Old Merc. 3.0L not 140hp?

[LilRedNeckGirl]

Re: Old Merc. 3.0L not 140hp?

Which I never said!

But again you misinterpret my post. Unlike a car, a boat has fixed gearing. Once you put a particular prop on, that's it, that's the load the engine will see THROUGHOUT THE REV RANGE, not just at WOT. If you are using a prop that is too big, it's too big for whatever throttle position you 'cruise' at, not just WOT. It's like cornering in a car in third gear, or taking off from the lights in second... Like not changing down to negotiate a hill....

But boats run on water, which allows the prop to "slip", not like a car or bike where there is rubber to the road traction.

As for lasting longer with a big prop on... Don't make me laugh!!! Go out and ride a push bike with fixed gearing. Which one would do you think you'd last longer on, one with high gearing that requires less revolutions, but more effort per revolution, or one with lower gearing, needing more revolutions, but less effort per revolution? I know which one I would prefer, and your boat engine is exactly the same!

Chris............

Just one last comment... Why do you think manufacturers even specify a recommended rev range? It's to do with longevity, economy, drive-ability and reliability....[/QUOTE

Cause a show room boat has to have an multi use prop, one that "does everything fair to middlin. Its common knowledge, that aftermarket props are installed, to fit the specific use of a boat, @ less pitch or more blades for the hole shot thing, and more pitch for a better top end....

 

[Bondo]

Re: Old Merc. 3.0L not 140hp?

Which I never said!

But again you misinterpret my post. Unlike a car, a boat has fixed gearing. Once you put a particular prop on, that's it, that's the load the engine will see THROUGHOUT THE REV RANGE, not just at WOT. If you are using a prop that is too big, it's too big for whatever throttle position you 'cruise' at, not just WOT. It's like cornering in a car in third gear, or taking off from the lights in second... Like not changing down to negotiate a hill....

But boats run on water, which allows the prop to "slip", not like a car or bike where there is rubber to the road traction.

As for lasting longer with a big prop on... Don't make me laugh!!! Go out and ride a push bike with fixed gearing. Which one would do you think you'd last longer on, one with high gearing that requires less revolutions, but more effort per revolution, or one with lower gearing, needing more revolutions, but less effort per revolution? I know which one I would prefer, and your boat engine is exactly the same!

Chris............

Just one last comment... Why do you think manufacturers even specify a recommended rev range? It's to do with longevity, economy, drive-ability and reliability....[/QUOTE

Cause a show room boat has to have an multi use prop, one that "does everything fair to middlin. Its common knowledge, that aftermarket props are installed, to fit the specific use of a boat, @ less pitch or more blades for the hole shot thing, and more pitch for a better top end....

Ayuh,.... I believe the point being made is that, the motor/ motors should be Able to spin up to the manufacturer's spec's...
Otherwise,...
If the motor is Unable, it's in a state of Lugging, Constantly...
Detonation is only a heartbeat away....

If the motor Can reach wot, rpms,... Ya can run Any rpms ya wanta run at, 'n the motor is in it's "Happy" zone....

Just 'cause you get away with it,... Don't make it the Right way to prop a boat.....

 

[dubs283]

Re: Old Merc. 3.0L not 140hp?

Cause a show room boat has to have an multi use prop, one that "does everything fair to middlin. Its common knowledge, that aftermarket props are installed, to fit the specific use of a boat, @ less pitch or more blades for the hole shot thing, and more pitch for a better top end

so i guess we can also say the gear ratio in the drive is meaningless seeing as how boaters can determine the best engine performance with thier choice of prop and running midrange rpms??

manufacturers have, over many years, determined the proper drive gear ratio, prop pitch/diameter, and rpm's throughout the entire range for optimum engine perofrmance/longevity based on boat size and design for a reason - if every boat owner put a prop on thier boat that they bought at a gargae sale because it fit, shops would be replacing a lot more engines

not to get off topic but some of the older "3.0's" are actually 2.5L engines, thus accounting for less horsepower

 

[RogersJetboat454]

Re: Old Merc. 3.0L not 140hp?

LilRedNeckGirl,

You are arguing with common knowledge here....
It's a pretty well known fact that over propping a boat 9 times out of 10 eventually WILL lead to detonation and engine failure.

You can throw around car analogies all you want, but boat's aren't cars. As stated by previous posters, boats don't have 3+ forward speeds to maintain the best engine RPM. Boats have far more drag than a car going down the road, and certainly don't coast along. Props do slip, but not a whole lot.

If you want a car analogy that matches the conditions of a boat, imagine a car chained to a heavy cement block thats dragging the block down the road. This car has only one gear which is the equivalent of say 2nd or maybe 3rd gear in a manual transmission. Now imagine that same car, with the same scenario, only this time the gearing is equivalent to 4th or 5th gear. You are multiplying the amount of load on the engine, which is explained by a simple understanding of mechanical advantage when it comes to gearing, and you are never going to get that cars engine up to where its rpm's belong.

 

[fishrdan]

Re: Old Merc. 3.0L not 140hp?

But boats run on water, which allows the prop to "slip", not like a car or bike where there is rubber to the road traction.

Cause a show room boat has to have an multi use prop, one that "does everything fair to middlin. Its common knowledge, that aftermarket props are installed, to fit the specific use of a boat, @ less pitch or more blades for the hole shot thing, and more pitch for a better top end....

Actually, boats have more friction riding across the water than a car/truck driving on land, it has little to do with a prop slipping in the water. Take your foot off the gas and a car/truck will coast for a long distance, take your hand out of the throttle on a boat and it coasts for a very short distance. A boat is constantly fighting to stay on plane and is best compared to a car/truck constantly pulling a heavy trailer up a hill, take your foot off the gas and it coasts a very short distance.

More and less pitch (for more speed or holeshot) is true to some degree, though you still need to select a prop that will allow the engine to reach it's proper WOT RPM range. We don't know the WOT RPM for your boat, so we can't say for sure that your boat is over-propped. Though,,, slow planing is a good indication of being over propped. Even if your boat's twin 140HP engines are running a 21P and reaching their WOT RPM, you can't recommend a 21P prop to someone else with an entirely different boat, just because they have a 140 Mercruiser too, they could have an entirely different load to push.

Mercury has a good prop selector website that gives prop recommendations for different performance characteristics, acceleration, top end speed, good over all performance, etc. It uses different variables; boat design, weight, load, engine, WOT RPM, usage, to determine what prop will work best for a specific application. IF, the WOT RPM is low it's going to suggest a prop with less pitch, if the WOT RPM is high it's going to suggest a prop with more pitch. They are the professionals, the guru's, and recommend propping a boat's engine within it's spec'ed WOT RPM range.

 

[fishrdan]

Re: Old Merc. 3.0L not 140hp?

not to get off topic but some of the older "3.0's" are actually 2.5L engines, thus accounting for less horsepower

What????

Mercruiser would be in deep dookie if they were selling engines stickered with "3.0L" when it's displacement was only 2.5L. With all the hungry lawyers floating around this country, they wouldn't have a chance.

If you are saying some of the newer 3.0L's put out 120HP or less, instead of 130, 135, 140, that's believable since there is nothing saying Mercruiser couldn't slap a "2.5L head" on a 3.0L block and then spec it with less horsepower. I actually think that's the case for certain years with the normal "3.0L" and then the "3.0LX" The 3.0LX has a better head/manifold, along with other stuff.

Top left - carpy manifold design (2.5L-120HP)
Top Right - old 140 HP design
bottom left - dunno, mid years I guess
bottom right- high flow, high performance, best design

 

[dubs283]

Re: Old Merc. 3.0L not 140hp?

Mercruiser would be in deep dookie if they were selling engines stickered with "3.0L" when it's displacement was only 2.5L. With all the hungry lawyers floating around this country, they wouldn't have a chance.

that is not what i meant, the reason i put 3.0 in quotes is because the block is the same

the older 2.5L engine was not labeled 2.5L or 3.0L, it was a horsepower model designation like 115 or 120 and it looks exactly like a 3.0L engine

 

[fishrdan]

Re: Old Merc. 3.0L not 140hp?

that is not what i meant, the reason i put 3.0 in quotes is because the block is the same

the older 2.5L engine was not labeled 2.5L or 3.0L, it was a horsepower model designation like 115 or 120 and it looks exactly like a 3.0L engine

A 2.5L block is not the same as a 3.0L block, different internals too, 153CI compared to 181CI. The 153(2.5L) was used in vehicles (IE: 68 Chevy II), while the 181/3.0 is a marine and industrial only engine. They look similar externally, kind of how a 283 and 400 small block Chevy V8 look similar. There are differences though, the 153(2.5L) doesn't use a vibration dampner like the 181(3.0), pulley only on the 153/2.5L, manifold, head, differences.

To muddy the waters even more is the HP rating change. Old 140HP crank rated is more like 120HP prop rated now. Newer 135HP prop rated would be more like 155HP crank rated of old. Throw in all the head, manifold, compression, displacement, etc, etc changes over the years and you get the 120HP 153CI(2.5L) crank rated and the 115HP 3.0L(181CI) prop rated...


Edited; Achris corrected my mistake, it's not a 120HP 3.0L, it's a 115HP 3.0L. (Though I guess there could be a 120HP 3.0L, I'm not lookin' to verify)

 

[dubs283]

Re: Old Merc. 3.0L not 140hp?

from mercruiser SM #2



note the hp rating and engine displacement between the 120 and 140

 

[achris]

Re: Old Merc. 3.0L not 140hp?

from mercruiser SM #2

View attachment 131681

note the hp rating and engine displacement between the 120 and 140

Not sure what you're getting at here dubs. The '120' is a 2.5L (2517cc) and the '140' is a 3.0L (2956cc).

If you have a look at service manual #13, page 1B-3, you'll also see that the 3.0L is rated at 115hp, and the 3.0LX is rated at 135hp. Both use the same 181 cu.in (3.0 litre) engine block....

Chris.....

 

[fishrdan]

Re: Old Merc. 3.0L not 140hp?

from mercruiser SM #2

View attachment 131681

note the hp rating and engine displacement between the 120 and 140

I couldn't read the page you referenced, so I looked at Mercruiser SM#2 and found...

(As Achris posted up)

120HP engine displacement is 153CI or 2517CC or 2.5L

140HP engine displacement is 181CI or 2956CC or 3.0L

 

[dubs283]

Re: Old Merc. 3.0L not 140hp?

yep,

what i was getting at is some of the older 4 cylinders are smaller displacement engines with lower horsepower ratings

at first glance one could easily see a 2.5L as being quite similar in appearance to a 3.0L

 

[sweet addiction]

Re: Old Merc. 3.0L not 140hp?

I don't know why everyone seems to think that a 15-17 pitch prop is so great for a 3.0 powered boat. I have a '94 3.0LX powered 17' Glastron with a 1.98 ratio drive that came with a 14.25 X 21 aluminum prop that had the motor running at around 5100-5200 RPM at perfect trim. Those that know this motor know that, that RPM is way too high. WOT is 4400-4800 RPM. The boat was topping out at around 41-42 MPH and had an insanely great hole shot in average conditions and 45 MPH in ideal conditions. I switched to a stainless 14.25 X 23 prop with vents. Everyone thought I was nuts. I proved them wrong. The boat now tops out at 45 -46 MPH in average conditions and 50 MPH in ideal, And that's with the added weight of 2 additional batteries(total of 3 group 29's) and all my stereo equipment. And my mileage went up and it still hole shots just fine. My current RPM range is 4200-4300 RPM. I know it's a bit on the low side but I feel that it's much better than the 5200 RPM I was seeing before. And yes I am going to try a 14.25 X 21 stainless this summer. All this being said I can not understand why anyone would ever recommend a 15 or 17 pitched prop stainless or aluminum. I feel that other than being a tad low on my WOT RPM, My 23p prop gives me great all around performance from hole shot to top end speed. After all It's not too often that you hear about a 17' 3.0 powered boat doing 50 MPH on a regular basis, At least here in Wisconsin that is.

 

[achris]

Re: Old Merc. 3.0L not 140hp?

I don't know why everyone seems to think that a 15-17 pitch prop is so great for a 3.0 powered boat. I have a '94 3.0LX powered 17' Glastron with a 1.98 ratio drive that came with a 14.25 X 21 aluminum prop that had the motor running at around 5100-5200 RPM at perfect trim. Those that know this motor know that, that RPM is way too high. WOT is 4400-4800 RPM. The boat was topping out at around 41-42 MPH and had an insanely great hole shot in average conditions and 45 MPH in ideal conditions. I switched to a stainless 14.25 X 23 prop with vents. Everyone thought I was nuts. I proved them wrong. The boat now tops out at 45 -46 MPH in average conditions and 50 MPH in ideal, And that's with the added weight of 2 additional batteries(total of 3 group 29's) and all my stereo equipment. And my mileage went up and it still hole shots just fine. My current RPM range is 4200-4300 RPM. I know it's a bit on the low side but I feel that it's much better than the 5200 RPM I was seeing before. And yes I am going to try a 14.25 X 21 stainless this summer. All this being said I can not understand why anyone would ever recommend a 15 or 17 pitched prop stainless or aluminum. I feel that other than being a tad low on my WOT RPM, My 23p prop gives me great all around performance from hole shot to top end speed. After all It's not too often that you hear about a 17' 3.0 powered boat doing 50 MPH on a regular basis, At least here in Wisconsin that is.

And all of this is with a calibrated 'shop' tacho and GPS, yes?

 

[LilRedNeckGirl]

Re: Old Merc. 3.0L not 140hp?

I hear all your saying, and agree that you can put too much of a pitch on a boat drive, I attain just over 4300 rpm at wot. I prefer to cruise at 3000/3200.
thats my 'happy speed' where the boat skims along effortless, easy and smooth. im on plane around 2500 rpm.
i look around the prop forums, and see common acceptance, that prop variation, both in blade numbers and pitch are widely accepted to tune the preformance to the particular use of the boat. its all good as long as you stay reasonably within the wot rpm range.
The rubber to the road, cars have near 100% posative traction between the tire and the road, hence the need for gears. gears allow for the start up torque and increase in speed, as there is no 'slip' in traction. A boat prop, on the other hand, is a fluid traction device, that generates thrust by spinning in the water. The start up is not instant, as water slips by the prop, building speed as prop speed increases, thereby increasing thrust. Tie a boat to the dock and idle up, prop spins, boat dont move. Try that with a car. Prop drive is much more forgiving and flexable then a car/tire drive. A steeper pitch will add load, no doubt, go faster with a lower RPM, but if its within the mfg range, the engine is responsive, and wot can be reached, it is an acceptable prop in my opinion. . i would bet that most on here have switched from what the mfg put on their boat, to a better preforming prop with a different pitch. the mfg one size fits all isnt always the best.

I dont buy into all the "draggin a cement block" analogies,as cars/trucks have a MFG towing limit, and , as a bunch of boaters typicaly get out there and drag a person along behind the boat, same difference, no ill affects, not overloading the engine or drive. Basicaly, its what they are designed for, and clearly, they have a wider range of operation, a variety of props that will work job specific, and a greater tolorance then the manufacturer ha let on to the mechanics.
Im no pro, but that is just common sence.

 

[fishrdan]

Re: Old Merc. 3.0L not 140hp?

I don't know why everyone seems to think that a 15-17 pitch prop is so great for a 3.0 powered boat. I have a '94 3.0LX powered 17' Glastron with a 1.98 ratio drive that came with a 14.25 X 21 aluminum prop that had the motor running at around 5100-5200 RPM at perfect trim. I switched to a stainless 14.25 X 23 prop with vents.The boat now tops out at 45 -46 MPH in average conditions

Thats "your" boat and if it can turn a 23P prop while still achieving it's WOT you did the right thing. BUT, you can't say every person with a 3.0/140HP should use a 23P or even 21P props as their boats are different. (I seem to remember Glastron's being fast hulls...) Myself, I'm running a 18P 4 blade and it's a perfect match to my boat, good holeshot and right at the top end of the WOT range, 4600RPM. If someone needs a 15P prop for a specific application they should use it, if they need a 17P prop they should use that also, I have both and use them for different conditions, heavy load or high altitude.

 

[sweet addiction]

Re: Old Merc. 3.0L not 140hp?

And all of this is with a calibrated 'shop' tacho and GPS, yes?

Yes I use GPS for my speedo.

 

[sweet addiction]

Re: Old Merc. 3.0L not 140hp?

Thats "your" boat and if it can turn a 23P prop while still achieving it's WOT you did the right thing. BUT, you can't say every person with a 3.0/140HP should use a 23P or even 21P props as their boats are different. (I seem to remember Glastron's being fast hulls...) Myself, I'm running a 18P 4 blade and it's a perfect match to my boat, good holeshot and right at the top end of the WOT range, 4600RPM. If someone needs a 15P prop for a specific application they should use it, if they need a 17P prop they should use that also, I have both and use them for different conditions, heavy load or high altitude.

I whole heatedly agree that every situation is a little different but....To be spinning 5200 RPM on a motor designed to see no more than 4800RPM is bad news. That was my whole point. Those were the RPM's I was seeing with a 21p. And no my drive couple is not bad/slipping.

 

[achris]

Re: Old Merc. 3.0L not 140hp?

I whole heatedly agree that every situation is a little different but....To be spinning 5200 RPM on a motor designed to see no more than 4800RPM is bad news.

Who says allowing the engine to spin easier is a bad thing? My engine, (also recommended WOT 4400-4800) runs to the rev limiter (5100) with the current prop, but if I put the 'right' prop on it'll make 4600, but in the mid-range it's a dog! The truth is I rarely use WOT, and if that's the case with OP, then having a prop one size smaller is GOOD news, not bad...

Those were the RPM's I was seeing with a 21p. And no my drive couple is not bad/slipping.

That's real funny, because with the 21" prop and those number you had 33% slip, but with the 23" your slip dropped back to a more realistic 12%..... Something don't gel!

Chris..............

 

[aerobat]

Re: Old Merc. 3.0L not 140hp?

well, i think everybody should use a prop whatever needed to reach the recommended rpm at WOT- at a light boat a higher pitched prop, at a heavier boat a lower pitch prop. the engine developes it rated HP not at every rmps but at its design rpm and when you pitch your boat to stay below or above this you waste horses since the engine turns to slow to develop its max power or it turns so fast that it is already "over the top" i had a 20ft cabin boat with a volvo 3.0 GS and the prop was 14x17x3 . a little to much for this boat- alone i reached 4100rpm, with 4 persons only 3800-3900. i think here a 15pitch would be fully correct.

does somebody know why the 3.0 GS was rated at 150 hp and the newer 3.0GL only 135?