IS IT SAFE TO USE 84 MM PISTONS IN A GEN 2 BUSA BLOCK?
Do I need to find a gen 1 block for my gen 2 motor?
The internet is a buzz with horror stories about gen 2 blocks cracking between the bores when bored to 84 mm. True?
The gen 2 block features cutouts in the bottom to help pumping pressures below the piston move from one bore to the next as the pistons rise and fall. This is an old race mod.
This makes the gene 2 block weaker than a gene 1. Under severe conditions, they can crack between the bores. How likely is this to happen? We have done nearly 100 gen 2, 84mms. We have had only two crack. Both of these were new motors on the dyno trying to set a tuneup. They most likely experienced detonation.
The weaker design makes them less forgiving if detonated than the older gen one blocks.
One of our customers who builds some of the most powerful Busa motors available, swears an 84mm gen 2 will not crack unless it detonates or nitrous is sprayed.
So the general consensus is that the breakage rate is less than 5%, closer to 2% for APE.
This has resulted in a rush to find gen 1 blocks to put on the gen 2s. However, as APE is the leader in the big bore exchange block programs for the busa motors, we are stocking a number of 83mm ,1407cc, finished gen 2s.
This gives the bores an addition in thickness between the bores. There are no known cases of an 83mm gen 2 block splitting.
The choice is yours. We have both 83s and 84s on the shelf.
Photo; The block on the left is a gen 1