Boats For Sale:
176 ideal prop? |
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phatsat67 
Grand Poobah 
Joined: March-13-2006 Location: Indiana Status: Offline Points: 6149 |
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 Posted: September-25-2014 at 10:04am |
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Gary! How dare you!
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Gary S
Grand Poobah
Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Posted: September-25-2014 at 11:30am |
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I tried Zack,we came in kinda last minute for a funeral Saturday and left Sunday morning :(
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Frankenotter
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Joined: August-26-2012 Location: Milwaukee Status: Offline Points: 1072 |
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Posted: September-25-2014 at 9:52pm |
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Today Steve loaned me his 422 and I took her for a test run after timing it last night.
We got 4700 RPM at 43mph. That speed was measured on a cell phone app and I had to back the throttle down after a few seconds (rollers on Lake Michigan). I think this is the sweet spot of the boat that Zach was referring to. I noticed a reduction in vibration and now I just have to ski it to check the hole shot. I think I have to adjust the carb now after changing the timing, but I'll post more stats when I get them. Cheers! Chris |
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1999 Ski Nautique 196
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21131 |
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Posted: September-25-2014 at 10:20pm |
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Get yourself a real GPS (or at least download the navionics app) and hold the throttle down a little longer. A 400rpm differential seems a little on the high side for a 176. If you're really pulling the 422 at 4700-4800, then you might want a 668 after all... I'm surprised the revs are so different from the 14x16. Ideally, you really want to turn 4600 or just below.
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skutsch
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Joined: June-19-2008 Location: Racine, WI Status: Offline Points: 2874 |
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Posted: September-25-2014 at 10:41pm |
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That Navionics App is cool!
Not 100% sure the tach is correct. It was my fault we had to shut it down. I should not have gone along. I told him to drop me off and make some passes on his own, but he would having nothing of it. He'll get some better data on a flat inland lake and I won't be with him. I also think that 14x16 is a VERY tired prop. I also offered up my 1442, we just have to get it off the Sport. AND I will give him one of my portable GPS's (which I forgot to take with us this trip). |
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Hollywood
Moderator Group
Joined: February-04-2004 Location: Twin Lakes, WI Status: Offline Points: 13512 |
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Posted: September-26-2014 at 11:07am |
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wat
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21131 |
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Posted: September-26-2014 at 11:50am |
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I know you're just busting chops, but I'll bite.
Taken out of context... I always recommend spinning the engine at max rated rpm (generally where it makes peak power) at a minimum, preferably exceeding it by 100-200rpm. For a 240hp PCM, the max recommended rpm is 4400, so 4400-4600 is the window, with 4500-4600 being the ultimate goal. You won't hurt anything spinning it at 4700-4800 but if there's a good prop out there that can knock the revs back to the range i just stated, you can gain a little bit of performance as well as some efficiency. I say "spin it to win it" to those afraid to exceed max recommended rpm for fear of "breaking things" or some such nonsense. Over propping to keep revs below max rpm is detrimental to both performance AND reliability as putting a large prop that loads down the engine is harder on components than over revving (slightly). |
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21131 |
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Posted: September-26-2014 at 11:55am |
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Steve, the 1442 will turn 200rpm higher than the 422 so it would be going in the wrong direction.
All of the "tired" props I've seen tend to lose efficiency at higher revs, meaning they allow rpm to climb higher without speed going up, presumably due to blade flex or some other issue. By holding rpm down at 4200 makes me think it's towards the steep (pitch) range of its tolerance and keeping the engine from reaching optimal rpm but I wouldn't call it tired. Just an older design that less precise and not a great performer. |
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skutsch
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Joined: June-19-2008 Location: Racine, WI Status: Offline Points: 2874 |
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Posted: September-26-2014 at 11:59am |
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Tim as always, you are 100% correct, but that old prop needs some time with a couple of hammers and some heat, it is pretty "out of shapes."
I agree with the assessment of the 1442, but we thought it would be fun to throw it on their just for chits and giggles. |
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Frankenotter
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Joined: August-26-2012 Location: Milwaukee Status: Offline Points: 1072 |
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Posted: September-28-2014 at 7:33am |
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Thanks Tim. I think I'll bring the Rpm a back down a little. I think with a new prop and a little carb tuning it will be a 45mph boat. For a little guy with a 240hp and over 1000 hr that's not bad.
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1999 Ski Nautique 196
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TRBenj wrote: