View Full Version : RPM on new OJ prop with 310hp
07-09-2012, 10:48 AM
My prop was bent on the 4th Eric sent me a new 14.25 and installed it in Friday. Definitely can tell a difference from the 13.5 it had on it stock. Saturday had more people on the boat and the RPM seemed higher than normal. What is the norm on your boats running 30-35 or 35-40 mph?
07-09-2012, 11:00 AM
when giving the dimentions of a prop, you need to include the pitch as well. i take it your prop is a 14.25(diameter)x14.5(pitch)? include the cup if you know it too.
i'm thinking you went from a 17 pitch to a 14.5 pitch, which would raise the RPMs significantly (offset somewhat by the larger diameter).
Also, when benchmarking speed/RPMs you really have to compare like boats, like engines and like altitude. I could give you numbers for my xstar but they would be meaningless, but in general, yea above 35 mph and i'm turning a ton of RPMs
07-09-2012, 08:49 PM
the 2004 owner's manual has the WOT RPMs listed.
When sizing a prop you need to work with your wide open throttle parameters. Your engine sould run 4400-4800 rpm when at full throttle. If you want more hole shot then go closer to 4800 rpm, better/lower rmp cruise speeds go lower in the range. One inch of pitch will raise or lower your rpm by a few hundred rpm.
07-10-2012, 07:39 AM
07-10-2012, 04:48 PM
with that 14.25 your rpm will def be higher especially at WOT. You can't run wide open with next to zero weight in the boat with that prop. IT will get you around 5k and some change which is around where the rev limiter will kick in......... IT does on my LTR.......again "around" the 5k mark on the tach as the weight, wind, amount of people and altitude will all play a factor.
If I am empty with gear and people its glass and I wot the boat with my Acme it will hit the limit easily.
Here is a link to a test I did little while ago. My estimates are just that.....estimates going off the tach on the dash not a computerized hookup/machine and with just me in the boat. However my speedo is accurate at its gps'd at east once every 2 weeks. (Iknow Anal) Keep in mind my prop is an ACME 14.5 X 14.25 and your OJ is the opposite at 14.25 X14.5 and I have the LTR 330 Engine. ALl in all though should give you an idea
Here are some numbers
3050rpm. @ 23mph
4200rpm. @ 32mph
4500rpm. @ 34mph
5550 rpm @ wot of 41 mph
Weighted up with 2700.
3300rpm @ 23mph
Holeshot at an unofficial just under 5 seconds to plane
OJ 13.7 X 17
3700 rpm @ 32mph
5100rpm @wot 43.5mph
Weighted with 2700
3000rpm @ 23mph
Holeshot weighted at an unofficial just under 6 seconds to plane.
We forgot to do ski speed holes shots but seemed the OJ was bit quicker to ski speed off top of my head Unweighted
My 2003 owners manual shows an x2 with the 310 horse had a 14 x 20 prop. The MCX 350 came with a 14 x 18