Engine Load Comparisons WOT vs Surfing

[oldjeep]

On 3/15/2024 at 8:28 PM, dizzygti said:

I understand everything you're saying,  I'm a mechanical engineer and gear head so this is all familiar.  I also play with turbo engines in toy cars so I understand manifold pressure vs atmospheric.   However, as I said, this "IS" WOT on my boat.   The accelerator pedal (lever) is as far forward as it will mechanically go.   The engine is limited to 5600 rpms.  Not sure what else to tell you.  

WOT is a spec provided by the engine manufacturer in terms of a max RPM (range)  has nothing to do with where your throttle lever is.

[dizzygti]

Just now, oldjeep said:

WOT is a spec provided by the engine manufacturer in terms of a max RPM (range)  has nothing to do with where your throttle lever is.

"WOT" is a non technical term and refers to the throttle plate being full opened.  Yes, it has nothing to do with the throttle lever.   The point is the throttle plate position is ECU controlled in a DBW throttle and will not always match "accelerator pedal" or throttle lever position.   I can't make the engine sit at throttle plate = 100%.    

[oldjeep]

Just now, dizzygti said:

"WOT" is a non technical term and refers to the throttle plate being full opened.  Yes, it has nothing to do with the throttle lever.   The point is the throttle plate position is ECU controlled in a DBW throttle and will not always match "accelerator pedal" or throttle lever position.   I can't make the engine sit at throttle plate = 100%.    

WOT is in your engine manual (or at least it was when indmar was building the engines)

[dizzygti]

Just now, oldjeep said:

WOT is in your engine manual (or at least it was when indmar was building the engines)

No, it's not.  I've looked....

[oldjeep]

37 minutes ago, dizzygti said:

No, it's not.  I've looked....

Yeah, I looked and there is no engine manual for the Malibu mfg engines   The boat manual mentions WOT 5 times, but not in relation to RPM or prop selection like the old Indmar engine manuals.

[dizzygti]

3 minutes ago, oldjeep said:

Yeah, I looked and there is no engine manual for the Malibu mfg engines   The boat manual mentions WOT 5 times, but not in relation to RPM or prop selection like the old Indmar engine manuals.

Yeah, I searched both the Axis and Malibu manuals for 2023, no mention of sustained rpms, high rpms, prolonged rpms, max rpms, high speed, max speed, sustained speed, prolonged speed, etc.   

Edited March 22 by dizzygti

[EchelonMike]

Lots of good discussions here.  I measure WOT as the TPS value = 100%.  I am sure if you watch your screen and pin the throttle from idle, you will see a TPS value at (or close) to 100% as the boat accelerates.  For those of you running low pitch props, you are effectively lowering your gear ratio and you won't need 100% of throttle/TPS to bang into the rev limiter.  

I just ordered a 2805 (arrived today) from Prop Depot for my 2022 23 LSV and I'm hoping that at 5,500 to 5,600 RPM, I am 90%+ on TPS.  I'll run factory ballast + PNP and see how she does at both surf, cruise and WOT/redline.

 

[justgary]

On 3/22/2024 at 6:54 AM, dizzygti said:

I can't make the engine sit at throttle plate = 100%.    

Put about 20 more people in your boat.  I have no doubt you can get to 100% with enough weight.

The concept of you trying several different props and posting the same data at surf, cruise (pick one speed), and WOT is very interesting, though.  Even better, give us data for every 200 RPM from surf to WOT.  The load in the boat has to be the same though, so no beer until you get done!

[dizzygti]

3 hours ago, justgary said:

Put about 20 more people in your boat.  I have no doubt you can get to 100% with enough weight.

Thinking this combo will do it.

I'm not worried about getting to 100%, that's what you want to see.  I wanted to show that there is no more load at full speed (since I can't request more) than there is surfing loaded.   I will compare with the new prop though. 

Edited March 24 by dizzygti

[justgary]

38 minutes ago, dizzygti said:

I wanted to show that there is no more load at full speed (since I can't request more) than there is surfing loaded.   I will compare with the new prop though. 

I suspect that if you add pitch you will add top end speed as well, and it will still be safe for your engine at your current cruise speed.