It must be my limited knowledge of the T but what is a T head? Is it the standard head or the high-compression head? Kind regards, kees.
The Z head is an after market high compression head.
http://www.modeltcentral.com/accessories_zhead.html
The compression is not what adds the huge increase in power though.. It is the different combustion chamber that makes the big difference and I can say from experience it does work and well worth the money.
When I rebuilt my engine I broke it in with a low head that I milled off. The Z head made a huge difference I could feel before I left my driveway.
It now pulls hills in high gear no problem.
I promise it will make you happy.
Conventional wisdom has it that a Z-head is good for an additional seven horsepower. That doesn't sound like much, but when you're putting significantly less than twenty horses through the rear wheels, an additional seven will be more than noticeable. On my 1915 Touring, I have a hi-compression head and a later version, NH carburetor on a larger-volume manifold. That's a very mild, fairly common soup-up, but when a sticky traffic situation requires a quick surge of power or I need to get up a long, steep hill, ol' "Penelope" can make it happen.
Bob - Actually, you say,...."that doesn't sound like much"......
Percentage-wise, an additional 7 hp is an increase of 35%, and that sounds HUGE to me, when you consider how easy it is to just swap cylinder heads!