The Stovebolt Site Forums The Shop Area Engine Shop swapping a 270 for a 350 questions

Replacing the complete engine&transmission from my GMC for a 350 w th350 trans.
What are some of the issues I might run into? How difficult is it to do? Using engine from 1983 chevy truck.
My truck is all stock- 1958 GMC truck with 270engine& 3spd trans.

Thanks in advance

Can I use my 58 truck radiator?

yes, if the stock rad is in good condition it'll work fine, just don't use a cap rated higher than the original 7# ... only issue you'll run into is mounting, which is very different than the I6, need aftermarket crossmembers for both the engine side mounts and the auto trans .... and of course some kind of auto shift setup

Bill

Bill ,
Thanks. Thinking I might be able to use the cross member in the donor truck?

no idea about '83 truck frames, possible I suppose, but doesn't seem likely

Bill

where would I find motor mounts that will work with my truck? Or are they "universal"

yes, 'universal', and any of the vendors will have them, like here at American Classic, see pictures - might also find them at local auto parts stores or a rod shop

Bill

Not sure why you need an automatic transmission. A manual chevy bellhousing will bolt to the gmc frame, and many transmissions will work with the v8.

because I am getting a 383 motor and auto trans together.

"383"? going Mopar or do you mean a 283?

Bill

guy told me it was a stroked 383-ie a 350 bored out...

I will guess that I am getting just a 350;unless I can confirm

Probably means it's a 350 with a 400 crank, and bored .030" over.

ok , thanks

So that engine and transmission should do okay with stock rear end?

Depends which rear you have, and what shape the rear is in.

Do you have the Ho33 rear which has a round cover and a dropout style pumpkin. 3.90:1 gears are most common with this rear

Or

Do you have the spicer 45 rear that has an elongated octagonal looking cover. 3.07:1 gears are the most common gears in this rear?

I am assuming your jimmy is a 1/2 ton, and not a 3/4 ton with the eaton ho52 rear. Most common gears in the ho52 would be 4.57 or 5.13 gears.

standard 1/2 ton--octagon looking rear?

I'd be looking for another rear... that spicer is likely to fail from age and parts are scarce. Run it till it stops, then swap it out.

Let's see, we take out an old engine that puts out maybe 250 lb. ft. torque, backed by a granny tranny with a 7.0 low gear, and replace it with a V8 with, say, 400 lb. ft. torque and an auto tranny with a 2.5 low gear.

250 x 7.0 = 1750 lb. ft. torque to the rear versus 400 x 2.5 = 1000 lb. ft. torque to the rear.

And how come nobody worries about the driveshaft and U-joint as well as the rear end?

Just sayin'

that's just another piece of the puzzle, right...

By that math the amount of torque is reduced by almost 50%.. so there is nothing to worry about? old 1750 > new 1000.

Or am I missing something?

So I will be pulling the 350&trans Weds nite to install in my 58 GMC truck. I have a cross member on my list of "things 2 git" what elese should I consider?

Set the driveline angle to match the pinion angle.

Set driveline angle.

are the frames the same distance apart? Was thinking I might try to use original motor/trans mounts.

Or do I need to get mounts??

A 383 is a stroked 350. But it doesn't matter...the blocks are the same. You have to buy or fabricate motor and transmission mounting since the old 6 cylinder and transmission mount differently. The original motor has a mount on the front of the motor and one on each side of the bell housing. The motor you are swapping in has side mounts on the motor and one mount on the rear of the transmission . So you need two crossmembers on your list.

Also....you will need to change the rear end eventually unless your truck has the 3:38 rear end that came in the automatic trucks.

You need to use the mounts that are compatible with whatever crossmember you decide to use.

Thanks 4 the info.So what rear end do I need to be looking for?

Guess I wasn't clear earlier-sorry

Can I use the V8 mounts out of the donor truck?
That's why I was asking about the frames being the same distance apart.

there's 2 parts to the mounts Danny, one that bolts to the engine, which is pretty much common for all years SBC, and the other half is the part on the frame crossmember, what's on the engine is probably useful, but you still need to fab up a crossmember for the 58 regardless, unless you want to hang something off the inside of your frame, which isn't a good idea

Bill

okay...