QSB fuel burn/ load

[Fireisland1]

Can someone review my data sheet. I almost always run my boat at 2000RPM . But it is burning more fuel then the Cummins graph shows it should. I don’t care as it it very efficient but I do not want to do any long term damage. I don’t know if you can actually get an engine to burn the exact amount across the board. My data is very accurate and hardly changes with load and Sea condition. Is this typical ? 450 hour engine, all gauges are within spec. I do not have exhaust temp gauge but no excessive heat around exhaust or turbo.

Topic

[Rob Schepis]

Got to be realistic as he is running so far below the top, the engine won’t care..

Look at the 300 MCD curve.. Same exact engine.

[Joe Monaco]

Still pondering this. Anyone figure out why Tony responded to the OP that He is not overloading his engines when the data he posted shows him burning .5 to 1 gph above the OEM rpm/fuel burn curve.

[Joe Monaco]

Thanks Steve,

So you’re thinking because the data point is farther left on the curve that it’s not as critical? So slightly overloading < 1GPH on say a MAX HP @ 2800 RPM motor at 2000 RPM is not as bad as overloading 1GPH at 2500 RPM for the same motor because it’s farther away from its MAX HP rpm? The Motors under less stress overall at the lower RPM making calling for more than rated HP at that lower RPM less problematic? Could be..

[Steve Lewis]

That's a goppd question…..

Joe,

I am kinda wondering the same thing. Let me take a crack at interpreting what Tony has written about fuel burn and see if he or Rob agree, or if they correct us on this:

Since fuel burn does not increase in a linear fashion as you run the engine through the RPM range then the overage at each RPM needs to be looked at carefully. What I think Tony is indicating is that at 2000 RPM the fuel burn is low enough as compared to Rated RPM so that 7.4 GPH compared to 6.6 GPH @2000rpm is just not bad. HOWEVER as you advance through the RPM range, say to 2600, the engine fuel mapping is delivering a whole lot more fuel(almost double the amount) and that needs to be at or below the curve because you are getting closer to Rated RPM and power.

When off plane and cruising at hull speed, Tony has indicated that the burn really does not matter that much since you are not pushing the engine at all. Not demanding much HP. The QSB380 is rated at ~375HP so I guess demanding 148HP at 2000rpm is not that much in comparison and being a little over the curve down at 2000 is not a bad thing. If you are over the curve at 2400 or 2600, now you are getting close to being dangerous to the long term health of the engine as fuel delivery is ramping up at non-linear rates.

Tony and team, what say you??

[Joe Monaco]

Is the consensus if you are burning .5 to 1 GPH more than the manufacturers fuel burn curve you still are not overloading? I thought below the curve was the goal or are these numbers close enough?

Is there a GPH over spec that is the maximum allowed?

[Rob Schepis]

Tony Athens wrote:

Can you post a couple of pics of the riser/shower head you bought?

Tony

Here you go:

https://www.sbmar.com/community/topic/qsb-exhaust-out-with-the-old/

[Tony Athens]

Can you post a couple of pics of the riser/shower head you bought?

Tony

[Fireisland1]

Aftercooler serviced as per Tony. New custom shower head from Marine Manifold . Good to go. Thanks

[Tony Athens]

Don’t give it a 2nd thought–Your engine, running at these loads/2000 RPM, is a “happy camper”.. Worry about you aftercooler, your exhaust design, and “Marine Age’ in general, and all that come with that..

Tony

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