Engine Casting Decoding...what does it really mean?

[84cutspreme]

Okay now I've had a few different blocks throughout my automotive history, and the question applies to all engine makes; however I am interested in chevy small block knowledge. What differences are there between each similar block. For example I have had three sbc 350's so far and every one had the same 3970010 casting #, just different coding. Do any blocks have differences in tolerances or oiling or cooling passages? excluding shitty mexico blocks...they don't count.

 

[GhettoRacingKid]

the 3970010 block and all the 350 blocks are all the same. The only difference is the metal content for strength and 2 bolt and 4 bolt. As far as I know nothing changes with oiling etc...

the 3970010 that has the 010|020 stamped under the timing cover and the back of the block is the strongest 350 block GM ever made.