I'm putting together another engine and have a set of new 0.020" high compression pistons that I could use with a stock high head that has been milled 0.060". Would this combination compare favorably with using stock 0.020" pistons and a Z head?? Thanks in advance. Bruce
High compression pistons and a low head milled will be closer to the Z head performance. IMO the Z head will make a bit more power.
I have both, 1916 with high pistons with a low head that was the lowest of several I had, under 2" in height and a 1916 with a Z head, 280 stipe cam, both with the same s/thru carbs
The Z combo definitely is giving more power.
Frank; Was your low head milled? Also, what effect would you expect to see with the 280 cam in the second engine over a stock cam in the first? Is it overall power, just top end, more torque??? Cheers : Bruce
Bruce, I've found that head heights to be all over the place, not often within Ford specs, low heads come in at 2" to 2-1/8" with anything in-between,may be a Canadian thing? I picked the lowest I had, surfaced and fitted.
I found the combo of 280 cam and high dome pistons gave me more power all round, top and torque but I can get the Z with a stock cam to be as good with a modified s/thru carb I have but fuel economy drops to about 16 mpg.
Bruce, I should re-read what I put up, the modified carb gives me about the same power as a Z'd engine on the high dome/280 low head engine.
Higher compression gives more power and better fuel economy. But the shape of the combustion chambers is also important, both the Z and the Prus heads gives about 5:1 in compression, but an engine with the Prus head gets about 2 hp higher top end power than the Z due to the Ricardo style squish surface covers more of the pistons in the Prus head.
Domed pistons may be great used with an OHV head, but in a sidevalve engine it won't help all that much due to the resulting unfavourable shape of the combustion chambers.
Low heads doesn't give much either, the more common 1912-17ish ones gives about 4:1 compression compared to std 3.8:1 with a std high head.