Two or a Four Yamaha.

[poundsterling]

Good evening,

I am new to the forum. At the higher hp end of Yamaha outboard motors which is the more efficient, economical, greater power, two or a four stroke ?

Thanks.

[rodbolt17]

at or near the rated HP and RPM, they both burn about the same.
at or near the rated HP you will find outboards tend to burn 1 gallon per hour per every 10 HP.
my F150 burns 15.2 GPH at 5800 RPM.
my buddy's two stroke 150 burns just a tad more at about 15.5 at 5400 RPM.
I ran a pair of F350s the other day that had a combined rate of 69.8 GPH at 5700 RPM.

see the correlation?

[boscoe99]

There are too many variable to fully answer your questions. Here are some pros and cons of each motor type. From my view anyway.

- Four strokes are typically heavier and more costly to acquire.
- Two strokes for the most part are no longer available from Yamaha USA.
- Highly subjective, but most feel a four stroke is more pleasurable to operate. No oil to be added frequently, less smoke and generally quieter.
- Greater demand if and when a four stroke needs to be sold.
- Power is power. A two stroke at 5500 RPM producing 150 HP is the same as a four stroke at 5500 RPM producing 150 HP.
- Perception is that a two stroke may have a better acceleration quality. I did not find this to be true in my transition from a two stroke to a four stroke. But then I am not a bass boater and don't jam my throttles to wide open whenever I go to get onto plane. It might depend highly on the application and the user.
- Economy is based largely on usage. Look at performance bulletins and you will see the RPM's and boat speeds that are most efficient. Does not change much between a two stroke and a four stroke. At cruise RPM's the four stroke may have a slight advantage.
- Almost any piston engine will consume in gallons approximately 10 percent of the rated HP at wide open throttle. So, a 150 HP will consume about 15 gallons an hour. A 350 HP will consume about 35 gallons an hour. Mr. Bolt noted this in his reply.

[rodbolt17]

my F150 on a 21 seapro CC has a hard top with a second station, hydraulic jackplate, on board charger and lenco tabs and holds 65 gallon of gasoline.
just me and a full tank, WOT at 5800 RPM gives a burn rate of about 15.5 GPH and a top speed of 43 MPH.
back it down to about 3400 RPM and play with the trim and the jack I can burn about 6GPH at about 31 MPH.

flow meters take all the fun out of boating .

but over the years the 1 GPH for every 10 HP at its rated HP is mostly universal.