GMT 400 W/T

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
5,446
Reaction score
8,679
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
I keep thinking about this thing. My son just turned 10, and he likes the body style of these truck. Might be something we can get fixed together, and be a first truck for him. So, has anyone ever pulled a 4.3 and swapped a 5.7 in one of these trucks? I can’t imagine there would be a tone of difference, since the trucks were offered with both. Any input? I’ve also thought about maybe rebuilding the 4.3. If nothing else, I may drag it home and pull the top end off of the motor and see what it looks like.
The 5.7 will go in real easy same transmission. I believe the same mounts,all the brackets and accessories swap. I think all its going to take is the 5.7 a prom for a V8 truck, probably a different fan shroud, if you use exhaust manifolds from a gmt with a small block I bet the exhaust even hooks up. The 4.3 is basically a 350,with the front 2 cylinders removed.
 
Last edited:

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
30,438
Reaction score
28,342
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
I've never compared them side by side, but I'm betting you can reuse the entire v6 engine harness. Iirc, the engine mounts are different, but the holes are there for the v8 mounts. If your donor v8 does not have the mount brackets on it, let me know, I think I have an extra pair that I can send you.
 

bluex

Full Access Member
Joined
May 9, 2013
Posts
1,970
Reaction score
2,574
Location
Spartanburg SC
First Name
Paul
Truck Year
1978
Truck Model
C15
Engine Size
350
The 5.7 will go in real easy same transmission. I believe the same mounts,all the brackets and accessories swap. I think all its going to take is the 5.7 a prom for a V8 truck, probably a different fan shroud, if you use exhaust manifolds from a gmt with a small block I bet the exhaust even hooks up. The 4.3 is basically a 350,with the front 2 cylinders removed.

To go from a 4.3 to a V8 he'll have to remove the offset brackets from the crossmember an install the mount directly on it. Not terribly hard but nit much fun either. A swiveling 13 socket is very helpful.
 

squaredeal91

Full Access Member
Joined
Mar 10, 2023
Posts
2,534
Reaction score
4,579
Location
Cave junction Oregon
First Name
Greg bush
Truck Year
1991 SB
Truck Model
K30
Engine Size
5.9 Cummins 12 valve
I'll add that the fan shroud will be too big. V8 ones are everywhere tho
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
30,438
Reaction score
28,342
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
I'll add that the fan shroud will be too big. V8 ones are everywhere tho

A saw will work too :)

It's way easier to make a big shroud small, than a small shroud big, lol.

Reminds me of a totaled '88 C1500 that a coworker had bought and repaired in the late 90's. He used a v8 shroud on the v6 truck. It was the dead of winter and we needed to move it for one reason or another. I put the jumper pack on it, he started it and I went to remove the jumper pack... somehow my hand ended up near the cooling fan and a couple fingers got bit by the fan. The cold weather made it feel SO much worse, lol.
 

squaredeal91

Full Access Member
Joined
Mar 10, 2023
Posts
2,534
Reaction score
4,579
Location
Cave junction Oregon
First Name
Greg bush
Truck Year
1991 SB
Truck Model
K30
Engine Size
5.9 Cummins 12 valve
A saw will work too :)

It's way easier to make a big shroud small, than a small shroud big, lol.

Reminds me of a totaled '88 C1500 that a coworker had bought and repaired in the late 90's. He used a v8 shroud on the v6 truck. It was the dead of winter and we needed to move it for one reason or another. I put the jumper pack on it, he started it and I went to remove the jumper pack... somehow my hand ended up near the cooling fan and a couple fingers got bit by the fan. The cold weather made it feel SO much worse, lol.
Ouch!! Everything hurts more when it's cold. Makes me think of that one Clint Eastwood movie lol
 

Grit dog

Full Access Member
Joined
May 18, 2020
Posts
6,970
Reaction score
12,220
Location
Auburn, Washington
First Name
Todd
Truck Year
1986, 1977
Truck Model
K20, C10
Engine Size
454, 350
I keep thinking about this thing. My son just turned 10, and he likes the body style of these truck. Might be something we can get fixed together, and be a first truck for him. So, has anyone ever pulled a 4.3 and swapped a 5.7 in one of these trucks? I can’t imagine there would be a tone of difference, since the trucks were offered with both. Any input? I’ve also thought about maybe rebuilding the 4.3. If nothing else, I may drag it home and pull the top end off of the motor and see what it looks like.
I’ll beat the GMT400/OBS bandwagon all day long with you. Still think they’re one of the best overall combinations of capability, reliability, looks, modern/comfort and easy/economical to repair. To this day…
And they’re going up in value, not down. Pre-classics if you will.
But I’ll be the voice of reason too. You said it last year, that truck is junk. And if it wasn’t, it is now if it’s still been just sitting. Gotta know when to walk away….
There’s 6 or 9 billion GMT400s out there. Which means there’s a FAR better deal or platform to start with all the way up to super clean need nothing trucks to be had.
Like the boat, time to be like the Frozen song and Let it go!

If you just want something that is cheap, beat up, but not rotted out and still runs, those are dime a dozen.

There’s still tons of nice ones out there too. Just harder to score a deal on those.
 
Last edited:

bigcountry78

Full Access Member
Joined
Apr 16, 2013
Posts
3,679
Reaction score
8,813
Location
Hickory, North Carolina
First Name
James
Truck Year
1978
Truck Model
K10 Custom Deluxe
Engine Size
350
I’ll beat the GMT400/OBS bandwagon all day long with you. Still think they’re one of the best overall combinations of capability, reliability, looks, modern/comfort and easy/economical to repair. To this day…
And they’re going up in value, not down. Pre-classics if you will.
But I’ll be the voice of reason too. You said it last year, that truck is junk. And if it wasn’t, it is now if it’s still been just sitting. Gotta know when to walk away….
There’s 6 or 9 billion GMT400s out there. Which means there’s a FAR better deal or platform to start with all the way up to super clean need nothing trucks to be had.
Like the boat, time to be like the Frozen song and Let it go!

If you just want something that is cheap, beat up, but not rotted out and still runs, those are dime a dozen.

There’s still tons of nice ones out there too. Just harder to score a deal on those.
You know, you’re right. And that’s why I like y’all, you’re down to earth and realistic about these sorts of things. The last thing I need right now is a time/money pit and another headache. Thanks for steering me straight lol.
 

Grit dog

Full Access Member
Joined
May 18, 2020
Posts
6,970
Reaction score
12,220
Location
Auburn, Washington
First Name
Todd
Truck Year
1986, 1977
Truck Model
K20, C10
Engine Size
454, 350
You know, you’re right. And that’s why I like y’all, you’re down to earth and realistic about these sorts of things. The last thing I need right now is a time/money pit and another headache. Thanks for steering me straight lol.
Hahaha don’t think you’re the only one….
Anyone wanna buy a Dodge?
It ain’t even a bad truck. Just a poor decision on my part to buy it. lol.

You must be registered for see images attach
 

Latest posts

Forum statistics

Threads
44,157
Posts
950,585
Members
36,271
Latest member
jstewart7501
Top