'70 455 vs. '74 455

[SBRMD]

Gentlemen: Can someone in the know point out the changes that were made by 1974 in the 455, relative to the '70 model? What all was done to the heads, piston, carb, etc? Were there any improvements? Does the '74 yet have HEI? Finally, can one make an essentially '70 spec motor using all the '70 parts on the '74 block? Further, are there any easily made mods (with current technology) in such a rebuild that would add to performance and economy without sacrificing driveability? Potential project = '70 Estate Wagon, currenty with '74 replacement engine; original complete motor (w/ cracked block) is included.<P>Thanks in advance for all suggestions and insights!<P>Steve Robin<BR>Minneapolis, MN

[The Old Guy]

If you use the late block ,and all the parts from the 70 engine,you will have for all intents and purposes ,a 70 engine . The only thing I would use from the 74 would be the front cover , the oil pick up tube ( which is larger diameter) and the block. If you use the heads ,intake , crank ,rod and piston assy ,and distributor , noone will know. The 74 should have HEI , but the distributor has a better advance curve ,so you may want to stay with it rather than use the HEI.

[Guest]

The late-'72 & later block (part# 1241735) is what's often called the 'double scallop' block. It has 2 extra bosses per side to seal holes in the same years' heads. I believe that prevents using pre '72 heads on '72 (or later) blocks. Unless it's originality is crucial, you'd be better off octane-wise with the lower compression '74 heads anyway.

[The Old Guy]

You can put 70 heads on a 72 block ,but you can't put 72 heads on a 70 block

[Guest]

i am not going to pretend to be an expert on the 455, but i do know that the 74 block has bigger internal oil passages, and originally would have come with HEI. it also has a bunch of exhaust cross-over stuff in the intake manifold and heads, and a much lower compression ratio.<P>you should be able to put the early heads on the later block, but i would be concerned about the compression ratio. you would need racing gas or octane booster.<P>the advance curve of the HEI can be changed quite easily, to be even better than the points distro, just change to the weights and springs from a buick 350 HEI.<P>i dropped a HEI in my 73 455, and it runs great.<P>of course, if it aint broke, dont fix it, leave the 74 motor in there...<P>allan