350 to 454 in a K10: What Motor Mounts?

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k10kole

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Hi all,

Long time lurker, first time poster. There is so much good info on here!

I am looking to swap a 454 into my '73 K10 short bed. I have read a lot of conflicting information about motor mounts and I have a few questions I'm hoping to get cleared up:

1. Is there a difference between the 454 and 350 motor mounts other than the bolt hole locations?
2. Is there a difference between the 454 and 350 clamshells?
3. If I use 350 motor mounts and clamshells, will there be clearance issues or will my fan hit the radiator shroud?
4. Does anyone have part numbers for the mounts and clamshells I need?

Thanks in advance!
 

bucket

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Hi all,

Long time lurker, first time poster. There is so much good info on here!

I am looking to swap a 454 into my '73 K10 short bed. I have read a lot of conflicting information about motor mounts and I have a few questions I'm hoping to get cleared up:

1. Is there a difference between the 454 and 350 motor mounts other than the bolt hole locations?
2. Is there a difference between the 454 and 350 clamshells?
3. If I use 350 motor mounts and clamshells, will there be clearance issues or will my fan hit the radiator shroud?
4. Does anyone have part numbers for the mounts and clamshells I need?

Thanks in advance!

1- Yes
2- I do believe so
3- No, it will all fit fine
4- I don't have the part numbers, just use what you have from the small block and it will work. Although, I highly recommend Energy Suspension poly engine mounts.
 

k10kole

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Thanks, bucket! That's good to hear. Worst case, if I get it together and have issues then I could always shim the mounts.
 

bucket

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Thanks, bucket! That's good to hear. Worst case, if I get it together and have issues then I could always shim the mounts.

You shouldn't have to. It's been done time and time again. The reason I recommended the poly mounts is because the factory mounts often sag badly. Even a small block can end up rubbing the balancer on the crossmember. I've used the Energy Suspension brand and I know they fit well. Sometimes it's hard to get the holes lined up when setting the engine down in, with replacement rubber mounts from the parts store.
 

k10kole

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Ok, that makes sense. Thanks again!

It's weird that GM decided to use different motor mounts and perches when they are more or less interchangeable.
 

Old Guy Bill

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I don’t know the particular years but some 4x4 trucks got 1/4” plates between the clam shells and the engine, they supplied a mounting point for transmission braces. These plates can affect the mount and engine alignment.
 

bucket

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I don’t know the particular years but some 4x4 trucks got 1/4” plates between the clam shells and the engine, they supplied a mounting point for transmission braces. These plates can affect the mount and engine alignment.

I *think* those started in '81.
 

Gordon

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What about the weight difference? Are you going to put in heavier springs so your not doing a nose dive?
 

bucket

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What about the weight difference? Are you going to put in heavier springs so your not doing a nose dive?

Truck springs have high enough spring rates that the ~200lb difference isn't really noticeable to most people. Especially a leaf sprung K10.
 

k10kole

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Bill, that's the first I've heard of those plates. Seems like GM really liked to mix things up.

Gordon, I wasn't planning on changing the front springs to start. Right now the truck sits pretty near level. I figured if I'd throw in a zero rate or leveling kit up front if needed.

Like Bucket said the springs seem really stiff, I've stood on the front bumper while working in the engine bay and it doesn't seem to dip much at all.
 

k10kole

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Here's a picture of the truck on a recent grocery run. Needs some paint, but it's pretty solid.
 

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Dooley

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k10kole

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The 454 I have was actually swapped into another K10 before, but it was missing a fan shroud, had destroyed motor mounts and had some other issues, I'm just trying to make sure I do this swap the right way. It came with the low profile fuel pump and all the accessory brackets.

My truck has an SM465, NP205, Dana 44 front and 12 bolt rear axles with .373 gears. Should be pretty fun with the big block!
 

Fat 454

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look at swapping in a rear 14 bolt full floater 8 lug with an lsd ( can be found cheap from a wrecked C20 ). You will need a matching set of 8 lug front rotors for the Dana 44 from Rock Auto ( No real advantage at the front, but allows a full set of 8 lug rims all 'round ) - until you can locate a Dana 60. That will get you a lot more smiles on the trail from the big block and NP205. Check out ORD 4x4 and "Billa-vista" .com for parts and info.
 

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