milled head

L

larry harding

Senior Member
somewhere i was digging thru literature and saw a formula for milling an a head
but don't know where i saw it . it was like a formula.... .0xx=5-1 c0mp, .0xx = 5.5 to m1, .0xx=6-1. anyone else seen this? it is probably in some manual or such that i have, but senior moments erase stuff really quick.
 
Depends on the combustion chamber shape. Measure the area of the combustion chamber then multiply that by the depth of cut and you will get the volume reduction. Each cylinder is about 50 cubic inches, so the volume change divided by the cylinder volume will give you the change in the compression ratio.

For instance, say the original head is 4.6 to 1. The volume of the original chamber would be 50 / 4.6 or 10.9 cubic inches. Lets say the area of the combustion chamber is 9 square inches and the cut is 0.10 inch, giving a volume reduction of 9 X 0.10 or 0.9 cubic inches. So the original volume is reduced to 10.9 - 0.9 or 10.0 cubic inches. The new compression radio is then 50 / 10.0 or 5 to 1.

You can estimate the area of the combustion chamber by tracing the shape onto some graph paper and then counting the squares included withing the tracing. Estimate the included fractions of squares that are cut by the tracing and include those fractions. Depending on your math skills, you could also integrate the combustion chamber shape to get the area.
 
Last edited:
Remember if you mill the head check for piston clearance. I have seen a lot of A and B Fords where the pistons pop up above the deck into the recess in the head.

Charlie Stephens
 
Charlie has a good point. Have the machinist re-cut the recesses in the head. There should be 1/16 clearance between the top of the piston and the head. When figuring out how much to cut, use the compressed thickness of the gasket.
 
nkaminar said:
Charlie has a good point. Have the machinist re-cut the recesses in the head. There should be 1/16 clearance between the top of the piston and the head. When figuring out how much to cut, use the compressed thickness of the gasket.
Click to expand...

Most Machine Shops without CNC capability are not going to be efficient at doing this. About the only way to do this with a typical job shop's tooling is to build a fixture plate to hold the head from the top side. Then have an adjustable sliding post for positioning under each cylinder where the head can be mounted inverted onto a rotary table and then indexed in. By the time it is centered and leveled, and then machined, it is believable to have an hour counterboring each combustion chamber. Just the price of the machine work alone (-sans building the fixture) will exceed the costs of buying a new high compression head.
 
Brent has a good point also. It is usually lower cost to buy a higher compression head than to shave a head and re-cut the recesses.

Not true on a Model T. No recesses needed. I had a shaved "low head" on my Model T that worked great. About 1/2 inch was removed and it was into the water jacket in places (that were closed up the head gasket). The low head is the original Model T head that had a higher compression ratio. It was changed to the "high head" early on to lower the compression ratio so that the poor gasoline of the era could be used. The high head lowered the horsepower to about 18 from the original 20.
 
thanks guys..... i,m probably going with a new hicomp head, some are expensive, others out of my range in price. i want a 6.5 comp. don't know which one to buy. one of the suppliers has an aluminum winfield style head which interests me. i'm going with insert bearings if they ever become available again. trying to mill a head is most likely beyond my abilities. i did see the chart somewhere showing how much to mill for a given comp, just can't remember where i saw it.
 
Snyder's have cast iron heads that are reasonable. The aluminum heads need a zinc anode to keep the aluminum from corroding. In my opinion, the Snyder 6.1 head has the better combustion chamber design than their 5.5 head.

You could ask around at your club to see if anyone has a used higher compression ratio head for sale, or check places like Craig's List or the usual magazines.
 
Last edited:
larry harding said:
thanks guys..... i,m probably going with a new hicomp head, some are expensive, others out of my range in price. i want a 6.5 comp. don't know which one to buy. one of the suppliers has an aluminum winfield style head which interests me. i'm going with insert bearings if they ever become available again. trying to mill a head is most likely beyond my abilities. i did see the chart somewhere showing how much to mill for a given comp, just can't remember where i saw it.
Click to expand...

IMHO, look for an iron Winfield if that's your desired booty.
I have had a couple aluminum ones come thru the shop here cracked pretty bad. One was basically broken in half, too thin of material.

Brumfield made one that really performed well.

FWIW, just milling a stock head is a bad idea, the chamber design just doesn't adequately atomize the charge and will detonate.

John
 
burtz lists a 6.5 head at a competitive price. you have scared me away from the aluminum. i want 6.5 if i can get it. any other suggestions.
 
larry harding said:
burtz lists a 6.5 head at a competitive price. you have scared me away from the aluminum. i want 6.5 if i can get it. any other suggestions.
Click to expand...
Aluminum is OK if you know who cast it. There have been many recasts of of the various brands over the years using many different patterns.

I've heard the Burtz is a good head with improved cooling and that it fits the block very well. Some of the aftermarket heads fall short of matching the block edges.
 
Larry

Yes as A29 mentions alum is fine for a head if the casting is done properly
The cracked heads happened to be repop Winfields which is not a tall casting such as the Brierley

Sorry if I scared you off aluminum

John
 
Head design is complicated by the need to move the air from the valves down into the cylinder during the intake stroke and by the way the squish area influences the turbulence for proper combustion. The compression ratio is just one factor.

I noticed just a little difference moving from the Snyder's 6.1 head to the Burtz 6.5 head. I have a test hill and judge any change by the road speed at the top of the hill.
 
I milled stock Model A and a stock Model B heads. Do not waste your money & time because there is very little compression to be gained. However, you may get except carbon knocks. It is far better to buy a hi-compression cylinder head
 
You must log in or register to reply here.
Back
Top