[Mgs] Overdrive Numbers

Paul Hunt paul.hunt1 at blueyonder.co.uk
Mon Jan 14 01:45:58 MST 2008


A given octane of fuel will produce the most power safely just short of 
knocking.  It may produce a bit more with light knocking but personally I 
wouldn't go that far.  Reduce the octane and knocking increases for a given 
rpm, throttle opening and load which is why timing has to be retarded for 
lower octane fuel.  That reduces performance and increases running 
temperatures.

When manufacturers advised a certain timing setting not only did it take 
that into account, but it also took account of the tolerances of various 
components that will result in knocking under the same conditions for 
different engines, but it also included a safety factor.  That is why some 
engines can safely be run with more advance than recommended, giving better 
performance and economy, and some can't.  Over the years I've experienced 
both.

PaulH.

----- Original Message ----- 
> Thinking about it now, it seems that the more power under light knock
> might be due to either: more advanced timing (producing knock), or
> higher energy (lower octane) fuel.


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