Hi Gang : I'm getting ready to rebuild a spare engine and have to decide on using either an aluminum high compression head or high compression pistons. I have a slightly used Z head and a new set of .020" HC pistons and rings already in hand, and the block will most likely need boring. I also have a stock cast iron high head that has been milled 0.060 and was wondering if I could use it with the HC pistons. Any suggestions?? Cheers : Bruce
use the pistons and the head it will be fine I don't like hc heads because of disimalar metals
I have tried two high-compression heads. Both produce improvements somewhere between significant and striking.
One is an aluminium head which looks like a Z head but has no 'Z' on it. There is an R near the water outlet but it isn't a Reeder. It has the squish area with a central 'gulley'. The CR is 5.7:1.
The other is an iron 'Giant Power Head' with a CR of 5.05:1. The combustion chamber shape is very similar to the aluminium head, but the flat area is about 1mm further from the piston (4mm minimum clearance instead of 3mm).
I prefer the Giant because, as well as having 'Giant Power Head' cast into the top, it is slightly less extreme, quieter and less harsh.
I felt that if I kept the aluminium head, something would break.
Both heads allow me to sustain 30mph up hills where I would have slowed to below 25. The response is better, and I cruise with much less throttle. I haven't yet measured fuel consumption, but I expect it will be better. I have a friend with a 1911 T with a similar head and he gets 28mpg whereas my 26 Coupe did just 20mpg.
Obviously raising the CR is good - but nothing less than around 4.5 is likely to be worth the effort. But I feel that the squish design is also important - based on Ricardo's work
If my sums are right, 0.060 only raises the CR from 4:1 to 4.15:1, but maybe the high pistons will be good with it.
You can't us HC pistons with a Z head, they will hit the head.
Thanks Rick, but I was asking about using the HC pistons with the milled stock high head. Bruce
Bruce, sorry, I should read the whole post, depends on how much is milled off the high head. I know there are people on here who have done this so maybe they will comment.
There are a lot of us out here using the Z heads as well as some using the Reeder or other aluminum heads. I use a Z and old style green antifreeze. Some folks prefer plain water and add a sacrificial anode. Either technique takes care of any issues with dissimilar metals.
When I rebuilt the motor for my 26 coupe I opted for the Z head rather than pistons for two reasons - many reports from satisfied Z head users and if I wanted to make changes in the future it's a lot easier to change the head than the pistons.
Funny... A buddy of mine and I just estimated CR of each of those setups. Domed pistons with Ford head is about 4.4:1 with the head shaved 0.060. So 4.4:1 for the cost of bore and hone or 5.7:1 for the cost of flat top pistons and bore& hone job. If you go with the z head, be sure to run a sacrificial anode.
I've ran the Hc Pistons with a low head. It had tremendous low and mid range torque not much top end though
I can't find any info on the C.R. with high compression pistons and a stock (unmilled) high head. If Aaron's calculation of 4.4:1 with the HC pistons and a milled head is correct, where is the gain coming from? I guess I expected at least that much of an increase from either the milled head or the HC pistons, and their combination to be closer to 5:1. What am I missing?? Cheers : Bruce
Aaron, I run a "Z" but no anode. How do I introduce the anode? Thanks
I think high compression pistons would work with any stock Ford head, regardless of how much it is milled. A stock T head is only so thick between the gasket surface and the inside of the water jacket in the head, so there is a limit to how much one can be safely milled without compromising the integrity of the head. I have heard of heads being milled 1/8th of an inch. Maybe they can even go to 3/16ths. I've never tried.
Why this insistence on an anode? Millions of engines have iron blocks and aluminium heads.
My 1967 Sunbeam Alpine has one, and has never needed repair etc.
You just have to use antifreeze with inhibitor - and they all have it (at least they do in the UK).
I would stay away from pink OAT antifreeze in an old car, but the blue stuff is fine.
I can personally attest that the auto companies are still designing and producing engines with iron blocks and aluminum heads. The chemicals added to antifreeze prevent corrosion and a sacrificial anode is not needed.
The Z and Prus heads will only give 5.7:1 compression if used with a stroker crank with Model A stroke, or if milled about 0.100" With a T style crank they give about 5:1 from the box. Still they give a substantial better power increase than the high compression pistons with 4.4:1 (or some more with a milled std head)
The difference is mainly because of the better combustion chamber shape you'll get with the Ricardo style squish surface above the pistons you get from the accessory heads.
The best use for high compression pistons would be with some old OHV head that may have low compression and can't be milled much.
I do not recommend using the domed high compression pistons because it limits head selection to either the stock high or low head.
Have a friend using domed H.C. pistons with a milled low head and the engine performs well. The H.C. pistons are a good choice when using a RAJO 4 valve head which has a domed combustion chamber.
If you have a Z head....buy a new set of flat top pistons and get on with life. If you CC a Z head and Prus head there is very little difference.....we have done it using a Brett for measurements.
I Have been using a Giant Performance head for years and it performs better compared to a milled low head. The combustion chamber looks similar to the W.R. but larger compared to the Z head. The squish area above the piston in a Prus head is very different by comparison having a machined surface vice cast. The Giant head does not provide as much compression compared to a Z or Prus head but does perform better compared to a milled (.060") low head.
Just MHO experience
The better high compression heads are designed to move the exhaust gasses towards the exhaust valves in order to give them a head start on leaving the chamber. High compression pistons are circular and do not direct the gasses toward the exhaust valve. The gasses are equally distributed all over and around the edge of the chamber in the head and all over the top of the piston and when the valve opens they are surprised and have to get moving toward the exhaust valve from a dead start and not all of them get out in time.
In other words a high compression head head offers a greater volumetric efficiency than do high compression pistons unless the top of the piston is shaped to guide the gasses towards the exit as in two cycle engines with specially shaped pistons.
It should also be noted that valve timing will assist with better breathing too. When both are utilized together with port matching and enlargement along with larger valves, all together they can bring smiles to your face and amazement to those not in the know.
The model T engine produces 20 horsepower out of 177 cubic inches and in today's world many engines are producing two horsepower per cubic inch. That would equate to 354 horsepower. It doesn't take much to improve the horsepower of a Model T engine. Henry made the T as a low speed high torque item in order to only require a two speed transmission. It was a profit deal and cheaper to make.
If you're not already in the habit of pushing the throttle wide open and using all of your engine's available power, there isn't much point in bolting on hi-performance parts. I always go very gentle on the throttle because joining the 2-piece crankshaft club is something I'd prefer to avoid. Unaware of the Model T's Achilles-heel crankshaft, upon purchase of my '15 Touring, I had a high-compression head and larger capacity intake manifold installed. But then I learned about that delicate crank and became too afraid to use the extra available power, so it wasn't worth making the changes. Live and learn, I guess.