webby
Active Member
No, I have only run at WOT once very briefly and can't remember what the RPM was it was.
New Jenneau Merry Fisher 855
- Thread starter webby
- Start date
No, I have only run at WOT once very briefly and can't remember what the RPM was it was.
Beyondhelp
Well-Known Member
That's not quite right. I speak as someone who as their day jobs programs ECUs in performance engines, so hopefully my input is a little helpful.
Lean burn is a true and valid technology. Ordinarily you have to have a fuel mixture of around 14.7:1 Air:Fuel for efficient combustion that is known as stoich or lambda (at least in my circles). Normally this ratio decreases down to 11-12:1 for high load high output petrol engines (were talking 2-300bhp/litre/turbo) - the kind of thing I work with.
However modern common rail fuel injection has allowed another type of combustion.
Firstly its helpful to remember (for those that may not know) that normally a petrol engines use a throttle body (air valve arrangement connected to the accelerator) to control airflow into the engine and thus control the power it produces, as fuel is always kept around a fixed ratio. This differs to the basic diesel engine where there is no throttle body and output is simply controlled by how much fuel you inject. The problem with petrol engines is that for all the time your NOT at wide open throttle (WOT/Full power) there is a relative vacuum on the engine side of the throttle body. This causes pumping losses - and they are very significant in petrol engines. The larger the capacity the worse the problem.
By creating specific piston and cylinder head designs it has become possible to localise fuel combustion within a cylinder and thus creating localised spots where combustion is still efficient, but if you were to take the cylinder as a whole the ratio between fuel and air would be hard or impossible to ignite (were talking 65:1 ratios). The interesting thing is it allows greater efficiency simply by allowing engine power output controlling during say light throttle cruising, by fuel injection (Just like a diesel) and still allowing the throttle to be wide open - drastically reducing pumping losses - again like a diesel.
So a good lean burn engine offers significant economy savings at partial throttles compared to a similar engine being controlled by traditional methods. I would therefore expect mid range rpm from a Suzuki to be quite noticeably better compared to a Yamaha if Yamaha does not use lean burn technology. From Suzuki own material they claim 40% saving or so at mid engine loads compared to their older engines.
It would be interesting to hear from an owner of such an engine...
PS.. Saw the 855 at the London boat show. I thought it was great! Perhaps one day...
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rustybarge
Well-Known Member
Romans8 is the first uk owner:http://www.ybw.com/forums/showthread.php?306455-Beneteau-Antares-8-80/page5
Looks like about 4-5 mpg......
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webby
Active Member
I can see that computes to 18ltrs per hour, which is very good with the loads Romans describes. Not sure how you get to 4-5 mpg from that info. Anyway I'll entertain my wife in a couple of weeks with fuel consumption analysis. One irritation I have with the Yamaha is that to calibrate the fuel tank you have to fill it by set amounts from empty! Given that it was supplied with some fuel in it I don't fancy riding around until it is empty and then rowing back to the pontoon to fill up in increments. I used the readout for the figures I posted earlier so will post the fill to fill figures in September.
D
webby
Active Member
That's not quite right. I speak as someone who as their day jobs programs ECUs in performance engines, so hopefully my input is a little helpful.
Lean burn is a true and valid technology. Ordinarily you have to have a fuel mixture of around 14.7:1 Air:Fuel for efficient combustion that is known as stoich or lambda (at least in my circles). Normally this ratio decreases down to 11-12:1 for high load high output petrol engines (were talking 2-300bhp/litre/turbo) - the kind of thing I work with.
However modern common rail fuel injection has allowed another type of combustion.
Firstly its helpful to remember (for those that may not know) that normally a petrol engines use a throttle body (air valve arrangement connected to the accelerator) to control airflow into the engine and thus control the power it produces, as fuel is always kept around a fixed ratio. This differs to the basic diesel engine where there is no throttle body and output is simply controlled by how much fuel you inject. The problem with petrol engines is that for all the time your NOT at wide open throttle (WOT/Full power) there is a relative vacuum on the engine side of the throttle body. This causes pumping losses - and they are very significant in petrol engines. The larger the capacity the worse the problem.
By creating specific piston and cylinder head designs it has become possible to localise fuel combustion within a cylinder and thus creating localised spots where combustion is still efficient, but if you were to take the cylinder as a whole the ratio between fuel and air would be hard or impossible to ignite (were talking 65:1 ratios). The interesting thing is it allows greater efficiency simply by allowing engine power output controlling during say light throttle cruising, by fuel injection (Just like a diesel) and still allowing the throttle to be wide open - drastically reducing pumping losses - again like a diesel.
So a good lean burn engine offers significant economy savings at partial throttles compared to a similar engine being controlled by traditional methods. I would therefore expect mid range rpm from a Suzuki to be quite noticeably better compared to a Yamaha if Yamaha does not use lean burn technology. From Suzuki own material they claim 40% saving or so at mid engine loads compared to their older engines.
It would be interesting to hear from an owner of such an engine...
PS.. Saw the 855 at the London boat show. I thought it was great! Perhaps one day...
Interesting input beyond help; A couple of things. A 40% reduction on their old models is a pretty meaningless figure unless we know how good or bad the old ones were!
I am not knocking the Suzuki, it is a very good engine, rather I was making the point that manufacturers will take one aspect of their engine design and focus on it in their marketing. A classic example was the way cars were labeled with 16V or i some years back. Pretty meaningless to the vast majority of people and not necessarily relevant.
My point is that all petrol engines would now claim to be lean burn, they wouldn't be in business if they weren't. Suzuki's claim to lean burn being better than anyone else's' seems to be that they predict engine requirements and adjust accordingly see article - http://www.charterworld.com/news/suzukis-lean-burn-control-system-faster .
Yamaha also claim lean burn controlled by micro computers but call it clean burn.
This could go on for ever and is very interesting, I guess the only real way to check comparative consumptions would be in very controlled conditions.
As I say I will try and post some more figures next month but would suggest that they are both very good engines and boats, one chooses based on a whole load of factors, ours was swung by the better interior (in our opinion!) and the sliding helm door which helps with coming alongside.
stevieb52
New Member
Looks a lovely boat contemplating getting one myself but how do you find it manouevres in the marina as i currently have a single engined american sport cruiser without a bow thruster and find it it difficult to berth at times and were you worried about the reliability of a single engine ?
Rhinoc
New Member
Sorry to ressurect an old thread but I'm struggling to get the best performance out of my MF855 with the same engine. What prop are you running and what height is the engine?
Rhinoc
webby
Active Member
More than happy with single 300hp set up, though bow thrusters are essential. Reliability of modern out boards is excellent these days so we have no worries. Go for it!
Rupes185
New Member
Hi, was there ever an answer to this? I’ve got a Saltwater II 17T-15.5 prop and struggling with poor mpg