39* versus 45* 400 blocks
#1
39* versus 45* 400 blocks
What are the differences between the two other than bank angles and .921 versus .842 lifters? Can you see the difference in the blocks from the outside? Same deck height?
#6
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#12
#15
The roller lifters in the 1985-90 307s are also 0.921. Interesting that the P/N for the standard-size roller lifters are different for DX and 307 motors, but the part number for the 0.010" oversize roller lifter is the same for both applications.
#16
I forgot about those powerful 307's. LOL
#18
#19
Joe - The part of these explanations I don't understand is the '66 GM Engineering Journal Memo states the 39° lifter bank angle ('66 & '67 400ci) was designed to allow space for tooling the block to accept the .921 lifters. If that's the case, why did they go back to using .842 lifters in '68 when the 39° lifter bank angle was retained? What am I missing?
#20
OK, this is the part of the reasoning that was missing from the decision to return to .842 lifters while still retaining the 39° lifter bank angle.
#21
neither one of those in the pic are .921” lifter bores…just so you know
another thing is don’t trust the drill spot as proof a 66 or 67 425 389244D .842” block is a 39CBA…like has been said here. proof is the pic on the right, no drill spot. I’ve got a few myself. You’ll need to have the intake off and check
dont trust the casting thickness around the lifter bore either. I have some 389244D .842” 45 deg blocks that do not have a thicker cast area like that pic on the left.
all 39CBA blocks are 42LBA
all 45CBA blocks are 45LBA
Last edited by CANADIANOLDS; February 27th, 2024 at 12:27 PM.
#22
only two big blocks came with .921” lifters. The 66/67 400 390925E and the 66/67 389244D in the Toronado which should have the identifying drill spot. both are 39CBA.
neither one of those in the pic are .921” lifter bores…just so you know
another thing is don’t trust the drill spot as proof a 66 or 67 425 389244D .842” block is a 39CBA…like has been said here. proof is the pic on the right, no drill spot. I’ve got a few myself. You’ll need to have the intake off and check
dont trust the casting thickness around the lifter bore either. I have some 389244D .842” 45 deg blocks that do not have a thicker cast area like that pic on the left.
all 39CBA blocks are 42LBA
all 45CBA blocks are 45LBA
neither one of those in the pic are .921” lifter bores…just so you know
another thing is don’t trust the drill spot as proof a 66 or 67 425 389244D .842” block is a 39CBA…like has been said here. proof is the pic on the right, no drill spot. I’ve got a few myself. You’ll need to have the intake off and check
dont trust the casting thickness around the lifter bore either. I have some 389244D .842” 45 deg blocks that do not have a thicker cast area like that pic on the left.
all 39CBA blocks are 42LBA
all 45CBA blocks are 45LBA
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