How much compresion will be lost using 781's on a .060 over 402 with 11:1 closed chamber pistons? I know I will lost some but I don't know how much. A good guess will be fine. Thanks, David
Open chamber heads with closed chamber pistons
- Thread starter dvanhorn
- Start date
You lose approx. 1 point going to the open chamber. I've run that setup in cars and boats. it works good.
Concur, They say there is a performance gain advantage of running the good breathing 781 Open Chambered over the 390 Close Chambered heads is worth the drop in compression.Barry 85 SS said:
My 427 with 11.1 Compression and 390 Close Chambered heads ran an 11.65 best, 3000 stall, 4.11 gear, footbrake. Would like to have seen what 781s would have done on this motor!
427 11:1 closed chamber pistons used in a 454 with open chamber rectangle port heads produces 10.2:1 compression. That's how every "XAA" code crate LS6 454 came.
Tommy
Tommy
what you lose in compression will be over came by what you gain in flow... also Call cometic gaskets and get you a smaller bore and thinner head gasket and you won't lose nearly asmuch..
well theres a 106 cc closed chamber head and some that are 97 cc. I would say you could lose as much as almost 2 points. You are going from worst case 97 cc to a 118-124 cc head. thats 2 points.
I forgot to add that combo is 10.20:1 with 116 cc chambers (188 casting) & stock steel shim gaskets. IIRC, if you use the 118 cc (990 casting) heads it's 10.21:1.
Tommy
Tommy
GUYS- HE'S JUST GOT A LITTLE PEA-SHOOTER 396/402 UNDER THOSE HEADS!
Anyone want to do a re-think here? Starting at a true 11:1 with the small chamber heads (97cc) I calculate roughly a 2 FULL POINT DROP going to (~118cc) open chamber heads.
Anyone want to do a re-think here? Starting at a true 11:1 with the small chamber heads (97cc) I calculate roughly a 2 FULL POINT DROP going to (~118cc) open chamber heads.
