fuel consumption

[1983 ercoa 21']

How much has it improved over the years?
cross flow vs looper?
looper vs fict?
fict vs etec ?
I believe the old rule of thumb was horsepower x10% equals gallons per hour.
does this still hold true?

 

[Chris1956]

Efficiency of the outboard motor has usually improved over the years. Crossflow motors had 1 transfer port and had to "blow" the spent fuel(exhaust) out of the exhaust port, at the sacrifice of fresh fuel/air going out the exhaust. Loop charging adds efficiency by using up to 4 transfer ports to sweep the exhaust out of the cylinder. Less fresh fuel is needed to sweep out the exhaust.

Direct Injection motors use air (no gasoline) and some oil to sweep out the exhaust, and then at the top of the compression stroke, add gasoline to make the power. So the efficiency of these type of motors is a lot better, rivaling the 4 cycle motors.

It is hard to use the old efficiency rule, as normally we do not run at WOT. Efficiency changes by hundreds of percent, depending on how the motor is run.

 

[1983 ercoa 21']

So at wit a cross flow 150 will use 15 gph
looper 150 ?
direct injection?
how much improvement % wise has been made with the changes of designs?

 

[Chris1956]

It is hard to generalize, however, if you ran a 150HP cross flow at WOT for an hour, the motor would approach 15GPH. If you ran a 150HP looper and a 150HP DI motor at WOT for an hour, the fuel used would be less, but probably not much less. Part throttle use of the DI motor would see a 40% efficiency increase (my estimate) over the looper, and the looper would see some smaller efficiency (10-15%?) increase over the cross flow.

If you investigate the efficiency claims of the DI motors, you will see the hype the manufacturers are publishing. I expect it will be inflated over actual, but will be in the ball park. The other good news is that less gasoline used means less oil used. Especially in the DI world, where the amount of gasoline used is not directly linked to oil used.

 

[1983 ercoa 21']

I run a cross flow now and was just wondering if in time a upgrade would pay for itself or not.

 

[Chris1956]

Trading in a crossflow for a new DI motor would cost $15K+, as you will not get much for your motor. If you use lots of fuel per year, it could pay for itself. Lets say you use 1K gallons/year of fuel, and the efficiency difference is 50%. (both of these numbers are inflated to make a point).

So with a new motor you save 500 G of fuel @ $3.00/gal per year. So that is $1500 savings per year. Your new motor will break even in about 10 years.