Thread: 402 BBC build

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Originally Posted by chevybuilder

Hello All. New to this forum. Hopefully someone can help me with my 402 rebuild. I am restoring my 1970 GMC sierra grande truck. I am currently going thru the engine. The indication is that is came with a 396 but i understand they marked the 402 as 396 also during this time. I have the engine apart and have done some research and found this is a true 402 block 0.040 over bore to 4.166. I want to get about 400+ hp when done. i think I can stay with my block/heads/crank. I want a good street rod and occasional play at the track but mainly street. Here is what i think I know.

Block:
Engine ID - T0406TBG
Casting - 3969854
2 bolt
This seems to be a 402 block built at the Tonawanda plant April 6th 1970 for a truck. Could pass as original equipment I believe but has been rebuilt at some time.

Heads:
Casting - 3931063
Open chamber
2.06/1.72 valves
From my research I have seen some info that indicates 96.4cc and some 100.9cc. Not sure which is correct.

Crank:
Casting - 3904816
Rod journals at least have been undersized 0.010. Going to mike out this weekend to verify these and mains.


My main trouble is the geometry between the pistons/cam/push rods/rocker ratio/valve springs etc. I can't find any formula to determine this and I don't have the experience to just know. Do I want to go roller cam? What duration/lift? I have found plenty of info to check these clearances once built but nothing to check before parts are purchased.

Thanks for any help to get me started.

the F on the pistons means front .. the piston to valve and all others stuff is check for your build. deck height .heads that are milled .were the valve are seating in the head all come in to play .push rod get check at mild lift they will not be same as stock pushrods if you go rollercam. valve springs are used for your cam you are going to use. welcome to engine building 101 i build all bbc for customers with hyd roller or solid roller for race engines . as for block .heads. rods. crank. good size and machine work /prep is what pays off all them parts can see 400+ all day long if all machine work is right and the engine is built right