Top fuel spark lead varies with the shape of the combustion chamber . Blown
fuel 392 hemis ran best with 19 to 28 deg with extreme of 32 deg . It took
several years for the Ramchargers , Keith Black and Garlits to realize that
426 hemis needed way more . In '66 or early '67 Black tried 40 deg which
wasn't enough and he quickly pulled it back for fear it was way too much .
Spark advance is not linear . When the piston is half way up the fuel burns
relatively slowly . A fellow I know got the mag a tooth off on his top
fueler which was about 140 deg and it ran about the same .
> Top Fuel engines need that much timing advance because of the fuel, not
> the
> rpm. Nitromethane burns much slower than gasoline, so the timing needs to
> be
> advanced more to maximize power.
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