Mercury 9.9 four stroke rpm questions

[Azoutdoorsman]

Thanks for the heads up John. I'll try to change it up in the next couple weeks.

 

[thedude]

Reliability compared to a 2-stroke?
I routinely run 2-stroke engines from the 30's 40's and 50's on 100 mile runs!
Just teasing you (not about the runs) but a cared for 2-stroke can be handed down to your grand kids the same as a 4-stroke.

[emoji3]

 

[Azoutdoorsman]

I really think you should consider replacing your 8.5 prop with a 6.5.

I did, and my pig of a heavily loaded 1648 went from 5.5 mph @ 4500 rpm to 10.7 mph @ 5850 rpm.

https://www.tinboats.net/forum/viewtopic.php?f=4&t=43098

All of the power is in the upper end of the rpm range. (It will do 13 or 14 with one person. More than I need for the reservoirs.)

Good luck. John

Thank you so much for the suggestions. Finally ordered a 6.5 pitch prop and took it out for a run this evening. Boat went from 4100rpms 7 mph to 5700 rpms and 11mph with 2 people and ran 13.2 by myself. Still may try a hydrofoil to help lift the rear a bit but night and day difference between the props.

 

[johnbt]

That's great, I'm happy it worked out that well. You picked up more rpms than I would have predicted.