Small block to Big block swap


Junior Member
I want to swap a big block into a 87 4x4 truck (1 ton) that was orignally equipped with a small block. I know all of the small block engine mounting brackets from the small block will "physically" fit the big block, however when you go to the GM dealer to start looking up part #s they are not the same. Furthermore, I remember reading a magazine one time which talked about chevy cars from the 60s, the magazine stated that the motor mount brackets were not the same. By not using the correct brackets you would not have the correct drivetrain angles which could cause problems. Any thoughts on the subject?
Hi a87:

I don't know about your '87 truck, but in my '71 Nova, when using small block mounts to fit in the big block (a 468 set up for drag racing), the engine sits much lower and further back.

So much so, that I cannot run an HEI distributor unless I perform major firewall surgury. I got around this by using an MSD billet distributor that comes equipped with a magnetic pickup and the small diameter cap. If you don't want to do that, Pertronix makes a kit to install a magnetic pickup inside a factory (pre '75) points-type distributor.

Also, my oil pan is extremely close to the crossmember. This makes it pretty much impossible to remove the pan with the engine in the car. Even if I remove the distributor, if I try to tilt the engine after removing the through bolts on the engine mounts, the heads will hit the firewall.

Looking at my '86 crew cab (also equipped with a small block), there may not be as much of a problem for you, but you may need to shorten your transmission mount. This was not much of a problem in my Nova since my transmission mount was fabricated when the roll cage was installed. To ease my situation (and for a performance increase), I'm using Moroso solid engine mounts and an Energy Suspension polyeurethane transmission mount. I WOULD NOT recommend this for your truck at all! The vibration will drive you crazy!

My suggestion: either go to a wrecking yard, the dealer, or a good parts store and buy the proper mounts. You may have to replace both the engine and frame mounts, or you may have to simply move the frame mounts to a different location (I'm sure a good service manual, other posters on this board or your dealer can help you with this information).

When performing this swap, don't forget about all the other little things that will creep up, such as rad hoses, accessory mounts and associated wiring/hoses (I'm thinking power steering and alternator especially here, not to mention air conditioning if so equipped), heater hoses, fan and spacers and their relation to the shroud, transmission and throttle linkage, radiator capacity (will it cool your big block?), fuel pump and lines and exhaust system, just to name a few.

All in all, this shouldn't be too difficult of a swap because the factory built thousands of trucks equipped with big blocks, so you may want to head to the wrecking yard to get as many of these little pieces as you can.

That said, I would highly recommend a big block for every truck! The torque difference is astounding. In fact, when my 350 finally gives out in my '86, I'm going to buy a brand new 502 cubic inch crate motor from GM instead of rebuilding the mouse. Six hundred foot-pounds of torque compared to three hundred? NO COMPARISON!!

Have fun!

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