Spark Plug & Points Gap

G'day all

We have an engine dyno on which we run in every race engine, and about half the road engines, before fitting them to the car. The dyno is calibrated regularly so we know what improvements (or otherwise) we are getting from changes in cylinder head design and camshaft profiles.

With standard points ignition, the maximum power is delivered invariably with .025" plug gap and .016" point gap - exactly what the book says. Let's face it - if BMC could have quoted a higher power output simply by increasing the plug gap, don't you think they would have done so?

We have tried different combinations of plug and point gap, but with the larger plug gaps (say more than .030") the coil doesn't produce enough power to deliver a good spark.

This last statement is not true of electronic ignition. You can open the plug gap to around .035" and gain around 2 ft lbs of torque at about 6,000 rpm - say a 2% increase. Below 4,000 rpm, electronic ignition doesn't deliver any more power than old fashioned points.

Already I can hear some "seat of the pants" comments about instant power increase when changing to electronic ignition. Most likely that's because you took out the 30 year old worn out distributor and the cruddy points with the weak spring, and replaced them with nice shiny new e.i. units. Or the dizzy shaft bush is loose and sloppy, your points gap was erratic, and e.i. is much more forgiving of this problem.

A properly serviced Lucas distributor, with quality points (eg: Cooper S with the stronger spring) and quality rotor, cap etc etc is as good as any alternative.

And when the points get dirty, you can clean them on the side of the road with a handy rock. Try doing that when the e.i. unit breaks down!