Best Rib with 150 HP

[John Kennett]

Originally Posted by jwalker

The literature refers to an absorption brake powerhead dyno so I guess they are powerhead figures.

Don't manufacturers quote the power at the prop?

John

[Jono]

..if we didn't get the Dyno figure we were expecting for the 'bike we did what any proper engineer would have done....... tried another Dyno...

[Manos]

Originally Posted by Rogue Wave

getting back to the original question ....then what about a fantum evo

Nice boat and fast. Hull and looks similar to the FALCON and is 2 or 3 times more expenssive. But a good boat nevertheless
Is there a resons that there aren't many of them Fantom Evolutions about? Just asking

[Manos]

Been down to the engineers today and we had a flick throufh some data they have from there Dyno measurements and also had some crash lessons on reed valves, cranck shafts and compartion ratios.

The measurements these people do I assume are all at the prop as this dyno thing they have you fit on the prop and they have to submerge the leg in the water tank for that.

Any way you may be interested to know that data that they had from a 150VMax 2-strokes showed 167 bhp and the data from three 200VMax showed three different results 226, 228, 231. In the manuals the manufaturers showed 150bhp and 200bhp respectively.

Originally Posted by jwalker

Except for an increase in engine capacity, the only engine modification which will give increased power over the whole of the rev. range is an increase in compression ratio. Generally, mods give extra power at increased engine revs. Note the word 'generally' because this is not necessarily a fixed rule.

On a two strokes engine I was told that this is always the case. More comprestion more power better fuel economy. And to increase compression ration you need to pack the cranck case.

[jwalker]

Originally Posted by Jono

Yanmar "315" engine is only rated at 40 C at the injector. I just wanted to know what a standard operating temperature was in this region...........
As for the outboards, if we take transmission losses into account ........

I dunno about that method of rating. The evapourating diesel will have a cooling effect but the cylinder air temp has to be high enough for combustion when the diesel is injected. Maybe the injectors stay cool but since burning is taking place against the injector, it's difficult to imagine it does.

Volvo recon a loss of 12.9hp through the sterndrive at maximum revs. Given two u/j's and 2 right angle bevel gear sets I would guess at a typical 200hp lower unit absorbing about 6-7-8hp max. Since the losses turn into heat energy, that's still a fekkin lot of heat to dissipate through the casing! About 5 electric fire bars glowing red hot! So, no, the powerhead figures are still at variance with the quoted rating.

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JK, yep the current hp rating for outboard motors is taken at the prop. The figures in the table are independent measurements. Nevertheless, since the lower units losses of the same make and, I would guess, of different makes are similar, it's easy enough to deduct 6 or 7hp from the figures.

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Dirk, could the 300hp rating have been at the drive output and the 315 at the flywheel? Just guessing.

[jwalker]

Originally Posted by Manos

And to increase compression ration you need to pack the cranck case.

Pardon?

That's the problem with crash courses.

Packing out the crankcase used to be done to increase the charge pressure and, hence, the combustion chamber pressure but it doesn't increase the compression ratio. In modern 2 strokes, there's not much space in the case to pack, but maybe it's still done.

[The Jackeens]

Originally Posted by John Kennett

there's no way any manufacturer is going to understate the output of their engines . . .

Perhaps for racing? Almost inconceivable though.......

missus

[Jonny Fuller]

Originally Posted by Manos

John Unfortunately we didn't race due to a serious illness.

Of a mental nature, no doubt.

[Jonny Fuller]

As with all sterndrives, the Yanmar 315 is crank rated, not propeller shaft, so it's only bringing it closer into line with the way OB's have been done since 1985.
Also, a Yanmar has a cooler on the return fuel line (to the tank) presumably to help keep tank and fuel supply temp's nice n low.

If those fig's JW posted are powerhead power outputs, they'd fall fairly well in line with prop ratings for most of them, I can't believe, as JK says, that it's common practice to understate power output, and if they did as far as power/badging, i'm sure they'd get some advertising value from the extra 'free' power.

IMHO

[Matt]

Since the late 80's I thought.

Originally Posted by John Kennett

Don't manufacturers quote the power at the prop?

John

[Jonny Fuller]

Look at the post above yours nobba! it's '85 that the yanks started doing as the Japs had done for years, and rated/advertised the power 'at the prop'.
Try and keep up!

[Rogue Wave]

Now hang on a minute Nobba , fgt nobba and not junior assistant nobba. The post above the post above the post above this one ,herinafter known as he post above (cubed). Seems to me to be in direct contradiction with the post above this one. (herinafter known as the post above this one )

I have some confusion.

In the post above (cubed) you clearly state that power is crank( not prop) rated and is in line with the way outboards have been measured since 1985. To me this infers that outboard power is measured at the crank shaft and not the prop shaft (by this I mean the bit of splined metal wot drives the screw).

In the post above this one you sate that the power is measured at the prop.

The last time I was this confused was when somebody pointed to two shovels and told me to take my pick.

[Jonny Fuller]

Na,what I was trying to say was, the 300 Yanmar, is actually 315 crankshaft horsepower, by the time it gets to the prop, it's probably in the region of 285/290, in other words, the Yanmar 300, is very nearly 300 at the prop, like OB's from '85 onwards.

now stop being fkkn awkward

[Matt]

Doh!

Originally Posted by Jonny Fuller

Look at the post above yours nobba! it's '85 that the yanks started doing as the Japs had done for years, and rated/advertised the power 'at the prop'.
Try and keep up!

[Manos]

Originally Posted by jwalker

That's the problem with crash courses.

Well never said that I will start modifying outboards my self

Originally Posted by jwalker

Packing out the crankcase used to be done to increase the charge pressure and, hence, the combustion chamber pressure but it doesn't increase the compression ratio. In modern 2 strokes, there's not much space in the case to pack, but maybe it's still done.

Thanks for the info JW

[Cookee]

Had a Maico 125 in a racing kart (quite a while ago now!) with packed crankcases - also improved the response a bit along with shortening the bellmouth on the carb and some other mods - it stopped very quickly when the stuffing tried to come up the ports!

[jwalker]

Originally Posted by Cookee

...it stopped very quickly when the stuffing tried to come up the ports!

[Manos]

Just out of curiosity what the term 'staffing' means. How do the 'satff' an engine. It sounds strange to me.

[Rogue Wave]

Originally Posted by Jonny Fuller

Na,what I was trying to say was, the 300 Yanmar, is actually 315 crankshaft horsepower, by the time it gets to the prop, it's probably in the region of 285/290, in other words, the Yanmar 300, is very nearly 300 at the prop, like OB's from '85 onwards.

now stop being fkkn awkward

you thinking of moving to Gloucester?

Ok so basically all outboard since 85 have had their power measured at the prop. Which was the American manufacturers way of coming into line with the Japs who had been doing it for years?

Is this a correct understanding

[Jonny Fuller]

Yup