Cummins Marine Diesel Repower Specialists › Forums › Cummins Marine Engines › Not getting RPM at WOT
- This topic has 38 replies, 5 voices, and was last updated 6 years ago by Tony Athens.
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May 6, 2017 at 8:58 am #18290
Hi everyone. Here are some details:
6BT 210’s pushing a 33 foot Riviera
Props freshly tuned by wilmington
2800 hours
well maintained and not abused.
I can easily get 2700 RPM ++ in neutral at the dock with no smoke. Underway I make 2400 and 2500 (Port/Star) with no smoke. Racors are fresh and clean.
Am I overpropped or am I overlooking the obvious?
Thanks all.
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December 31, 2017 at 7:17 am #26704
Tony AthensModeratorVessel Name: Local Banks
Engines: QSB 6.7 550 HP
Location: Oxnard, CA
Country: USA
Steve,
Your propping / engine load at 2600-ish is really good–Your are “by the book” with a QSB 5.9 380 meaning you have lots of reserve if you add some weight or want to run at 2800-2900 for an hour or two .. It’s good to check WOT numbers for a minute or two each time the weather presents the opportunity on your trips..
Keep your aftercooler on a 2 yr max service cycle unless you fresh water flush– then you can 2-3X that..
Go fishing & enjoy the New Year.
Tony
December 30, 2017 at 7:53 pm #26691
SteveParticipantVessel Name: Cabrillo
Engines: QSB 5.9 425hp
Location: Huntington Beach, CA.
Country: USA
Today we got 12.5gph @ 2610rpm and 16.7k sog. 2550 rpm gave 11.9gph and 16.2k sog.. The 2500-2600rpm giving 16-17knots felt really good. The engine felt comfortable and smooth and that speed was just fine. I recorded data for various rpm from 2400-2600 but the 2500-2600 has the best overall boat feel and the 12-13gph looks pretty good to me.
Happy New Year Gentlemen. Thanks for all your expertise and advice.
SteveDecember 30, 2017 at 8:30 am #26674
Tony AthensModeratorVessel Name: Local Banks
Engines: QSB 6.7 550 HP
Location: Oxnard, CA
Country: USA
Early QSB 5.9 425
IMO, their really is not and optimum RPM other than what is comfortable.. If you need 280-300HP to make your boat travel at 17.5 Kts (14-15.5GPH), then your engine is way happier making that power at 2600 RPM than it is at 2400 RPM…. Propping a high output engine like this really needs to based on the power you need to CRUISE at, not just where you are at WOT.. Look at the Prop curve on the attached data sheet.. This is your engine–An early QSB 425..
So what is your GPH at 2600-2650 RPM? That is the key to proper engine loading in your case. The prop curve shows 14.6 -ish GPH..
Tony
December 30, 2017 at 8:12 am #26673
SteveParticipantVessel Name: Cabrillo
Engines: QSB 5.9 425hp
Location: Huntington Beach, CA.
Country: USA
By “Optimal” I was looking for a safe RPM ceiling for general purpose cruising. For us that’s primarily the 26 miles to Catalina Island. With our old “over propped prop (23DX26P), we’d make about 17.5 knots at 2400 RPM. With our corrected prop (23DX24P), 2400 RPM gets us about 14.5 knots. I was looking to see if I could bump up the RPM to get back a little of the speed. Tony’s last post helped me with that.
Although your approach is truly the best. Now that we’re propped correctly, I’ll start plotting our performance, comparing it to the Cummins data and determine our boat’s true sweet spot based on the data.
December 30, 2017 at 8:00 am #26672
SteveParticipantVessel Name: Cabrillo
Engines: QSB 5.9 425hp
Location: Huntington Beach, CA.
Country: USA
Sir,
All the throttle readings came from the SmartCraft DieselView LCD display. The throttle lever “all up” was confirmed as 100% on the display. I can get photos if you’d like them.
Here are our Serial Numbers
Engine: QSB 5.9 425hp #46709654
Trans: ZF85A 20 1.96:1 #30027PYes the boat was our standard Catalina Island load, RIB/outboard, full fuel, full water etc. 2650-2700…that’s higher than I guessed….although I gotta say our engine sounds tight and strong when at WOT. Just a low smooth rumble with purpose. I’ll still most likely keep it between 2400 and 2600 though…We’re never in that much of a hurry and I like to think I’m soft on the engine.
Thanks for Everything and have a Happy New Year !
SteveDecember 30, 2017 at 7:59 am #26671
Rob SchepisForum ModeratorVessel Name: Tenacious
Engines: 6BTA 5.9 330's - "Seaboard Style"
Location: Long Island, NY
Country: USA
Optimal?
What do you mean by optimal? How hard you can safely “push” the engines? Or best cruising speed? You should plot your GPH and SOG at the rpm increments of the printed data from Cummins. At each rpm, calculate your MPG as SOG/GPH and see where she does best.
December 30, 2017 at 7:08 am #26670
Tony AthensModeratorVessel Name: Local Banks
Engines: QSB 6.7 550 HP
Location: Oxnard, CA
Country: USA
If the numbers you posted represent the vessel fully loaded as you use it, then you can safely run at 2650-2700 RPM or less, if you need that speed–You are propped to about a QSB 380 based on your numbers……A Good place to be
One thing to check– When you say 100% throttle, it that the % number from the digital instruments, or in that just your “throttle lever” travel to the stop.. At that WOT GPH, your engine should go to about 3080+ RPM. You can check that at the dock, engine OFF, but ignition/instruments on.
What exact instruments do you have? Got a picture of the dash? Also, post you serial numbers..
Tony
December 29, 2017 at 8:53 pm #26665
SteveParticipantVessel Name: Cabrillo
Engines: QSB 5.9 425hp
Location: Huntington Beach, CA.
Country: USA
Pitch Reduction – New Data – Optimum Cruise RPM?
Sirs,
Wilmington Propellers reduced my pitch by 2″. We are now running a 23D24P on our 2008 Back Cove 33. Here are my new numbers:
2430 RPM. 10.6GPH. 60%Load. 74% Throttle
2500 RPM. 11.2GPH. 60%Load. 77%Throttle
3050RPM. 18.2GPH. 81%Load. 100%ThrottleShe easily runs up to 3050 RPM at WOT and stays there. I’m hoping we’re dialed in now. I used to cruise at 2400RPM because I heard somewhere that 80% of WOT is generally where you should always run the engine.
My question is – What Is The Optimum Cruise RPM for my 2008 QSB 5.9 425hp? Is the “Load” a factor or is it a simple 80% of WOT?
Thank You,
SteveNovember 27, 2017 at 8:48 pm #25645
SteveParticipantVessel Name: Cabrillo
Engines: QSB 5.9 425hp
Location: Huntington Beach, CA.
Country: USA
Got it. Thanks Tony. I appreciate it. I’ll tell Gary you said hello as well.
Thank You
SteveNovember 27, 2017 at 8:27 pm #25643
Tony AthensModeratorVessel Name: Local Banks
Engines: QSB 6.7 550 HP
Location: Oxnard, CA
Country: USA
Vessel specs =
Make, model, best guess as to weight, current speeds & RPM’s , and anything else he asks about it’s current performance/condition….
Tony
November 27, 2017 at 8:01 pm #25642
SteveParticipantVessel Name: Cabrillo
Engines: QSB 5.9 425hp
Location: Huntington Beach, CA.
Country: USA
When you say my “vessel specs,” do you just mean year/make/model or is there additional info I should have ready?
Thank YouNovember 27, 2017 at 7:48 pm #25641
Tony AthensModeratorVessel Name: Local Banks
Engines: QSB 6.7 550 HP
Location: Oxnard, CA
Country: USA
For propping purposes, when Gary asks, tell him this as to the engines rating:
You have 420 BHP at 3100 RPM....
Then tell him your vessel specs and the RPM you are getting now..
Be sure your prop is “tuned” to Class 1 specs or better..
Tony
November 27, 2017 at 7:06 pm #25637
SteveParticipantVessel Name: Cabrillo
Engines: QSB 5.9 425hp
Location: Huntington Beach, CA.
Country: USA
Copy that loud and clear. I’ll be taking the prop into Wilmington this week. Thank You…
November 27, 2017 at 6:50 pm #25633
Tony AthensModeratorVessel Name: Local Banks
Engines: QSB 6.7 550 HP
Location: Oxnard, CA
Country: USA
May I ask where you have been doing any research or getting info as to proper loading for this very fine engine?
Close enough? Where did that come from?
Your numbers are scary as you are operating your engine is a grossly overloaded condition..
This engine, for PROPPING purposes, needs to see 3080 RPM, and see it EASY..
Until you pitch down to do that you are not only leaving performance and overall fuel economy on the table, you are thermally overloading your engine to where you risk early catastrophic damage..
Tony
November 27, 2017 at 5:31 pm #25630
SteveParticipantVessel Name: Cabrillo
Engines: QSB 5.9 425hp
Location: Huntington Beach, CA.
Country: USA
What is Close Enough? Or is There Such a Thing?
I’m going to jump on board the WOT/RPM Topic please…..
We have an 2008 QSB 5.9 425hp. Per the Performance Chart, we should get 11gph at 2400rpm (our preferred cruise speed) and WOT is 3000 rpm.
With a regular load of fuel, water and people, I get 14 gph at 2400 rpm and make 2850-2880 rpm at WOT. It will flicker up to 2900 but not for more than a few seconds. This is with a clean bottom on calm seas.
Am I overthinking it to view the 14gph vs 11gph as an indicator the engine may be working too hard? Same with the 2850 vs 3000 at WOT?
Is there such a thing as “close enough” or is anything less than performance chart numbers unacceptable? My current plan is to reduce pitch (we have a 23D 26P) but I’d like to confirm if I’m thinking correctly or if I’m overthinking unnecessarily.
Thank You Gentlemen….
November 22, 2017 at 9:22 pm #25510Thank You!
Thanks again Tony. Have a great Thanksgiving!
November 22, 2017 at 6:19 pm #25505
Tony AthensModeratorVessel Name: Local Banks
Engines: QSB 6.7 550 HP
Location: Oxnard, CA
Country: USA
Henry,
You “done good”, really good!…………………Just for those reading and really want learn this particular version the the Cummins B 5.9’s.. This engine performs best if it actually sees a tad over an accurate 2700 RPM when propped for all it can give, and still comes back for more..
Thanks again..
Tony
November 22, 2017 at 5:26 pm #2550235 Hour follow to this post
HI all- I just wanted to give a follow up to this thread after 35 hours of running. To save you the time of reading the whole thing, I was over propped and it wasn’t good. I had 2 inches of pitch taken out and now I can easily achieve 2600RPM (P) and 2600+RPM (S) on these 6BT210.
What have I noticed?
1) Better fuel economy
2) No more black soot on my transom
3)Lower operating temperature.
4) Quieter- By a lot!
5) Smoother at cruise, less vibration because less load on engine.
6)Better speed in the higher RPM zone (say 2300-2400) MUCH better speed!All I can say is when Tony talks about being overpropped listen to him. Having the proper prop pitch is so important in having your engines run the way you want them to! It took me lots a trial and error but is was so worth it!
August 22, 2017 at 8:35 pm #22146Thanks Tony- It’s been a great education and I will shoot for 2750!! What a difference proper pitch makes. All the difference in the world!
August 19, 2017 at 8:50 pm #22035
Tony AthensModeratorVessel Name: Local Banks
Engines: QSB 6.7 550 HP
Location: Oxnard, CA
Country: USA
Glad all worked out 98%……………………………You still have left some HP and performance on the table, so next time out, lets shoot for 100++ percent.. A tad UNDER PROPPED never hurts..
Tony
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