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87MCProstar
06-08-2011, 08:18 AM
Hey guys, just fooling around and looking at both Acme's and OJ's websites at props. And just a quick question, how does the cup affect the properties of the prop?

What is going to be the biggest difference between these to props for example:
13 X 12 .090 cup 3 1" LH
13 X 12 .110 cup 3 1" LH
13 X 12 .080 cup 3 1" LH

DooSPX
06-08-2011, 08:38 AM
The more cup, lowers RPM's. OJ typically uses more cup than Acme.

TRBenj
06-08-2011, 09:58 AM
Adding cup will have a similar effect as adding pitch- more cup = fewer RPM's. It doesnt seem to have quite as much of a holeshot penalty though. In other words, Ive seen a wickedly cupped 13x12 turn the same RPM at WOT as a 13x13 with minimal cup... but the 13x12 came out of the hole better. The downside to cup is that while adding it will bring down RPM, the prop seems to become slightly less efficient... so even if you bring your RPM's closer to your intended RPM (hopefully to match the RPM at which your engine makes its peak hp), you may not gain any speed. Dialing in the pitch seems to be the better way to go in this regard. Also, cup is only effective in a certian range- notice that most ski boat props will be cupped in the .080-.150 range.

For your boat, Id go with the Acme 541 or the equivalent OJ XMP (13x12, .080-.090 cup).

87MCProstar
06-08-2011, 10:09 AM
Okay guys, thanks. That makes sense. I have the 541, but was just wondering I guess for knowledge sake.

DooSPX
06-08-2011, 10:24 AM
I think OJ says their 13x11.5 is closer to the 541 performance. I know BrianM has tested both on his 97.

tideengineer
06-08-2011, 10:31 AM
This is interesteing topic...the 96 Prostar 190 LT1 I just purchased has the original 3-blade prop....I know nothing about it....I'm wondering how far i should go with this type of upgrade possibly....

87MCProstar
06-08-2011, 10:32 AM
Tid, great thing about this board is there are tons of information and people who have more! its a great place to learn everything 'bout our boats and the drivetrain

DooSPX
06-08-2011, 10:34 AM
Call or PM EJ OJPROP. Tell him the boat, engine, trans ratio and what you want from the boat. You will be a 100% happy. He will send you props to try.

tideengineer
06-08-2011, 11:05 AM
Awesome....thanks guys. This forum has already saved me money with just a weeks worth of reading! Fixed sending unit....removing oxidation....bout to install depth finder....exciting.

DooSPX
06-08-2011, 11:11 AM
It is a great forum.... just have to get by some BS occasionally. Still worth it.

DooSPX
06-08-2011, 11:13 AM
BTW, in case you do not know, Eric is the owner of OJ Props and OJ makes the props and all running gear for MasterCraft.

Jesus_Freak
06-11-2011, 05:55 AM
The downside to cup is that while adding it will bring down RPM, the prop seems to become slightly less efficient.

Yes, in a similar way that adding a spoiler to a car accomplishes the desired task but reduces its efficiency.

G-Star
06-11-2011, 10:46 AM
Yes, in a similar way that adding a spoiler to a car accomplishes the desired task but reduces its efficiency.

What about this one?? :D

http://3.bp.blogspot.com/--SIATMrWp0o/TZhqvawHrgI/AAAAAAAAAv4/ExWJia7GwfI/s1600/spoiler.jpeg

Jesus_Freak
06-19-2011, 06:05 AM
What about this one?? :D


Sharp! (as a bowling ball)