octane fuel such as premium was being
used and advanced the ignition timing
accordingly for more power and torque.
Currently EFI is available in four-
strokes down to 9.9hp, replacing single
carbies in even twin-cylinder engines.
EFI has the benefit over carbies that
under light loads such as when trolling,
an engine uses less fuel than its carbie
counterpart. Even when fully planing
fuel consumption is less, only using
more when coming out of the hole when
the engine is under heavier load.
BATTERY-LESS EFI
Pioneered by Tohatsu in its MFS 25/30,
this provides all the diagnostic benefits
of conventional external battery EFI in
manual-start outboards.
This system was adopted by Mercury
in its F25 and F30 and has since filtered
down to 9.9hp in Tohatsus and 15hp
in Suzukis. Yamaha’s recently released
lightweight twin-cylinder F25 also has
it along with NMEA2000 compatibility
for connecting to digital engine
instrumentation and fish finders.
Combined with decompression
starting, battery-less EFI makes manual
starting of these smaller engines very
easy and overall improves fuel efficiency.
The engines troll smoother too.
Injecting fuel into individual cylinders
instead of one carbie feeding them
creates better engine efficiency and
allows for a smaller displacement and
lighter power head for output. Tohatsu’s
recently released battery-less EFI MFS
20E is a prime example. Its single carbie
20D predecessor developed 19.7 brake
horsepower at 5750rpm from 351cc and
weighed 51.5kg in short shaft form. But
combined with a new slimmer leg and
plastic engine pan to further reduce
weight, the 20E develops the same
output at the same revs from 333cc yet
weighs only 43kg. It’s now even lighter
than Suzuki’s battery-less EFI DF20.
Maximum torque is now 26Nm at
4500rpm compared to 25.5Nm at the
same rpm for the 20D.
Opting for battery-less EFI in its 20E
has enabled Tohatsu to offer a four-
stroke 20 that’s only 2kg heavier than the
long-running 294cc two-stroke M18E2,so it won’t adversely affect hull balance
when re-powering an older tinny. And a
lighter outboard means less hull weight
and fuel needed to plane a hull.SUPERCHARGING
Mercury pioneered this in its Verado
range from 2004 onwards. Supercharging
allows for smaller power heads to be
used over naturally aspirated four-
strokes but still provide the upper-end
power and torque of much larger
engines. For example the 2.6lt straight six
used in L6 Verado models can develop
up to 400hp, whereas Suzuki needs a
4.3lt V6 and Yamaha a 5.3lt V8 to develop
350hp with substantially greater weight.
By running small displacement
power heads Verados are incredibly
fuel efficient from trolling to mid-range
before the supercharger comes on
boost. At Wide Open Throttle (WOT)
they do use more fuel than the naturally
aspirated competition but few boatersTOP Evinrude E-TEC lead the way with emissions through clever technology in their direct
injection two-strokes.
TOP RIGHT Suzuki have led the way with low-maintenance chain-driven camshafts.
BOTTOM RIGHT Tohatsu’s LPG-powered outboard is a real head turner and not just for
the smell, it goes well too.34 trade aboat.com.au