shaving cyliinder head surface to increase compression

[Wortttie]

Hello to all.  I would like to know the amount of material I can safely remove from a head surface of a set of C4AE heads.  I know the combustion chamber on my heads are right at 72cc's.  I want to decrease the chamber size to 68-67cc's.  We have experimented with a junk C4Ae head and found that around .010" is equal to 1cc.  I would like to know if removing .040 to .050" is safe to do.  My good heads have not been cut yet  I appreciate your help.

[Joe-JDC]

According to Ford, milling a FE cylinder head ~.0065" will decrease the combustion chamber 1 cc.  Milling the heads .030" would be a safe start, check the combustion chamber, and final mill accordingly.  Most machine shops will do this for a nominal fee while the machine is set up.  Joe-JDC

[winr1]

Is your mill assembled less heads and how far below the deck are your pistons ??


Ricky.

[Stangman]

So Joe when he mills them .030 after clean up  how much do you gain in compression. Like what does it take to gain a full point. And checking piston to valve clearance

[SJohnson]

So Joe when he mills them .030 after clean up  how much do you gain in compression. Like what does it take to gain a full point. And checking piston to valve clearance

.006 for 1 point in compression

[Joe-JDC]

.030"/.006"=.5, or 1/2 point of compression.  Simple math.  To increase the compression a full point, most FE iron heads would require ~.060-.065" milled from stock head.  Valve job, valve margin depth, valve face flat or concave, all will affect the actual cc of a chamber.  Mill a certain amount that you know, such as .030", and check the ccs.  If that changed the ccs 5, then you can finish mill to the desired compression by reducing the firedeck .006" per cc.  Any competent machine shop can do this for you.  Example:  .0065"/cc to reduce the combustion chamber one cc, and you want to reduce it 8 ccs, then 8 x .0065" =.052" removed.  Always complete your valve job first.  That includes guides, hardened seats if you need them, valves replacement if you need them, and use same sparkplug you will be running for the cc test.  Milling will be the last machine work before cleanup and assembly of the heads.   Joe-JDC

[wayne]

Do you run steel shim head gaskets.If you cut the heads to much you may have to cut the intake.

[Wortttie]

To All

than k you for you replies and experience

Allow me to respond to some of your questions

1. Head Gasket type:  I am going to use Cometic head gaskets with a compressed thickness of .027 and a bore of 4.25. 
2. Valve to piston:  The pistons are keith black units they have a 28cc dish and are down bore .018".  Cam timing at .050" is only 214 intake and 222 exhaust.  lift is .585" I & E.  It is an hydraulic roller.  Based on this the valve to piston should be fine but I will check it.
3. the heads I plan to use are C4 units with a 72cc chamber (already measured)
4. The heads will get the intake side milled to allow proper alingnment with the manifold.   
Given the current combination I will be around 8.75:1.  this is too low to make efficient power.  I need to get the compression up to 9.50:1.  So doin the math I
 need to reduce the chambustion chamber by 5-6 cc's.  So I will mill off around .040".

Again thank you for your responses. 
Phil

[Rory428]

Just curious why you wouldn`t just run a piston with a shallower dish, between milling the heads, and using a thin head gasket, you will likely need to also cut the intake side of the head to make the intake manifold fit decently.

[winr1]

I looked  into thinner cometic head gaskets but for what they cost I can get the block decked and run 0 comp height

Using pistons I already have plus 0 comp height and way cheaper head gaskets if I ever need to tear down
.............

For you smart guys... if Wortttie decked his block .018 with his current pistons... what would his compression be ??



Ricky.

[frnkeore]

Assuming a 4.080 bore, this is that you get by decking:
.028 = 6cc
.0233 =5cc
.0065 = 1.39cc
.010 = 2.14cc

If you deck a 10.17 block, to 10.15, you loose 4.28cc.

[Wortttie]

to all

Rory428 inquired why I just didn't use a piston with less dish.  Good question and the best option would be different pistons.  The reason I went with these pistons is simply I already had them and they were new.  I also had the heads as well. 

Phil

[MRadke]

to all

Rory428 inquired why I just didn't use a piston with less dish.  Good question and the best option would be different pistons.  The reason I went with these pistons is simply I already had them and they were new.  I also had the heads as well. 

Phil

I was thinking the same as Rory.  Maybe look into finding a trade partner before anything more than clean up machining operations.  With parts being as hard to find as they are, I'm sure someone has the opposite compression problem as you.