Dual Spark Plugs

All the V8 hotrods seem to have 8 plugs.

OK, on a serious note, dual spark plugs are not needed for a Model A because of the head design. The turbulence designed into the flat head means that just one spark plug is needed. Dual plugs are needed where there is not much turbulence and the extra plug is needed to fire off the combustion completely and quickly. You see them a lot on T head engines.
 
My first thought is maybe that head is for an airplane with dual ignitions in case one fails.
 
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He talks about the part number for the head with no ID there. Above someone mentioned Charlie Yapp. One imagines dropping a few coin for the head - although the rest of the parts seem common enough.


Joe K
 
I have owned several dual-ignition Model-A/B heads over the years including a Funk ead used in an inverted Model-A engine. The deal with most aero heads is their compression ratio is about the same as stock. The Lion (Yapp) head was available in twin spark plug configuration, and I think at one time the Dan Price made Thomas head was too. In the aero world, most used a Wico magneto in the stock location, and another magneto driven off of the camshaft gear. The distributor on the video is from a mid 1980s Nissan Z-series engine that was used in their pickups. The issue with these is they use a leading/trailing ignition timing to help with emissions. In other words, one set of spark plugs fired something like 4°-5° after the first set as a way to ensure that all of the gasses had been ignited on that cycle. In a Model-A/B application, this is useless as far as performance.
 
In a Model-A/B application, this is useless as far as performance.
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Kind of like painting your engine "red" - it's good for conversation.

My brother held to the opinion that anything painted red must obviously go faster.

Delusional. He's the one who wanted a car to get GURLZ - not to work on.

Joe K
 
Many antique fire engines used dual plug ignition systems. This was done for reliable engine starting. One plug ran off a magneto and the second off a distrubutor. Initial starting was done using the magneto. Once the engine started the magneto was switched off and the distributor ignition was turned on. When battery power was low the engine was started using the mageto and hand cranking.
 
Here is a head from a Pietenpol airplane.
 

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For the head shown in post #11, the crown of the pistons must have not protruded above the block.

Several cars, like early RR, used the dual ignition systems for reliability. And, as Brent pointed out, so did airplanes. However, very early cars that used the T head design used two plugs because of the large distance the flame front had to travel and the lack of any turbulence.
 
not sure i understand all the inferences of the mechanics, but it's an interesting subject none the less.

(to me, anyway. i don't know what i don't know)
 
The Model T had a magneto and a battery for the ignition. From what I understand, you select the battery when starting, then switch to magneto which provided a stronger spark. A magneto only produces electricity when spinning fast enough, so starting requires enough rpm’s for long enough to fire the engine.
Floyd Clymer wrote in a book of Model T remembrances that a burly guy in his town showed off by hand cranking his T on magneto.
I tried to kickstart a Harley-Davidson panhead with a magneto. I launched my weight on that pedal as hard as I could with no results. After the third try I had reached my cardiovascular limit and was panting and seeing little sparkles in front of me.
 
The Model T was a 6 volt system so the battery for starting was 6 volts. The magneto was alternating current and higher voltage depending on how fast the engine was turning over. If the magneto was in good condition (they got bad over time and miles) then the magneto voltage, when rectified, was just enough to charge a 6 volt battery. It was only 1/2 wave rectified because of how the magneto was wired. The later Model T's had generators to charge the batteries which were much like a Model A generator.

I don't know what voltage the early motorcycles were but I suspect it was 6 volts.
 
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