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Any ideas what pitch this prop is???
|Author||Topic: Any ideas what pitch this prop is???|
posted 05-16-2003 10:00 AM ET (US)
I have a 1989 Johnny 70 on my 15' Striper. She pulls about 6200 @ WOT (about 42 MPH GPS). I want to drop the RPM's down to rec. redline (5500), but I can't determine the size of the existing prop. I took the prop off last night and literally looked it over with a magnifying glass and bright light. The only markings I could find anywhere on the prop were in the hub area where the diameter and pitch are usually engraved. Those markings were as follows:
MICHIGAN CUP 90 PJ
I know what the Michigan is (Michigan Wheel), but the rest of it is greek to me! Obviously I need to know the pitch and diameter of this prop in order to determine the new size I should try.
posted 05-16-2003 10:55 AM ET (US)
Did a google search on Michigain wheel and found their website. That code is listed in the PDF file they have online for their catalog in the index section. Looking it up on Page 31 of their catalog shows the prop to be 13 1/4" diameter, 17" Pitch, 3 Blades, Right Hand Rotation with Cup. Equates to an OEM prop#=391199
posted 05-16-2003 11:58 AM ET (US)
I didn't even think to check out their web site.
Now I guess the question is what prop to go with? If my understanding of pitches and cupping is correct, this is the equivalant of about an 18" pitch. From what I have read here, that is about par for what most are running with this setup.
I will do some research on the site and start a new post if I have further questions.
posted 05-16-2003 12:25 PM ET (US)
Going up 2 inches in pitch should drop you 500-700 rpms and get you into the range you want.
posted 05-16-2003 12:45 PM ET (US)
Your numbers from your RPM and WOT tell me that you've got a 17" pitch. My 15' Sport will run those numbers with the 17" 3-blade aluminum I have. A 19" SS will put you back down below redline, especially if you get a cupped one...
Hole shot with anything in tow will be the trade-off. I have a 19"SS, and a 17"Aluminum, Both cupped. When I go skiing, I stick the 17" aluminum on, because the hole shot with a slalom skier is sad using the 19"SS. However, if I have the 19"SS on, I can do 50mph WOT (solo). The 19" will still get on plane with 3 adults aboard, that's not a problem.
posted 05-16-2003 12:56 PM ET (US)
I think I'm going to try a 19" and a 21". As long as I don't hit anything, I can keep the one that works best and return the one that doesn't. I talked to the dealer and he said that since I'm looking at used props anyways, this wouldn't be a problem.
posted 05-16-2003 05:44 PM ET (US)
That's a deal. I probably should have picked up the 12.75"x21" SS I saw on Ebay a few months back. Even with the higher pitch, the smaller diameter would help my windup with the Slalom...
Or, I can go back to carrying my Firestorm cordless drill along, and keep up-sizing my vent holes until I vent it enough to wind it up...
posted 05-19-2003 10:03 PM ET (US)
You might want to have a prop shop repitch that one and see how it works. I believe they can repitch for only about $50, if aluminum.
posted 05-20-2003 01:30 AM ET (US)
You will loose 200 rpms for each inch of pitch added, 2 inches more equals 400 rpms less, not 5 to 700.
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