D12 Turbo Boosts at various RPM

[jrudge]

I cant find this on line. Does anyone know the speficied boost at a given RPM? I appreciate this will vary a bit with sea state as this is how it keeps the revs static ( I can see the boost rise up a wave or change as you turn)

This is part out of interest and part that I am using ( according to the reported fuel consumption ) more than the curves say on the engine spec. Again I know this is probably as reliable as a VW on a rolling road, but I am using lots more! So a comparison of expected boost would be useful.



Thanks


Jeremy

 

[petem]

I cant find this on line. Does anyone know the speficied boost at a given RPM? I appreciate this will vary a bit with sea state as this is how it keeps the revs static ( I can see the boost rise up a wave or change as you turn)

This is part out of interest and part that I am using ( according to the reported fuel consumption ) more than the curves say on the engine spec. Again I know this is probably as reliable as a VW on a rolling road, but I am using lots more! So a comparison of expected boost would be useful.

Thanks

Jeremy

Does it vary with sea state? Surely for a given RPM there is n litres of exhaust gas generated that will spin the turbo at n RPM generating n PSI of boost?

Therefore the only variables are the RPM and temperature of the exhaust gas (queue Portofino)?

Are you trying to ascertain the condition of your turbos?

 

[jrudge]

Think of it as a car on a motorway at 2000 rpm.

Go uphill, you apply more throttle but the RPM is the same.

The boat governs RPM. Load changes on the prop, governor opens the throttle to keep RPM static, fuel consumption and boost goes up.

Turn to one side or another, one engine can be laser than the other but the RPM remains static.

Yes re turbos. I have no issues I know of, but the boost without a reference is no use. They are the same give or take the odd bit of decimal point, but again that could be the electronics.

 

[Portofino]

Pete s on the right track .
What changes with sea state is the boat speed that’s all .
Once set at a rpm the engine load ( that’s different ) and turbo boost of the engines stays the same .
The props are underwater happy as Larry turning away neither the props or the engines know anything about “ waves “ in front , upwind, down wind big or small

 

[petem]

Yes re turbos. I have no issues I know of, but the boost without a reference is no use. They are the same give or take the odd bit of decimal point, but again that could be the electronics.

Incidentally, I'm told that Universal Turbos in Fordingbridge can recondition VP turbos (at least for my engines) http://www.universal-turbos.com/ and insert sleeves where the casings have 'worn' away.

 

[Portofino]

The turbos are truck based engineering like the rest of the D12 so they don,t suffer corrosion like the less powerful dedicated marine VP dervived engines like yours Pete .

Here’s some hopefully useful fuel deltas from mine .
Not VP , D12 715 ,s but 12.7 L straight 6 ,s rated at approx 700 Hp —— so a reasonable forum ballpark idea of typical burn rate .
The last pic is a boost pressure looks like 1.7 bar @ about 1700 or 1780 rpm .

Seriously nothing changes on the 4 screens at a set rpm in any sea state - as said the knots change a bit - as the sea flattens waves decreases s the knots increase , or as the state worsens waves increase they drop a bit

The waves create more drag , bigger primary resistance wave , change the AoA , etc etc temporarily.
The props / engine are oblivious of what the hull is doing or the effect of water / wave are doing on the hull .

https://imgur.com/a/Gnd2qs1

 

[MapisM]

I don't think it's so obvious that the boost remains constant for any given rpm.

As we all know, engines can produce a variable amount of power at any given rpm, depending on their load, which can be affected by several variables.
For instance, just to stick to PF example, each of his engines can produce up to 570hp at 1600rpm (full load), which obviously is not what is happening in his first pic, because he would be burning some 120 instead of 70 lph, with 100% instead of 71% load.
And of course, he would burn/produce even less (MUCH less!) if he would be spinning at 1600rpm in neutral.

So, I suppose there MUST be a difference in the exhaust volume, to generate almost 600 vs. 60 (or even less, whatever) ponies.
And higher/lower exhaust volume = higher/lower boost, I reckon?

 

[Portofino]

Fuel consumption
How are you measuring it ?
What control are you using to think it’s excessive?

Generally excess kg,s weight and fouling are the enemies of fuel burn for a given speed at @ given rpm .
We don,t know where you are with those .
If you had load instruments you would see the load rise .

 

[Portofino]

I don't think it's so obvious that the boost remains constant for any given rpm.

As we all know, engines can produce a variable amount of power at any given rpm, depending on their load, which can be affected by several variables.
For instance, just to stick to PF example, each of his engines can produce up to 570hp at 1600rpm (full load), which obviously is not what is happening in his first pic, because he would be burning some 120 instead of 70 lph, with 100% instead of 71% load.
And of course, he would burn/produce even less (MUCH less!) if he would be spinning at 1600rpm in neutral.

So, I suppose there MUST be a difference in the exhaust volume, to generate almost 600 vs. 60 (or even less, whatever) ponies.
And higher/lower exhaust volume = higher/lower boost, I reckon?

I was thinking set rpm to cruise at what ever speed , over a period of few hours .

I think you are thinking the whole range , dock , pootle D and P etc .
Turbos operate in a range below which say for me under 1200 rpm they have zero or .1 or .2 boost .
However when they start to spool up over 1200 rpm suddenly I see 0.8 then at 1500 1.6 ( doubled in 300 rpm ) then
Gradual to about 1.8 ish @1900 when presumably the waste gate starts to open ,further rpm increasing to WOT shows insignificant rise in boost as the waste gate dumps the excess .
It’s not linear ,buts it not a All or nothing either , more a big rise “boost “ from 1200 to 1500 as the turbos spool up and the boat speed rapidly increases .
I don,t think the boost pressure has anything to do with apparently reported excess fuel burn .
Btw the EGT rapidly rise from below 250 to over 500 - 560 ish too in seconds when reving up from 1000 to 1800 or what ever .
But as said turbos are not the cause of reported excess fuel burn .

What we need to know from Jez is what rpm and speeds he’s cruising at and go from there, with some indication of the measuring accuracy?

 

[MapisM]

How are you measuring it ?

LOL, I was referring to your engines, not mine (cue "just to stick to PF example").
All my previous numbers were taken either from your pics or MAN specs.

Anyway, with P boats, ignorance on fuel burn is bliss, I'm beginning to think...

 

[MapisM]

I don,t think the boost pressure has anything to do with apparently reported excess fuel burn.

I didn't say it does, I was just thinking that theoretically it could.

And it ain't a matter of "excess" fuel burn, btw - I was just considering the simple fact that it takes more fuel to produce a 570hp output at 1600rpm (which your engines are capable of at 100% load, according to MAN specs), rather than half of that or whatever at exactly the same rpm.
In other words, I'm not thinking of how your boat (or any other, for that matter) behaves "normally" at any given RPM.
I was just comparing your "normal" 1600rpm situation with a theoretical one where you are using 100% load. Think of towing another vessel, for instance.
If in that situation you must squeeze from your engines all the 570hp they are capable of, I would think that the boost pressure might well get higher, compared to the same rpm in a "normal" situation.

A topic for LS1, I reckon. Happy to be erudited, if by chance he's reading this.

 

[Portofino]

LOL, I was referring to your engines, not mine (cue "just to stick to PF example").
All my previous numbers were taken either from your pics or MAN specs.

Anyway, with P boats, ignorance on fuel burn is bliss, I'm beginning to think...

We looking like a bowl string here .

I was addressing post # 8 @ the Op Jez , not you P —-

 

[MapisM]

We looking like a bowl string here .

I was addressing post # 8 @ the Op Jez , not you P —-

Aha, ok. The OP ain't Jez, though...

 

[Portofino]

I didn't say it does, I was just thinking that theoretically it could.

And it ain't a matter of "excess" fuel burn, btw - I was just considering the simple fact that it takes more fuel to produce a 570hp output at 1600rpm (which your engines are capable of at 100% load, according to MAN specs), rather than half of that or whatever at exactly the same rpm.
In other words, I'm not thinking of how your boat (or any other, for that matter) behaves "normally" at any given RPM.
I was just comparing your "normal" 1600rpm situation with a theoretical one where you are using 100% load. Think of towing another vessel, for instance.
If in that situation you must squeeze from your engines all the 570hp they are capable of, I would think that the boost pressure might well get higher, compared to the same rpm in a "normal" situation.

A topic for LS1, I reckon. Happy to be erudited, if by chance he's reading this.

Agree
But Jez has not ( Yet ) said he,s towing here .

Aside as said ^^^^ excess kg and fouling will have the effect as you describe, which is not as obvious as towing a boat behind

As the season progresses the - % load increase for a given speed for me .
Just fouling particularly props .Even after a good DIY scrape say in August / Sept , they are never as clean as say in May .
Early May having had a lift and acid clean of ALL the stern gear ,that’s P brackets and shafts and whole rudders .
I notice the L/ h increase same as the load .

It’s vital in the Med in the high season ( warmer water = rapid growth) that you pay attention to stern gear hygiene.
Your doing your engines no favours in the absence of load gauges attempting to run at what you think should be normal cruise with fouled stern gear for long periods .

In the absence of load gauges or if you can,t get the sterngear clean ( for what ever reason ? ) you could do short WOT to determine V max then run a lot lower .
Eg fresh in after annual @ Easter typical 50 ft FB - 15 years old WOT is 31 knots cruise 24/25
August with 6 week gaps between visits / use - now WOT is 25 knots if that .
So you should cruise at below 20 say 18/19 until the stern gears been cleaned up imho

But what’s happening if the owner mentally only knocks a knot or two off ?
Say sets cruise at 23/24 - the rpm seems from memory the same ish ? , buts he’s on the cusp of overload way up in the high 90,s % near 100 % with the coresponding increase in fuel burn - mpg etc ?

Or worse still the rpm seem the same ish cos it can,t actually rise much further from 100. % load due to the fouling or excessive extra Kg,s ?

 

[Anders_P42]

It makes sense the boost will fluctuate dependant on sea condition, if the engine load increases slightly as you plough through a wave rather than planing on top of it.

The ECU senses extra effort required to push through wave, dumps some extra fuel in which creates larger explosion in engine which in turn makes turbo work harder. The ECU could might even close the wastegate as soon as the extra fuel goes in to help keep emissions in check (if it has wastegate).

I've seen boost fluctuate on my D6 riding waves, no wastegate.