400 to 454 swap

[alek310]

Hi all! Just bought a 1977 k20 has no engine I decoded the vin and it says that a 400 small block was the original engine. My question is will the harness fit the 454? Also should I be concerned affecting the other drivetrain components such as transfer case, rear diff? I already ordered my engine just want to know what I’m looking at. Will it mount up right? Thanks guys

 

[bucket]

The harness will work fine, but modifications may be needed if you go with a serpentine style accessory setup.

Your fan shroud likely won't fit and neither will your existing exhaust pipes.

You will need a flywheel or flexplate that works with your current trans.

Big block engine mounts are technically not the same, but small block mounts do work perfectly fine.

 

[alek310]

If I purchase a fan shroud made for a 454 will that work?

I’m also purchasing a painless harness.

 

[fast 99]

What is wrong with the current harness?

400-454 is an easy, almost direct bolt in with minor changes as noted above.

 

[alek310]

Awesome! Thank you can’t wait

 

[alek310]

It’s the original and I want to update it just becuase it’s a rolling chassis and some wires look fraied

 

[fast 99]

Do they make a harness thats a direct fit?

I used one of their harnesses several years ago, it wasn't. Caused a lot of extra work. Good thing there was a donor SB around otherwise the owner would have been flocked. He cut the old harness up.

 

[Ricko1966]

@alek310 I've done some pretty weirdo swaps and have always been able to make the original wiring work,even rewired/repaired one harness after an engine fire. I've used a Pontiac engine in an Oldsmobile with the Olds harness I've used a Buick engine in a Pontiac with the Pontiac harness,I've used a SBC in a Pontiac with the Pontiac harness,and a couple others. I'd buy some plastic loom and some electrical tape and save my money for things that will make a difference.Look at some other builds like the 80 K-10 Squircle build factory harnesses cleanup nice.

 

[alek310]

@ricko will do. Thank you sir

 

[alek310]

@fast they make a painless harness that should have all the connectors ready to install

 

[varnell1980]

The harness will work fine, but modifications may be needed if you go with a serpentine style accessory setup.

Your fan shroud likely won't fit and neither will your existing exhaust pipes.

You will need a flywheel or flexplate that works with your current trans.

Big block engine mounts are technically not the same, but small block mounts do work perfectly fine.

I bought big block engine mounts and they definitely don’t fit the holes on the perches. I got 350 mounts and they did fit the holes but when I lowered in my 454, the holes don’t line up. They did on one side and the other side was about an inch away from the mounting holes. I used the clamshells from the 454 engine with the 350 engine mounts. At a loss.

 

[bucket]

I bought big block engine mounts and they definitely don’t fit the holes on the perches. I got 350 mounts and they did fit the holes but when I lowered in my 454, the holes don’t line up. They did on one side and the other side was about an inch away from the mounting holes. I used the clamshells from the 454 engine with the 350 engine mounts. At a loss.

I guess it all depends on terminology. Depends on what you are calling the mounts, clamshells and perches.

But when it comes down to it, if you use everything from the 350 then it will bolt in. If you mix and match ANY parts, all bets are off. The trick is to keep it simple and don't over think it... just use what was already there in use.

 

[varnell1980]

Yeah I think I’m calling the wrong thing clamshells. I’m calling the part that bolts to the motor the clamshell but I guess people call that the cup? The rubber mounts with the metal covers are the clamshells? And the perches are the parts that bolt to the frame with the holes in them for the rubber motor mounts to attach to? I guess I’m confusing myself too. Lol

 

[bucket]

Yeah I think I’m calling the wrong thing clamshells. I’m calling the part that bolts to the motor the clamshell but I guess people call that the cup? The rubber mounts with the metal covers are the clamshells? And the perches are the parts that bolt to the frame with the holes in them for the rubber motor mounts to attach to? I guess I’m confusing myself too. Lol

Lol, I use the same names for the same parts. But many other people don't.