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The Vacuum Advance, or what it is for...

Sorry Ace, the vacuum advance is used as an economy measure only... The flame propagation in the chamber that has been subject to a sub-atmospheric induction is such that it can use an early start point for ignition... The dynamic compression ratio is MUCH lower than static under these condition and will withstand more total advance... OK in English... the fuel burns slower when there is less of it (and air) in the cyl... soooo you gotta light the match sooner if you want the stuff to burn and reach maximum pressure at the proper time in the cycle. Ifin' ya' don't,the pressure builds after the optimum time and all the push is wasted ,sometimes out the exhaust!(if you don't believe this,retard the time and FEEL the exhaust pressure at the tailpipe. Leave it this way and watch the manifold get red hot!)So with the advance non-functional the rover will need a (slightly) larger throttle opening to developed the power to overcome friction than would be necessary if you were burning the fuel in an efficient manner. When you womp the go pedal to the floor(which in a 109 is always) the "vacuum" goes away and the static or mechanical advance setting takes over as the max. advance that the engine can stand at that rpm and temperature during max. cyl. filling... whew... This is one way that the modern engines get the fuel mileage that they do.. they electronically control the timing and with knock sensors and such keep the timing at the highest possible setting eg: just short of"Knocking" The land rover along with any car of the period will often run well shy of the optimum timing to prevent engine damage (the timing needs can be dependant on so many things that there is not a single mechanical device that can cope with all the changes in fuel, temperature, air density etc. This explains the low compression ratio on the Lander...the folks at Solihull do not have any control on the type of "Camel piss" that you will be putting in the tank at 117 F. w/o enough water in the radiator,while pulling Montana up mount Everest.....

OK I'll stop.....I'm goin' ta' school to teach this if there were a course in keeping students AWAKE........

(More than)
'nuff said

Steven M. Denis

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