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BarryW

Prop Size

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I have a 2007 236 SSI with 70 hrs. OEM motor was a Merc 5.0. This boat sat for 5-6 years in storage and after about 10 hrs of use last year after I bought it, the motor took on water and then TaTa to the motor. I replaced it with a new merc 5.7 and all is good now but it seems like it over revs way too much. Like to the point that the alarm goes off. Over 5,000 rpm's

It has a swim platform and I dont have a trailer so it is not to easy to get to the prop to see what I have and what maybe I can change it to to find the right size and pitch.

It get's out on plane pretty quick but when you give it 3/4 throttle, it rev's too high.

Any ideas?

Thanks in advance,

Barry

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Make sure drive is all the way down then you are gonna have to get the prop size to see where to go. What drive is on it?

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Alpha One. When drive is all the way down, it seems ok, but still might over rev a bit. When you try to trim it up just a bit to give you less drag, it really revs high and starts to cavitate!

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Never drove a 236 SSx without a Bravo 3 drive, but that model uses the same hull as the 216/220 SSi, and 236 SSi. Weighs more than the 216 and 220 versions, but a person with a 236 SSi with 350 Mag MPI Alpha or Bravo 1 should have the same prop pitch as you require.

Generally, the boats were spec'd to run a 19" or 21" prop. Whatever pitch of prop you have currently, go up 2" of pitch for aluminum to aluminum, or ss to ss.

Personally if the boat were mine, I would run a Mercury Revolution 4 ss prop probably in a 19" pitch. No question the 5.0L MPI is a dog performance wise vs the 350 MPI.

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Did you change the gear ratio in the drive? 5.7 uses 1.50   5.0 uses 1.84

Michigan makes a 14 3/4  x 24P #953524

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On 6/3/2017 at 8:04 AM, Bt Doctur said:

Did you change the gear ratio in the drive? 5.7 uses 1.50   5.0 uses 1.84

Michigan makes a 14 3/4  x 24P #953524

1.84 aka 1.81 was used on some V6 engines with Alpha 1 drives, but I don't think I've seen it on a V8 Alpha 1 before. Maybe used on high elevation set up? 

Bravo 3 (dual prop drive) uses a 1.81 ratio, but I've only seen them on big block powered models with a favourable power to weight ratio. Generally a small block V8 was matched with the 2.20 gear ratio, and rarely the 2.00 for the Bravo 3.

Bravo 1 (single prop) gear ratio offerings are 1.36, 1.50, and 1.65. Would think the 1.65 gear ratio was on the 5.0L MPI, Bravo 1, and probably for the 350 Mag MPI Bravo 1 spec'd powertrain too.

NOTE: sometime around 2007, MerCruiser changed the rev range for the 350 Mag MPI. Previous models ran 4600-5000 RPM at wide open throttle, while later models used a different cam and ECM, and ran 4800-5200 RPM at wide open throttle. Regardless, the sticker on the plastic engine cover will give the desired WOT RPM range. Recommend allowing the engine to reach the higher side of the rev range with an average load for optimal performance.

Example below is an older Bravo 3 with a 2.00 gear ratio.

Mercruiser-Bravo-3-III-Outdrive-200-rati

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58 minutes ago, Shepherd1 said:

1.84 aka 1.81 was used on some V6 engines with Alpha 1 drives, but I don't think I've seen it on a V8 Alpha 1 before. Maybe used on high elevation set up? 

Bravo 3 (dual prop drive) uses a 1.81 ratio, but I've only seen them on big block powered models with a favourable power to weight ratio. Generally a small block V8 was matched with the 2.20 gear ratio, and rarely the 2.00 for the Bravo 3.

Bravo 1 (single prop) gear ratio offerings are 1.36, 1.50, and 1.65. Would think the 1.65 gear ratio was on the 5.0L MPI, Bravo 1, and probably for the 350 Mag MPI Bravo 1 spec'd powertrain too.

NOTE: sometime around 2007, MerCruiser changed the rev range for the 350 Mag MPI. Previous models ran 4600-5000 RPM at wide open throttle, while later models used a different cam and ECM, and ran 4800-5200 RPM at wide open throttle. Regardless, the sticker on the plastic engine cover will give the desired WOT RPM range. Recommend allowing the engine to reach the higher side of the rev range with an average load for optimal performance.

Example below is an older Bravo 3 with a 2.00 gear ratio.

Mercruiser-Bravo-3-III-Outdrive-200-rati

My old 2002 220SSi and my current 2005 220SSi both had 350/B3's with 2.0 ratios. I think Chaparral switched the 220SSi to a 2.2 ratio in 2006 or 2007.  I think all 5.0 motors with B3 drives came with a 2.2 ratio.

I always prop for the high end of the RPM range. 

brick

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As a point of reference for you, my 220 with 350 and B1 with 1.50:1 ratio has a 17 inch prop on it.  It won't go past 5000 rpm with this particular prop which is pretty aggressive.  

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