Hey y'all....I scored a set of heads for my Y (which means that I have gotten a 3 speed trans, a complete engine less heads and now a pair of heads all for nothing! WOO HOO!).

Anyhow, I'm machining them now, and am about to mill them a little. Not too much, but enough to true up their decks and maybe knock up the compression a little. Here are the obligatory questions...

1) How much is needed to mill the heads for a 10:1 ratio? Or, is there info
someplace that will show the CR change corresponding to how many
thousandths are removed from the heads?

2) Is there a big problem with port matching the intake manifold/water
jackets after milling?

I will have the block decked here soon, maybe .002" just to get it smooth. So, on top of that....that's where I need the CR info!

I realize that 10:1 will make it necessary to run on Avgas or Blue Flame, but that's the point isn't it? The smell of racing gas and the sound of a good rumble while driving by, just adds to the heads snapping around when you cruise by! Aaahhhhh!

 

Shane,
You didnt state the codes on the heads you're wanting to mill. ECZ-G heads I wouldnt do any more than a cleanup. I had some small valve heads (C1TE) that looked like about .080 had been taken off.

I think if you want higher comp the deck of the block should be "ZERO" decked. You need to find out which piston of the 8 sits the highest in the bore and the that measurement from the highest piston to the deck is the maximum amount to be removed.

Kevin Bigwin

 

What heads? Cant tell nothing unless you provide data.

Also what will you be doing to the engine, overbore, etc?

Here are some simple formulas to use for calculating:

Swept Volume: SV = 3.1416 x 4 x Bore squared x Stroke

Then CCFV = total combustion chamber free volume at TDC. You can get cc tables from Mummerts charts, then deduct for domed pistons, piston to deck clearance, and add for the gasket.

Then CR = CCFV + SV divided by CCFV

As an example for stock, uncut ECZ-G heads you have nominal 69cc chambers. Lets assume flat top pistons and the block zero decked. With a .050" gasket we have to add volume so lets use 15cc as a close guesstimate.

So now CR = 84 + 583 / 84 = 7.94

Note that Mummerts table says 9.0 CR but this is strictly a head volume calculation and does not reflect the gasket, decking, etc. A stock 312 with the same heads would be around 8.4 cr

Ive also seen the pi x 4 replaced by a constant of 12.8704 which will give about a tenth point increase in cr.

If you want to play with the numbers go here for an excellent tutorial by an FTE regular:
http://jniolon.clubfte.com/compressionratio.html

Now be aware that G heads are thin to start with and cant take much beyond a .050" mill so a 10 cr is not very practical.

Also, head chamber sizes are all over the place, Ford didnt have very tight tolerances. If you want to build a strong engine start by cc'ing all chambers and then machining to match the largest; I try for a .5cc match in all 8. This can be done with a die grinder.

 

286merc's calculations match 9.7 my builder said my punched and stroked 325 CID would be. Using his formula, it calculates 9.77. Maybe my gaskets are thicker than .050. In the '60s the rodders ran thinner (steel?) head gaskets to inccrease compression.

I've read the G heads w/o posts could have problems, but everything I found indicated that was using a 9:1 or so engine and then adding boost. Normally aspirated 10:1 and below should not be a problem. We made several mods to the engine (cam, Blue Thunder intake, headers, 600 cfm carb, dynamic balance, etc.) so I can't say how much the heads made but the final product really runs strong.

Rocklock
'56 Victoria

 

The heads that I have are 1959 5750-471....The list I have shows them either as Mercury heads or truck heads. Everything is the same, except the comp. ration. Mercury shows 8.7 and the truck shows 8.0 (which doesn't make any sense to me).

Anyhow, I have bored my block .060" over already. I want to have it line honed while honing the cylinders. I was planning on milling the block a little and the heads a hair to help bump the compression a little. I will also be porting and polishing right after I get them out of the hot tank Monday.

Hopefully, this info will help you guys to help me!
Shane

 

The heads that I have are 1959 5750-471....The list I have shows them either as Mercury heads or truck heads. Everything is the same, except the comp. ration. Mercury shows 8.7 and the truck shows 8.0 (which doesn't make any sense to me).

Read those formulas and reread those head specs. You will notice that one ratio is for a 292 and the other for a 312. No mystery there.

All the info you need is in the formulas.

 

Awesome. Thanks to John for providing those formulas.....I always paid attention to math in school, unlike the other morons who thought "I won't need this kinda math in my lifetime!"

Thanks for all the info!
Shane