it is not thinner oil that has solved the problem, it is electronic oil pumps (on the E-TEC design anyhow) which precisely meter just the right amount of oil to just the right place. What oil is used is completely burned (and any hydrocarbon which burns completely leaves no smoke, it only produces water vapour and CO2). I spoke at length with the project leader of the E-TEC engine at Evinrude (was prepring an article about the then-new technology) and those boys really did their homework. The injector used in that engine, the heart of the technlogy, uses magnetic impulses and operates on a principle similar to a speaker. This was the breakthrough which allowed them to get over the previous rpm barrier they had to content with. It also allows them to switch between stratified and homogeneous mixture modes, somethign the other designs (including Yamaha`s HPDI) fail to do.
FI in itself does not widen the powerband per se, it is the cimputerized power (exhaust) valves (such as the three-step eRAVE used in the Rotax 600 HO E-TEC) which really get the job done in this regard (that and modern reed valve technology)
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