I was thinking of putting some high compression pistons from Langs in my 26. When I put the engine back together, I put in new aluminum pistons 0.020 over but they are "standard" and are flat top. I was concerned because the old original pistons were dome topped but was told that the new flat tops gave the same resultant compression ratio. How much of a change in compression ratio will I get with the " high compression" pistons and what would be the improvement in engine performance. What I'm after is better hill climbing capability. I live in central Virginia and flat ground is a premium. The engine starts well and runs smooth. I get 40-45 out of it on what level ground we have and the compression test shows between 45 and 48 psi on all cylinders. The high compression pistons have to have special rings so the whole conversion will be a little over $300 with gaskets and the hassle of tearing the engine down. If the benefit is marginal, than I would like to know that ahead of time. Thanks for your experience and knowledge.
With the dome top high compression pistons, you are limited on what cylinder head useage. .... standard Ford head only.
If you use the standard pistons, either cast iron or aluminum, one can use any of the era "high" compression cylinder heads, or the current manufacture "Z" head that is sold thru the Vintage Ford magazine.
I believe using a high compression cylinder head along with the larger bore aluminum intake manifold would be the combination for better power on the hills,,,,, without tearing down the engine as you stated to change pistons.
The Z (or Prus) head is not much more than $300, so if you already have good alu pistons with good rings there are no reason to change pistons.
A ricardo style head (like the Z and Prus heads) will give a better power increase than the same compression increase from high compression pistons. The hich compression pistons may be heavier than the ones you already have - another disadvantage.
You may want to grind the valves while you have the head off.
The domed pistons raised my compression from about 50 to 75 psi.
The Z or Pruz head will raise the compression to about 95 or more.
Neither increase is recommended for a tired engine, which 40 psi might suggest.
One of our club members got almost 5 miles out of his T after he put on a high compression head.
He still needed rod bearing after he put the original head back on the engine.
The more compression you ad is more stress on the lower end. I would not ad power without installing a modern crankshaft. Id hate to see you become a member of the two piece club.
I opted for a Z head, purchased directly from the folks that build them. Much easier conversion and better design to the combustion chamber. All done in a couple hours and a much happier 26 coupe that will now pull hills easily that used to be a real strain. I don't drive it any faster than before, just have better overall performance. Living with hills, I'd not hesitate to do this again.