I have an unknown block sitting in my garage and i know for a fact that it is a bbc chevy because of the lifter bores being offset and also that the word "HI Perf" is cast into the cam gear location of the block. I found these numbers on the back of the driver side head location but i could not find on the internet what the numbers mean. If anyone can tell me what these numbers mean it would be greatly appriciated.
Casting Number as Follows: TI 217CTW and beside that was 10 15331
I am completely positive that those are the correct numbers.

Go here, http://www.mortec.com/bbc.htm . I just got a BBC also, but the numbers I looked up was behind the passenger side head. And the head #'s were inside, between the push rods. Hope this helps.

the CTW usually refers to a suffix code... you might look in a Hollander Interchange manual for it.

generally there are no letters in the casting numbers on a big block. You can find the date it was cast and decipher it, too. the date is cast into the upper right(passengers) side of the back of the block just forward of the bellhousing.
it will look like "C 12 8" which deciphers to March 12, 1968.

If you found the CTW on the deck surface at the passengers front corner, it is the suffix code to look up the installation info for that block. Could be you have a truck block from 1974.... but I dont know. Older Chiltons or Motors manuals have the Suffix codes, although very incomplete.

Hope this helps.


edit: oh... duh... I would measure the bore. if its got a 4.25 or larger bore, its a 454/427 block. if its 4 1/8 bore, its a 396/402 block.