Another prop question, '97 SN with GT 40

[Ceruzziracing]

I just purchased a pristine 97 SN and after searching the forums and web have not found an answer to my question. The prop on the boat is a Johnson Legend with the # 0943 stamped on it along with date stamp of 7/97. I know the previous owner has had the prop tuned and/or repaired in the past but it looks pretty flawless. I have been unable to find the pitch/diameter #'s for this prop either on this site or the OJ prop site(they don't list a prop # anywhere near that high). We use this boat for light wakeboarding but I want to get back into slalom and also use the barefoot boom that came with her. I'm noticing what feels like cavitation on launch through achieving plane, plus she doesn't feel like she's pulling as hard as I would assume with the GT motor. I'm thinking she's underpropped but don't have a good starting point (since I don't know the numbers). Should I be looking at the 422 for my 97 hull or perhaps a 3 bladed prop?? Tachometer jumps all over the place but top speed on my one functioning speedo is low 40's, plus no additional ballast other than the wife and kids :-)

[toddrswenson]

I replaced my stock prop on my 97 SN GT-40 with an Acme 422 last year. I picked one up at about half off was the only reason. I don't really notice any difference torque or power wise with the 422, but it does seem to run smoother. I'm not sure what the original prop is. I can check and see what my stock prop has stamped on it when I get home. You're going to love that boat.

[Ceruzziracing]

Looked everywhere I can think and still can't find a reference to a Johnson Legend 0943 prop...

[east tx skier]

I think the original on my 98 was an OJ Force 13x16x1 RH. Force was the 4 blade, Legend the 3 blade IIRC.

I replaced the stock on my 98 Ski with the 422 found that not only did it run smoother, but that the wake seemed a bit softer. I'd recommend it if you're considering an upgrade.

[Ceruzziracing]

I'm leaning to the 422 and having this one as a spare (as soon as I pony up $430 for a new prop I don't really need yet ). I forgot to mention that the 0943 I have is a 4 blade prop...

[DanielC]

The boat originally came with with the OJ 13 x 16 prop, and sometime during the run of the TCS1 hull, the prop was changed to the Acme 422, 12.5 x 15.5. My understanding of the change is that the Acme propeller ran a little smoother, out of the box, the OJ propellers did not, until you had the OJ prop rebuilt, or straightened. Then they ran smoother.
I have used both propellers on my 1997 Ski Nautique 2267.8 hours. The OJ propeller lets the engine rev a bit more than the Acme propeller. (Why do I think of Roadrunner cartoons every time I talk about Acme propellers?)
Both propellers are fine for your boat.

For your speedometer, unscrew the nut that clamps the speedometer hose on the pitot tube. Then blow compressed air backwards through the tube. DO NOT BLOW COMPRESSED AIR INTO THE TUBE GOING TO THE SPEEDOMETER.
You should feel a solid stream of air coming out of the bottom on the pitot tube.

[DanielC]

More info.
the easiest way to check the speedometer is to get a hand held GPS, and compare the readings. When you are traveling in a straight line, at a steady speed, with a constant RPM, you can assume the GPS is reading the correct ground speed. If you are in a river with current, you need to go both up and down river, and adjust your speedometers to match the GPS.

Your boat is propped about right if it will run up to 5000 RPM at sea level.

Here is a tip for you to do someday. Take out your back seat, and run the gas tank down to somewhere between 1/4 and 1/2 tank, and get a light driver, and a lighter observer, and go for a slalom run.

[Ceruzziracing]

Dan, thanks for the info. I tried the tip the other day for clearing the tube, air flows fine, gauge face is fogged. I'm betting diaphragm inside is bad. I'll have to keep an eye on top mph next time out, been watching tach just because I'm getting needle jump over about 3500 and was concerned about overrev. Actually got the factory manual with the boat (albeit it was a bit moldy ) and if I'm reading correctly the GT 40 EFI has a rev limiter. I've been avoiding top speed runs because of that (worry about overrev). Also, changing out impeller tomorrow. Asked previous owner about last time it was changed and to my amazement he said NEVER! He was second owner of boat, purchased when it only had 50 hrs on it 12 YEARS AGO! Talk about dumb luck!!! Oh, and I'm with you on the Roadrunner thing, I guess we're showing our age ;-)