Hmmmm....let's see now, the Lister has a mechanical governor so it can't increase RPM, only change the rack position.
40% horsepower increase ??!!
That's why the warning. Nobody is mad, only tired of wading around in internet BS and we've decided to sit under the tree of truth through experience and swat spammers.
THAT being said--- I'm a firm believer in thin synthetics, whether it be Amsoil, which I've used for thirty five years, or another brand. There IS less load on the engine and auto engines usually idle too high. It DOES decrease the amount of gear drag in transmissions. I've driven over a million miles with it in several very high milage rigs without an oil related failure. THAT'S all *I* know.
I'm going to try (a more readily availble) synthetic in my Lister once I have a date certain for bearing changes. I *think*, from past experiences with used trucks, there will be a drastic increase in oil consumption and probably a knock. With other engines I've had good luck adding STP to kill the knock and just add oil and a filter once in a while and forget 'changing' the oil.
Amsoil is GREAT stuff in manual transmissions and differentials in cold weather. There can be some amazing increases in winter-time gas milage with no other changes.
*your milage may vary.*
<my dad once cornered a fast talking 'gas saver' salesman at the county fair. The guarantee was "10% gas savings, buy two and save 20%." My dad ask why not buy eleven of them and make gas? The sales guy finally had to back off when the heckling started.>