Chevy Big Block Casting numbers

[joewill]

I currently own a 1970 3963512 454 Block. I have been watching Chevy Big blocks for sale and I see certain casting dates advertised. Some of these blocks have next (under) to the 3963512 casting casting numbers a 'T' or a 'P' or otherwize nothing. What do these mean? I have been trying to find a correct block replacement for my corvette based on date code but 2 blocks close in date may have a different T or P or just blank. I have heard T for tonawanda, and T for truck, and P for passenger.. does anybody know what these mean? I have seen 4 bolts have one and 2 bolts another and it seems to be random.

[nuch_ss396]

Look for "HI-PERF PASS" cast into the block down by the oil
filter boss ( left rear of block ) or under the timing cover
area. The use of these "signifiers" was not constant throughout
the years though. I have also heard that the "T" was for Tonawanda,
but never "TRUCK". Truck blocks have tall decks and a '512
doesn't. Most likely, the "T" is for Tonawanda and the "P"
is for passenger.

BTW, what are the casting dates of the blocks you have?

Steve

[elcamino]

Per many indentification books, no 3963512 were HD truck* engines, impossible due the design of block.

Only the high HP versions were 4 bolt, the 425 and 450 hp version per Chevy by the Numbers.

*The HD trucks block have "TRUCK" cast into the block behind the timing cover. I have seen this. Also, truck block means Medum and Heavy Duty trucks, not the average 1/2 & 3/4 light duty pickups, which use the same as the cars. They used 2 oil control pistion rings in these truck engines instead of 1 in the rest, making the cylinders 0.400 in longer.

According to Chevy by the numbers, all Tonawanda cast blocks will have a "T" cast into the surface. Tonawanda cast all parts used there.

[joewill]

I have one, that is H 19 9, it does not have a T or a P under the casting number, I have another block C 25 70 that has a P under the casting number.. I think I read somewhere that all Big Blocks of that era were cast at tonawnada..

[nuch_ss396]

YEP! Tonawanda was the BBC place.