correct prop size on suzuki 140

[ciaranp]

what would be the best prop size to have on a 140 suzuki on the back of humber 5.8 destroyer to get maximum revs? currently has a stainless steel prop on it.

[Cypman]

My DF140 was hung on the back of a Humber 6.3m Ocean Pro. The engine came with a 21in ali prop as standard which gave me a WOT of 6000rpm. I then fitted a Suzuki 20in Stainless Steel one, it was a couple of knots slower than the ali one but acceleration was much better with a WOT of 6300rpm.

[BassBoy]

Mine was also supplied with 3x14x21' alloy. Bit down on top speed and on limit of WOT so tried 23' alloy. Got another 2knots on top end and WOT of 6000rpm (25knots =4200rpm)

Then tried 22' SS and lost a knot but better holeshot and less ventilation in the rough stuff. 6200 WOT and 25knots =4500rpm.

P.S. Owner manual says WOT range for DF 140 is 5600-6200 rpm

[Chris]

Ciaran. looking at the data you posted on your other post about overheating I can see that the engine has done 514 mins between 5 & 6000 RPM and 0 Mins above 6000rpm

According to the specs for your engine you are supposed to be running between 5600 - 6200 RPM - http://www.suzukimarine.com/sr_08/df...5-90/features/

The fact that the engine has spent comparitively low hours in the 5000-6000 bracket does suggest that the engine is only just able to reach 5000+ RPMs and that a lower pitch would be required. However until you get your boat and take it out for a blast you can't do much more.

If you find that MAX RPMs are below 5600 clearly you need to drop at least 2inches in pitch. However if you are up in the 5800 area you will probably be close to maximum performance.

[ciaranp]

ok thanks for that. You suggest so if im not getting full revs to get a bigger prop?

[Chris]

Originally Posted by ciaranp

ok thanks for that. You suggest so if im not getting full revs to get a bigger prop?

er.. no I said if you are below your target revs you would need to DROP a couple of inches.

Prop size is not relevant its pitch that you are most likely to need to change.

Do you understand what I mean by pitch?

[ciaranp]

ye understand you. its a stainless steel prop thats on it.

[BassBoy]

Might be helpful to know that Suzuki supply alloy props in odd No. pitch i.e. 19' 21' 23' and SS props in even No. pitch i.e. 20' 22' 24'

[ciaranp]

ye ok. There a S/S on it not sure which one