Re: High compression head choice.
One needs to realise the improvement in the quality of petrol since the Model A was new.
I run a 7:1 head, still low by todays standards and I am running it on 91 octane petrol without problems. Early pre-ignition problems were solved by fitting a Mallory distributor, which together with the harmonic balancer pulley were the two greatest improvements to the smooth running of the engine
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