I've just got hold of the official Rotax data sheet for the new 912ULS and
thought it would be a good idea to share the numbers with you power crazed
Europa builders, since there have been various requests for this information in
the past.
Primary difference with the 912UL is an increase in bore size from 79.5mm
(3.13") to 84mm (3.31") pushing the capacity up from 1211cc to 1352cc. The
stroke remains the same at 61mm (2.4"). Compression ratio goes up from 9:1 to
10.5:1, which is presumably where most of the extra grunt comes from. Ignition
timing is retarded from 6 degrees BTDC to 4 degrees BTDC up to 1000 rpm where
it advances to 26 degrees BTDC (as does the 'UL), possibly to ease starting
with the higher compression, coincidentally this is the same as the 914.
With no information on valve timing, it isn't possible to say whether the cam
has been changed or not.
The reduction gear (PSRU) ratio changes from 2.273:1 to 2.43:1 to accommodate
the new power delivery, which is almost linear to its maximum 100hp (73.5kW) at
5800rpm (max). Torque curve is a lot more "peaky" than the 'UL climbing
steadily to very useful 128Nm (94ft/lb) at 5100rmp where it tails off. The 'UL
by comparison, has a much flatter torque curve, climbing to 102Nm at 4000rpm,
flattening off to its maximum 105Nm at 4800rpm.
If the figures are to be believed, the larger engine is actually 3lbs lighter
than its smaller brother...... 56.6kg (124.8lbs) as opposed to 58kg (127.8lbs).
Having studied the line drawings supplied with the data sheets, Rotax now
appear to have realised that in order to get the most power out of the engine,
the fuel pump needs to be connected to the carburettors. In an act of
uncharacteristic generosity they are now incorporating a fuel line plus four
way distribution block (fuel in, 2 x fuel out plus fuel return) with the
engine. This is presumably in response to puzzeled customers enquiring why
their engines were so difficult to start and why there was such an overpowering
smell of fuel. Also included are a pair of carburettor retention springs (to
stop the things dropping off).
Alas Rotax still don't supply (as standard) a generator cover so this vital
component is just as vulnerable to inadvertently dropped iron based detritus.
All in all, Rotax appear to be fighting back the threat of competition from
the likes of Jabiru and Subaru. At =A36000 (Ex VAT and ancillaries) here in the
UK the price is marginally less than I paid for my 912UL two and a half years
ago .......I wish I had waited......but then if I could predict the future, I
wouldn't need to worry about the price!
Nigel (147)
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