GM NOS 3967811 7115 6223 Crankshaft Casting change
 

When did GM change the casting numbers on the crankshaft from 7115 to 6223 on NOS cranks 3967811. Are they the same or is there a difference. Thanks, Larry

I believe 7115 is a 427 crank and 6223 is a 396 crank also i belive the counter weights are 7/8 think for 427 and 3/4 on 396. just my opinion.

I've always wanted to learn more about the differences myself. I, too, have heard that the 7115 was for a 427. But the L72s in COPOs use the 6223 crank. Why? What is the real difference? I have never had a 7115 crank to compare.

The 7115 crank with the heavier weights are for the larger 427 pistons. All 427's should have been equipped with the 7115 from Tonawanda.
Its my understanding that the 6223 can be made to work in the 427 with weight added.

7115=L/88 ZL1 6223= all other 396 427 with forged cranks

Thanks for clearing that up Jerry. How did the factory get the 6223 to balance with the heavier 427 pistons?

I probably didn't ask the question correctly the first time. When opening three NOS cranks in the boxes all with part number 3967811. Two of them were a block casting 6223 and one was a regular marked crank 7115. All three are cross drilled and nitrated with the same paint marks. Just curious why the difference in them. Thanks, Larry

What he said except what along with why?

Thanks for the "why" and also add when did they start the change to it. The boxes aren't dated. Larry