New 5.5:1 Cylinder Head Availability

[Jim/GA]

Originally Posted by alexiskai

The idea that Babbitt bearings can’t handle higher compression is a myth.

It's not that babbit can't handle it. It can.

The problem I have experienced over and over is that the average Model A driver with the average original engine advances the spark too much on the 6.0 head and the engine knocks. The driver can't hear it knocking (for various reasons, including old age loss of hearing) and they pound the babbitt out in a short time.

Many drivers start the engine, then pull the timing lever down all the way and leave it there all the time. You can explain to them all you want about what they need to do with the timing, but they just pull it all the way down. The stock cylinder head is low enough compression that it is very forgiving to this sort of behaviour. With the 6.0 head and an engine that is timed to TDC like Henry called for, that engine won't last long.

So I mainly recommend the 5.5 head to save the driver from themselves. You get a little performance boost but less risk of hurting the engine.

[alexiskai]

Originally Posted by Jim/GA

It's not that babbit can't handle it. It can.

The problem I have experienced over and over is that the average Model A driver with the average original engine advances the spark too much on the 6.0 head and the engine knocks. The driver can't hear it knocking (for various reasons, including old age loss of hearing) and they pound the babbitt out in a short time.

Many drivers start the engine, then pull the timing lever down all the way and leave it there all the time. You can explain to them all you want about what they need to do with the timing, but they just pull it all the way down. The stock cylinder head is low enough compression that it is very forgiving to this sort of behaviour. With the 6.0 head and an engine that is timed to TDC like Henry called for, that engine won't last long.

So I mainly recommend the 5.5 head to save the driver from themselves. You get a little performance boost but less risk of hurting the engine.

I agree with this notion that people who can't be bothered to manage spark timing should not run high compression heads. I was specifically addressing the separate babbitt concern that someone else brought up.

If someone does have the skills to manage spark timing, I would actually say I think the Burtz head is the best option. Not because it has the highest compression, but because they changed the design of the water jacket. The Burtz head blocks the large central return vent in the stock head, which forces more coolant toward the rear cylinders. These cylinders run hotter in stock configurations and are more prone to gasket failure, valve failure, etc. Getting more cooling to them is an investment in the lifespan of the engine – provided that you don't undermine it by over-advancing the spark, that is.

[jeepguy1948]

Are the high compression heads marked in any way indicating what head/compression ratio it is?

[alexiskai]

Originally Posted by jeepguy1948

Are the high compression heads marked in any way indicating what head/compression ratio it is?

Typically they are attempting to "pass" as stock heads, so with a couple of exceptions, the only way to know is to examine the shape and size of the combustion chamber.

[jeepguy1948]

I would think that they could be discretely stamped with a 5.5 or a 6.0. I would not think that there would be enough difference between the two combustion chambers to determine what it is.

[jeepguy1948]

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If someone could post some pictures comparing the various combustion chambers that would be great. I have a head that I have been told “might be” a HC head but I have no idea if it is or not. I do not have a stock head to compare it to.

[alexiskai]

Originally Posted by jeepguy1948

If someone could post some pictures comparing the various combustion chambers that would be great. I have a head that I have been told “might be” a HC head but I have no idea if it is or not. I do not have a stock head to compare it to.

The 5.5 head has a heart-shaped chamber that projects deeper into the cylinder bore. The 6.0 head is "stubbier," more rounded.

FordGarage has a page that shows some older heads.

[Y-Blockhead]

Originally Posted by jeepguy1948

Are the high compression heads marked in any way indicating what head/compression ratio it is?

The 5.5 heads from Snyder's have two dots on top and they are physically smaller.


I can't tell you about any others.

[nkaminar]

B Butturff, To tell what kind of bearing you have without opening up the engine, you can use a bore scope and insert it into the hole after you take the breather tube out. The poured bearing at the rear has a large poured flange at the forward end that is used as a thrust bearing.

The 6.0 head puts out slightly more torque and horsepower than the 5.5 head, which may be because of better breathing rather than the higher compression ratio. In my opinion the hart shaped combustion chambers do not breath as well as other designs. See https://www.snydersantiqueauto.com/c...%20release.pdf

[BButturff]

Originally Posted by nkaminar

B Butturff, To tell what kind of bearing you have without opening up the engine, you can use a bore scope and insert it into the hole after you take the breather tube out. The poured bearing at the rear has a large poured flange at the forward end that is used as a thrust bearing.

Neil, thanks for this tip! I've never read or heard of this before and will do it very soon.

[alexiskai]

Originally Posted by BButturff

Neil, thanks for this tip! I've never read or heard of this before and will do it very soon.

If it's insert bearings, instead of a gray flange on that rear bearing, you'll see a brass thrust washer.

[BButturff]

Originally Posted by alexiskai

If it's insert bearings, instead of a gray flange on that rear bearing, you'll see a brass thrust washer.

Thank you too. The brass should be readily apparent with the illumination from my bore scope.