High Compression Z Head


By E. Meloan

(This article was originally published in the November, 2000 issue of the Spark Coil.)

Howdy, Fellow Model T’ers!  In 1909, the Model T was a revolutionary machine.  Quite advanced and known for it’s excellent ratio of power to weight.  The first T’s weighed about 1200 pounds and the engine produced twenty-two and a half horse power.  That  was plenty of power to move the T at good speeds over the dirt roads of the day.   The nimble T would frequently pass the much heavier cars of the period.

But as roads improved and T’s got heavier the once quick T gradually became slower and more cumbersome.  The additional weight of closed bodies such as the centerdoor, tudor and fordor as well as the weight of the starter, generator and demountable rims all combined to drag the T down.

To make matters worse, the number of cars on the road caused shortages in gasoline and refiners increased the supply by diluting gas with kerosene.  This forced Ford to lower the compression ratio to prevent harmful pre-detonation.  So the already over-worked engine dropped in horsepower to twenty from twenty-two and a half!

Add to this, just two speeds forward instead of three or four and our T’s really have to struggle to keep up with modern traffic.

One popular solution is to add a two speed Ruxstell rear axle.  While this does help, it’s a relatively expensive change and adds to the mechanical complexity of the T.  And so… with this long preamble I now get to the subject of today’s “Thoughts from the Model T Garage”.

If I were asked what single thing I could do to a Model T to improve its power and responsiveness I would quickly suggest a new aluminum high compression head!  I don’t think you can beat this improvement as an easy and reasonably inexpensive change.  There have been high compression overhead valve conversions available for the T almost  from the beginning of the T’s existance.  They are great for the fella who wants to race or hill-climb but I am talking about the much simpler plain aluminum head that all the T suppliers offer and which is also sold direct by the manufacturer in ads in both Vintage Ford and Model T Times.

It’s easy to install… requires no adjustments and works instantly!  What’s more, it adds a much needed 6 or 7 horsepower that has to be felt to be believed!  When you only have 20 to start with, that 6 or 7 makes a really noticeable difference!

The head gets this power by increasing the compression from about 4.5 to 1 to 6 to 1.  Can our babbit bearings take this additional strain.  Most of the experts say yes.  6 to 1 is safe and will not cause damage to the bearings.  That seems to be proved by the number of heads being run with great success and very few problems.

If you want to be convinced, find someone who has one of the “Z” heads and ask them to let you drive their car.  Find a hill that your T has to struggle with and watch the Z head take that hill like it wasn’t even there!

Add to this, the fact that the improved combustion chamber of the “Z” head causes the fuel to burn more evenly and efficiently and you actually get better mileage as well as increased power and a cooler running engine.

The “Z” head can be purchased with spark plug openings for the standard T plugs or the modern 14mm plugs available for a buck each at your local auto store.   While the price is certainly nice, the real advantage of the 14mm plugs is that you can choose the heat range that works best for your engine.  Installation is easy.  Just be sure you use the stainless steel washers, supplied with the head,  on each head bolt.  You’ll also want to apply a little anti-seize compound to the spark plugs when you install them.  Once installed the head looks just like the stock one.

Try it!  I think you’ll really like it!

See ya down the road…