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-   -   Cruising RPM (http://www.wakeworld.com/forum/showthread.php?t=782276)

skiboarder 08-02-2010 10:00 AM

Cruising RPM
I have 2010 VLX and just recently converted my Acme 14.50 x 14.25 to a 14.50 x 13.25 to improve hole-shot when weighted down.

I anticipated an increase in RPM, but at 24mph with 2,000 lbs of ballast and wedge my cruising RPM has jumped to 3800 rpm. I was at about 3500 before.

With the 350HP motor do you think 3800 is too high?? I am considering tempering the prop back to its original pitch.

wake77 08-02-2010 10:05 AM

As far as hurting the motor? 3800 RPM is fine. You will use a tad bit more gas.

alans 08-02-2010 12:49 PM

3800 is fine. I wouldn't cruise with full ballast and the wedge down though, not very fuel efficient.

skiboarder 08-02-2010 1:46 PM

By cruising speed I meant riding speed: 24mph.

dave27 08-02-2010 2:03 PM

my boat it 30 mph at 3600 RPM. I can do that speed with full ballast around 2400 plus 5-8 people. BTW I reproped my boat with a ACME 911

alans 08-02-2010 2:16 PM

Dave, you must have a very different gear ratio than his indmar. If you have a 1:1 trans. With a 10.5" Pitch at 2400 RPM, you would be going 23.4 MPH with 100% efficiency, which is impossible.

cadunkle 08-02-2010 3:50 PM

3800 sounds pretty high to me. Sure it'll be fine but it's a lot of gas burned and extra wear on the engine. If it needs to rev that high to make the torque to maintain a steady speed then that's what it needs, but if not I'd try to drop the RPM a bit. Generally I like to cruise at 3000 RPM or less. Not much comparison but my beater is at about 2400-2500 RPM at 22 MPH or so (where I like to ride). What size engine and what ratio transmission do you have? If it's a 350 Chevy I wouldn't expect it to need to rev that high unless you're seriously weighted down.

rallyart 08-02-2010 5:10 PM

A small block Chevrolet like yours will run at 3800 all day but you would be better below 3500.
The bigger problem might be the wedge at 24 mph. You've got a huge downfoce at that speed so you'll have high prop slip. That would be why your rpm is so high.
Try running that speed with no load and see what the rpm is.

rio_sanger 08-02-2010 7:03 PM

Art is right on here (as he usuallay is). - With the wedge down, it's acting like an anchor, so the engine needs to work harder (more rpm's) to make the boat get up to speed.

mikeski 08-02-2010 7:20 PM

I would not run a prop with less than 14" of pitch on any modern V-drive. The blade shape of an OJ is slightly different, might call Eric Johnson, he's been known to let guys try props from time to time. I ended up keeping my Acme but that was for non-wakeboarding reasons. You can also get Acme props cut to different cup tolerances, a bigger cup will reduce your rpms.

skiboarder 08-04-2010 9:54 AM

I called Indmar and they told me that there should be no concern in running the boat at 3800 rpms as long as I do not exceed 5200 at any point in the pick-up. In fact, he said that running a lower RPM under such a load will cause more problems.

The biggest problem he sees is with boats that spend most of their time wakesurfing.

dave27 08-04-2010 11:39 AM

Alan, I will have to take a look at my RPM to MPH, again. I for some reason can't remember now if I stated it correctly, now where did I put that beer!

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