Do high compression pistons increase the operating temperature of an engine, particularly with a low head? Specifically will it run hotter compared to stock pistons, all other things being the same?
Do water pumps actually help lower temperature due to the increased flow? Meaning all things equal, including a good radiator, will it make a difference in operating temperature?
PLEASE DO NOT high jack this thread with arguments about the pros or cons of water pumps, or opinions on them, there are dozens of threads on that already. I want to hear what people have actually experienced or know as facts.
Compression raises temperature. The higher the ratio the greater the heat.
That's why diesels run at much higher ratios (23:1 or so vs. a gasoline engine average of 8:1).
As to the Great Water Pump Debate, I cant see why a device that helps circulate coolant- if even slightly- would be detrimental to the "T"s system, but as you allude to, opinions vary widely (and wildly!) on that subject.
Apparently that question can only be solved on an individual, engine by engine basis...
In a "T" engine I believe that the effect on operating temperature would be negligible, and a water pump would only help IF you went to a pressurized cooling system. Where most water pumps I have seen they are mounted on the "Cool" side of the cooling system and their effectiveness is in question under the best of circumstances.
Here is a blog on EGT compared against compression ratio's
High compression heads with domed piston are not a good combination with a stock Model T lower end (unless running pressured oil to main and rods) . Babbit takes a hell of a hit and the Great Debate concerning water pumps, well, circulation with a thermostat is an improvement and keeps equal temperature though out a system. Introduction in a thermo-statical helps start an equal warm up and prevents premature cylinder wear. Henry Ford's engineer's found this out with the Model A, another steam non-pressure system.
Just an opinion with personal experience,
Higher compression raises temperature.
A water pump will lower the temperature, so much that a thermostat is then needed. The engine runs better and will last longer if it operates at the the correct temperature, not too cold or not too hot.
No high compression head, those would hit, just HC pistons with a low head that has been milled. Not excessively, but surfaced a couple of times.
I may not have all the technical terms used with absolute correctness and I know someone will set me straight, but the idea goes like this.
The combustion of fuel in the cylinder produces heat and potential energy. That energy is converted to work as the piston is forced down, rotating the crank. For the same amount of fuel, if a high compression piston produced more horsepower (our measurement of the work), then it must follow that less of the combustion process ended up as heat. The principle of conservation of mass and energy always applies.
I've heard water pumps, at least most, move the water too fast for the radiator to do it's job, heating up the water.
Recently installed a Prus high compression head. I have more power and the engine runs cooler than the stock head. I am actually running a two bladed fan now due to excessive cooling. I do not have a water pump. Just my experience.
I am wondering if you engine runs cooler because you are burning less fuel due to the better efficiency? I will have to get out my thermodynamics books. I know that if you compress a gas to a higher pressure the temperature goes up.
I believe Rich and Bob are correct.
Increasing the compression ratio raises thermal efficiency. So, as Rich astutely opines, taking more of the energy input (fuel) out as power to the wheels, there must be less heat (energy) wasted to water and exhaust. We have observed that diesel engines take a longer time to warm up, and less hot water is available for the heater of the cab. They also cover the front of the radiator to keep heat loss down when it is cold. Some diesel powered vehicles have an auxiliary diesel fuel burning heater to heat the cab in cold climates.
Neil, With the high compression head, I noticed that the throttle does not need to be opened as far to maintain cruising speed. Have not done any proper testing. However, the engine appears to be running a bit more efficiently due to improved fuel economy.
Depending on whether the Prus replaced a low or high head it may have increased coolant capacity; it holds 1 quart more than a low head.
Does anyone have specific, personal experience on temperature change after swapping to HC pistons from standard pistons, without going through an entire rebuild, etc... so the change was only the pistons?
Does anyone have specific, personal experience with a change in temperature by installing or removing a water pump, without other changes to the particular car at the same time?
Had a Berg's water pump on my '24 which was run only short distances over a couple of years. On a long run of 50 miles the T boiled over, literally. Coolant level was OK at start, but overheated.
Found after refilling the rad that the fan belt was way too loose. Caused the pump impeller to move little, so that blocked any relief the natural thermo syphon could provide. With the stalled out impeller at the coolant return to the block, the motor overheated.
Remove the Berg's and the T has never overheated again, with lots of 500 mile tour weeks now.
No experience on HC domed pistons, just 'Z' heads and the new Prus head. IMO, would never consider domed pistons, with the avail high compression alum heads.
Besides, how do you scrape off carbon from a dome topped piston ?
To answer the original question yes.
Rich and Bob and then Roar nailed it.
Gary, Many years ago I had a fresh, but broke in 1926 engine in a speedster on the Endurance Run. The engine was stock but had a Z head, a Stromburg OF carb, and a T era water pump. The car had a new 3 row high flat tube radiator. On the first big climb the engine boiled and I had to stop at a pull out to let it cool. Checking the engine showed that the water pump pulley set screw had broke off and the pulley came off taking the fan belt with it. I had a stock fan belt with me so I was able to by pass the pump but keep the fan and refill the radiator. The car made the biggest climb up Mt Hamilton in low gear but didn't boil. I think that keeping air moving threw the radiator to take away heat thus keeping the water just below boiling is the most important thing in a T at any T era compression, say, 3.9:1 high head to 5.5:1 Racardio head.
Good discussion on thermal compression and efficiency. I find that the Prus head I installed does indeed run cooler than the stock head. Now if that is due to the higher compression ratio, extra capacity, or the design of the head itself...I don't know. I just know I like it. In other applications I suspect at some point the higher the compression, the higher the heat. Not exactly sure where that break point is though, or if it really is applicable to the discussion at all.
I have some personal experience of removing a water pump. The car, a friends, had a water pump and thermostat. It ran with a proper engine temperature and a cool radiator. The water pump was remove to add a belt driven generator (no starter on this engine and no generator driven off the cam gear). The engine boiled over until the thermostat was discovered and removed. It now runs at the proper engine temperature and does not boil over or get too hot. The top of the radiator is warmer as the hot water rises to the top.
I have no experience with high compression heads or pistons, but do have some experience with waterpumps.
My first T came with a water pump when I bought it. It did not have a thermostat. One cold morning our group took a trip into the mountains. After driving for about an hour the group made a stop. Almost everyone stood in front of their cars to capture some of the heat from the radiator. My engine had not even warmed up!. At a later time the pulley slipped and the lock bolt turned the end of the shaft like a lathe. That was when I removed the pump and installed the inlet fitting. No problems with overheating or running too cold since them. (for those who were on the "Goldmine tour" my overheating was due to a coolant leak of which I was unaware and ran low on coolant).
My suggestion would be to try it without the pump and if it overheats, try using a pump. If it then runs too cold, install a thermostat. The simpler you can keep things, the less problems you will have.
In this case I have a fresh engine with HC pistons and an almost new round tube radiator. Water jackets were all cleaned. The engine and radiator were both changed at the same time. I'm running hotter than I did with the flat tube. I will drive the car as-is until I have about 100 miles on the engine, then take temperature readings on the radiator. I'll install the water pump I have and immediately take additional temperature readings. At that point I'll have readings immediately before and after installing the water pump and will post the results. I've never run a water pump or a round tube radiator before, so at least to me this will be interesting. I believe the radiator is one of the Bergs brass ones that was built; it has the correct corners on the front and I prefer that over the Brass Works ones. If the water pumps lowers it to where I want I'll continue to run it, if not I'll replace the radiator with a flat tube again. It will be a few weeks before I have results, I'm in the middle of moving my daughter right now and have to finish that first. At the very least it will be interesting to have the readings with just the water pump change.