I got a question for the gurus here on the HAMB. Over the years I have noticed that on some flathead engines the manufacturers seem to locate the spark plugs over the valves moreso than the piston. As a young man I found this strange when I first encountered it. Still not real sure of why, figured it improved performance, just not sure how. Any thoughts? Bones
Near to the exhaust valve, has to do with flame movement and where the air fuel mix is at time of spark ( it will be travelling towards a still open exhaust valve initially ) this is a very basic version , someone will be along shortly with a long version
Not longer: the principle as I recall is, burn the end gas in the coolest part of the combustion chamber.
Bringing down the head on top of the piston accomplished several good things. It gave higher compression, the piston nearly meeting the head squirted the mixture towards the spark plug and caused turbulence, good for rapid complete burning without knocking. And reducing the combustion chamber in size allowed the fuel mixture to burn quicker. All these things reduced knock and ping while increasing power and efficiency. But, they meant the piston nearly touched the head at the top of the stroke so, it was impossible to put the spark plug there without it getting hammered flat. As Torana pointed out, above the exhaust valve seems to have been the preferred position.
Do a search on Sir Harry Ricardo and his book ‘High-Speed Internal Combustion Engines’ for your answer. He sued Henry Ford for robbing his design ideas in the ‘32 flathead V8 (and won). Sent from my iPhone using Tapatalk
If you haven't seen any of these videos before, it's quite interesting to see just what's going on in the combustion chamber of a running flathead. Even if it's just a Briggs & Stratton.
I understand that the exhaust valve is the hottest part of the combustion chamber. The spark plug is located there to burn away deposits that formed on the electrodes and caused fouled plugs. When I made my flathead for my 32 Plymouth engine I put one plug centered over the piston and one next to the exhaust valve in the conventional position. Most of the time I ran both. But sometimes I only ran one or the other to see if it made any difference. If it did I couldn't tell and didn't see it on the timing slip.
Spark plug placement is a science. In a perfect world the spark plug is centered between the valves in the center of the combustion chamber. Most engines do not have hemispherical combustion chambers and with a side valve motor this goes completely out the door. I am going to make a non scientific conjecture here. On a side valve engine with the spark plug placed near the valves it is so that the fuel charge lands near the point of combustion and then the flame travels across the top of the piston. This is just conjecture and is based on an old porting principle where you cut your ports in such a fashion that the incoming charge land as close the he sparkplug as possible.
Very interesting. Questions: 1. Would it be a good idea to add a pint of rubbing alcohol to a full 16 gallon gas tank to improve engine performance and clean out the carbon? 2. Would it damage the engine, seals, rubber hoses or gaskets?
I run Edmunds heads on both of my 8BA's because the spark plug has been moved juuuust enough so the electrode is not over the exhaust valve. It's still damned close, but moved enough so that it allows me to run extended tip plugs. Between this and carefully preparing the heads to obtain the proper "squish", the last two engines I built are the best runners I have had.
It takes some time for the flame to spread throughout the combustion chamber. The longer time it takes, the earlier you have to ignite it, the earlier you ignite it the longer you have to have the piston rising towards TDC fighting the rising combustion pressure. Maybe not as horrible as it may sound, but it is far frim ideal. A "modern" 4 valve per cylinder engine with the spark plug in the center (and usually some squish area near the edges of the cylinder) will have a nice, quick burn where the flame doesn't have to travel very far. Two stroke engines has even better combustion chambers, as they don't have to make room for valves at all. Older 2 valve heads with the spark plug off to one side will have a longer way for the flame to travel, and also a slower burn. A few large cylinder 2 valve engines have had dual spark plugs to combat the problem (and as far as I know many aviation engines has it too, but more for the sake of redundancy). Rotary (wankel) engines often has double spark plugs, in the very long combustion chamber. Now, the flathead... Large combustion chamber, even if the head has a squish area tight against the piston, generally low compression. Not a good shape for a quick burn. In theory the plug would be located somewhere near the center of the combustion chamber to limit flame travel distance, but I wouldn't be suprised if other locations have been used to help keep the valve clean/not foul, especially as the fuel, oil and air filters weren't the best back in the day.
So.....what is the advantage of running 2 spark plugs per cylinder as seen on several style Ford flathead heads?
I theory it should speed up combustion, and require a bit less ignition advance. Possibly a little more power and better fuel economy.
Most two plug heads that I have seen put the plugs pretty much side by side and I guess that just gives you twice as much chance at lighting the fire. I put my plugs as I stated for the reasons stated.The big round motors I used to work on put the plugs on opposite sides of the hemi combustion chamber. I don't know why. Seems like two in the middle would have a flame front moving out evenly. Less detonation prone. But they seemed to work fine and lots of Pratt and Whitney and Curtis Wrights were used all over the world. I thought my Plymouth was interesting. But I didn't really learn much from it. Some may remember that for a while some top fuel engines had 3 plugs. Two in the middle and one by the exhaust valve. Heard it worked but NHRA banned them.
I am running a yapp lion cast iron speed head on my model A with the plugs centered over the cylinders. They claim a hp increase over the standard location of the model A. as they have tested it on a dyno. some of their heads run 2 plugs per cylinder. the engine ran its best with one of their scalded dog manifolds.which uses manifold heat from the exhaust manifold to heat the incoming fuel from the carb. I had to run a thermostat as a was having a problem getting water temperature over 110 degrees. I think this was due more to head design with improved cooling over the model A stock head.
Datsun used a head with 2 plugs per cylinder. I assumed it as for emissions though. They were on opposite sides of the cylinder. So one was close to the exhaust valve, and the other to the intake valve. I never had the head off to see what the chambers were shaped like. But one side quit, due to wiring problems. The truck ran normally. When fixed, there was no change as far as I could tell.
We’ve got a Ford ranger that has a four cylinder and eight plugs. Some of our old fire trucks also had two plugs per cylinder, but I though that was in case one system went bad the other would get you there. But on the Mack’s, you could select right, left or both systems. At an idle it would make no difference between right or left, but when you would go to both, the idle speed would pick up a little. Bones
I have added up to a quart of alcohol to my gas tank to soak up and eliminate any water or ice. Never noticed any damage or bad effects. To improve performance and clean out carbon use water injection. It eliminates knock from too high compression or too low octane. It also steam cleans the combustion chamber. I rigged up a water injection setup purely for cleaning purposes using a windshield washer tank and pump wired to plug into the cigarette lighter with a sprayer that went in the carburetor or fuel injection system after the air filter. You can borrow it if you want. For a more permanent installation there are water injection systems you can buy. There is more to it than just squirting water if you want it to work right for controlling spark knock.
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