|
När
du tänker ersätta din bensinmotor med en dieselmotor från
MarineDiesel är det inte alltid så lätt att veta vilken motor du
ska välja. Här följer en guide som får dig en bättre
uppfattning om våra motorer.
5.7L
250Hk
Fördelarna med en MD250 jämfört med en bensinmotor på 5.7L är
många. Bland annat får du mycket högre vridmoment, bättre
effektkurva och bränsleförbrukningen minskar med 30% - 50%
7.4L
330Hk
Det
man ska tänka på när man jämför en dieselmotor med en
bensinmotor är att man ska titta mer på vridmomentet än på hästkrafterna,
då vridmomentet har större inverkan på dieselmotorers effekt. De flesta
kunderna tror att deras 250hk bensinmotor ska ersättas med en
250hk dieselmotor, men det stämmer inte. Med dieselmotorn
så förlorar man ca 1000rpm jämfört med bensinmotorn och därför
behöver dieselmotorn mer kraft, mer vridmoment. Dieselmotorn kommer
också att använda sig av en större propeller än bensinmotorn
för att kunna komma upp i samma hastigheter eller högre jämfört
med bensinmotorn.
7.4L/8.2L 385Hk & 415Hk
När
man bedömer prestandaskillnader mellan MD300 och 7.4L Magnum eller
8.2L Magnum motorerna ska man främst veta detta: De här två
bensinmotorernas vridmoment ligger på runt 620Nm. MD300 motorn har
ytterligare 50Nm men det räcker inte för att kunna matcha
bensinmotorernas maximala varvtal med hjälp av olika
propellerstorlekar. Därför tappar MD300 motorn ca 6.5km/h (~3knop)
toppfart. Men det tar den igen genom att man kan ha större
propeller med MD300 motorn och därför få vridmomentsspetsen på
1600rpm jämfört med 3500rpm för de två bensinmotorerna. Detta
resulterar i bättre acceleration i lägre farter, bättre
cruisehastighet och halverad bensinförbrukning.
When looking to re-power from an existing gas engine up to diesel it’s
common to wonder about the proper method of estimating the performance gains
associated with the MarineDiesel product. The following information serves as a
guideline in assisting customers develop a feel for what they can expect;
350 Cu In (250
Hp)
When estimating the
performance gains with an MD250 versus the 350 Cu In gas engines, the diesel
will outperform this range of engine extremely well. This gasoline engines
produce torque in the range of 350 Lb-Ft and therefore the additional 125 Lb-ft
produced by the MD250 is more than adequate in compensating for the loss in rpm.
It is common to see significant gains on top speed and cruise speed as well as
extremely good low speed acceleration versus the gas engines. Customers can
expect to see fuel savings in the range of 30% - 50%.
454 Cu In (330
hp)
The main thing to
consider when repowering from gas to diesel is that the torque rating is what
has to be compared rather than the horsepower. It is common for customers to
expect to replace a 250 Hp gas engine with a 250 Hp diesel. The fallacy in this
is that with the diesel engine you lose approximately 1,000 rpm versus the gas
engine, and therefore need additional torque to offset the difference in prop
speed with a larger prop. The rule of thumb is
that for each pitch of prop is equivalent to 200 rpm., and therefore 5
additional prop pitches would be required to offset a 1,000 rpm reduction. For
example the MD300 compares out very well against the 330 Hp 454 due to the fact
that the MD300 produces approximately 100 Lb-Ft more torque than the 454. It is
this additional 100 Lb-Ft that allow the prop pitch to be increased as required
to make up for the loss in rpm. The larger prop then allows the boat to plane
much better as well as much improved cruising speeds. In some cases the gear
ratio will even stay the same while simply making the necessary adjustments
through propping. Note - When re-powering relatively heavy boats (10,000+ lbs) the increase in pitch will be less than when re-powering lighter boats; typically in the range of 3 propeller
pitches.
454/502 Cu In (385 & 415
Hp)
When estimating the
performance gains with an MD300 versus the 454 mag or 502 mag engines the main
thing to consider is that both of these engines produce significant torque and
therefore expecting the same top speed is not realistic. These gasoline engines
produce torque in the range of 460 Lb-Ft and therefore the additional 50 Lb-ft
produced by the MD300 is not adequate to offset the 5 prop pitches required to
compensate for the 1,500 rpm, since these engines normally run between 4,800 and
5,000 rpm. Therefore it can be expected that 2 – 5 mph at top speed may be
sacrificed. However, the MD300 by utilizing a larger prop and making it’s peak
torque at 1,600 rpm versus 3,500 rpm with the gas engines will therefore yield
much better low speed acceleration, better cruise speeds and significant
reductions in fuel consumption ranging between 40%-60%.
|
