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View Full Version : questions about RPM, prop size and WOT


brucemac
05-27-2008, 12:12 PM
i have a few questions. hoping you folks can answer.

so boat is 03 X-2 with MCX

the boat runs awesome, no vibration and i had the shaft aligned a few weeks ago as part of a preventative maintenance and check-out at my mechanic. everything checked out good, but they only fake-a-laked it, no actual water test under load or anything.

the one thing i noticed when i first test drove the boat as well as having spent some time on it the last couple weekends is that when running WOT the tach is only reporting about 4600-4700 RPM's. this is in the pacific northwest, so close to sea level, only 2 people in the boat and minimal gear. i don't feel anything out of the ordinary and the engine sounds pretty darned wrapped out.

according to the manual i should be running between 4800-5200 rpm's with the MCX.

when i was in negotiations with the owner he did state that he had the prop replaced after hitting a log in the river. i think he said replaced, obviously worst case it was repaired.

so my questions are:

1. is there a way to check the specs of the prop without pulling it? it is a 4-blade, that's all i can tell you at this point.
2. is it possible i'm over propped? maybe when he replaced it he accidentally over propped it?
3. is this a bad thing? if so should i replace it with a lower pitched prop? using this current one as a spair?
4. what else could be going on here? could the tach be reporting incorrectly?
5. rpm's will continue to decrease as load and weight inside boat increases, correct? or am i wrong on that.

thanks for any advice. i don't want to make more of it than it is, but obviously looking to the experts for some guidance here. again i should state that the boat runs awesome. it's got less than 70 hours and i've had the oil changed twice since i've owned it (less than 2 months), as well as the fuel filter, cap and rotor and impeller changed.

brucemac
05-27-2008, 12:25 PM
hey also since i obviously need a spair anyway, can you guys recommend one?

i'll give eric a call, but was wondering what you folks think. we're 80% boarding, with some tubing for the kids and occasional recreational slalom.

we have the capability for ~2K in ballast, but will probably only ever run about 1250 or so, give or take.

i'd really like a good all-around prop that has plenty of poop in the low end, but that doesn't hit my rev limiter when our ballast is dry. is there such a prop?

P-hat_in_Cincy
05-27-2008, 12:40 PM
so my questions are:

1. is there a way to check the specs of the prop without pulling it? it is a 4-blade, that's all i can tell you at this point.
2. is it possible i'm over propped? maybe when he replaced it he accidentally over propped it?
3. is this a bad thing? if so should i replace it with a lower pitched prop? using this current one as a spair?
4. what else could be going on here? could the tach be reporting incorrectly?
5. rpm's will continue to decrease as load and weight inside boat increases, correct? or am i wrong on that.
For #1, you should be able to locate the information on the prop. See attached picture.
For the rest, you could email/call/PM Eric at OJ props.

Here's what I've been up to (different engine).
Prop thread. (http://www.tmcowners.com/teamtalk/showthread.php?t=9026)

Take care,
Paul

brucemac
05-27-2008, 12:59 PM
thanks p-hat, i'll give eric a call this afternoon or tomorrow after i take a closer look at the prop.

swatguy
05-27-2008, 05:20 PM
Bruce check my signature


The 14.25 prop whether Acme's or Eric's from OJ is the best prop hands down on that boat pulling the load.

I was always partial to Acme, but guys with the Oj give the same reviews of theirs.


I ran that old 13.7 X 17 for a small time(did the job) and then swapped it when they came out with the 14's 14.25's. Much better hole shot on the new 14's

Roonie's
05-27-2008, 05:25 PM
I will second the 14.25 x 14.5 prop. I have the OJ and it is an awsome hole shot and great prop for wakeboarding. I have it on my 07 X2 and I wouldn't want anything different. All prop info is located on the hub of the prop as shown in pic above. Yes prop size will change RPM's.

Jerseydave
05-27-2008, 07:08 PM
My buddy's X-1 (310 hp) had the stock 13.7 X 17, now has the OJ 14.25 X 14. Made a great difference for wakeboarding with extra ballast, better holeshot than stock.

If you primarily wakeboard, I'd recomment this prop.

brucemac
05-27-2008, 07:59 PM
so I looked at the prop. all it says on it is

2 0 CUP OJ

then on the side parallel to the shaft it says 12 02

i'll snap a picture

brucemac
05-27-2008, 08:10 PM
here's two pics...

http://img167.imageshack.us/img167/8168/dsc4199mediumms2.jpg

http://img301.imageshack.us/img301/3629/dsc4200mediumuu0.jpg

what is this?

brucemac
05-27-2008, 08:23 PM
i've emailed OJ to see if they can help me out and given them my contact info. hopefully they can tell me what this is and we can talk on the phone about getting a replacement. i'll just use this as a spare. anybody know what this one is though?

P-hat_in_Cincy
05-27-2008, 08:35 PM
i've emailed OJ to see if they can help me out and given them my contact info. hopefully they can tell me what this is and we can talk on the phone about getting a replacement. i'll just use this as a spare. anybody know what this one is though?
Looks like the days before OJ CNC'd the props? I don't see any machining lines. Also, looks like there might be something very faint just in front of the "12 02". Looks like you at least have "14 20 CUP OJ" on the end of the hub.

brucemac
05-27-2008, 08:56 PM
p-hat

i just don't know enough about props. does that mean if your theory is right, i'm over-propped right?

and would also support my tach readings of 4600-4700 at WOT with low load?

P-hat_in_Cincy
05-27-2008, 09:05 PM
:confused: I couldn't tell you and be sure I was accurate. I was just pointing out what I noticed in your pictures.

I will say that with the XMP EDGE I was running, I could easily hit the rev limiter at a pretty low MPH (it's built more for pulling power and hole shot), so maybe if your prop characteristics are at the other end of the spectrum you would be hard pressed to get to the rev limiter.

Eric will know what you need and, as stated in his posts on here and my experience, let you try it to be sure you like it.

brucemac
05-27-2008, 09:39 PM
thanks for the replies paul. i'll wait to hear back from eric.

rick s.
05-27-2008, 10:00 PM
Overpropped would be my guess. Same thing happened on my x45 with the mcx. Would only run 4800, standard prop was OJ 13.7 X 17. Eric at Acme suggested coming down a little in pitch, up a little in diameter adding a little cup. Boat now runs 5200, no speed loss, still 41 at WOT, but much better hole shot.




p-hat

i just don't know enough about props. does that mean if your theory is right, i'm over-propped right?

and would also support my tach readings of 4600-4700 at WOT with low load?

edwinfuqua
05-28-2008, 01:51 AM
At least you are not over reving the engine. I had several props and one would give me more than 6k and I did not like that, the next gave me 5500 and would give K+ on wake overs, the last (I think... 14.5x22 4blade by OJ will only let me turn 4700 WOT. Well heck, peak HP 425 is at 4500 or some wheres about so why do I need to get 6K out except to turn the prop blue? I am still testing, I am running the most aggressive prop now-the 14.5x22x4blade and so far happiest with it. It seems easier to throttle up to 2k watch the person skiing get up then ease up to about 35k and thats all they want.

When using the 13.5x20x4 blade it was too easy to get above 2k on launch and I would loose most skiers- probably because of too much take off pull.

Now if I was going to pull up 12 or so at the same time I would use the 13.5 and keep the RPMs about the same but at the same time using the smaller prop it would be easy to over rev the 454, you know 6K+ if you skip a wake.

Im still not sure either, Im not even sure my motor is broke in yet, so I will just do what feels good and is good for the motor. Make my mind up on the prop I want to keep and go for that.

On Q#4 'rpms' I can anchor it to the beach and get the same rpms at WOT, just wont be going anywhere.

Check your Max RPM and like any good trainee, shift at the max HP and don't over rev the engine. Both my props would give me about 50MPH the one Im running now at 4500RPM the other at 5500RPM. My max HP is 420 at 4300RPM.

Ive about made up my mind, just looking for a few more pulls to satisfy. Those guys at OJ can put it on the money for you. I testify to that.

brucemac
05-28-2008, 09:59 AM
eric's recommending this one...

14.75 X 15.5 LC XMP EDGE Splined 4-blade

off to re-read paul's post...

brucemac
05-28-2008, 02:50 PM
i just bought their part# 522, which is the 14.75 X 15.5 LC XMP Edge Splined 4-Blade.

Excited to try it out. I know it's not as aggressive as Paul's, but we're still novice boarders so the ballast for the most part won't typically be as much as Paul's running. On the occassions where we are sacked out Eric seemed to think this prop would be fine and said it's standard fair on quite a few of the 08 MC's (if I understood him correctly). Either way, he said I'm way over-propped with that 14x20 on their now so I should see better hole shot and higher RPM's without hitting the rev limiter. All for the price of about 3-4 MPH he said.

Jerseydave
05-28-2008, 05:30 PM
I had the 14 X 20 stainless OJ on my '03 230 Maristar before changing it. Made a huge difference in holeshot. Keep your stock prop for a spare, or if you want to barefoot and/or cruise a big lake all day.

What was your top speed with that 14 X 20? I could get 49 with mine, fun passing prostar 197's once I caught them! :)

brucemac
05-28-2008, 05:51 PM
yeah, it seems REALLY fast!!!

mine says 50 on both speedos, but i know they're not that accurate

i never measured by GPS, my friend keeps forgetting to bring his garmin out with him. i've almost bought one twice now, but i can't bring myself to do it when there's other goodies i need more. i.e.; perfect pass. :)

i have to lay off the spending for a bit. i know i keep saying that, but my wife's borderline losing her patience. ;)

there just always seems to be something. you know?!

i've spent quite a bit already and the boat wasn't cheap either. ;)

ultimately, i need 4 things now

spare rim and tire
perfect pass
plumb my ballast system
new audio install

will pick up the spare before my two road trips this summer and probably have to wait until later this season for PP and then fall/winter for the last two.

looking back, i should have listened to you guys and bought the PP before i bought all the fly high stuff, but live and learn. i figure a couple outings with her driving and she'll realize how important it is.

father's day is coming too...maybe she can start a piggy bank for it or something.

:)