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Looking for prop size advice

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Old 06-10-2018, 04:55 PM
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Default Looking for prop size advice

boat has Ilmor 650ís, Iím new to these and learning. Brovo XR drives, 1.5 ratio. Last year owner hit something in water and messed up a herring 26 pitch, 5 blade prop. He bought 26Ē non herring props from Teague. Boat seems to be way under propped to me.

Suggestions? Thanks in advance.
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Old 06-10-2018, 05:16 PM
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What is your WOT RPM, and GPS speed?
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Old 06-10-2018, 06:52 PM
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Max rpm is 6300 according to Ilmor. Max hp is at 6000, boat runs 91 to 93 mph at 6000-6100. Iíve only test driven the boat. Waiting on funds to settle and transport to get it here. Chime walks pretty good above 90 mph.
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Old 06-10-2018, 09:54 PM
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I don't think you are under propped if you aren't banging off the rev limiter.
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Old 06-10-2018, 09:54 PM
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Not under propped at all. Actually the numbers look about perfect assuming 1.5 ratio drives. Its at 8% propslip.
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Old 06-11-2018, 02:39 PM
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Thanks for the input, I am no expert, and I know that, more like I know just enough to be dangerous and ask dumb questions.

I was test driving the boat and the seller was quite generous, good guy, he let me run it as I wanted to, but I am not one to beat on other peoples stuff. So I did not run it really hard, got it into 5400 - 5700 RPM at 93 mph, and it started getting slippery so I got off the throttle. New boat to me, so I was not willing to push it, and not sure exactly how she would preform. I am pretty sure she would have hit rev limiters easily, there was quite a bit of throttle left when I got out if it. Everything else looked and acted better than my expectations so I purchased it without running it really hard. Also seemed like on take off it was missing some bite.

That plus SnaponMorgan, a pretty regular here, has the same boat with 700 HP GM motors and I think he is running 32's. He has offered to let me try his 30's, will see what those do.

Again, thanks for the education on this. I know most around here know this topic better than I.
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Old 06-11-2018, 06:26 PM
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Originally Posted by Numbers View Post
Thanks for the input, I am no expert, and I know that, more like I know just enough to be dangerous and ask dumb questions.

I was test driving the boat and the seller was quite generous, good guy, he let me run it as I wanted to, but I am not one to beat on other peoples stuff. So I did not run it really hard, got it into 5400 - 5700 RPM at 93 mph, and it started getting slippery so I got off the throttle. New boat to me, so I was not willing to push it, and not sure exactly how she would preform. I am pretty sure she would have hit rev limiters easily, there was quite a bit of throttle left when I got out if it. Everything else looked and acted better than my expectations so I purchased it without running it really hard. Also seemed like on take off it was missing some bite.

That plus SnaponMorgan, a pretty regular here, has the same boat with 700 HP GM motors and I think he is running 32's. He has offered to let me try his 30's, will see what those do.

Again, thanks for the education on this. I know most around here know this topic better than I.
He is probably making 700hp at a lower rpm though and would be using taller props. You want to run the Ilmors so they are propped for 6000-6200 rpms at WOT. Too big of props will lug the engines and make them work harder and increase the risk of detonation.
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Old 06-12-2018, 01:05 PM
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Get that thing home Dean. I am not afraid to run the snot out of someone else's rig. We will see what it needs. As far as the chine walk, mine did it too above 90. I removed the 280 bottom plates and installed 380 plates. It has helped a lot. Saw 96mph a few weeks ago in some pretty rough water.
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Old 06-12-2018, 03:20 PM
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Thanks Joe! Transporter picking up in the morning, just did the wire transfer and literally 2 minutes ago seller confirmed he got it. I'd like to know what she will do, I just know not to take to many chances whit that scenario, my current boat spun out once and threw me across the cockpit, 24 stitches and 3 cracked ribs later I limped her home. May have it this weekend, if not, definitely for the Cannon Ball run

Last edited by Numbers; 06-12-2018 at 03:24 PM.
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