Hey guys,if I use high compression aluminum pistons with the original cast iron head and thermosyphon
cooling, will the engine run hot? The engine ran nice and cool before, I never had a problem.
i have them in my 26 four door never had any over heating problem been on lots of tours with it and worked it hard always cool
I have them in my '13 with a stock "low head", a bit of a cam and a Stromberg OF. I've put lots of miles on it in 16 years and like the combination just fine. Never a over heating problem
We use them on a regular basis during rebuilds.
We don't have issues with the engines over heating
I use them and a 300 lift montana 500 cam on all my rebuilds and I never had an issue
Jonathan - To answer your question, I asked that some question some time ago on this forum, and was very surprised by the answer I got! Like you, I wondered if higher compression would cause the engine to run hotter. The answer, by several engine guys a lot sharper than me, was that, "no,....the engine will actually run cooler". And it was further explained to me that the reason for this is that you get more power from burning a slightly less amount of fuel. Makes sense when you think about, it,.....FWIW,......harold
So which is better. Using a high compression head or using the high compression pistons? Just curious since I've been thinking about buying a higher compression head that's been available for a while.
Maybe install high compression pistons during a rebuild and not the high compression head if there's not any noticeable difference?
Probably the head. But it adds to the cost. Typically you need pistons. Just remember that I don't believe that you can use the high dome pistons with a high compression head
John - There are many that are much more qualified to answer you than me, however, I think I can actually give you a pretty good answer on this:
First, high compression pistons will give you a bit more power, but not all that much. And, something to consider carefully,....if you install high compression pistons, you will not have the option later to go to the high compression head. This is because the HP pistons will interfere with the HP head.
The reason is due to the fact that the HP head has a different shape combustion chamber shape which does not provide clearance for the HP pistons. Having said that, if yo want to be sure to have a definite increase in power, your best bet would be to stick with standard aluminum pistons and just install the HP head. It will give you much more additional power, due to the fact that more power comes from the better designed combustion chamber for better "flow" of gasses, as well as more power from the higher compression.
Now then, and this is just personal opinion, I don't particularly care for installation of an aluminum head on an iron engine block. I guess this is a very successful modification for a very noticeable increase in power, and I can't honestly say that I've ever heard of anyone having any trouble with the alum head on the iron block; but even so, I guess I just have it in my head that there just has to be two different expansion rates of the two different metals during heating and cooling of the engine and I guess that just bothers me, as wall as occasional discussion on the forum here about electrolysis. Again, can't say I've really heard of any real problems in that area,....I just don't like the idea of the two different metals, again, that's just me.
Again, having said all that, (I sound like a broken record, huh?) but having said that, there is now a newer version of the high compression head that I've heard about that's available in iron, and I sure like that idea! That iron HP head is made by a Mr. Kevin Pruis, and I'm pretty sure that I've spelled that name wrong, but somebody else will no doubt "chime in" on all my "blabbering" here with more and better information. In the meantime,....hope maybe I've been some help,.....harold
Sorry Les,....you and I were typing at the same time,.....harold
Harold - the Pruis head is what I've read about and thought about trying. Yes I do know about the clearance issue of using a High Compression head and pistons together. It wont work.
These days using std. aluminum pistons is the way to go when rebuilding a T engine which I have in my 3 T's.
Some in some earlier posts on this subject said that there was just a minimal difference using a high compression head. If I remember it seemed like the difference was in climbing hills.
That would be a plus in a T for sure.
HC piston can limit your head choices but if you want run a look factory then HC pistons are a good choice.
My last T I used low head and HC pistons didn't give anymore top end but had alot more torque, but I will go bach to an HC head and stock pistons
Thanks Bob, That's about the way I was thinking too. I used the earlier low head on my 21 Touring high head engine thinking it would give me a little more power. If I remember the earlier T engines with the low head supposedly had more compression the later engines with the high head.
Or maybe its wishful thinking! Anyway thanks.
The compression was lowered due to poor quality of gas during ww1 or so story goese
Also water capacity was increased to help in cooling
The '24 runabout which I purchased last year came with high compression pistons and a high head. It has a Brassworks flat tube radiator and a Holley NH straight through carburettor. It runs well, does not overheat, and climbs almost all hills in high gear. I am unable to make a comparison between this setup and one with a high compression cylinder head regular pistons and all of the rest the same. The high compression pistons work for me. Your milage may vary, Bill.
The high compression pistons deter the breathing because when the valve opens there is nothing to direct the gasses to the exit. They are distributed equally all over the top of the piston. They are spread out all over the place and don't know how to get out. A high compression head with a properly designed combustion chamber has better breathing and the gasses are all lined up and ready to get out when the valve opens. So high compression pistons will increase torque and horsepower but not at as high a speed on the revolutions as a better breathing high compression head. I tried to make it a simple explanation.
But if you make special pistons and get a better breathing cross-flow high compression head and then get a strong well lubricated crank You should also change the cam and some other stuff like porting and relieving and it would go like stink. But then would it still be a Model T ?
Some more on the science of combustion:
SO HAROLD : IT DONT BOTHER YOU MIXING THE
TWO METALS , IRON BLOCK AND HEAD WITH THE
ALUMINIUM PISTON ?
ARE NEW PISTON MADE OF IRON AVAILABLE ?
AND HEAD ?
I TELL YOU ... I THINK I WOULD STAY WITH
ORIGINAL IRON AFTER READING ALL THIS LOL
Cylinder heads made of aluminum have been used successfully for decades. That said, I have nothing against using a cast iron Prus head. I think my choice would be based on cost of aluminum version vs the iron one.
As for cast iron pistons. I admit I am not entirely sure your question/comment is serious but aluminum pistons have proven their superiority since Ford made the switch to aluminum pistons for the Model A. The important thing to keep in mind is how pistons shed the heat of combustion. Through contact with the cylinder wall. In high load situations a cast iron piston is very nearly glowing red in the dead center of the crown. An aluminum piston conducts that heat much more rapidly and effectively out to the cylinder walls.
In addition, the aluminum piston is significantly lighter, thereby reducing the load on rod and main bearings when it is forced to make the sudden starts and stops required in a reciprocating engine.
There are so many alum Z heads running on T's mine included without any problems simply using antifreeze just like modern cars today.
I like the alum heads just because of the weight difference. I've had mine a few years now and had it off a couple of times and it looks nice inside. I run the conventional antifreeze at a 60 : 40 mix.
NO DOUBT ALUMINIUM IS BETTER DEAR GENE !
BUT AS HAROLD WAS TALKING ABOUT MIXING HEADS
AND BLOCKS OF DIFFERENT METALS , I JUST
WANTED TO ASK EVEN MORE IF THE ALUMINIUM
WOULD MAKE ANY DIFFERENCE . THATS ALL FALKS .
ANY Ts CAME WITH FACTORY ALUMINIUM ?
STARTING WHEN ?
I GUESS YOU SAID BEFORE TAHT HENRY FORD STARTED WITH MODEL A , OK . THAT ANSWERS .