Do these new aluminum heads dissipate enough heat, fast enough over the old case to be a great advantage?
I can't say for sure but I went from an early low head to the Z. It has quite a bit more volume so should offer more cooling. But one might argue that it develops more hp so that should equal more heat generated.
My T runs pretty cool even with the belt so loose that the fan barely turns. I keep it on for looks.
Good question? I've never run a cast head on my engine, so I don't know if I'm qualified to make any comparisons. I do know the Prus head has a greater volume of coolant than the z-head. When I replaced the z-head on my engine with the Kevin Prus' head, I had to put in nearly an additional quart of coolant coolant mix(and I didn't spill any taking the old head off). Both heads seems to cool fine. Even on the hottest days (90's), the motometer only hits the bottom of the circle.
I don't think there is significant difference comparing a Z head to a regular Ford head. Both run cool. There is not any noticeable difference. If you have a car that overheats now you will still have a car that overheats. Fix the problem, a Z head won't change that one bit.
Performance wise the Z head is a huge improvement in usable torque. It is the best $300 you will ever spend. You will go up hills in high with four people in the car that will need the low pedal with the normal head.
I don't know if the ones with fins make any difference or if it is all for looks.
In the July/August 2013 issue of the Vintage Ford I wrote an article on overheating. What made the biggest difference was adding the aluminum head. There was over sixty degree difference between the block and head temperatures.
I am building an engine so not a heating issue yet. Was just wondering about a new alum head or the pop up pistons for a little more power.
Higher compression makes the combustion more efficient, turning more of the burned gas into useful work instead of heat that has to be cooled off, so it's not only the increase in water capacity and aluminum that helps keep the heat down with a high compression head.
A high compression head like the Z or Prus with Ricardo style squish areas over the pistons will also give more increase of power than the same increase of compression would have given without the better shape of the combustion chambers, so high compression pistons may be the cheaper option, but it's also less of an improvement. High compression pistons can't be combined with a Z or Prus head.
"High compression pistons can't be combined with a Z or Prus head"
Why is this... interference or too high a CR, or ???
The pop up pistons (or "high compression" for you old guys) will hit the top of the combustion chamber. Not enough clearance.
For some reason I cannot post the photo, but if you look at my profile photo you can see the high compression pistons. They stick up roughly an inch or so above the top of the block. I run a low head and average about 67 lbs of compression per cylinder. Compression was checked when the engine was cold and the throttle wide open. Mark.
I have a high-compression, aluminum head and it cools okay. _The engine is less sensitive to spark timing, and by that I mean it doesn't seem to care whether I retard the spark for hills and low speeds in high-gear. _I retard the spark for that stuff anyway because I know it's kinder to the crankshaft. _The high-compression head makes for greater power, of course, but I'm very cautious about putting too much torque through the crankshaft, so maybe for me it would have been just as well to stick with the original, cast-iron Ford head.
Bob - Your last statement just might be a pretty good argument for high compression pistons. When Steve Tomaso of "Steve's T Works" rebuilt my depot hack engine, he and I selected parts pretty carefully and we discovered that the high compression pistons only cost a few bucks more than the standard pistons. I'm pretty careful about abuse to my stock "hairpin" Model T crankshaft too Bob (I try to avoid speed of over 35mph) and if I had it to do over again, I still think I'd go with the HC pistons on a rebuild,.....FWIW,......harold
I would say the high compression pistons might be a bigger harm for the crankshaft than a high compression head since they're heavier than std pistons.
The worst strains on the crank comes from the harmonically amplified twistings in the crank that gets worse with heavier pistons and by driving at certain rpms where the "thum" is pronounced - listen to your engine and drive it so it feels like it runs at a good pace
Another plus with a Ricardo style high compression head is slightly better gas economy - ok, takes some time to save $400, but still a plus ;)
Roger, while I agree with you adding piston weight adds kinetic weight to the crank, however, I would guess the weight difference between the original cast iron piston to the alum HC piston is still a great reduction in weight.
I built an engine for the guy next door. It is a standard engine with the exception of pop up pistons, a tighter valve lash and wood bands. The engine runs near as smooth as a modern engine and has power enough to pull the long hill we live on in high with a little notice of pulling down in RPM's.
If the motor is being rebuilt, the price difference between standard and high top pistons is minimal while replacing the head will add $350 to $400 to the total bill. If price is the driving motivator the pistons win. Still, I find it a lot quicker to change just the head rather than pistons and rings. I opted to get a Z head when I rebuilt the motor for my coupe to gain compression and the improved combustion chamber design. That motor runs just fine and I'd do it that way again if the need arose. If for some reason I wanted to go back to stock compression it would be simple to replace the Z head with the high head sitting on my shelf.
I used high top pistons though on my speedster that has a Fronty "T" head to bump the compression some. They work fine in the speedster with the mild version of the Fronty.