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Hey all. New to the forums. I have a 71 cutlass with a 355 that in going to replace with a 425 once I finish building it. Any tips and tricks from you guys that I should keep in mind? Thanks all. Also pic of the car the 425 is going in
Last edited by Korbo72cutlass; Sep 25, 2022 at 08:21 AM.
I assume that "355" is an Oldsmobile motor? The biggest external difference between Olds big block and small block engines is the deck height. You'll need the A-body big block exhaust manifolds or headers. Use the water pump, accessory brackets, and pulleys from the 350 as a matched set to avoid belt alignment issues. Be sure to note and correctly reinstall the spacers on the power steering pump bracket. Use the motor mounts for the 350 (Anchor 2261 or equivalent). Do NOT get the so-called "big block" mounts. Like all 1964-67 Olds motors, that 425 will need the correct early (64-67) flywheel or flexplate due to the different crank flange bolt pattern. If the 425 is from a Toro, you'll need to swap the oil filter adapter as the FWD adapters are different. And of course you'll need a radiator sized for a big block.
I assume that "355" is an Oldsmobile motor? The biggest external difference between Olds big block and small block engines is the deck height. You'll need the A-body big block exhaust manifolds or headers. Use the water pump, accessory brackets, and pulleys from the 350 as a matched set to avoid belt alignment issues. Be sure to note and correctly reinstall the spacers on the power steering pump bracket. Use the motor mounts for the 350 (Anchor 2261 or equivalent). Do NOT get the so-called "big block" mounts. Like all 1964-67 Olds motors, that 425 will need the correct early (64-67) flywheel or flexplate due to the different crank flange bolt pattern. If the 425 is from a Toro, you'll need to swap the oil filter adapter as the FWD adapters are different. And of course you'll need a radiator sized for a big block.
