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Mercruiser 3.0

I think my question was more like, If same block and rotating assembly are same, is it safe to run a standard 3.0 at 4800 rpm? I'm evaluating several props right now.
 
PB48052 said:
I think my question was more like, If same block and rotating assembly are same, is it safe to run a standard 3.0 at 4800 rpm? I'm evaluating several props right now.
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Hard to say i would assume bottom end is the same but do recall the older ones have a max of like 4200 rpm. What year and what engine do you have? Im assuming you have a 3.0 L rated at 115 hp vs the LX rated at 135 hp? Are you trying lower pitch props for holeshot and water sports use?

if so intermittently going a tad over recommended wot rpm probably wont hurt assuming the engine is mechanically sound.
 
....keeping in mind that the 4800 RPM figure, like the 4200 RPM figure is not intended as a continuous operating RPM..
 
sandkicker said:
....keeping in mind that the 4800 RPM figure, like the 4200 RPM figure is not intended as a continuous operating RPM..
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There has been an engine swap, ID sticker on rocker cover is unreadable. Will be looking at block for more numbers. Tune up info sticker on block says 4600 max. I'd really like to see a power/torque curve and aim for that number. I've always liked to prop for redline with lightest possible load. Boat is used on large lake, general cruising, occasional tube/ski. Long runs at cruise speed. Usually 20-50 miles in a day.
 
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This is my opinion,

Using a brand new three bladed Mercruiser/Mercury properly cupped prop and in all cases the drive trimmed up for maximum performance.

Lets say a 17 pitch prop.

You reach 4800-5000 RPM with good acceleration (like for pulling a water skier) then you have over shot the target of 4600 RPM Max.

You then use a 19 pitch prop and you now are in the 4600 4700 RPM range with slightly less performance (most likely not really noticeable) then you are in the "safe range for MAX RPM. but gained 1-2 MPH vs 17 pitch prop.

You use a 21 pitch prop and you are now in the 4300-4400 RPM range and are closer to the lower MAX RPM spec. You may gain an additional 1-2 MPH but will sacrifice your acceleration/out of the water performance.


So in my opinion, these are your choices.

After all it is most likely a 17 ft with a 4 cylinder motor. Not your average V6 or V8 pleasure boat so there is no real expectation of any real "performance"....
It will be what it will be performance wise.

Trying to achieve a MAX RPM will not get you a whole lot but based on how you use the boat, the choices I explained gives you something to expect based on prop choice.
 
Correct, we just bought a 18' Sea Ray bowrider, 1995. Not my 1st boat, and so far, a solid 40+ mph, very pleased. Just trying to ID this engine and dial in a rpm range. I understand the limits of this motor and don't feel handicapped, nor am I looking for the ultimate top speed. This was with a 21p, which I just had reconditioned and will be testing today with shop tach. Thank you for your help,
Will report on it later.
 
PB48052 said:
Correct, we just bought a 18' Sea Ray bowrider, 1995. Not my 1st boat, and so far, a solid 40+ mph, very pleased. Just trying to ID this engine and dial in a rpm range. I understand the limits of this motor and don't feel handicapped, nor am I looking for the ultimate top speed. This was with a 21p, which I just had reconditioned and will be testing today with shop tach. Thank you for your help,
Will report on it later.
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I had a similar size '91 sea ray 170 ( i think 17'6") with a 3.0, what I arrived at was two props Both Aluminum michigan vortex 4 blades- I used a 18" for cruising/tubing, and a 16" for skiing. At the time I was clocking in at about 265-270 lbs and it would pull me up fairly good on two skiis. The 18" did womnders for sternlift and lower planing speed at the expense of 3 or 4 mph top end which you never get to use due to waves anyways... Lower planing speed was nice because the 3.0s are always a little loud so the PM booze cruise was more pleasant for the wife...
 
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