Hi all!! Question. I have a late build (10/69) 69 GS400. The bore & stroke on this motor from the factory was 4.040 x 3.900. Now, the 70 455's bore & stroke from the factory was 4.3125 x 3.900. My question is, regarding the block only, were there any other significant differences to the blocks other than the bore size? Someone once told me that the engineers at GM knew in mid to late 69 that they were going to increase the displacement to 455, and that my 400 block has the water jackets of a 455. Is this true? I was reading an article a while back that also said that all GM did to the block was increase the bore. I'm not familiar with th 70 455 block and therefore need some info from knowledgeable folks. The water jackets on my 69 block appear open at the back of the block where the head sits, but at the front, they appear filled in. Can anybody enlighten me as to the differences in these blocks? Sorry for the long thread!!
Not sure if what you say is true or not....makes some sense though. Conventional wisdom is that 400's and 430's share a block and no issues boring a 400 to 430. Rather than risking ruining the block, have the cylinder wall thickness sonic checked. That should tell you whether or not there is sufficient material for the bore you are looking for. Good Luck
I don't think you can take a 400 to 455 bore size. But I've read that the later 430's (ie '68-'69) can go to standard 455 bore size.
As I understand it, the 400-430 are made out of the same block. I definately am planning a sonic check prior to any boring. I just wonder if what I have been told is true, that the later part of 69, the 400-430 block had the 455 water jackets. I'm pretty sure I would need to enlarge the oil galleries, but not sure of any other differences.o No:
