Re: [Amel Yacht Owners] Re: Expected RPM at WOT

Rudolf Waldispuehl

Hi Gang
Very interesting and great thinking scenarios Dean made. Definitively worth to check!

Just for curiosity and for completion if someone is interested. I made same RPM test with and without load today. Test with AUTOPROP, Calm sea, little wind, no current. 
Interestingly my "no-load" turbo pressure number are lower than those reported from Dean (ink. 2 with 0 kPa on 1600/1800). I’m not an Engine-Engineer, so I can’t interpret the difference. 

For your reference, load test with AUTOPROP , RPM, temp. turbo pressure numbers :

RPM.  Temp  kPa
1400 78 10
1500 79 10
1600 79 20
1800 79 40
2000 79 60
2200 80 90
2400 80 110
2600 81 110
2800 82 120

My no-load (neutral) numbers are as follows:

RPM. temp kPa
1400 76 10
1500 76 10
1600 77 0
1800 77 0
2000 77 10
2200 77 10
2400 77 20
2600 78 20
2800 78 30
3000 78 30
3200 78 30 (WOT)


Von: <amelyachtowners@...> on behalf of "trifin@... [amelyachtowners]" <amelyachtowners@...>
Antworten an: <amelyachtowners@...>
Datum: Samstag, 1. September 2018 um 17:16
An: <amelyachtowners@...>
Betreff: Re: [Amel Yacht Owners] Re: Expected RPM at WOT


Further to my last ...

Here’s a scenario...

Let’s assume your boost sensor is reading higher than it should (faulty sensor) or the pressure IS higher than it should be (faulty Turbo?).
Let’s also guess that the software which reads this pressure signal reacts by limiting the rpm from going any higher when some max pressure value is reached, say 120/130kPa. (Seems like a reasonable reaction),

This scenario would produce the symptom you are seeing.

In the no-load situation, the boost pressure does not get high enough to limit the rpm, and it just tops out at 3200 as usual.
In the load situation the pressure (or pressure perceived by the sensor) reaches a maximum limit and the software prevents rpm from going any higher.

This could also explain the Autoprop effect you saw. The AP may have loaded the engine erratically, such that max boost was reached in an instantaneous way because of the erratic load and the software immediately tried to reduce rpm. The smoother load curve of the fixed prop would probably not affect the engine so dramatically.

Guesswork in the dark.


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