MTFCA Forum

Does anybody out there run a low head with high compression pistons? And is there a noticeable difference between a low head and a high head?????

We’ve had several friends / customers run a low head with domed pistons. Things to note before you slap one on. Your low head should not be milled already or if it has been milled you need to do a squish test (do this with any low head) to make sure that all pistons do not touch the top of the combustion chamber. When we test we don’t use a head gasket to do the test. As far as a performance enhancement I’m not sure how much it improves the compression, it depends on what you do to the head. We do a compression test once installed and it only changes a few pounds max. Others may have a different result. If you can’t use a Scat crank, domed pistons do give you better compression coupled with a new cam, high volume intake, adjustable lifters & SS valves gives you some advantages. All that said a balanced transmission aligned correctly with very little run out will improve your performance on a stock engine. Just my opinion.
I believe all the above would be even better with a 280 cam with a 7.5 built in or 280 & 7.5 timing gear if not built into the cam plus a stromberg OF as a good combination.

I knew a lot of guys that ran high domed pistons me included, I ran domed pistons with a roof overhead it pumped 125 pounds of compression and would go 60mph+ I'm no longer interested in scaring myself with speed lol, I just want a good flathead with good performance at this time. Just wanted to know the real difference between a high and a low head, I heard of a guy that milled so much off a low head that when he took off he broke the whole combustion chamber out of the head !!!!!!

Quality of castings makes a big difference on just how far one can push their luck and maybe get away with it? However, I have never been a fan of milling heads any more than is necessary to clean it up flat and seal onto the block properly. An extra eighth inch cut off simply doesn't buy much more performance! And much more than that has ruined a lot of now valuable low heads and OHV head conversions!
I met a guy years ago that had about a dozen or more Rajo/Roof/Frontenac eight and even a couple sixteen valve heads sitting on a shelf. Every single one of them, the first thing he did after he bought them was to mill as much off the head as he "thought" he could get away with! Several were cut so far he actually cut into the spark plug's space! I figured when I saw them that he had totally destroyed at least half those heads, all for what? He never ran more than three of them himself! At least one of those he blew out when he first ran it.
A few years later, someone bought one of his heads. That one didn't get any miles on it either before the head went to pieces.

I have seen the same thing happen with early model T low heads as well.

I actually have one myself. I bought it years ago along with a bunch of other stuff. Basically, it was free. I looked it over. Maybe it was cut too far? Maybe it will hold up? I put it on an engine quite a few years ago, intending to try it and run it. One thing and another? I have not yet tried to start that engine. Maybe some day I will find out about it? If by chance I do start it, and it holds together? If I then take the car on any significant tours or distances? I will carry a spare head. I ain't no fool.

High compression pistons can increase compression numbers a bit. However, the simple high dome pistons still do not increase performance very much. A simple high dome doesn't improve combustion flow the right way. To increase performance one also needs to provide a properly shaped "squish" zone concentrating the compressed fuel vapor near the spark plug, and then shaped to flow the expansion of hot gasses to push the piston down efficiently.
Such a design would be a critical fit to match specific heads. Such pistons would be expensive to make. And unless a lot of engineering went into the design, the oddly shaped piston would have to be fairly thick! And that thickness would pretty much defeat the whole purpose of "lightweight " aluminum pistons.

I have often thought that coming up with a real performance boosting piston design could be an interesting project? However I have neither the time or money to even consider it myself. Anybody reading this and wanting to consider it? One more consideration. The model T Ford common high and earlier low head designs are different enough that one really good design couldn't really work for both of them. Their combustion domes are too different in shape