Difference between Mercruiser 3.0 and 3.0LX

crenshaw4x

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Jun 5, 2010
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Hello, I have a 1993 mercruiser 3.0. I am wondering what the difference is between this motor and the 3.0 LX which has more horsepower. I am looking to see what I can do to increase performance of my 3.0.

Are there bolt-on carbs or ignition kits that give more horsepower ?

Thanks, appreciate any ideas.

Doug
 

John_S

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Re: Difference between Mercruiser 3.0 and 3.0LX

I thought it was just power steering, but some 3.0L experts will know for sure. No easy or economical HP upgrades. Just keep it up to par with good maintenance.
 

atomb

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Re: Difference between Mercruiser 3.0 and 3.0LX

The cylinder head on 3.0 lx are the major difference - no bolt ons for this engine she is what she is a plain old good engine.
 

crenshaw4x

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Re: Difference between Mercruiser 3.0 and 3.0LX

Well the manual that came with the boat says this particular 3.0 is 115hp and the 3.0LX is 135hp. Which is odd because if you look around for a prop or other parts the 3.0's always seem to be 125hp and up.

The boat does fine, it's very low hours for a '93, spent most of it's life up north in a drystack. I get about 35-37mph WOT at about 4500-4600, which seems to be normal. I have a 14.5X19 prop, and I am considering trying a 21" pitch so I can lower the cruise rpm's a bit.

First I/O I have owned, everything up to now was either a sailboat or an outboard, so I am just trying to learn more about this particular set-up. Thanks for the reply, hopefull an expert will let us know !
 

crenshaw4x

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Re: Difference between Mercruiser 3.0 and 3.0LX

Cylinder heads, eh ? Do they up the compression then ? That would make sense, since it is the same size engine. I guess that's not such a simple bolt on as a carb would be, but maybe when it's time to re-build it might be worth it. It would just be one head right ? Straight-line 4 cylinder ?

Thanks for the reply, good to know this stuff.
 

atomb

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Re: Difference between Mercruiser 3.0 and 3.0LX

the port size is larger i believe on the cylinder heads. a larger carb i dont believe would add to the horespower or torque for that matter.
 

crenshaw4x

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Re: Difference between Mercruiser 3.0 and 3.0LX

Thanks for the info, sounds like I will learn to live with it. Sokay though, the boat runs good and that's what matters most !
 

Bondo

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Re: Difference between Mercruiser 3.0 and 3.0LX

Thanks for the info, sounds like I will learn to live with it. Sokay though, the boat runs good and that's what matters most !I get about 35-37mph WOT at about 4500-4600, which seems to be normal. I have a 14.5X19 prop, and I am considering trying a 21" pitch so I can lower the cruise rpm's a bit.

Ayuh,... Goin' to a 21" prop will lower the rpms into the Lugging range,+ probably detonate the motor into an anchor...

But you Might see better gas mileage til it gets there...:rolleyes:;)
 

crenshaw4x

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Re: Difference between Mercruiser 3.0 and 3.0LX

Well educate me a bit there then !

My understanding (limited) from the manual is that this engine should be 4200-4600 rpm WOT. I get right at the top end with a 19" pitch. 2" of pitch should change that number by somewhere between 200-400 rpm I think. Is that wrong ?

I cruise it now at 3500rpm which gives me about 25mph. I figured the 21" pitch should give me the same speed at about 3100 rpm's or so.

If I am wrong someone please tell me. I can take it, I'm a big boy.
 

crenshaw4x

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Re: Difference between Mercruiser 3.0 and 3.0LX

Hey Bondo !

So I don't want another anchor ( I have two already) and that engine would be hard to stow when I wasn't using it.

But what is a good range for cruising rpm's ? I am doing 3500 right now with the 19" pitch prop, getting about 21-25mph depending on load, wind, waves, etc. I was thinking the 21" pitch prop (same diameter of course) would take it down to about 3100rpm's. Is this too low, in your opinion ?

Thanks, appreciate the info.
 

John_S

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Re: Difference between Mercruiser 3.0 and 3.0LX

You may want to repost in the "Prop" section, but the answer will still be: "Your current prop is the correct pitch for your boat, based on the info you provided. Going to a higher pitch will lug the engine, which will ruin it." Find the best compromise with your current prop, be it cruise speed or fuel economy.
 

Bondo

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Re: Difference between Mercruiser 3.0 and 3.0LX

But what is a good range for cruising rpm's ?

Ayuh,.... As I said in the pm,....
You prop for rpms at WOT,... Cruise rpms fall wherever they may....
 

crenshaw4x

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Re: Difference between Mercruiser 3.0 and 3.0LX

Ok guys, I got it, WOT rpm's are what matters.

So........

The plate on this engine says the WOT should be between 4200-4600. I get the top end of that range. I am guessing that is where you want to be ?

You see where I'm going with that right ? I know ya do !
 

John_S

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Re: Difference between Mercruiser 3.0 and 3.0LX

Are you getting 4600 with your typical load or just by yourself? If with full load, what rpms can you get by yourself, 4800?

If you really want to change it, go ahead. You still need to be able hit that range with all loads. Even if you can, your time to plane will suffer over current prop. Pulling skiers out (if you do that) will be much harder.
 

180shabah

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Re: Difference between Mercruiser 3.0 and 3.0LX

If your 19" prop get you to the top of your WOT range and you started this thread looking for more power - then switching to a 21" will give you exactly the opposite of what you are looking for.

Your holeshot will suffer, you might not even be able to plane when the boat is loaded. You will lose top end speed because the engine will not be able to get to the rpm where it is making full power. Mid range acceleration will be sluggish due to the increased load from the higher pitch.

You MIGHT get better cruising economy, but it will be so slight you will not be able to measure it. Plus it will be offset by the longer time it takes to get on plane etc....
 

crenshaw4x

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Re: Difference between Mercruiser 3.0 and 3.0LX

Just for the sake of the discussion, I get 4800 with the whole family of four onboard, including a cooler and junk. I have yet to get out on the boat by myself. The boat comes on plane very easily, I usually do not even give it full throttle to get up.

The reason I was looking for more power in the beginning was to go the 21" pitch prop so I could lower the cruise rpm's. It just seemed to me that 3500 was on the high side. If I pull back to about 3000 she starts to settle and come off the plane.

It's really not so much about economy as it is engine noise.
 

John_S

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Re: Difference between Mercruiser 3.0 and 3.0LX

Just for the sake of the discussion, I get 4800 with the whole family of four onboard, including a cooler and junk. I have yet to get out on the boat by myself. The boat comes on plane very easily, I usually do not even give it full throttle to get up.

The reason I was looking for more power in the beginning was to go the 21" pitch prop so I could lower the cruise rpm's. It just seemed to me that 3500 was on the high side. If I pull back to about 3000 she starts to settle and come off the plane.

It's really not so much about economy as it is engine noise.

Then try the 21" and see what your wot rpms are at, and if you prefer it over the better hole shot.
 

BajaDan

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Re: Difference between Mercruiser 3.0 and 3.0LX

Then try the 21" and see what your wot rpms are at, and if you prefer it over the better hole shot.

Just a beginner here, but changing a prop sounds like wasted money to me. The boat and motor/prop combination was engineered for optimum performance from the factory with a wide range of speed and load characteristics. If you want more power, do it the all American way. A bigger motor in another boat...
 

oldjeep

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Re: Difference between Mercruiser 3.0 and 3.0LX

Just a beginner here, but changing a prop sounds like wasted money to me. The boat and motor/prop combination was engineered for optimum performance from the factory with a wide range of speed and load characteristics.

Um - nope

And this is a 2 year old thread
 

BajaDan

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Re: Difference between Mercruiser 3.0 and 3.0LX

Um - nope

And this is a 2 year old thread

Yep, not very timely. Realized it after I posted it. Guy at the parts house convinced me that a prop upgrade isn't money well spent. I'm still learning and appreciate the comment.

Regards,

Dan
 
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