Can i swap a 70's chevy motor into a 1990 gmc with a 4.3L without changing my 5 speed transmission?

Question

I'm wanting to build a little hot rod out of my 90 GMC . It is lower 6" in the front and 8" in the back. I'm wanting to build a 383 carb motor. Any help I can get will be helpful and THANKS !!

Answer 1

I own a shop, and yes it will bolt right up. One thing to pay attention to is this. One: the 70's motor doesn't have a pilot bearing, it will have a bushing for the input shaft to go into, or if it came from an automatic vehicle it may not have one at all. The 5 speed has a floating input shaft, and the tip that goes into the back of the engine MUST go into a bearing in order to work properly. To install a new bearing into the old engine, clean the hole it goes in to, and sand it with some paper that is about mid grade such as 320 grit to polish the hole out. You must have a lead in for the bearing to go straight in to. This bearing must be .001-.0015" press fit, so it doesn't lock up, or collapse the cage the rollers are in. I have had to cut the hole a little with a brake hone in order to get a good fit, but go slow, and take only small cuts at a time. DO NOT drive the bearing in, as this will damage it. The best way is to freeze it, and if you are quick enough you can slide it right into place without any problems. It must be tight, but not so tight it puts a drag on the input shaft. To remove an old pilot bushing, pack it as full of grease as you can, and use an old input shaft, or something that fits the bushing good, and smack it with a hammer. The force of the grease will push the old bushing out. Outside of this, I see no problems with it aligning with your V-8, and there should be no problems with the bolts. If the bearing is in the hole too tight, the clutch won't release, and you can't get the transmission in any gears because the input shaft will continue to turn even though the clutch is engaged. On an engine where the main bearings have been resized (align bored) the dowl pins the bellhousing sits on, must be moved to center up the bellhousing. They make offset dowl pins for this, and you center the bellhousing with a dial indicator by turning it around in the hole the transmission goes in to. Once the bellhousing is centered, you tighten down the bellhousing bolts, turn the dowls until they are tight, lock them down, and you are good to go. If you have never did this type of operation, you might want to discuss this with a machine shop, and have them do this for you before you put the engine into the vehicle.
Glad to help out, Good Luck!!!

Answer 2

I was about to not put my 2cents worth in because musiclicker gave the same advice i was going to tell you the other person must not have noticed that the trans you have in you truck is a mg5 getrag (or what i call getraggy) trans in it. That trans was a standard no matter if you had a V6 or V8 trans in:
CT1500 88-91 5SPD MT, 4X2
CT1500 92 MT, 4X2, w/intgrl bell hsng
CT2500 88-90 5SPD MT, 4X2
CT2500 91 5SPD MT, 4X2, w/intgrl bell hsng
CT2500 92 MT, 4X2, w/intgrl bell hsng
SUB20 88 5SPD MT, 4X2
SUB250 88-90 5SPD MT, 4X2
CHEVAN 88-89 5SPD M.T
CFWD 89-90 5SPD M.T
GM1500 88-91 5SPD MT, 4X2
GM1500 92 MT, 4X2, w/intgrl bell hsng
GM2500 88-90 5SPD MT, 4X2
GM2500 91 5SPD MT, 4X2, w/intgrl bell hsng
GM2500 92 MT, 4X2, w/intgrl bell hsng
GMCVAN 88-89 5SPD M.T
These will fit by including speed sensor and shift lever
CT1500 93-95 MT, 4X2, w/intgrl bell hsng
CT2500 93-95 MT, 4X2, w/intgrl bell hsng
GM1500 93-95 MT, 4X2, w/intgrl bell hsng
GM2500 93-95 MT, 4X2, w/intgrl bell hsng
GFWD 88-90 5SPD M.T
CT1500 93-95 MT, 4X2, w/intgrl bell hsng
The integral bell housing makes it a getrag and the non integral bell housing would have made it a New Process or New Venture Gear, MT8 or MW3.
Now the 2 cents worth if your going to a hot rod.. i would put the 2 speed powerglide in it and have a drive shaft made. The powerglide will hold up to a lot more power. Second if you looking for a lot of power go to a sb 400 and bore it out and you will know the difference.......

Answer 3

All small blocks will fit the 4.3L bolt patterns. A lot of other stuff needs to be changed but I'm sure you know that.

Answer 4

The bolt pattern on the small block V8 is the same as your 4.3 but it isn't going to last long behind a built V8 when it was designed for a stock V6...