Mercury V12 600hp Verado Outboard Engine

[Whippersnapper]

This behaviour is the same seen with conspiracy theorists. They make assertions and provide no evidence. Their claims are refuted with evidence so they ignore that and make a different assertion or provide “evidence” that is not relevant to the question.

Bottomline. I have provided evidence that a modern 600hp diesel will burn ~120lph at full power. The Mercury v8 300 burns around 145lph at full power so the 600hp v12 will be >250lph.

Spot on.

QBhoy, you don't need to convince anyone that modern outboards are good. They wouldn't sell as hot cakes if they weren't.
It's when you jumped in the conclusion that petrol engines are "more fuel efficient" than diesel engines, that you dug the hole in which you are now.
And from where, as the old saying goes, you'd better stop digging.

See, the point is that there's only one commonly accepted definition of fuel efficiency of internal combustion engines, and it's the Brake-Specific Fuel Consumption, aka "BSFC".
There are actually slight variations on that, because some engine manufacturers use the weight rather the volume of fuel, and you can either use kW or hp to measure power, but this is just hair splitting.
Essentially, it's meant to measure the amount of fuel that one engine burns for each unit of power produced.
And the crux of the matter is that there are physical reasons why even the worst diesel engines are, and will always be, more fuel efficient than the latest and greatest petrol engines.

Of course MPI, direct injection, and many other tricks all contributed to improve the fuel efficiency of petrol engines over the years - as well as others factors did with diesels, anyway.
But none of these factors, neither alone nor all together, can circumvent physics.

For this reason, if you take the following table, which is obviously generic and based on averages, and you compare it with the specs of ANY engine, you will be surprised to see how valid the approximation is.
Don't take my word for it, give it a try.

Worked perfectly for my 260hp turbo diesel. 54lph at full power

 

[MapisM]

Worked perfectly for my 260hp turbo diesel. 54lph at full power

Goes without saying that I wouldn't have posted the table if it weren't that I already know it's generally very accurate.
FWIW, my 800hp turbo diesel engines burn 162 l/h according to the manufacturer's specs, and 168 according to the previous table (0.21 * 800).
Which means a 3.7% difference, i.e. good enough, in my books.
Not to mention my funny feeling that the generic table might well be more accurate than the manufacturer's specs...

But as I said, I'm not pretending that QBhoy takes my word for it.
I'm genuinely curious to hear if he also finds that the table works for him.
He said that he has a 300hp petrol engine, which according to the previous table should burn 99 L/hr (0.33 * 300) at its max rated power.
Let's hear from him if he thinks that this number makes sense.
It's obvious that the vesselview screen that he posted previously is totally irrelevant, because we don't know how many of those 300 hp the engine was producing, at an RPM which is surely way below WOT.

 

[madabouttheboat]

TBF Qboy hull must be very unusual cos most petrol powered boats, both inboards and outboards, are not on the plane properly until much higher revs, usually 3000prm ++

 

[MapisM]

But that's irrelevant, when talking of fuel efficiency of petrol vs. diesel engines in general.
You can determine that on a dyno, irrespective of the boat where any engine will be installed.

Besides, the fact that some types of boats are better suited for petrol engines is a given.
I don't think anyone objected to that.

 

[MapisM]

Worked perfectly for my 260hp turbo diesel. 54lph at full power

Again on the subject of how accurate (or not) the table is, it popped to my mind that I still had on my PC a copy of the Mercury engine power declaration related to my last petrol boat.
The engine was a 496 HO model, rated for 425hp max.
Not exactly the latest and greatest, but a pretty modern engine anyway, fully electronic MPI, Smartcraft, and other bells and whistles.
Now, according to the previous table it should burn 140.25 litres at the max rated power (0.33 * 425).
And guess what does the Merc power declaration states in the field "Hourly max consumption"?
Believe it or not, 140!!!

 

[ontheplane]

TBF Qboy hull must be very unusual cos most petrol powered boats, both inboards and outboards, are not on the plane properly until much higher revs, usually 3000prm ++

From memory he has a small light boat with a big MPi propped to give 60mph top end so that does allow him to plane at lower than usual rpm. From this however, he has managed to deduce that petrols are more efficient than diesels - a bit like, “if all dentists wear jeans sometimes, then everyone who wears jeans must sometimes be a dentist” kind of logic.

For a small lightweight boat, a petrol may (for blasting around) be the right choice - it doesn’t follow however that it is more “efficient”.

I don’t think I can top MapisM’s table as the perfect, and accurate, solution to the question “which is more efficient”.

I don’t think there will ever be a spark ignition gasoline engine that will get within 20% of the efficiency of a compression ignition Diesel engine ——- ever.

Sadly he isn’t able to grasp that because his engine is under a very light load at 2000 rpm, it doesn’t use masses of fuel - however at that point it may only be producing 100hp - simply put, at its peak power of (from memory 260/270 HP) it will be burning about 70 litres per hour at WOT according to MerCruiser 3.0 Fuel Consumption 135 HP | Test & Specs | 181 mpi/tks (need to scroll through to 5.0 mpi)

Same website, for the Mercruiser cummings diesel of 320 HP (so significantly more) it uses 71 lpg (or the 200hp - which has way more torque of course) 49.6 lpg.

 

[ontheplane]

So from the above, the 320 HP uses 22.187 litres per hour for every 100hp produced.
The 200 HP uses 24.8 litres of fuel per hour per 100hp produced

And the petrol? 26.92 litres per hr for every 100hp produced.

Average of the 2 diesels is 23.49 litres per 100 HP so the diesels are 14% more efficient......... However I strongly suspect that at mid-throttle the difference is way more than that.

 

[ontheplane]

An even better example - Volvo Penta D4 260 HP - so similar size, same power (masses more torque of course) at wot producing 260 HP.... 52 litres per hr

So 20 litres per hour per 100 HP produced, or just 74% of the consumption......

D4 300hp - 54.8 lph at wot - so 18.2 litres per hr for each 100hp or just 69% of the fuel use of the petrol........

So Qbhoy - you asked for ONE engine, I’ve just given you four (it’s the same for every single VP diesel as well).... In fact, surprise surprise, there wasn’t a single diesel that was even close to the petrol, they were all way more efficient... which isn’t a surprise as Diesel engines are more efficient.

If you are going to tell people who know what they are talking about that they are talking rubbish, might be wise to know what on earth you are talking about first - especially when every single piece of factual data would seem to indicate you are very wrong.

No-one is saying the modern outboard isn’t good, or that MPI inboards are not massively better than the old carb 2 and 4 strokes of old or even that in light very fast boats the petrol engine doesn’t have a place in the market, it does.

BUT - petrol will NEVER be as efficient as diesel, end of.

 

[QBhoy]

I think you are deluded with the figures you are quoting above , but tell me the exact boat and engine combo and i'll happily admit if I am wrong.


Edit

From your own post below, your fuel consumption is more like 25 to 28 lph, if your figures are correct. Up to double what you quote above. In the boat in question diesel would simply be the wrong choice, but however you look at it, diesel gives you more MPG than Petrol, often by a considerable margin as I demonstrated in a previous post.

It’s well documented thst this boat has changed a good few props since then. But your assumptions are still wrong, even at that. My figures are correct. Look up the specs. Jeez, I’ve even sent a screen shot of the smart craft ecu data. What more do you need. It’s there in black and white. 17 litres per hour is correct.
Look... The bottom like is. I actually have these engines to compare. 2 Tamd61, mpi v8, Merc125ct and a 150 V6 2 stroke. Real life stuff.

 

[QBhoy]

An even better example - Volvo Penta D4 260 HP - so similar size, same power (masses more torque of course) at wot producing 260 HP.... 52 litres per hr

So 20 litres per hour per 100 HP produced, or just 74% of the consumption......

D4 300hp - 54.8 lph at wot - so 18.2 litres per hr for each 100hp or just 69% of the fuel use of the petrol........

So Qbhoy - you asked for ONE engine, I’ve just given you four (it’s the same for every single VP diesel as well).... In fact, surprise surprise, there wasn’t a single diesel that was even close to the petrol, they were all way more efficient... which isn’t a surprise as Diesel engines are more efficient.

If you are going to tell people who know what they are talking about that they are talking rubbish, might be wise to know what on earth you are talking about first - especially when every single piece of factual data would seem to indicate you are very wrong.

No-one is saying the modern outboard isn’t good, or that MPI inboards are not massively better than the old carb 2 and 4 strokes of old or even that in light very fast boats the petrol engine doesn’t have a place in the market, it does.

BUT - petrol will NEVER be as efficient as diesel, end of.
[/QUOTE

 

[vas]

I don't think anyone disputed the correctness of your figures QBhoy.
What is disputed is that the values are not comparable since your 17lph implies a demand from the engine which is Xbhp, and then you compare that with a different boat which is burning 30 or 40lph but which engine is asked to output Ybhp.
then you go on to conclude that petrol engine rated at say 200bhp only burns 17lph, whereas a diesel rated at 200bhp burns 30lph.
numbers are fictional cannot be arsed to go through the thread to get them down properly, you'll excuse me.

The others are saying that unless the two consumptions refer to the same power demanded from the two engines, values are meaningless.

V.

 

[QBhoy]

Still haven’t given me an example if one that will do what the mpi will do...like for like.
let’s face it. Diesel is soon to be no more, in pleasure boats. Time we all got with it.

Look at modern cars.Lots of small efficient petrol engines are the trend. It’s a fact guys.

 

[vas]

and btw even WOT consumption values on two 200hp engines (one petrol one diesel) would be meaningless unless we know they are proped accurately to produce the 200hp at wot (which I guess rarely happens...)

 

[Mr Googler]

Where’s Porto when you need him.

got to be 1000 words arriving any moment ?

 

[Whippersnapper]

It’s well documented thst this boat has changed a good few props since then. But your assumptions are still wrong, even at that. My figures are correct. Look up the specs. Jeez, I’ve even sent a screen shot of the smart craft ecu data. What more do you need. It’s there in black and white. 17 litres per hour is correct.
Look... The bottom like is. I actually have these engines to compare. 2 Tamd61, mpi v8, Merc125ct and a 150 V6 2 stroke. Real life stuff.

Where is it in black and white? Your screen shot doesn’t show consumption. Even if it did it doesn’t support your argument in the slightest. The fuel economy of your boat doesn’t provide evidence of the efficiency of petrol vs diesel

 

[QBhoy]

I don't think anyone disputed the correctness of your figures QBhoy.
What is disputed is that the values are not comparable since your 17lph implies a demand from the engine which is Xbhp, and then you compare that with a different boat which is burning 30 or 40lph but which engine is asked to output Ybhp.
then you go on to conclude that petrol engine rated at say 200bhp only burns 17lph, whereas a diesel rated at 200bhp burns 30lph.
numbers are fictional cannot be arsed to go through the thread to get them down properly, you'll excuse me.

The others are saying that unless the two consumptions refer to the same power demanded from the two engines, values are meaningless.

V.

Thanks. Agree with this. But I’m afraid some have disputed my figures. Such a shame. I can’t do anymore than I have.
Too many arm chairs researchers on here. Instead of fact based real life stuff. I’m afraid I’m out for good. Such a disappointing forum these days. So full of smart arse guys kidding themselves on. Far too quick to critique everything they read.
I enjoyed it in the early days. Now...not so much.
All the best.

 

[QBhoy]

Where is it in black and white? Your screen shot doesn’t show consumption. Even if it did it doesn’t support your argument in the slightest. The fuel economy of your boat doesn’t provide evidence of the efficiency of petrol vs diesel

Look up the consumption of it. You’re quick to do that for other engines.

 

[Whippersnapper]

What an idiot. Ignored

 

[QBhoy]

What an idiot. Ignored

Come have a chat with me fella. You know where I am all of the summer.

 

[longjohnsilver]

You don't need to even remove the cowling for servicing until a 1000 hours.

for the average boater doing 50 hours a year, that would be 20 years before looking under the cowling! There must be some other servicing requirements?