Specific Fuel Consumption- different engine types

[twistedtree]

It was multi-port electronic fuel injection. I think all but the smallest outboards are EFI today and I would expect those will also be EFI before too long. EFI eliminates many ethanol fuel problems since the entire fuel system is sealed. Carbs are vented which means that moist air can get in and screw with the fuel.

David

I was wondering if carbs might be the reason for poorer fuel economy, but I guess not.

Gotta love EFI for the reason's you mention. I have a Yamaha 40 that is EFI and love it. It's probably on even smaller engines now too.

 

[FF]

Folks looking to make efficiency part of the boats equation should look at the Mfg specs for all 4 engine loadings .

At times an engine can carry a good low RPM load and be able to have a far higher load , for a limited period of time, in hours.

The mfg of larger marine engines will have published tables and time limits ,

the auto ,tractor or lawn implement marinizations will not.

 

[DavidM]

I told you that my last post would be my last on this subject, but.... I saw a new boattest report on the newish 4.5 liter Mercruiser 250 hp v6 gas I/O engine and I had to see how the best of the automotive derived gassers stacked up against the O/Bs, so here goes:

The Mercruiser engine burns 20.2 gph to make its 250 hp and right out of the starting gate that is as good or better than any O/B I have seen at 12.4 hp per gph. Not too surprising as I am pretty sure that the O/Bs dump more fuel in at wot to keep pistons and valves cool given that the O/Bs usually are operating on 1/3 less liters so there is less cooling available to dissipate the heat.

It took just a slight tweak, less than 5% to get the boatdiesel calculator to match the 250 hp and wot speed of 40.5 kts. So looking at the 4,000 rpm midrange like the others I have checked, the Merc requires 134 hp to go 30 kts and burns 10.6 gph for a specific fuel consumption of 12.6 hp per gph. That is as good as the best O/B I have looked at.

I also ran a case at 3,000 rpm since that is a common cruising rpm for I/Os and it gave essentially the same specific fuel consumption as at 4,000 rpm.

Not sure why a V6 gasser with more liters than the equivalent O/B does as well as the best O/B as I would have thought that the parasitic load would be higher given more machinery going up and down and round and round. My new Mini Cooper has a tiny 1.6 liter turbo charged engine that gets better gas mileage than the 2.0 liter engine it replaced, so generally the smaller the engine the better the specific fuel consumption at the same power output (except for wot as discussed above where the EPA never checks emissions and an overly rich fuel/air ratio is a long standing trick for HO engines).

David

 

[twistedtree]

So Fiat had it right back in the 70s. Gas peddle to the floor and revs at the red line, or brake peddle to the floor, and nothing in between.

 

[DavidM]

Actually the Mini's 1.5 liter engine (sorry, I misstated it as 1.6 earlier) produces as much power and torque (but at higher rpms) than the 2.0 liter engine it replaces. Other than a bit of turbo lag, it gets up and goes just fine for this 71 YO former big block hot rodder.

Nothing at all like the old Fiats.

David

 

[Art]

In juxtaposition to our beloved, white, 67 Buick Wildcat... with 430 cid, 360 hp beast-engine... we also have a little white Prizm... we call Mini Me! LOL

 

[twistedtree]

Actually the Mini's 1.5 liter engine (sorry, I misstated it as 1.6 earlier) produces as much power and torque (but at higher rpms) than the 2.0 liter engine it replaces. Other than a bit of turbo lag, it gets up and goes just fine for this 71 YO former big block hot rodder.

Nothing at all like the old Fiats.

David

I suppose it's how one wants to drive it. I rented a mini for a few weeks some time ago and it was a blast. Full gas or full brake, and nothing in between.

 

[FF]

Turbo car engines feel great as they produce big torque at low RPM .

Econoboxes with 6 second 0-60 are great fun.

Boat engines frequently will need to operate at a fixed RPM and load for hours.

A turbo boat engine (car conversion) might have difficulty with endurance.

I am sure the outboard and IO mfg take this into consideration.

I would be reluctant to re chip a car engine outboard for "more" power .

The next generation of engines will probably be multi fuel , and about 1/2 the weight of current designs.

This should be great for speed boats , but even trawlers will enjoy the ability to carry a replacement engine on board, or up a flight of steps for an engine exchange.