Originally Posted by gl0rywagon
Hi will a 425 olds. motor interchange with a 455 olds. I found a 1965 olds. tornado with a 425 motor. Would like to install it in a jet boat that had a 455 olds. in it. Any suggestions? Thanks Danny Sorry this post was suppose to be listed under motors don't know how to move it.
All big block Olds motors are externally identical but there are a few things that you need to be aware of:
The Toro wasn't released until 1966, so be sure you know what you're getting.
ALL 425 Olds motors have forged cranks.
The 64-67 Olds motors used a different crankshaft flange bolt pattern than the 68-90 motors. You must use the flywheel or flexplate for a 64-67 motor. The flywheel from a 455 will not work.
The Toro used a different oil filter adapter than the RWD cars. I don't know what's in the jet boat now, but use that one.
The Toro used different accessory brackets than the RWD cars. Also, the 64-67 motors used brackets that had some differences from the 68-up motors. I assume you'll just use what's already in the jet boat now.
Olds used different length water pumps. A/C and HD cooling pumps were longer than non-A/C pumps. The pump, pulleys, and brackets must be used as a matched set. If this boat installation uses a flat front cover with a remote water pump then this doesn't apply.