high compression head

[harleynut]

Recently bought a 1930 Phaeton from an old timer that claims a higher compression head was installed when the motor was rebuilt. I did a compression test and got 60 pounds in all cylinders. What I don't know for sure if the compression would read higher with a higher compression head. My way of thinking it would. I could tell if I drove the car but I'm not ready to put it on the road yet.... haven't checked out the brakes and steering parts ....... also my plates haven't come. Any thoughts would be appreciated.

[Juggler]

Yes a higher compression head will give a higher compression test readout

Many variables to consider, not least the accuracy of your compression tester and the overall condition of the engine.

Somebody posted this ready reckoner not so long ago

A few variables to throw into the mix, but as a general guide and quicker than taking the head off and cc'ing the chambers...

Checking compression with the throttle open will give you a close guess on the compression ratio.

Data from F.A.S.T. Magazine

Ratio PSI

4.6 69
4.8 73
5.0 77
5.2 81
5.4 85
5.6 90
5.8 95
6.0 100
6.2 105
6.4 108
6.6 113
6.8 117
7.0 121
7.2 126
7.4 130
7.6 135
7.8 140
8.0 144
8.2 148


So your readings are on the low side, even for a stock head

[ronn]

stories wo receipts are often just that- they enhance the sale......................

[Pete]

A modified camshaft will generally reduce compression gauge readings.

[Bob C]

How about posting a picture of the head and any markings on it,
maybe we can identify it.

Bob

[H. L. Chauvin]

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High Compression Head:

In years gone by, (quite a few that is), I heard the term high compression head now and then which incorrectly sometimes meant and included taking an original Model A head and from it removing 3/16" on a milling machine.

After years of experience, by word of mount, machinists agreed that 3/16" was a safe amount to remove.

Have no idea the increased compression ratio, but many swore it helped tremendously.

Appears similar to the incorrect appliance term used by thousands today: "Hot Water Heater" ..... why waste money on a device to heat water that is already hot? LOL

[Mike V. Florida]

Originally Posted by harleynut

Recently bought a 1930 Phaeton from an old timer that claims a higher compression head was installed when the motor was rebuilt. I did a compression test and got 60 pounds in all cylinders. What I don't know for sure if the compression would read higher with a higher compression head. My way of thinking it would. I could tell if I drove the car but I'm not ready to put it on the road yet.... haven't checked out the brakes and steering parts ....... also my plates haven't come. Any thoughts would be appreciated.

I drove my car too many miles before my plates came in, just could not wait.

How many miles on the rebuilt motor? That could effect the readings as well.

[PC/SR]

Bad or worn rings (or valves) will reduce the compression reading on any engine, no matter what the head compression ratio may be. The only true measure is to cc the head. 60# is not high compression, but is very drivable.