powering

[1bassman]

Hi All,

I've outgrown the estury trecker and almost decided on new float, will be between a Blue fin Wildcat / Warrior or Stacer barra elite. Looking at power options between 60 / 70 Yamaha 4s or 75 Opti. Unsure how on specs a 4s can be 50kg lighter than a di 2s? Any thoughts on best options? Used as an allrounder (me casting Bass / Barra and a family boat also).

Cheers Brad.

[kizza1]

there is a huge difference between a 604stroke yamy and 75 opti.
the yamy is a 1ltr engine and the merc is a 1.5ltr.
thats 50% larger. thats the main reason for the weight difference.

[Noelm]

when you look at the motor HP "families" you will se the 70HP Yamaha is the last and biggest HP in that group, when you move up to an 80 (to fully compare to the opti) the weight rise is dramatic for 10HP I think they are 170+ KG I am going through all this now looking for 80 to 90HP motors, the pick seems to be (for me) plain old 90HP yamaha 2 strokes, next best is the Suzuki which has the 70/80/90 coming in at 158KG, weight is your enemy when you are searching for the best HP per KG these days.

[1bassman]

Thanks guys, still find it strange for 5hp gain a 2s can be 50kg heavier than a 4. My small brain is still in XR v CR mode.
cheers Brad.

[kizza1]

as the other guys said its a different family class that same 75 opti can push out 125hp with different computers and injectors.

also you will find on a dyno the opti will hit peak hp at MUCH lower compared to the yamy 70hp.

for example
the opti may reach 75hp at 3000rpm and then stay at 75hp through to 5750rpm. where as the 70 yammy may not reach 70hp till 4500rpm and then stay at 70hp till 5750rpm

NOTE THESE FIGURES ARE PLUCKED OUT OF MY ASS. JUST FOR THE PURPOSE OF THE EXERCISE SHOWING DIFFERENT CUBIC CAPACITY ENGINES VS HP

it all depends on what is going to be ideal for your boat. last thing you want is for it to bury the back end or porpoise.

then to make it even more confusing the manafacters may be using the 10% leeway with hp ratings to there advantage or disadvantage.

not trying to sway you one way or another just trying to explain/justify the weight difference between the 2 completely different engines

[FNQCairns]

+1

the opti is greatly under stressed and would pull that competition backwards and underwater........also and not often considered there is every chance the opti will push what amounts to a final drive near 2 pitch higher, this means more speed for rpm and less fuel per km travelled than any 'typical' litres per hour estimation/comparison would pretend to convey.

[Noelm]

I guess in a sort of way, the best motor in a "family" would be the lower HP models, say like in the Suzuki 4 strokes I am investigating, the 70, 80 and 90 are the same basic engine, so probably the 80 would be the "nice" one, being not the pushed to the max 90, and not as "choked" as the 70, whereas the 70 Yamaha is a tiny engine by comparison (also tiny in weight) but it has the max HP rung out of it. Then we go into the old world of the carby 2 stroke, the very bane of the 4 stroke lovers life, but it is a 90HP simple, and very light tried and tested engine, that is cheap compared to it's 4 stroke counter parts, which way to go? what a dilemma!