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PendOreilleSkier

RPM's at WOT - different at altitude?

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PendOreilleSkier

Just wondering if anyone notices a difference in wide open throttle RPM's at different elevations ... breaking one in at 2200-2400 ft , thx.

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WakeGirl

RPMs will be lower the higher the altitude. What exactly is it in relation to break-in that you're talking about? 2200-2400 isn't terribly high, but you'll see a bit of a difference vs. sea level.

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PendOreilleSkier
RPMs will be lower the higher the altitude.  What exactly is it in relation to break-in that you're talking about?  2200-2400 isn't terribly high, but you'll see a bit of a difference vs. sea level.

Well, I just finished 10 hours of breaking in, and from 5-10 hrs I was able to go to WOT for a bit following my manual (no more than 2-3 minutes) and I wasn't sure if it (not getting to the top of the engines RPM range) was a product of a fresh engine being tighter or higher altitude, realistically I will always run at this altitude so I may prop down to get more rpms ... part of me just wanted to get up to 5K during the initial break-in period, realistically there is not much more speed to gain on this hull

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WakeGirl

How far off were you? Propping down for running at altitude is pretty typical, I've done it for most of my boats (we run between 3k & 5k feet).

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PendOreilleSkier

I could get 4750, the range is 4800-5200 ... so I am close to the low end and should probably just deal with it... what was more of an annoyance was that there was no speed gain in the last 250 rpms, so propping down wont help with more speed and holeshot is awesome with the gear reduction ... since I don't foot the speed is not a big deal, but I know one thing the Response has is a higher top end speed ... next year I will be looking for a pull behind one of "yours" as I bet the Yacht Club will put more than a few new boats on the water. I've got to find some skiers up here that are good to go for another month or so. Plus, it is always fun to ski behind a different boat once in a while.

Its simmilar to the Monsoon right?

Displacement: 5.7L / 350 CID

Cylinders: V-8

Bore & Stroke: 4.00 x 3.48

Compression Ratio: 9.4:1 (High-flow Vortec heads)

Fuel System: EFI - custom Indmar multi-port tuned induction system

Computerized Total Engine Management System: Delphi 3-dimensional system manages fuel,ignition and air. Custom calibrated by Indmar it uses GM's marine specific ECM (engine control module) computer with sealed ceramic circuit board. Uses latest MEFI software.

Ignition: HEI (high energy electronic ignition)

Fuel Required: Reg. or unleaded, 89 octane minimum

Oil Type: Pennzoil Marine (SAE 15W-40) SJ/CG4

Max. RPM: 5,200

Warranty: Indmar’s exclusive 3-year limited warranty includes fuel and electrical system.

Edited by PendOreilleSkier

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WakeGirl

Yeah, IIRC the MCX is a direct comparison with the Monsoon. I'd really give that motor a chance to properly run in before making your final determination. You are very close, & if you come down 1500 feet, you'll be right within the range so I can't see propping down over that, especially if you're happy with the power on the other end of the curve.

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VinRLX

How many people are in your boat when you are turning 4750? What are the RPM at typical ski speeds?

I would not want my boat propped under the range. No way, no how. Theoretically, you want it toward the TOP of the range.

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WakeGirl

I agree Jack, but I think it would be a good idea to get more hours on it to see where it falls in before making that decision. At the very least it will be more exact when going to get a new prop.

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VinRLX

Absolutely, more hours loosens her up a bit.

Still, curious to have the answers to my above questions. I love prop talk. Drool.gif

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