Engine Swap

[potionmaker]

Hello all. First time here. Looks like a great forum!! I have a question already. I have a 1986 K5 blazer, 4wd, 305 ci, 4 bll. Can anyone tell me if I can swap the 305 ci out with a 400 ci without modification to motormounts, etc? I do know i will need a new flywheel.

Thanks for the help!!

BB

 

[73k5blazer]

Straight bolt up. No troubles.

 

[potionmaker]

wow....that was quick! Thanks alot!!

 

[trailblazr81]

Check the balancer/damper. Believe its different like the flywheel. But everything else bolts on no problems. Maybe some accessory holes for brackets and such may be different on the block or heads if its alot older casting.

 

[dyeager535]

Won't the 305 use the goofy exhaust manifolds that won't work on the 400?

Haven't messed with the 400, but the mid 80's 305's all had the over the plug 7 bolt manifolds, no?

 

[potionmaker]

Thanks everyone for the info! Good point about the exhaust manifold. Im not sure about that. I believe I'm just gonna redo the exhaust, starting with headers and continuing with true-duals. Thanks again to everyone for the info. If anyone has any suggestions or tips, I would love to hear 'em.

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[diesel4me]

Exhausted...

The exhaust manifolds should fit ok,as long as the 305 was originally IN a truck..as far as I have seen,only the 79-86 Camaro,Malibu,and some other passenger cars had the different heads with the goofy 7 bolt pattern..they used manifolds that went above the spark plugs and ran alongside the valve covers..also had a 2 bolt "y-pipe"flange instead of the usual 3 bolt ones..some company sells adaptors to make them fit anyway--seen them in Jegs catalog??..or you could use headers if the manifolds prove to be a hemmroid..

 

[muscle]

400 will bolt right up. Also had no problem using some bracketry from 305 to use pancake style ac pump.

Also the 400 runs a lot hotter. I had problems when I would be hunting and creeping along. If you plan on using a 2 core radiator i would recommend against it. I purchased a brand new 3-core radiator for the diesel. (about 8 inches wider) Go to junkyard for the uppermounts, the core support already has holes for it. Also need to find the shroud.

my 84 jimmy before with tired POS 305 boat anchor installed.

After, with purdy new 375 HP 400 sm blk installed. (I swear im gonna hook up dat green wire, lol)

Pic of the 400 mocked up on the stand.

 

[potionmaker]

Dang, Muscle!!! What a difference. That looks amazing and Im sure made a huge power difference. Thanks for the heads up on the overheating problem. I will definitely check into that.
Keep the tips and suggestions coming!! I need all the help I can get.

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[dyeager535]

The exhaust manifolds should fit ok,as long as the 305 was originally IN a truck..as far as I have seen,only the 79-86 Camaro,Malibu,and some other passenger cars had the different heads with the goofy 7 bolt pattern..they used manifolds that went above the spark plugs and ran alongside the valve covers..

Both the 305 in my truck and the 350 in my friends (both 83's, his one ton, mine K5) had the over the plug manifolds. You are probably right though, under the plug manifolds will probably bolt right up, it's easy to see no matter what vehicle.

I was doubting myself at first, but I recall when we swapped the 305 from a Monte SS into his truck for the original 350, we had to put the 350 manifolds into the truck to make the exhaust bolt up, and he had to grind the top of the "log-style" truck exhaust manifolds to clear the valve covers, as they had swelled over the years. My 305 had the 4 port AIR injection in the exhaust I had to work on, I clearly recall the manifolds being log-style.