68 427 engine-first design vs second design?

[Patrick N.]

I understand there may be a first design and a second design 427 casting, casting numbers 3916321 and 3935439 for the 68's.
In the interest of learning, can someone educate me if this is accurate?
Also curious on what the differences are and why the change was made?

Best,
Pat

[Clem Z.]

Re: 68 427 engine-first design vs second design?

I understand there may be a first design and a second design 427 casting, casting numbers 3916321 and 3935439 for the 68's.
In the interest of learning, can someone educate me if this is accurate?
Also curious on what the differences are and why the change was made?

Best,
Pat

the later BBC were cast with more clearance in the bottom end to clear the longer stroke of the 454 BBC. i am not sure what year this happened but the 454 came out in MY 1970

[Patrick N.]

Re: 68 427 engine-first design vs second design?

Thanks Clem, Makes sense. Some ressources show the changes listed as first/second design others as early/late production but no real info.

Thanks again.
Pat

[Stuart F.]

Re: 68 427 engine-first design vs second design?

Does it seem possible that they would anticipate stroking the engine that far in advance?

Stu Fox

[Patrick N.]

Re: 68 427 engine-first design vs second design?

Does it seem possible that they would anticipate stroking the engine that far in advance?

Stu Fox

Was it GM's habit to phase in a change to the motor in this manner? it would give them a year+ to test and develop prior to the 454 release.

Pure speculation, but given the R&D activity on developing horesepower during that time period, they may have had this in development in 66-67 and well ahead of the curve on this one.

Pat

[Joe L.]

Re: 68 427 engine-first design vs second design?

I understand there may be a first design and a second design 427 casting, casting numbers 3916321 and 3935439 for the 68's.
In the interest of learning, can someone educate me if this is accurate?
Also curious on what the differences are and why the change was made?

Best,
Pat

Pat------


There are really very few differences between these two block castings. The GM #3916321 has no provisions for dowel pins for the timing cover; the 3935439 does have such provisions. There are other minor differences.

I believe the block that clem is referring to is the GM #3963512. That block, first used for late 1969 427, had crankshaft reliefs cast to accommodate the longer stroke 454 crankshaft and was then used for 1970-71 454's.

[Patrick N.]

Re: 68 427 engine-first design vs second design?

Thanks Joe
Sounds like it was a change of improvements and running changes.

Is it fair to say that this was the typical reason a casting number changed in the same year on the same motor? i.e. 3935439, 3955270, 3963512- all 69 427/400hp.

Thanks once again for passing on some more of your knowledge!

Pat

[Joe L.]

Re: 68 427 engine-first design vs second design?

Thanks Joe
Sounds like it was a change of improvements and running changes.

Is it fair to say that this was the typical reason a casting number changed in the same year on the same motor? i.e. 3935439, 3955270, 3963512- all 69 427/400hp.

Thanks once again for passing on some more of your knowledge!

Pat

Pat------


Yes, as a general rule, changed casting numbers for a block in a given year were the result of relatively minor changes and probably represented a very modest improvement in some parameter of functionality.

[Richard F.]

Re: 68 427 engine-first design vs second design?

Joe, When you talk of provisions for dowel pins, I assume you mean holes. My March 5439 block has no holes, but the timing cover does. Can't say if the cover is original though. By the way, the block would not accept 7/16 rods without some grinding.

[Joe L.]

Re: 68 427 engine-first design vs second design?

Joe, When you talk of provisions for dowel pins, I assume you mean holes. My March 5439 block has no holes, but the timing cover does. Can't say if the cover is original though. By the way, the block would not accept 7/16 rods without some grinding.

Richard------


The 5439 block should have the small bosses added for the holes for the dowel pins. I thought that all these were drilled for dowel pins and had them installed. If yours does not, then it must be that all did not.