Maximum RPM for Merc/omc 165 6 cyl.

[revsound]

I recently replaced my 140 4 cyl. With a rebuilt OMC 165 in line six. I immediatly had to change my gearing, the local marina recomended 1.84 and installed them. I tried several props and wound up with a 27. I am running 4600 RPMs at 3/4 throttle and I am not sure I sould push it any higher. What is a safe RPM at wide open throttle? The factory manual does not say, clymers says 4300 which seems low. Help!

Thanks, Greg

[revsound]

I recently replaced my 140 4 cyl. With a rebuilt OMC 165 in line six. I immediatly had to change my gearing, the local marina recomended 1.84 and installed them. I tried several props and wound up with a 27. I am running 4600 RPMs at 3/4 throttle and I am not sure I sould push it any higher. What is a safe RPM at wide open throttle? The factory manual does not say, clymers says 4300 which seems low. Help!

Thanks, Greg

[JW]

That Clymer manual might be right on. I am not familiar with the 165, but I know the old 120 had a max rpm at around 4,000. They are not high revving engines. I would first recommend you check your tachometer for accuracy. It could be way off. That prop and lower unit gear ratio shouldn't spin that motor that high. Once you have a known accurate tach, then try props.

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Checkmates owned: 1995 Pulsare 2100BR/1995 Mercury Promax 225 2.5 EFI. 1995 Persuader 183/4.3 LX V6. 1992 Pulse 171/1992 Mercury XR6 150 hp 2.5 liter.

[revsound]

How do I check the Tachometer for accuracy.

Thanks, Greg

[175checkmate]

The only way that I know how to verify the tach is to install another one and compare the two.

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1975 Checkmate Tri-mate 2, 2.4 200+ / Sky jacker 6" plate / 25p Laser 2 prop, Currently the boat is undergoing overhaul.

[JW]

Take it to your local NAPA dealer, they may be able to test it for you, or will know where you can take it for testing............

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Checkmates owned: 1995 Pulsare 2100BR/1995 Mercury Promax 225 2.5 EFI. 1995 Persuader 183/4.3 LX V6. 1992 Pulse 171/1992 Mercury XR6 150 hp 2.5 liter.

[Chris E]

It sure sounds like the tach is suspect, however, try and get your hands on an old service manual for that omc. I have a 160hp merc inline six max revs are 38-4200 rpm. these inlines do not like revs - but they are bulletproof. Mine is a 1968 and is as smooth as ever.

[revsound]

I think you might be right, this engine is the same as a merc 165. I did some quick calcs the tach says 3400 RPM and the speedometer only reads 34 MPH. with a 1.84 gear and 27" pitch I should be going 60 mph (without slippage). I need to figure out a slippage factor.

[JW]

I like to use 11% for a prop that is in NEW condition........

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Checkmates owned: 1995 Pulsare 2100BR/1995 Mercury Promax 225 2.5 EFI. 1995 Persuader 183/4.3 LX V6. 1992 Pulse 171/1992 Mercury XR6 150 hp 2.5 liter.

[revsound]

Thanks for the slippage factor, I was able to check my tack with test tach. It looks like my tach was about 200 RPM high. How do I test my speedometer?

[Chris]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by revsound:
Thanks for the slippage factor, I was able to check my tack with test tach. It looks like my tach was about 200 RPM high. How do I test my speedometer?<HR></BLOCKQUOTE>Comparing it with a GPS is probably the best way. http://www.checkmate-boats.com/infopop/emoticons/icon_smile.gif

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