. We were the first to introduce a
digital Electronic Fuel Injection four-stroke;
an idea that allowed the DF60 and DF70 to
receive further recognition from the
International Marine Trades Exposition and
Convention when they captured the IMTEC
Innovation Award. We were the first to offer an
automotive type self-adjusting timing chain in
a four-stroke engine with performance-
enhancing dual overhead cams and four valves
per cylinder. This brought us recognition again,
when our DF40 and DF50 received the IMTEC
Innovation Award making Suzuki the first
manufacturer to receive this distinguished award
two years in a row, and also giving us our third
IMTEC award, again an industry first. DF90/115
and DF140 are the first to offer an offset
driveshaft with a two-stage cam drive system and
two-stage gear reduction system, making them the
most compact outboards in their class.
At its first showing at a special preview
at the 2003 Miami International
Boat Show, the DF250 captured the
NMMA (National Marine
Manufacturers Association) 2003
Innovation Award making this the
fourth Innovation Award for Suzuki. 2
The flagship DF250 is the industrys first
250PS (184kW) V6 four-stroke outboard and the
most powerful outboard ever built by Suzuki. Its
3614cm
3
(220.5 cu. in.) displacement is of
course, our largest to date, and the largest to
date in the industry as well. At 69PS (51kW) per
liter, it holds the greatest power to displacement
ratio the industry has ever seen in the four-
stroke category. Additionally it holds the indus-
trys greatest power to weight ratio and is the
lightest outboard motor in this category.
"The Ultimate" DF250
Relying on experience weve gained through the
manufacture of not only outboards, but techno-
logically-advanced motorcycles and automo-
biles, our engineers have put decades of knowl-
edge into the design, development, and produc-
tion of an all new V6 motor designed specifically
for outboard use. This new V6 holds some of our
most advanced innovative ideas to date, making
it a showcase for Suzukis advanced four-stroke
outboard technology. 3
The Ultimate in Performance
Cam Position Sensor
Rotation Direction
VVT Actuator
Throttle Opening Angle
Water Temp
Feed
back
Cam Position
Crank
Position
Manifold Pressure
Water Temp Sensor
Throttle Sensor
Map Sensor*
Intk Cam Shaft
Ex Cam Shaft
Crank Position Sensor
Duty Control
Crank Shaft
ECM
Target
Advance
Actual Valve
Timing
Intk Cam Shaft
Retard
Advance
Drain
Oil
Filter
Oil
Pump
Oil Pan
Engine Oil Pressure
Oil Control Valve (OCV)
Signal
*Manifold Absolute Pressure Sensor
T
ORQ
UE (50N m)
LOW
MID
ENGINE SPEED (rpm)
HIGH
with VVT
without VVT
Diagram of VVT Mechanism
Torque Curve
DOHC 24-Valve with VVT Delivers
High Performance
Our engineers designed a 3.6-liter V6 enginethe
largest displacement found in the industry thus farand an
aggressive cam profile designed specifically for the DF250
to create the industrys first 250PS (184kW) four-stroke
outboard. However, our goal was not just to create an
outboard that could deliver 250PS (184kW), but to create
an outboard that could deliver high performance that suits
its 250PS (184kW) output along with the many benefits
that a four-stroke can deliver.
A high performance camshaft designed to deliver
250PS (184kW) produced the wanted power output, but to
get the strong mid and low-end torque outboards need
when accelerating requires altering valve timing. In
general, only using a camshaft setting like those found in
racing engines produces an engine that develops insuffi-
cient low and mid range torque. This is because the valve
timing for intake and exhaust differs according to load and
engine speed.
* At the comparison test, Multi-Stage Induction System of
the motor was operated. 4
The common idea is that the intake valve opens after the
exhaust valve is fully closed however, the intake valve
actually starts opening before the exhaust valve fully
closes, creating a momentary overlap in the timing where
both valves are open. Using VVT (Variable Valve Timing)
in the DF250, this overlap can be increased or decreased
by altering intake timing with the camshaft, thereby
optimizing camshaft timing for low range and mid range
operation. As the DF250s camshaft is already setup to
deliver maximum output at high rpm, a change in timing in
this range is mostly unnecessary. Increasing the overlap is
necessary during acceleration in the low and mid power
range, but no change in timing is required for stable idling.
In the DF250s VVT system there are two chambers within
the VVT actuator, one on the phase angle forward side and
another on the phase angle backward side, to which
hydraulic pressure is continuously applied to change the
valve timing of the intake cam. When the engine is
stopped, idling or other times that there is no oil pressure
in the system, the VVT actuator locks, disengaging the
system.
Graph Illustrating the Variance in Valve Lift
Using VVT
Cylinder Block
Cylinder Head
Camshaft
Valve Overlap
V
alve Lift
Ex Valve
Advance
40
°
Movable Angle
Intk Valve
Retard
Crank Angle
Intake
VVT
Exhaust 5
Multi-Stage Induction
Multi-stage induction enhances engine performance by
changing the length of intake manifold pipes according to
engine speed. The system utilizes two intake manifold
pipes per cylinder, one operating at low engine speed and
another operating at high. When the engine is operating at
lower rpm, air enters the combustion chamber through the
Air Flow in Multi-Stage Induction Module
Lower rpm
High rpm
Multi-Stage Induction Module
Close
Open
T
ORQ
UE (50N m)
LOW
MID
ENGINE SPEED (rpm)
HIGH
without Multi-Stage Induction
with Multi-Stage Induction
Torque Curve
longer, curved manifold pipe. The length of the pipe is
designed for entering the most suitable volume of fresh air
into the chamber to improve combustion and boost low-
end torque.
As rpm pass a preset threshold, the valve on the direct
intake pipe opens up letting air enter directly into the
combustion chamber. Short, straight and lacking resistance
it gets a greater volume of air into the chamber, increasing
the engines ability to breathe at high rpm, thus improving
high speed power output.
The engine cover is designed with a large air intake,
which extends from the back of the cover, well around
both sides to provide maximum airflow into the cowling. 6
Two-Stage Gear Reduction
With such a high performance engine now at our
disposal, losing any power in the propulsion system would
be a waste, so our engineers chose an efficient means of
supplying maximum propulsion. A propeller rotating at
high speed in the water has a tendency to slip and when
two propellers of the same pitch but different diameters
are rotated, the smaller propeller will slip more than the
larger. So to obtain maximum propulsion, spinning a larger
diameter propeller with a suitable pitch is the answer.
But to spin a larger propeller, more torque in the
propeller shaft becomes necessary. In order to obtain the
required amount of torque however, the corresponding
increases in weight and resistance due to the use of larger
gears and a larger gearbox do not always provide effective
results. The answer to this dilemma is found in the use of a
two-stage gear reduction system that provides the neces-
sary torque without adding unwanted bulk and weight.
The DF250 utilizes a first stage gear reduction (32:40)
between the crankshaft and driveshaft, and a second stage
reduction (12:22) in the lower units gear case, resulting in
an overall gear ratio of 2.29. This is the largest gear
reduction ratio found in any outboard over 200PS (147kW)
two-strokes included. Such a powerful reduction allows
the DF250 to turn a 16-inch diameter propeller, which,
while being larger than the 14-1/2-inch diameter propeller
found on the two-stroke DT225, is also larger than those
previously used on a V6 outboards. The propeller used on
the DF250 is specially designed for greater acceleration
and maximum speed.
Along with greater acceleration, the gear reduction in
combination with the four-stroke engines wide power
band is capable of handling a wide variety of loads, which
is a significant benefit to boaters whose loads vary from
day to day.
DT225
DF250
Propeller Diameter Comparison 7
55-Degree Bank Angle Creates a
Compact V6
With the DF250, one major design objective our
engineers set out to realize was to design and produce a
compact, narrow profile motor. This was met by abandon-
ing the 60-degree bank angle normally utilized in V-type
blocks and designing an all-new V-design block using a
55-degree bank anglean industry first. When compared
to the industry norm of 60-degrees, as shown in the engine
cover comparison, the difference in size is quite clear.
Compact Designs
Engine Cover Profile Comparison
Offset Drive Shaft
Offset Driveshaft
Suzukis utilization of an offset driveshaft in the DF90,
115 and 140 has proven successful in reducing the size of
the outboard. The DF 250 benefits from this same design
which positions the crankshaft in front of the drive shaft,
simultaneously moving the outboards center of gravity
forward. This system adds to the compactness of the
outboard and provides an improvement in power perform-
ance. It also places the engines axis of inertia, the point
where vibrations produced by the engine are at a mini-
mum, up over the upper engine mount thus