changing compression

[import convert]

i have a sent of cylinder heads that have 69CC chambers and with stock pistons ill have about 8.2:1 compression but i want it to be higher.

i want it to be over 9:1 compression but i didnt know if i could just do it by changing to a thinner head gasket and milling the heads. the other thing id do is buy pistons that a slight dome to them.

what do you guys think would be the best idea?

[Lincolnmania]

have the heads shaved......better off with e5 heads than those things

[import convert]

i got a set of E7 heads but they were damaged while being shipped so i got a set of D80E heads form my girlfriend and noticed they had 69CC chambers after we got them. they were cheaper then fixing my E7 heads but yes i now have to make up for the larger chambers. so i was getitng ideas on what i can do and,
1) my first idea is to run a thin head gasket and have them shaved.
2) the other is get pisotns with a slight dome and do it that way.

[Lincolnmania]

just get the heads milled......a rebuild and some bowl work would help too......how many miles on these heads? are the valve seals still soft or do they resemble hard plastic?

[import convert]

the guy said the valve seals are bad but if the pictures are right the heads are all cleaned up but im not sure about how many miles are on them. ill look at the valve faces when i change the seals. now i gotta find out if the valve springs i got for the E7 heads will work on the D80E heads.

[1987cp]

i got a set of E7 heads but they were damaged while being shipped so i got a set of D80E heads form my girlfriend and noticed they had 69CC chambers after we got them. they were cheaper then fixing my E7 heads but yes i now have to make up for the larger chambers. so i was getitng ideas on what i can do and,
1) my first idea is to run a thin head gasket and have them shaved.
2) the other is get pisotns with a slight dome and do it that way.

Your girlfriend charged you money for those things????

Check your other thread ... I did notice these pistons with a 6.8cc dome .... valve clearance may be kind of tight, though ..... http://store.summitracing.com/partde...6&autoview=sku

[import convert]

how many CC's do you think can be safely be dropped by milling hte heads and runnin a thinner head gasket?

[phayzer5]

if you mill the head deck too much then you're going to have to mill the intake side to match it up right

[88grandmarq]

if you mill the head deck too much then you're going to have to mill the intake side to match it up right

it depends how far you mill the heads. according to Mike Schultz (guy that does thumper ported heads www.thumperoforangepark.com) you can safely mill the E7 heads .025" which yields a 57cc combustion chamber and not have to machine the intake for fitment. you will have to either get shorter push rods or shim the rocker arms for proper lifter pre-load.

I have no idea what needs to be done for older heads for proper lifter pre-load or how far you can machine them.
Personally, I would say the D8OE would probably require more machining and rebuilding than tjhey are worth and probably dont flow any better.

[packman]

From what I have read, I would get a thinner head gasket and have the machine shop mill the heads to yield a safe valve-piston clearance. That way you increase your compression and create better squish zone to better atomize your fuel mixture.


Packman

[import convert]

so if i milled the heads .025" then id need pushrods that are that much shorter or is their a minimum amount i can shave without changing the pushrods?

[1987cp]

You'll be wanting to double-check pushrod length on any performance build. Even on my really basic junk, I didn't, and I get to listen to a noisy valvetrain every time I drive the car. :3gears:

[import convert]

well i decided id get pistons and leave the heads alone. im down to these 2 choices.

.030" over for $323 and -11CC"

or

.040" over and $318 and -10.6CC's

im not fully sure which one im gonna go with but keep in mind i have 69CC chambers so the lowest i could go is 58CC's compression wise which i know would put me in the 10:1 to 11:1 CR range. im not sure which i want to go with though? any thoughts?

[1987cp]

I thought we'd been over this - first you get what fits the cylinder bore you end up with after machining, then you decide on exactly what piston you want. Either way, the difference in those two dishes shouldn't make a whole heap of difference.

Not taking gasket volume into account .... cylinder volume is 568cc ..... so 568cc/58cc = 9.8:1 compression .... right? No, wait, it would be (568cc+58cc)/58cc = 10.8:1 .... though that would mean 9.4:1 with flattop pistons with no valve reliefs at zero deck ....

guess that doesn't take into account the piston dish that produced the heads' original 8.3-8.5:1 CR, does it .... so (568 + 69 + dish) / (69 + dish) = 8.5 ..... meaning 637 + dish = 8.5 dish + 586.5 .... so 50.5 = 7.5 dish, or dish = 6.73 .... so I guess the original pistons for those heads would have had about a 6.73cc dish on them.

[import convert]

i understand that i need to decide if im gonna go with a .03 over or .040 over. what im deciding is what i want for a CR. i dotn want to try and make a thinner head gasket and shaved heads make up the cc's caus ei odtn want to run into trouble wiht taking too much off and have problems getting my intake manifold to fit and i dont want to try and find the right push rods wither. im mena ill ahveb to double check to see that they dont have too much slack but i think you get what i mean. i figure getting pistons is hte easiest way but im not good with the whole numbers hting you just did so i figured id ask a few more questions and see if someone could figure ou the CR id end up with. so, thanks for hte info