Shell M is a castor based oil with synthetic additives, much like Castrol 747.
The castor base gives a very high film strength, the oil stays attached to the surface it is meant to be protecting, the synthetic additives give a high lubricity, the surfaces slide more easily over each other than with pure castor.
747 allows one to dilute the oil down to 2% but advises that it is condition monitored. It the engine shows signs of lack of oil, increase the mixture up to 4%. (4% = 40 ml per litre, 2%-20ml per litre).
In theory the extra 20 ml of petrol per litre of fuel should mean more performance, but you would need to have teh carb set absolutely accurately to take advantage. I don't think any kart carb works to that accuracy, they aren't mapped that accurately for acceleration or slow running.
Acceleration for example needs a non linear increase in fuel, in carburetted carbs this needed
accelerator pumps or vacuum slides.
The problem with excess castor is that it forms a varnish that coats everything, from the fuel line to the carb internals. You get some idea of the amount in the fact that it leaves a carbon deposit on rings and piston head as it burns off.
There is no advantage in running 'more oil' than necessary, it doesn't add any more protection.
You shouldn't see higher or lower temperatures if the engine is adjusted properly, the oil being burned has an energy content very similar to the fuel it replaces, but you might see higher temperatures if the rings begin to rub instead of sliding in the cylinder.
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Oil to fuel ratio by 'MVJ' (09 Aug 2011 @ 20:01)
