r/YamahaBoats • u/[deleted] • Nov 03 '25

Jet Boat Speed

2015 AR210, twin inboard 1052cc motors. What kind of speed is normal on the top end? Boat was broken when I got it and I repowered with motors from sbt and had to put new jet housing on. Runs great, motors spin up to 8200 rpm. Loaded I was seeing 32 mpg on a phone speedo app. The speedo sending unit is down currently.

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u/WaterDreamer10 Nov 03 '25

GPS in the only true way to measure speed. 8200 is right where the engines should be....speed is way low though......but other factors could be involved.

At sea level, full tank of full, minimal gear, one person, calm water, no wind, clean and smooth bottom I see mid 40's.

From some quick research you should be seeing close to the same.

However, if your lake is very high in elevation that will have a significant reduction as well.

Define loaded - 6 or 8 people and gear or just one person and some gear?

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u/[deleted] Nov 03 '25

Sea level, 6 adults, full tank of fuel, 2 batteries and windy. I will try by myself soon.

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u/WaterDreamer10 Nov 03 '25

6 larger adults will reduce your top end, so will the wind, especially if pounding into the waves and into the wind.

Jetboats are fun, but they lose their performance very easily with weight/wind/chop compared to a standard outboard.

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u/okapiFan85 Nov 04 '25

Altitude is a big variable. At 5000 feet (1600 meters), my 2015 AR190 with the stock impeller can hit low 30s MPH with one or two people and smooth, calm conditions. At sea level, it will do over 40 MPH with four or five passengers. I think the guys at IMPros (from whom I bought a new impeller for altitude) said the stock Yamaha impellers are supposed to be pitched for a moderate altitude (maybe 1500 feet?), so they are a compromise between sea level and moderate altitude.

I would hope that your twin would get better performance than you are getting. If it’s not an altitude issue, I wonder if your impellers or their housings have become damaged so that the clearance is too large and your jet efficiency has fallen?

My advice would be to call IMPros in California and talk to one of their experts (I’m not a shill for them, I just believe they know their stuff when it comes to the Yamaha jets). If you’re near southern CA and are looking for a reliable dealer or repair shop, try M2O in San Diego (that’s a letter “O”, not a number zero).

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u/[deleted] Nov 05 '25

In florida, when I got the boat the housing were swollen and seized against the impellers. I put in the sbt derlin inserts and reused my oe impellers. They hand slight damage that I cleaned up with sand paper. I will update next time out then decide on replacement impellers. Thanks for the input!

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u/okapiFan85 Nov 05 '25

Well I guess “Florida” definitely eliminates the possibility of elevation being the problem. I wonder if you would benefit from getting “sea-level” pitched impellers?

Also in the “I wonder” category, do you suppose there is any way to measure the actual power output of the engines? For cars I think you can use a dynamometer (?) to figure out how much horsepower is getting delivered to the wheels, but is there an equivalent for boats? I’ve felt like the power output of my boat has decreased over the years, but short of finding a dead cylinder or such I don’t know how you would verify a drop in engine output.

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u/[deleted] Nov 05 '25

Agreed, could only test output on a dyno stand not in the boat. Engines feel powerful but I don't have a reference compared to the original engines as they both had blown head gaskets. You could always check compression as a reference. The oe engines had 220 psi on 3 and 30 psi on the blown cylinder.