Quote:
Originally Posted by Bob Bidonde
The spark plug gap is set on the basis of:
> The amount of hi-voltage available to jump the gaps in the distributor & spark plugs;
> Volumetric efficiency of the engine's intake system;
> Compression ratio;
> Combustion flame development in the cylinders;
> Density of the fuel in the cylinders;
> Power the engine makes.
A rule of thumb is that the more power an engine makes, the smaller the smaller the total gap needs to be (rotor to distributor + spark [plug gap).
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In laymen's terms, The Model A engine is an inefficient design that needs a big spark to light the fire.