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?

 

The only meaningful difference is the lifter bore location.

 

What are the pro/cons between the two angles? Why did they change?

 

From the 1Q1966 General Motors Engineering Journal article about the new Toronado:

 

Thank you Joe.

 

One picture is worth a thousand words! Do these .921 lifter bore blocks have a special casting number?

 

That's an engineering solution. Deviate from the intuitively derived bang-on measurement but still be within parameters so you can actually make the thing.

 

One way to tell from outside the block is they have a drill spot right next to the oil tube:

 

^^ This, any 39 degree block will have the drill spot.

 

To clarify, that's any 1966-67 block. All 68-up Olds motors are 39 deg and don't have a drill spot.

 

I thought 67 was last year for 39 deg block and they went to the long stroke 400 in 68 and 69.

 

The stroke has no connection to the lifter bank angle, and every Olds block from 1968-1990 has a 39 deg lifter bank angle.

 

OK, but .842 lifters?

 

Yes unless it's a diesel.

 

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.

 

I forgot about those powerful 307's. LOL

 

As in 330 , 400 and 425 always have it?

 

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?

 

Simple. Why have two machining setups and two cam types when one would work? Standardizing on 39 deg meant there was no chance of putting the wrong crank in a block on the assembly line. And apparently the lifter diameter problem wasn't as big a deal as first thought, given that the W30 cams worked with 0.842 lifters.

 

^^^^^^^
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.

 

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

 

Humor me...CBA and LBA...so I don't have to guess wrong

 

Cam Bank Angle and Lifter Bank Angle.