GuyFawkes made some comments about the compression valve and it's use on a S-o-M.
The manual is not clear on the use of the compression valve, mentioning it only in the case of an emergency hand start, where it says the valve should be screwed in. This implies that it should be on low compression for normal use. Since the starter system is capable of cranking the engine over several compressions, the high comp. setting should no be needed for starting.
When I said CS valve in for starting and up to 50% loads that wasn't an opinion, that was factory recommendation, YMMV, but over the years I've found it to be sound advice.
He also said that since the alternator was only 2.5Kw, it did not constitute a high load for the engine.
2500 Watt, divided by 746 (Watt to hp) gives 3.35hp
Lets be reasonably generous for the alternator and give it an 80% efficiency
3.35hp divided by 0.8 gives 4.2hp
Twin V belt drive say 90%
4.2 divided by 0.9 gives 4.6hp
That's about right for a full generator loading on a nominal 6hp engine.
you miss the point, the Lister 6/1 was rated at CONTINUOUS duty, "high load" in a continuous duty engine means >95% rated output on a 100% duty cycle, therefore by definition 4 hp is not a high load.
your closing comment about a "normal 6hp engine" says it all, the Lister CS 6/1 is anything but a normal 6hp engine.
Fuel quality has indeed increased somewhat since the war years, but the real advances that absolutely dwarf any fuel quality increases have been in lubrication oils (and automotive tyres as it happens) and these advances have been of orders of magnitude... you can go into an auto supply shop now and buy off the shelf lube oil that was simply inconceivable at any price 60 years ago.
Note that compression pressures don't (in theory) alter much when your raise working RPM of a motor from say 650 to 800, but, compression temperatures so, the faster you compress the gas the warmer it gets, so you adjust fuel and compression ratio to suit.
As for dropping the CS valve itself, hearsay testimony from the lister factory was that this was done for purely economic reasons, as it cut the cost of the head in half, so between a sixth and an eighth off the manufacturing cost of an complete engine.
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going back many years when the Bowdens of Plaidy were chairman of the Vincent owners club ( we're talking 150,000 miles before de-coking the head in machines that were used for european touring) and the vincent was an incredibly desireable machine, I ran into a chap doing a tour on a Brough Superior, we had a long chat about the merits of various things (I was running around on a 1975 FXE at the time) but the astonishing thing about the brough was the mpg he was getting out of it, by dint of actually using those "primitive" mixture and advance controls on the handlebars as they were meant to be used, as he rolled from one country to the next and each tankful of fuel was a different grade, as the day warmed or the atmosphere dried out, or as he gained or lost altitude, he would adjust the engine while going along....
"automatic" ignition advance and lazy drivers did away with all that, just like points and coils did away with magnetos, but the new replacements were not superior, just "easier" and "good enough" and most of all "cheaper to make".
I haven't been anywhere near drag racing for decades, but when I was electronic ignition was anything but new as a technology, and yet despite the extra weight and power consumption of magnetos nobody used electronic.
Nobody who has ever held on to a magneto (K2F on a BSA A10 doing 40/50 mph when the left plug cap came off..... you think matey on here with the starting handle was a classic dumb mistake.... just as well there were no digital cameras back then) is ever going to convinced that electronic ignition is in any way superior to a magneto.
Similarly nobody who has used a CS in anger for any period of time will be convinced that fixed compression is in any way superior.
Variable compression KEEPS coming back, as fixed compression ratios are one of the fundamental technical flaws on the internal combustion engine, and you only have to look at the heath robinson nightmares that people like SAAB etc came up with (in an abortive effort where the requirement to have a design that is unique enough to be patentable outweights many more sane considerations) in the SVC motor, the russians are doing it, the japanese are doing it, everyone is doing it, but all their designs are hideously complex and therefore expensive, so the old Lister CS / Brough Superior approach beats them hands down every time.
You just have to learn it.
