WOT rpm range

Hantsman

Cadet
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Jun 28, 2022
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Looking for some opinions on WOT rpm range. Do most people aim to reach the upper end of recommended rpm range or the middle? I have a 60hp merc 4 stroke (5500 to 6000). Can hit 6000 rpm with a 13p blackmax. Should I try a 14p to get in the middle of thr recommended range?
 

jimmbo

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May 24, 2004
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There are several theories. Some will prop as close to the upper end with a Light Load, others will prop closer to the Rpm where the engine is making peak HP. That can be difficult to find and it not always what the Spec says. Case in Point, for years OMC made a 90hp, a 115, and a 140, all sharing the same displacement. All were rated their respective HP at 5000 rpm and all had a WOT range of 4500 - 5500. They did not all make their Highest HP at 5000. The 90 made it's highest power at 4600-4700, the 115 was closest to the 5000 mark, and the 140 did it's best between 5350 and 5450 rpm. If propped to hit the highest HP rpm, that is where you will get the Highest top speed. Propping for either side of that Rpm will result in a slightly lower Speed as less power made. A 90 revving to 5500, is making less HP than it did at 4700
If propped to it hit the top of the Rpm Range when lightly loaded, means you or anyone else is not going to Over Rev the Motor. Propping too low, does increase the Temp of the Piston Crown, and that can cause Oil in Ring Grooves to cook and turn into Carbon, resulting in all sorts of Misery

If I were you, I would leave the 13 on it, adding pitch will also slow down the Acceleration
 

QBhoy

Admiral
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Mar 10, 2016
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6,375
Looking for some opinions on WOT rpm range. Do most people aim to reach the upper end of recommended rpm range or the middle? I have a 60hp merc 4 stroke (5500 to 6000). Can hit 6000 rpm with a 13p blackmax. Should I try a 14p to get in the middle of thr recommended range?
If you can hit it easily and with a bit of gear onboard…yeah. Certainly. If it’s only just hitting the limiter with light load…it’s not so bad. These engines like to run up high. Within the realms of being sensible of course
 

jimmbo

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If the engine had a RPM range of 5500-6000, the Rev limiter is not going to kick at 6000, it will take a few hundred more rpms before it does its thing
 

Hantsman

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Jun 28, 2022
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Not really worried about hitting the rev limiter trying to find a good balance between top end and acceleration. 6000 rpms was with the wife and kids and some fishing gear.
 

jimmbo

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I have found that within a given Prop Line, the differences in Top Speed are less than 2 mph, unless the rpm is outside the WOT Range. Switching Prop Lines, and that includes Brand, you will be starting with a New Anchor point
 

Hantsman

Cadet
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Jun 28, 2022
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Ya I have noticed that. Tried the same pitch of black max and hustler props. The 13p hustler seems to get on plane a bit quicker but overall the mercury props seem better overall on my setup.
 

jimmbo

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Mercury has been making some of the finest Props for many Decades. In the 50s, 60s, and 70s, they were Leap Years ahead of the Competition.
 

QBhoy

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So are you hitting the limiter or are you just saying you can reach 6000 ? My outboard rpm range is 5000-6000…I run a prop that will hit the limiter if I let it go long enough. Or a prop that will just see 6000 rpm. The rpm limiter on mine is about 6100/6150 or there abouts. If I ran a prop that would result in only 5000 rpm…it would be a dog of a thing. I tried one that saw about 5500 rpm and it was actually slower by a few mph than the lesser pitched props that would see 6000
 

jlh3rd

Petty Officer 3rd Class
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Jul 10, 2017
Messages
79
so, I propped my pontoon boat to operate with people on board and tubing. That results in being able to actually exceed my 6000 rpm upper range when running with just me and girlfriend. But when loaded, I'm in the middle or slightly higher of the 5000 - 6000 recommended range.....
I lost about 3 mph top speed changing to the prop I have now...
It's all about what you want , or how you perceive your treating the motor..
 

QBhoy

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Mar 10, 2016
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It will reach 6000 rpm. I think the rev limiter is 6250
It’s not quite as high as that. More around 6100 or a wee bit over at most. I’ve got the smart craft readout and vessel view. Gives exact rpms from ecu and currently propped that it will hit limiter if I let it go long enough. At around 43/44 mph gps and about 6100.
 

Texasmark

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Dec 20, 2005
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14,271
Not really worried about hitting the rev limiter trying to find a good balance between top end and acceleration. 6000 rpms was with the wife and kids and some fishing gear.
You have your best hole shot with what you have. Obviously running alone, having a rev limiter or you controlling yourself with the throttle will maintain your 6k rated performance. My engines have always run at mid to top end and when I got older and got to boating alone, I always ran the top end. My Mercs loved it. Been boating over 65 years and never lost an engine.
 
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