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Old 11 April 2004, 18:26   #1
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Engine revs

Handbook for the Suzuki 40 says engine revs between 5200-5800. On the rev counter it was showing 6000 at wot. Should I be concerned?
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Old 12 April 2004, 10:52   #2
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Maybe if you want to make your engine last longer!.
I would think it proped wrong, would have thought going up a pitch will bring you to about 5800 rpm.
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Old 12 April 2004, 12:24   #3
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Quote:
Originally Posted by Turbodiesel
I would think it proped wrong, would have thought going up a pitch will bring you to about 5800 rpm.
2 questions: 1) Does going up a pitch affect torque at the lower end or speed at the top end? The prop on is the one that came with the engine and is rated at 11.5 x 13, so 2) what would be the next one to go for? Thanks
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Old 12 April 2004, 14:59   #4
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Upping your pitch will decrease your engine revs by roughly 150- 200rpm per inch of pitch.
Too much pitch will bog you down at take off and too little will give you massive acceleration but overrev the engine and riun your top speed.
You need to find a happy medium for the engine and boat.
try steel developments for prop advice they'll sort you out.
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Old 12 April 2004, 15:02   #5
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sorry me again.
read your prop measurements try a 11.5 x 14 alloy or 11.5 x 15 stainless.
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Old 12 April 2004, 18:34   #6
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What's the reason for two inch increase in pitch for stainless compared to one inch for alloy?
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Old 13 April 2004, 15:06   #7
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I was told by my local dealer and it seems to ring true with the props i've swapped that the stainless prop has more momentum so will turn faster than an alloy one. so increasing the revs And the ss is also more efficient.
try steel developments they did mine and were very helpful.
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Old 17 April 2004, 04:42   #8
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My 60 Mercury Big foot has not reached peak revs yet with a standard 19pitch, stainless is it the way to go ?
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Old 17 April 2004, 05:08   #9
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Quote:
Originally Posted by xr770a
My 60 Mercury Big foot has not reached peak revs yet with a standard 19pitch, stainless is it the way to go ?
Suggest you try a smaller Ali prop to get the revs up, then having found the right pitch you might want to think about S/S and keep the Ali for a spare. The boat will be faster and more responsive with the right size of prop.

There will be a gain in performance by going S/S but nothing like that gained by using the right size of prop.

Shame but just sold a S/S 17" prop that would have fitted.

Pete
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Old 17 April 2004, 08:33   #10
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I had a heavy 18' taskforce dory with 85 premix yamaha, came with 19" prop. It used to stall as you engaged gear when cold, it struggled to accellerate until it got to 1500rpm then was ok but wouldn't go above 5100rpm. Changed to 17" and all my problems gone, WOT 5400 (limited 5500) no change in top speed (not measureable anyway) but MUCH better accelleration and it didn't stall.
Incidentally the Yamaha dealer I was getting bits from used to race these engines, they used to remove the limiter and run them at 6500 rpm and didn't have any problems.

I got a propellor repairer to exchange my props for new pitched ones, cost 50 each but got the equivalent of brand new for old into the bargain! (and they were tatty)
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