I am planning on machining a new Cylinder Head for my son's Pulling Garden Tractor over the winter. It is a single cylinder Kohler Flathead engine. Any thoughts on what is the best location for the Spark Plug? I know some people say it needs to be directly over the Exhaust Valve(gate valve), some say centered on the piston, any thoughts?

Put in both.... and fire it with a Harley dual coil.

It will wake things up, but you will probably have to back the timing down a little.

On the typical Ford flathead engine, the spark plug is more centered between the valves, just off the edge of the piston.  This is considered a turbulent area.

Nevertheless, I agree that if you are going to be making a custom cylinder head, you might as well twin-plug it. I'd put one over each valve, offset towards the cylinder.

"Conventional" thinking says put it over the exhaust valve but think about the space you need to have over that valve in the combustion chamber? Really wanna lose all that compression? Your head design will have alot more to do with location. You will not see a big reduction in timing in any location on a stock class engine assuming 4000rpm's?

As for machining the head, I do mine on a manual mill and handwork it to final design. I have a head blank I use for flowbench R&D and then copy that design over to my alum blank.

I'm in the same boat as you . . . building on a shoestring. I designed and built my own flowbench (now help others do the same thing on my website) fabricated my dyno. Purchased a mill, lathe and various other shop toys for less than the cost of a good NQS Pro Stock engine. Nice thing about doing it yourself, nobody knows what you have in your engine. If you buy an engine everybody knows what the other engine builders build.

Do I win? I enjoy pulling and do it at a very reduced cost in the class I run in. So in a way I win everytime I go out I spend alot less money to not win maybe $100.00? So in a way I am "winning" and having fun running what I build and not what someone else built for me! Right now I'm more focused now on flowbenching and building flowbench parts than building engines/parts for others so the tractor sits.

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