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Old 13 November 2015, 07:22   #1
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Difference in engines

Hi,

I read a post or two talking about the difference in 20HP engines... it seemed to focus on which had more power (can't find post now)... now forgive me if I'm wrong but doesn't 20Hp mean 20Hp so they're all the same? Yam/Honda/Merc/Suzuc/Twat/etc...

I get that 2-stroke will be lighter/lay down the power different to a 4-stroke, and that perhaps EFI will again be a bit different to carb...

But really, is there ANY difference in what these engines can do to propel your 4m SIB forward?

Thanks

Stig
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Old 13 November 2015, 10:20   #2
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Hmm! A couple of things to consider. The ICOMIA standards by which engines are rated allows for a +/-10% variance from what it says on the cowl. So a 20hp engine could be 18-22hp in reality & at these low HPs, 4 is a lot. It could make the difference in running the next pitch prop up or down. The standards are from the old carbed engine days when it was virtually impossible to produce an engine with an exact HP output. The advent of DI/EFI & Engine Management has changed this, hence we now have "HO" engines in the BRP line up, as they are tuned or "Mapped" to the top end of the allowed HP range. If you take the 75hp Etec as an example, this has a reputation for being a "strong" engine & punching above its weight, in theory it could be outputting 82.5hp. The 90hp on the other hand is known to be a tad "Flabby". In theory, the 90hp might only be delivering 81hp. A cynical chap, might argue that the 75&90hp engines are one & the same, but with different cowl stickers & a 500 price difference

The other thing to consider is torque, 2strokes tend to be "Torquier" than 4 strokes, i.e the power is delivered lower down the rev range & with more grunt. Without wanting to re-ignite the whole 2s v 4s argument, in my experience, 2s are faster off the mark that 4strokes due to the low down oomph!
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Old 13 November 2015, 13:31   #3
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Quote:
Originally Posted by Pikey Dave View Post
Hmm! A couple of things to consider. The ICOMIA standards by which engines are rated allows for a +/-10% variance from what it says on the cowl. So a 20hp engine could be 18-22hp in reality & at these low HPs, 4 is a lot. It could make the difference in running the next pitch prop up or down. The standards are from the old carbed engine days when it was virtually impossible to produce an engine with an exact HP output. The advent of DI/EFI & Engine Management has changed this, hence we now have "HO" engines in the BRP line up, as they are tuned or "Mapped" to the top end of the allowed HP range. If you take the 75hp Etec as an example, this has a reputation for being a "strong" engine & punching above its weight, in theory it could be outputting 82.5hp. The 90hp on the other hand is known to be a tad "Flabby". In theory, the 90hp might only be delivering 81hp. A cynical chap, might argue that the 75&90hp engines are one & the same, but with different cowl stickers & a 500 price difference

The other thing to consider is torque, 2strokes tend to be "Torquier" than 4 strokes, i.e the power is delivered lower down the rev range & with more grunt. Without wanting to re-ignite the whole 2s v 4s argument, in my experience, 2s are faster off the mark that 4strokes due to the low down oomph!
The main thing in my experience your after in any RIB is Hole shot and grip...last year Chris and I did a Hole shot...short drag test with my 250 Suz...low hours against his..a new 25O e-tec...(Both Boats propped perfectly) which he filmed.
Boats more or less same size ...although mine is a bit heavier. A Real world test flat water...(St Martins Harbour)
result...NOTHING in it at all!
So ( at least with the the Big uns)...you may want to re-think that one Dave
By the way Top end would be within a knot or two as well.
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Old 13 November 2015, 14:06   #4
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IMO there are so many variables on the finished installation engine to boat that I go for largest hp the boat can take unless budget prevents, the reason I like redundancy, because how you use it today can be totally different tomorrow, in my diving days weight was crucial 4 m boat 25hp engine 2 divers plus kit and a boat man on the plane ok, 3 divers and kit not a hope in hell, we even use to start the aux to get it on the plane.my take is 5hp is a lot when you need it so when buying get more power than you need cost goes up of course 20 to a 25 but if it doesn't perform changing to a 25 later costs more.i agree with both Dave & max Dave's theory and Max's trial if Dave is right would two engines perform exactly the same which would affect Max's trial if they didn't ?

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Old 13 November 2015, 14:47   #5
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The main thing in my experience your after in any RIB is Hole shot and grip...last year Chris and I did a Hole shot...short drag test with my 250 Suz...low hours against his..a new 25O e-tec...(Both Boats propped perfectly) which he filmed.
Boats more or less same size ...although mine is a bit heavier. A Real world test flat water...(St Martins Harbour)
result...NOTHING in it at all!
So ( at least with the the Big uns)...you may want to re-think that one Dave
By the way Top end would be within a knot or two as well.
Hmm I would put the RC at a much heavier build than the other. so what your saying is that there was nothing in it?
With this accurate info to hand ,this kinda dilutes the necessity to run a two stroke(with very expensive oil) at all if performance is mirroring or less than a four stroke AND with a much heavier boat.
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Old 13 November 2015, 14:49   #6
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So ( at least with the the Big uns)...you may want to re-think that one Dave
Aye! 'appen Chris had a full tank of fuel
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Old 13 November 2015, 14:54   #7
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I wonder who got back to the mainland first? the Etic or the Suzook?
Gonna put me money on the Suzuki!
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Old 13 November 2015, 14:55   #8
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Aye! 'appen Chris had a full tank of fuel

Oooh🙈🙈
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Old 13 November 2015, 15:01   #9
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Gonna put me money on the Suzuki!
Double or quits?
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Old 13 November 2015, 15:04   #10
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Double ha ha and a used tin of WD 40
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