I'm going to be going and getting a 403 next week and I need as much info on this block as possible. I know that it can be bored up to 70 over. I thought it was a big block but I have read in a couple of places that it's a small block with the ability to bolt on big block heads? I desperately need info.

 

403 what, Olds? If it's not a chev block then it won't bolt onto your trasnny. The B-O-P bolt pattern is different. BBC has a 402 which is a factory bored .030" over 396. A .030" over 400 SBC is a 406.

Chev has big/small block distinction because of the different bore spacing between the blocks. BBC and SBC heads are not intrchangable. Oldsmobile blocks all have the same bore spacing so there is no such thing as a big block or small block Olds.

 

Go to RealOldsPower.Com and do a search on 403.

Do the search and read the results BEFORE you ask anything. There'll be a lot of stuff to read, so that'll keep you busy for a while.

And let me save you some trouble...
There's no such thing as a solid main web 403.