them you have to cut a section out and then splice the end back on. You already know you need new radiator hoses, may have to trim them or something, I think we used a monte carlo lower hose, and now that same motor, radiator, and hoses are in my 85 monte carlo that came out of my 76 2wd. maybe need to reroute or need new power steering hoses, not sure though they may have enough room to move the pump or they may be to short.

[1974gmc]

when i swapped my 74 from a 250 6cyl and 3spd manual to a 305 and th-250, i had to move the frame mounts(motor) up to the next set of holes. Rad hoses i used the ones made for the truck but for a 350 and i am using the 6cyl rad still and runs at normal temp. I used the original throttle cable but it has a bit of a loop and used the kickdown that came with the motor and tranny so no problems there. I used the power steering pump from the 6cyl with no problems

[1983shorty]

thanks guys. looks like i should be able to handle it . i was going to buy the car yesterday but the kid got pulled over with no license and got the car impounded. im going hunting for a week now and wont be able to get it until next sunday. kids !!! lol