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lordy
13-05-2004, 08:18 AM
The question is "will a larger motor use more fuel go at the same speed?". ie would a 60 at full pace use less fuel than a 75/80/90 going at the same pace but reving lower?


cheers

dnej
13-05-2004, 10:50 AM
I have a 60 hp Mariner on a 17 foot aluminium cuddy cab. My brother has a similar boat but fibreglass, and a 75 hp Mariner. He runs at 3500 revs, and I have to run at 75% throttle to keep up with him, and I use more fuel.
Compare a V8 with a 6 cylinder. THen think about the type of work you do with the vehicle.
Hope this helps
David

NQCairns
13-05-2004, 10:51 AM
Hi Lordy it depends, what is the max rated hp of the hull?

Dnej, good comparison, are both those engines the same apart from hp? Who's is the fastest?

lordy
13-05-2004, 11:39 AM
I have a 60 hp Mariner on a 17 foot #aluminium cuddy cab. My brother has a similar boat but fibreglass, and a 75 hp Mariner. He runs at 3500 revs, and I have to run at 75% throttle to keep up with him, and I use more fuel.
David


so do you think he uses less fuel because his boat is better aerodynamically or because 3500rpm is more fuel effiecient/km?

loozitt
13-05-2004, 12:12 PM
I have two mates with excatly the same boat.

First mate runs twin 90 Honda 4 stroke - carby - cruises at 4500 rpm

Second mate runs twin 115 Merc 4 stroke efi - cruises at 3300 rpm

Outcome - fuel comsumption is practically the same, sometimes the hondas even chew slightly more.

The_Walrus
13-05-2004, 02:14 PM
All things being equal, for a set speed, a larger engine (within reasons) should use less fuel than a smaller one working harder for the same speed.

Luc

Big_Kev
13-05-2004, 03:56 PM
Far to many variables.
Some engines are more efficient than others in generating energy.
An engine from 25 years ago will only use about 25% of the fuel it burns to actually create energy to turn the prop,the rest is just waste.
Fuel injection and other developments will improve on this with dramatic effect.
But as for one of the questions I would say that the 60 being pushed harder will burn more fuel than the larger engine not being pushed as hard in the same application as long as the technology is the same.

peterbo3
13-05-2004, 04:08 PM
Hi Lordy,
There is probably not going to be a great deal of difference in the fuel used but a motor running at WOT all the time is not going to last as long as a bigger donk running at 3500-4000. This is where the larger initial cost is more than justified. You cannot beat large capacity motors working within their cruising rev band.

lordy
13-05-2004, 06:10 PM
Thanks guys. Looks like bigger is better with in reason.