plumbers crack

TORE APART 502 MOTORS,everything is in good shape ,trying to settle on compression ratio.stock pistons Je700 with slight dome.buying new merlins port &polished gasket matchedand would like to run crane 139741 cam.with 119cc heads whats the compression ratio with these pistons?Are these 4cc domes?oso member gave me breakdown but im aliitle lost with regard to decking block.If Iwant to make 575 hp with this cam optimum comp ratio 9.5?If compression ratio is at 8.5 this cam would be no good?

mcollinstn

flattops are -3cc or -4cc (as in less than zero) due to the valve pockets.

RickR

Pretty sure OE pistons have 1cc dome.
You can call JE
http://www.jepistons.com/

TomR

Assuming the block is zero decked and you are going to use a head gasket with no more than .039 compressed thickness, and the heads are surfaced just enough to make sure they are perfect, you will be approaching 9 to 1 but no more!
I run a similar setup and the cam is borderline too much!!
I was thinking of going to 110cc Edelbrock aluminum "marine" rectangular port heads!
I would be interested in any feed back from anyone who has tried these heads.

plumbers crack

Mcollinstn,what do you think about 741 cam and 9.1 cr
do I buy pistons or buy 111cc heads to bump up to 9.5 cr?following your advice on past reply,I would make approx 540hp with stock ported heads and 8.75 cr.Now that Im buying new heads,what would you estimate increase in hp and torque?Obviously the motor should not have to work as hard to make power,but interested in feedback .If small gains I might just save the $3,000.

TomR

ttt

RickR

Please check my math but

You can mill the heads to increase compression but the intake may have to be milled also.

0 Deck , .039 gasket, 118cc open chamber head milled .035 (equals -6.8cc), 1cc dome you get around 9.64 to 1

.005 deck = 9.54 to 1

mcollinstn

RickR

0/.039/118-6.8/1 on 4.470x4.00 = 9.39:1
.005 deck = 9.30:1

JE shows the BBC flattop at "minus 3cc".
They also list a "minus 4cc" piston, but don't show it in a standard bore size. The next dome for a std bore 502 is 13cc.

plumbers crack

okay then what about 111cc heads?

Bad to the bone

I had my afr heads milled to 105 made a huge difference
along with better flow. I did not have to mill my intake.