I have a 350 HO. I want to mill the heads but I'm not sure I know what I'm doing. Could someone help me? I want to raise my compression to 10:1.
I found the deck height cc (15.055) from assuming the head gasket cc is 5.766 (.028"). Is this correct?

The Auto Math Handbook gave me this formula.

((new displacement ratio - old DR) / (new DR * old DR)) * stroke = Amount to mill

((9 - 8.4) / (9 * 8.4)) * 3.48 = .02761905

Is this all I need to know? Sorry if I messed this up. I'm a straight C student.

thanks
Mike

hey mike,
its early but i'll give it a shot.
for a .029, 4.1 bore gasket i get 6.2276cc
for a .028, 4.1 bore i get 6.06cc
thats using a 0.0610244 ci/cc conversion.

also, how did you measure deck height ?
15.055cc with a stardard 4 inch bore yields about 0.0731 deck height,(with a flat top piston)
do you have dished pistons?
general consensus is to keep the quench(deck height plus gasket) in the .035-.045 area.
whats the rest of your info-head cc, piston type, current comp ratio?
check out pat kelly's compression ration simulator....
http://cochise.uia.net/pkelley2/crc.htm
this lets you adjust the variables to reach your goal....
i'm not sure how accurate that equation you posted is. i would hope your machine shop can go over the amount to shave off with you...but its definitely good to know yourself.
hope this helps
good luck

kip

My motor is all stock 350 HO. I couldn't find info on the pistons except that they're just cast aluminum. The comp. is 9.4:1.

The chamber volume has to be around 21 cc with 712.5cc cylinder and a 64cc head, so I subtracted the head gastket thickness 6.057 from 21 and I get around 14.9. But is this the right head gasket?

Mike

you have vortecs, i missed that even though its in you thread title, coffee hadn't kicked in yet....64 cc chambers and i read from others with them that they cc'd them at 62.
i get your 712.5 cc swept volume number, but thats with a true flat top-no dish or valve reliefs. right?
you subtracted the gasket height and also subtract out the deck height, .025"(4"bore) = 5.15cc's... thats brings you down to like 9.75 which would be the dish in the piston.

to get 9.4:1 with those heads,a 3.48 stroke,.028 gasket, and a deck height of .025, i would guess your pistons have about a 10cc dish to them. we really need to know the deck height here to get an accurate picture. i have read the .025 is a normal production height from the factory.
heads gaskets for your engine come in many thicknesses,(.015 steelshim,.029, .039, .041) and others.
without touching the bottom end, to get 10:1 it looks like you would need to run about a 58cc chamber.
anybody else,is this about right?
did you try pat kelly's compression calculator?
jim68, i think, thats his name, from hillsborough nj has a cool excel spreadsheet in his sig, try to search around for that.
good luck, hope this helps you out.....
kip

I was going to say that I thought the Vortec's were 64 cc's or so, therefore with 350 four notch, flat-top pistons, you are over 10 to 1 CR. regardless.

But I forgot about the possibility of your engine having dished pistons... pdq67

ok, vortecs are around 62CC. The piston is probally a flat top.... with 4 2.5 CC valve reliefs. thats a 10CC dish. You guys arnt figuring how low the piston sits in the block. .025 + .005 or .01 in the hole is .03 and plus .028 is a .058 piston to head clearence. so its bascially a 72CC head with a flat top piston which is around 9-1. Its not a 10-1 engine because of the excessive clearences between the piston and the head and the 4 valve reliefs. Try to find the compression height of the piston, it could be a low height which would even drop the compression lower. 1.560 is a normal .05 in the hole, 1.52 is a .01 in the hole, thats a big difference.

We are talking about true flat-top pistons with only the four notches in the top, aren't we??

I ask this b/c my nephew has a four bolt main truck short block sitting on one of his engine stands that has dished flat-top puistons with four notches in the bottom of the dish!!

This is where I get the 7.9 to 8.1 or so CR. number estimate for a later model truck engine...

pdq67

Personally, I wouldn't give 'em more than a light surface cut to make sure they are flat. The decks are pretty thin. The gains for .6 compression is, IMO, not enough to justify the work and cost, and the potential to create more problems (thin decks, intake gaskets not lining up right, etc). The cheapest and easiest thing to do would be to use a set of fel-pro 1094 head gaskets. They are .015 thick rubber coated shim gaskets with a 4.100 bore size. They end up about 3.4cc if I remember right and would be worth about .2 compression over a .028x4.166 gasket, and they will tighten up the quench area too.

I was going to get them milled because I am taking them off for a valve job and a little porting work. What would be the max that you would get them milled if you wanted higher comp but wished to stay close to the safe side?

thanks
Mike

My Vortecs varied from 64-66cc...

Not all the same!

I have vortecs on the motor in my car. I remember in the searh for what needs to be done to these heads for more performance, I read that this head has a particularly thin deck.