Pistons not compatible w/ BBC GEN V or VI

[Bad Bowtie]

Anybody know why these pistons are not compatible? Here is the link and it is posted in the notes about non compatible.
http://store.summitracing.com/partde...5&autoview=sku

I have a new set of these and were preparing them for a GEN VI 454. Not sure now which way to go. I think it may have to do with closed chamber design piston, but I anticipated using a 119cc open chamber head. Any responses are welcome.

[Madspeed]

Ill Bet its because of the Gen V and Gen Vl heads
the Gen V an Vl heads are Cathedral ports like a new LSX..
Hence the valves and Combustion chambers arre not the same anymore.

I have seen the new heads at my machinests shop the intakes look killer but the exaust ports look like they couldnt pass enough air to blow out a birthday candle.

[Bad Bowtie]

Madspeed,
Thanks for your input. I know which intake port design (cathedral) you are thinking of but I'm working on an earlier Gen VI motor, the ones that have standard rectangular intake port. This is actually one of the 454/425 HP HO motors. Seems as though the problem is not related to closed chamber piston design or the combustion chamber design but the crankshaft. Supposedly these pistons are not clearanced for the counterweights of the one piece rear main seal crank. So it looks as though I have two options... buy correct pistons or put a earlier Mark IV 2 piece rear main seal crank in it with the rear main seal adapter. I think i'm going to mock up the the rotating assembly and verify if this is correct and see just how much interference occurs.
BB

[Madspeed]

Madspeed,
Thanks for your input. I know which intake port design (cathedral) you are thinking of but I'm working on an earlier Gen VI motor, the ones that have standard rectangular intake port. This is actually one of the 454/425 HP HO motors. Seems as though the problem is not related to closed chamber piston design or the combustion chamber design but the crankshaft. Supposedly these pistons are not clearanced for the counterweights of the one piece rear main seal crank. So it looks as though I have two options... buy correct pistons or put a earlier Mark IV 2 piece rear main seal crank in it with the rear main seal adapter. I think i'm going to mock up the the rotating assembly and verify if this is correct and see just how much interference occurs.
BB

Ohh.. Well that puts a whole different paint job on things..
Sounds like your on the right track..
Let me know what the end result is im game to learn somtin new

Ken F

[Bad Bowtie]

Well the verdict is in...
I have assembled the shortblock and had no interference problems at all. The pistons cleared the counterweights with room to spare. I did not find anything abnormal during assembly that would cause these to be incompatible with my GEN VI 454. Hope to get the heads on it soon and get it fired up on my test stand.
BB

[EFI69Cam]

Ill Bet its because of the Gen V and Gen Vl heads
the Gen V an Vl heads are Cathedral ports like a new LSX..
Hence the valves and Combustion chambers arre not the same anymore.

I have seen the new heads at my machinests shop the intakes look killer but the exaust ports look like they couldnt pass enough air to blow out a birthday candle.

\

The cathedral ports are the 8100 heads. Gen 7 BBC