mercury 115 vs johnson 150

hi guys,
i m debating on which engine to put on my 18 foot cc wellcraft boat. my merc is a 115 91 model..good compression.all cylinders 135 + on all cylinders. Then i have a 150 johnson 90 model v6 . the compression on it is all in low 90s to high 70s.,which i was told was normal for some of the big v6 engines. my question is i know horsepower is king but considering ill have to completely change over all my binnacle controls,wires,etc, if i go with the johnson,will the performance increase be enough to justify everything that will need to be done. im kinda caught up here..i want the best engine on my boat. What kind of mph difference do u think they might be. all info and opinions are welcome. thanks

Re: mercury 115 vs johnson 150

You want to have at least 100 psi on the cyl. and all of them at least within 10% of each other. The Mercury Inline 6 a.k.a Tower of Power is a solid good running motor.

Re: mercury 115 vs johnson 150

The last tower o power was the 1986. If the Johnson ran well it would have much more power. That said: 79 to 91 maybe too much of a spread to run, (the difference between cylinders is the real key). Sometimes the compression tester doesn't give high readings but the engine runs fine if they are even. JR

Re: mercury 115 vs johnson 150

The Mercury would be my choice.

Re: mercury 115 vs johnson 150

Whisker, I have owned and run versions of both of those motors. Specifically I had a '77 Merc inline six 150HP for years and now I have a '98 Johnny 150HPV6. I believe the Johnny will have more low end power and use more fuel. It also weighs 100# more than the Merc. The Merc will provide the same mid-range and high speed operation, but less out of the hole. If weight or slightly less fuel use is an issue on that boat, pick the Merc. It is just my opinion, everyone has one....

Re: mercury 115 vs johnson 150

Chris1956 said:

Whisker, I have owned and run versions of both of those motors. Specifically I had a '77 Merc inline six 150HP for years and now I have a '98 Johnny 150HPV6. I believe the Johnny will have more low end power and use more fuel. It also weighs 100# more than the Merc. The Merc will provide the same mid-range and high speed operation, but less out of the hole. If weight or slightly less fuel use is an issue on that boat, pick the Merc. It is just my opinion, everyone has one....

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Chris: are you sayin' a 1991 115 Merc is an inline6?????????? NOT A CHANCE. I believe the 1991 was a 4 cylinder. JR

Re: mercury 115 vs johnson 150

EDIT to my last two posts. The inline 6 was built until 1988. A 1991 WAS A FOUR. PERIOD. I do agree with Chris that the Johnny is heavier and would drink more fuel for over 20% MORE POWER!!!!! JR

Re: mercury 115 vs johnson 150

Just a thought, a 91 115 is definitely an Inline Four.

That being said, if you're planning on doing a lot of watersports, this motor isn't necessarily the greatest choice.

The way that Merc achieved a very low idle speed on these Fours was to drastically lean out 2 cylinders so they'd drop out at idle and leave the other (2) doing the work. This works well enough, and the lean-idling cylinders have an accelerator pump to reduce any off-idle lean issues.

But, the transition from dead-lean-idle on these cylinders to pulling a load at speed is rather abrupt. So, you may have issues with fine speed control when you're pulling tubers or wakeboarders at low-to-medium speeds.

In other words, it's gonna kick in and out and speed will go up and down; this may happen at exactly the "sweet spot" for your boarder's speed and you know how irritating this will be.

Now, if you're doing watersports exclusively, you could prop down 2" or even 4" in pitch. The increase in engine speed and less load on the engine will lessen the transition period. But of course you're limiting top end and economy won't be so hot.

You could also get one of those fancy Torque-Shift props that would have a real low pitch starting out, then shifts up for higher-speed ops.

But, if you're not much into watersports it probably won't bother you much.

I'd certainly cast my vote for an Inline Six but you might find you'll be very happy with the Four on your Wellcraft.

HTH & let us know how things work out...........ed

Re: mercury 115 vs johnson 150

hi,
thanks for input. this is just my fishing boat. my main concern is pushing my 18footer without alot of pain(so to speak). i was just wondering how much more a 150 would give me mph anyways if everything else is the same.

Re: mercury 115 vs johnson 150

whisker said:

hi,
thanks for input. this is just my fishing boat. my main concern is pushing my 18footer without alot of pain(so to speak). i was just wondering how much more a 150 would give me mph anyways if everything else is the same.

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A 150 is 30% more power then a 115.

I don't know what the 1991 115 weighs but the additional weight of the 150 would cost some of that extra power and you would burn fuel to generate said power.

If both engines are in cornparable shape, (you need to weigh this fact), the 150 is what I would choose as it would likely be at least 20% faster if your boat can take the extra power and weight.

The 115 inline 6 the other posters were thinking you were talking about would be a better choice then the 115 you are asking about but even that engine would be inferior to the Johnnyrude v6 and Johnnyrudes fair better in salt water then the old inlines. I dunno about the 1991 Merc in salt water.

Me overpriced $.02. JR