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SeanK

WOT and top speed

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The other day, Lake Pontchartrain was finally flat enough for me to see how fast my 2012 216 SSI would go (stock 220 HP 4.3 MPI Mercruiser).  It was just me and my wife with a full tank of gas.    The Merc manual states WOT is approx. 4600 RPM.    Reading posts, I assume top speed is around 48-50 mph - I used that as a benchmark.

At around 2700 RPM, I was at 35 mph.   With the throttle lever at horizontal, I was at 45 mph but only at 3300 RPM.    I did not go any further thinking my RPM gauge could not be reading correctly.   Do these numbers seem correct?   With 1300 remaining RPM to WOT, it seems like I could get it to 60 mph (not that I ever want to go that fast), but never heard anyone getting it that high.   30-35 mph is my comfort zone.

Thanks for the reply.

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11 hours ago, SeanK said:

The other day, Lake Pontchartrain was finally flat enough for me to see how fast my 2012 216 SSI would go (stock 220 HP 4.3 MPI Mercruiser).  It was just me and my wife with a full tank of gas.    The Merc manual states WOT is approx. 4600 RPM.    Reading posts, I assume top speed is around 48-50 mph - I used that as a benchmark.

At around 2700 RPM, I was at 35 mph.   With the throttle lever at horizontal, I was at 45 mph but only at 3300 RPM.    I did not go any further thinking my RPM gauge could not be reading correctly.   Do these numbers seem correct?   With 1300 remaining RPM to WOT, it seems like I could get it to 60 mph (not that I ever want to go that fast), but never heard anyone getting it that high.   30-35 mph is my comfort zone.

Thanks for the reply.

Go for it. The rev limiter will keep you honest. If she drops out around 4,800, then you may be under-propped. If she does not self-limit, and the tach is reading over 4,800, then the tach is off.  W

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13 hours ago, SeanK said:

At around 2700 RPM, I was at 35 mph.   With the throttle lever at horizontal, I was at 45 mph but only at 3300 RPM.    I did not go any further thinking my RPM gauge could not be reading correctly.

Do you think you had more room to push the throttle beyond horizontal?  You might've already been at its limit. 

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I just assumed that the horizontal position would be around the max, but it was only at 3300 RPM.   I will have to try it again.   Good to know there is a Rev limiter to keep me from overspeeding the engine.

My prop is a 3-blade, 19 pitch, Mercury Enertia.

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On ‎10‎/‎2‎/‎2018 at 12:25 PM, SeanK said:

I just assumed that the horizontal position would be around the max, but it was only at 3300 RPM.   I will have to try it again.

I don't know about Merc, but on my VP, I can push the throttle all the way in either direction without the engine running.  Then I can see where the ends are in both directions.  I've done that and put a little piece of blue tape to line up that full position as a reference point so when I was out, I can see how far I have left on the throttle without actually going WOT.  Maybe try that instead of actually pushing it to WOT?  That should let you know.  I have barely another 1/2" of movement beyond horizontal, if that.

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If your tach is set to the 8 cyl setting and is showing 3300 rpm, then your 6 cyl engine is actually spinning 4400 rpm.

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11 hours ago, SeanK said:

Dash gauge.

The dash gauge tach has a selector switch on the backside of it to select between a 4, 6, or an 8 cylinder engine. It very well may be on the 8 cylinder setting.

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I believe he is answering my question about where boat speed was read from?

12 hours ago, SeanK said:

Dash gauge.

 

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On 10/2/2018 at 8:29 PM, cyclops2 said:

Time to check the cylinder selector switch on the backside of the tachometer.

I think you nailed it, Clopadopadopadus! :clapsmiley: There is some value to 80 curmudgeonous years after all, ey? :)

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5 hours ago, Dennis A said:

I believe he is answering my question about where boat speed was read from?

 

Oh, duh, my bad.  :slap:

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3 hours ago, Hatem said:

I think you nailed it, Clopadopadopadus! :clapsmiley: There is some value to 80 curmudgeonous years after all, ey? :)

Did you just diss Cyclops in your native tongue?  :scratchchin:  :D

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15 hours ago, tomnjo said:

Did you just diss Cyclops in your native tongue?  :scratchchin:  :D

Mmm...you got me thinking what Cyclops is in hieroglyphics....oh yeah, I know!

eye+horus.jpg

LOL! :D 

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You could also tap onto the engines computer. Most newer GPS units can display engine readouts.

Not hard to do, just need to add a gareway. 

 

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1994 1830SS 4.3LX Alpha 

Prop: Alum 3-blade 14x19p

Revved to 5,200rpm at 40mph

I know my RPM should be more like 4,800 and my top speed should be 45ish

I had a 14x21p on there before it got banged up and it ran me around 5,000rpm and 45mph. 

So, I'm thinking of going with an aluminum 4-blade 14x21p. I'm hoping the extra blade will lower the rpm and the 21p will increase my top speed. 

 

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11 hours ago, Hatem said:

Mmm...you got me thinking what Cyclops is in hieroglyphics....oh yeah, I know!

eye+horus.jpg

LOL! :D 

Hahah

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There is no way you were getting 45 mph at 3300 RPM with a 19 inch pitch prop. Either your RPM or speed (or both) are incorrect. 
brick

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