[MJL529]

Just bought a new SX21 (2007) and appears that WOT MPH is about 40 MPH with 5.0 mercruiser and alpha 1 drive. Wondering if that should be about 10 MPH faster based on what I can read? Not sure of the prop size/pitch as boat is down at lake-will look this weekend
What is the best cruising RPM to not overwork the engine?

[darkcalling]

I would suggest checking rpms at wot to see if you are maxed out you should be revving about 4500-4700 rpm stock to stay in the safe range and is that speed from gps or the boats speedo?

[mikeyt]

Yes you should be up in the mid-high 40's in that boat. Check out what prop is on it first and if you have an opportunity check the rpms at WOT. Being down around 40mph makes me think its either badly propped or in need of a tuneup. Let us know what you find?

[MJL529]

Might have been some bad gas (bought it with small amount of gas which have been from last year). Boat is running closer to 48-50 mph when trimmed up slightly. Thanks for the replies from both of you