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Old 02-20-2013, 02:59 PM   #1
TDO
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Default high compression heads

Never saw one of the high compression heads on the market. So why can't you shave the stock head to raise the compression. If so whats the max you can take off.
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Old 02-20-2013, 03:02 PM   #2
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Default Re: high compression heads

This was covered a while back so it should show up in a search. Bottom line is the head is too thin to mill enough to raise compression.
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Old 02-20-2013, 04:04 PM   #3
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Default Re: high compression heads

The effect of milling the head is minor, just a few tenths increase. HC heads have a different, significantly smaller volume chamber geometry. Here's one that I am currently using, about 117.5cc. Stock is well over 200cc. Compare the shape to a stock head.
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Old 02-20-2013, 07:18 PM   #4
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Default Re: high compression heads

What was the process to polish as in your picture??
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Old 02-20-2013, 09:03 PM   #5
BILL WILLIAMSON
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Default Re: high compression heads

In 1954, I milled one .075" & OH! YES! It was """FASTER"""! Bill W.
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Old 02-20-2013, 10:24 PM   #6
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Default Re: high compression heads

TDO, Ford Motor Co changed the standard head in 1932 by reshaping the combustion chamber so that air/fuel mix was compressed into a space just under the spark plug. The standard Model A Head's combustion chamber uses the theory "If it's bigger it must be better". Yesterday, my car got a Snyder 5.5 Head from the shop in Loxahatchee Groves. The car runs like new; many thank yous to Ken and Patrick.
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Old 02-21-2013, 08:29 AM   #7
Terry, NJ
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Default Re: high compression heads

Hey, I was thinking, Why doesn't someone make domed valves to suck up a few of those extra CCs? I was told that some guys were welding up their combustion chambers. That sounds a little risky to me without a furnace. I have "Dropped" my spark plugs down about .030 for what ever gain that will give me. Jes thinkin' bout it!
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Old 02-21-2013, 10:57 AM   #8
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Default Re: high compression heads

FWIW: Knew a machinist who lightened thousands of Model A flywheels & shaved thousands of Model A heads in the 1930's & 1940's.

He told me in the late 1950's that in the 1930's & 1940's that he could remove 3/16" from a standard Model A head with no problems to increase compression.

Have no reason to doubt it, he was a well known respected machinist who provided intricate detailed work.
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Old 02-21-2013, 11:19 AM   #9
BRENT in 10-uh-C
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Default Re: high compression heads

Quote:
Originally Posted by Terry, NJ View Post
Hey, I was thinking, Why doesn't someone make domed valves to suck up a few of those extra CCs? I was told that some guys were welding up their combustion chambers. That sounds a little risky to me without a furnace. I have "Dropped" my spark plugs down about .030 for what ever gain that will give me. Jes thinkin' bout it!
Terry
Terry, what do you when the top side of the domed valve head hits the roof of the chamber? You don't get something for nothing. Higher valve lift is generally more important than compression.



Quote:
Originally Posted by H. L. Chauvin View Post
FWIW: Knew a machinist who lightened thousands of Model A flywheels & shaved thousands of Model A heads in the 1930's & 1940's.

He told me in the late 1950's that in the 1930's & 1940's that he could remove 3/16" from a standard Model A head with no problems to increase compression.

Have no reason to doubt it, he was a well known respected machinist who provided intricate detailed work.

Yes, I don't doubt there were some that probably shaved .180-.200 off of a head trying to increase compression. I entered this in my computer engine simulator and came up with 4.735 c/r using 200cc as a baseline for head chamber volume. Naturally this calculation could be off but I dropped the volume of the chamber to 175 cc to compensate for the 3/16 cut and it raised the CR to 5.106703. Naturally someone would need to calculate the CC in real world to get an accurate chamber volume but a notch more of compression back then was about the most that one could expect. By today's standards, that doesn't seem worth the bother does it?
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Old 02-21-2013, 11:41 AM   #10
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Default Re: high compression heads

The shape of the chamber means a lot too. The A chamber would tend to detonate with high compression. The Winfield and Chrysler chambers are much better, similar to the Ford V8. Spark plug location is important too.
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Old 02-21-2013, 12:02 PM   #11
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Default Re: high compression heads

Brent,

Thanks, & if one wants to investigate further, one should be able to come fairly
close to finding the cc differences on such shaved heads by:

1. Levelng an upside down un-shaved head, with spark plugs installed on a table using a level & fill one (1) standard combustion chamber with a liquid & measure the cc's added in a measuring cup.

2. Fill adjacent combustion chamber with same liquid to within 3/16" from top & measure difference in cc's.

In knowing this particular machinist very well, he did all this work for free after work hours.

Also have a hunch that all who requsted this flywheel & head machinist work in the 1930's & 1940's were under the age of 25, & were Depression Era youngsters trying to find an inexpensive way to impress others by increasing Model A acceleration & top speed -- even sounds familiar today.

Last edited by H. L. Chauvin; 02-21-2013 at 12:04 PM. Reason: typo
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Old 02-23-2013, 10:43 AM   #12
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Default Re: high compression heads

Not to beat a dead horse, but how does one hold a head down on the table of the milling machine? I tried it on a Bridgeport and it didn't work too well. If one skim cuts the bolt spotfaces so they're all in the same plane and then using some kind of 1-2-3 blocks under the skimmed off corner bolt surfaces and then use a T bolt thru the sparkplug hole, it would work, I think. I was using someone else's Bridgeport and couldn't tie the machine up for long. and the leveling wasn't level, so I gave up in mid job. Same thing on a grinding table except you have magnetism pulling for you.
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Old 02-23-2013, 10:58 AM   #13
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Default Re: high compression heads

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Originally Posted by Terry, NJ View Post
Not to beat a dead horse, but how does one hold a head down on the table of the milling machine? I tried it on a Bridgeport and it didn't work too well. If one skim cuts the bolt spotfaces so they're all in the same plane and then using some kind of 1-2-3 blocks under the skimmed off corner bolt surfaces and then use a T bolt thru the sparkplug hole, it would work, I think. I was using someone else's Bridgeport and couldn't tie the machine up for long. and the leveling wasn't level, so I gave up in mid job. Same thing on a grinding table except you have magnetism pulling for you.
Terry
hold downs through the spark plug holes and 123 or parallels on the machined head bolt surface
tk
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Old 02-23-2013, 01:57 PM   #14
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Default Re: high compression heads

Quote:
Originally Posted by TDO View Post
Never saw one of the high compression heads on the market. So why can't you shave the stock head to raise the compression. If so whats the max you can take off.
I have one for sale in the swap section.
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Old 02-23-2013, 02:43 PM   #15
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Default Re: high compression heads

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Originally Posted by kelley's restoration View Post
hold downs through the spark plug holes and 123 or parallels on the machined head bolt surface
tk
There are as many ways to hold the head down as there are head milling machines, and that is a lot.
The one I personally like best is the Storm Vulcan Headmaster which holds the head face up and it sits on jack stands, pulled down to the table by bolts either through the plug holes or tapped head stud holes. With the face up setup you can easily see what is going on and if any spots didn't clean up. No mirrors required as on some machines.
It is extremely fast to set up with 2 bridge fixtures that the jacks push the head up against.

Last edited by Pete; 02-23-2013 at 05:36 PM.
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Old 02-23-2013, 05:45 PM   #16
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Default Re: high compression heads

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Originally Posted by Jim Brierley View Post
The shape of the chamber means a lot too. The A chamber would tend to detonate with high compression. The Winfield and Chrysler chambers are much better, similar to the Ford V8. Spark plug location is important too.
X2 and roger on that.
Here is a pic of a V8 aluminum head and when you fill a model A head and remachine it to this chamber shape, it REALLY works.
A stock cast iron A head could be reworked the same except the cost of welding would scare most people away.
With the aluminum you can just wire weld it.(MIG)
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