How to Calculate Engine Load...without diesel view

1000islander

1000islander

Member
Jul 9, 2007
115
1000 Islands
Boat Info
420 Sundancer
Engines
Cummins
Now that my engine is back together and has been re-propped down and inch, how do I go about calculating engine load. I have a 480ce engines without diesel view. I am very close to what Cummins recommends for fuel burn, I am within .4 gph @ cruise and get better the faster I go. I would feel better if I could get a formula to calculate engine load, if there is one. It seems the higher RPM I go the better the fuel burn rate is compared to the Cummins fuel burn charts. The higher RPM GPH indicate that I am below the recommended fuel burn, which I think translates to a lower load percentage? Better for the engine. The fuel burn with the old props were consistently ABOVE the recommended burn rate(by 2gph and climbing the higher the rpm went).

Any thoughts?
 
Might be a better question for Boat Diesel, but I think the fuel burn curves and WOT RPM is the best indicator of load even with Diesel View.

Yes, lower burn at each RPM would indicate lower load than "rated" which is a good thing as long as you are not over the max WOT RPM specified for that engine which I believe is 2685 RPM and under the rate RPM of 2600.

An under-loaded engine is almost as bad as an overloaded one.
 
I'm way under Cummins fuel rate table at lower and high rpms. I typically cuisine around 2600 rpms and burn around 14.8 gallons an hour. That is close to 2 gallons more than the Cummins burn rate but according to Vessel View I am at 64% engine load.
 
JBJ said:
I'm way under Cummins fuel rate table at lower and high rpms. I typically cuisine around 2600 rpms and burn around 14.8 gallons an hour. That is close to 2 gallons more than the Cummins burn rate but according to Vessel View I am at 64% engine load.
Click to expand...

What are the boost and EGT numbers?
 
trit21 said:
Please explain why an under loaded engine is as bad as an overloaded engine.
Click to expand...

Should have clarified or dropped that line, meant a severely under-loaded engine, which I highly doubt he is running into.

Everything I have ever read about diesels says keep within design parameters and you can expect a long happy life with good maintenance.
 
swaterhouse said:
Might be a better question for Boat Diesel, but I think the fuel burn curves and WOT RPM is the best indicator of load even with Diesel View.

Yes, lower burn at each RPM would indicate lower load than "rated" which is a good thing as long as you are not over the max WOT RPM specified for that engine which I believe is 2685 RPM and under the rate RPM of 2600.

An under-loaded engine is almost as bad as an overloaded one.
Click to expand...

I did pose the question to Boat Diesel. They recommend propping the boat similar to a 450 Cummins. So based on that I would still have to come down to maybe 25.5 or even 25" props. They also said under propping the boat was nearly impossible as the electronic governor would keep the engine from over revving. The motor currently runs WOT at 2690 with the 26" props. When it had the 27" props it would do 2650ish. I really think it is quite close to where it needs to be, my new cruise rpm is 2200 up from 2100, the fuel rate at 2200 is right on the recommended fuel curve for the 480. As I go higher the burn rate falls below the curve, similar to the 450 Cummins. Changing props get pricey. I would really like to know how the engine load is calculated, boat diesel did not answer that question. I would also like to install a Diesel view on the boat, but am not sure it is possible. The engine data is available from the ECM, the Cummins tech was able to view through the diagnostic port at the dash, so I think it should be available to connect to a diesel view?
 
OK, I'm going to ask a really dumb question.....

Why is it important to know the engine load on a diesel. I'm assuming with mine that when I run at hull speed ( ~950-1000 rpm's) they are underloaded and engine temps are about 135*-145*, but still they're pushing about 58,000 lbs through the water. When I'm running on plane ( ~1750 rpm's) I'm running about 22kts and the engine temps climb up to about 155*-160* and I assume the engines are neither under- nor over-loaded. WOT is at 2150 rpm's, speed is about 30.5kts and temps are up to about 165*-170* and I assume the engines are a bit over-loaded.

Am I correct in those assumptions? And why is it important to know how much the engines are loaded at any given rpm?
 
The "load" factor tell how hard the engine is working. I monitor fuel flow, the engine is designed to produce xxx power at a given rpm and x GPH. If the engine has to use more fuel at a given RPM then the spec calls for then it is assumed to be overloaded. more fuel = more power. The engine is rated for a specific fuel flow at a specific rpm to produce rated hp. If it requires more fuel to reach rated rpm than it is working harder then it was designed to do. The engine coolant temp is not a good indicator of an overloaded condition. My motor that failed was running at its' normal temp of 163, yet it seized a piston. EGT is a better indicator I think. But by the time the EGT is higher it may be to late. Therefore the load of the engine and gph should be monitored....or so I am told.
 
I will try to get the numbers this weekend. I do know that I can hit the rev limiters 3385 rpms at 95 % engine load
 
Here are my numbers before/after the prop change from 27" to 26" The Spec column is what Cummins recommends for the 480ce engine is, the other 4 are for port/starboard. After 2200 rpm with 26" props, the fuel burn falls below the Cummins spec. Which I think indicates the engine is more efficient and is NOT overloaded. With 27" props the fuel burn exceeds the spec at nearly every RPM plotted and climbs as I go faster. I only plotted to 2400, the max rpm is somewhere around 2680/90 with 26", and 2600 with 27" props. I am a bit gun shy with the new parts in my port motor.

RPM 27 Port 27 Stb Spec 26 Port 26 Stb
800 1.4 1.3 1.2 1.1 1.3
1000 2.3 2 1.9 1.8 2.1
1200 3.9 3.5 3.0 3.4 3.1
1400 5 4.9 4.5 4.7 4.4
1600 6.8 6.8 6.4 6.3 6.3
1800 9.4 9.7 8.5 8.1 8.7
2000 12.8 12.9 11.2 11.3 11.6
2100 14.4 14.3 12.5 12.9 12.9
2200 15.8 15.6 14.5 14.5 14.2
2400 20.8 19.8 19 18.5 17.6
 
The best ( but not fully correct ) way to determine your engine load is to compare your actual fuel Flow at a given rpm vs the manufacturer published fuel flow at full throttle at the same given rpm. Divide your numbers vs the full throttle numbers and you will have a roughly load in % at a specific condition. Its not fully correct since the full throttle specific fuel consumption is not the same aa part throttle specific fuel consumption but good enough for anything that may be of interest for a skipper.
 
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