QSB 330 performance question

[Kevin Murphy]

First time posting. I have read through a ton of posts and articles regarding increasing HP on the QSB 330 to 380 which then pointed me in the direction of determining whether my 330s were performing properly today.

So, I did a performance test and the results were far below specs (gph at all rpms and lower WOT rpm) and also below an online review of my boat (Meridian 368) that I found online.

From the articles there are a number of steps to check before pinpointing the cause, so my question today is simple – does the fact that the engines reached a WOT rpm of 2880 in neutral rule out some of the possible causes of it only reaching 2650 under load? Meaning, I don’t need to check the tach for accuracy or condition of after cooler and i don’t have a fuel delivery issue because the engine obtained desired rpm at WOT in neutral and I can jump straight to being overpropped or hull condition or weight as the cause? Or that’s just one metric but doesn’t rule out ways the fuel delivery could could result in a high gph or lower WOT rpm.

Thanks much

Topic

[Tony Athens]

What kind of tach do you have?

Pictures of the display?

No load RPM in neutral?

If what you are posting is accurate, you engines are a solid 200RPM+ over propped and you are asking them for something they will not or cannot give.

At an accurate 2400, GPH should be a 11 gph as you noted

[Kevin Murphy]

Thanks – this is what i measured the other day, but per other posts and articles, i need to verify tach, service aftercoolers, and check fuel input, so I am assuming the below is premature. If i understand correctly , if i do the above and results are pretty much the same as below then it’s a boat / prop problem and not an engine problem.

Cummins 18-Aug-21
Chart Port Star
RPM GPH GPH GPH
600 0.4 0.4
1000 1.3 1.2 1.2
1200 1.8 1.7
1400 2.7 2.9 2.8
1600 4.7 4.3
1800 5.4 6.9 6.6
1900 8.4 8.1
2000 6.9 9.6 9.3
2100 10.9 10.7
2200 8.9 12.2 11.6
2300 12.8 12.5
2400 11.0 13.7 13.6
2500 15.0 15.2
2600 13.4 16.1 16.3
2650 (WOT) 16.2 16.4

[Tony Athens]

Post accurate GPH #’s under your fully loaded conditions at 2200, 2300, 2400, & 2500 RPM.. Then you’ll get an answer of where you really are….

Tony

[Fireisland1]

WOT in neutral and under load are 2 very different things. Read every tip and trick on this site. I did and learned a lot

[Author]

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