# Merc 25hp 2-stroke and 4-stroke comparison



## noeettica (Sep 23, 2007)

Cool test Tom ...

How was the Vibration with the 4 Stroke ... The Low frequnecy Vibration Drives me Nuts ...

Another Point is That You only have to Carry half the fuel with a four Stroke 

Sure Wish Jan would throw an E-Tech 30 into The "shoot Out "

But his reasons for Not doing so are Legit ...

Dave


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## out-cast (Jan 27, 2009)

Looks familiar......boat ramp rd?


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## TomFL (Oct 2, 2007)

> Looks familiar......boat ramp rd?


Yes indeed. A great test place, deserted ramp allows you to change motors or work on your trailer. 

Or let your wife practice her "backing up the boat trailer" skills

-T


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## out-cast (Jan 27, 2009)

> > Looks familiar......boat ramp rd?
> 
> 
> Yes indeed. A great test place, deserted ramp allows you to change motors or work on your trailer.
> ...



Hhmmmm. No that's some good thinkin' :-?


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## Brett (Jul 16, 2008)

30.4 with the 4 stroke, better gas mileage at lower rpms
30.7 with the 2 stroke, less weight on the transom
25 hp is 25 hp, the difference is in what you're using it for.
If I was gonna run top end all day, I want a 2 stroke.
For trolling or cruising I'd want a 4 stroke.
Thanks for the test results Tom.


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## mark_gardner (Mar 18, 2009)

the best i could ever do with my 25  4 stroke with me, battery and misc. gear was 27 mph in the mud minnow, i know they arent the same boat but the hulls i'm pretty sure are about the same ( the mud was splashed from a gheenoe) and i'm pretty sure i'll do the same with my merc 25 2 stroke all i need is a hydrofoil to keep it from porpoising. your right though it does feel like your going slower with the 4 stroke but like you said its probably because its a lot quieter and smoother. the thing i like about the 2 stroke is it's lighter weight and it's much easier to tilt, because of my poling platform thats  a nice feature that my back really appreciates . one thing i dont really care for about the 2 stroke is always having to mix gas, its been several years since i have had to do that  and of course i could run all day with a few gals. of gas with the 4 stroke


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## lemaymiami (Feb 9, 2007)

Great comparison running the two on the same hull and same conditions... What would you guesstimate the difference in hull attitude at rest? In other words what's the weight differential and does one let you pole shallower than the other? There are probably a few of us that are always much more interested in how a hull poles with different setups on the back... than how fast it books...


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## TomFL (Oct 2, 2007)

> Great comparison running the two on the same hull and same conditions... What would you guesstimate the difference in hull attitude at rest?  In other words what's the weight differential and does one let you pole shallower than the other?  There are probably a few of us that are always much more interested in how a hull poles with different setups on the back... than how fast it books...


Good point, and one I often overlook as I'm not too concerned about being super-skinny with this skiff, nor do I pole a boat. I did not do any comparison like that, nor do I have a place to test that unfortunately. 

From the seat of the pants I don't think there was much difference honestly. We're talking 54lbs, and I don't know if that will make a difference on this hull. Remember, depending on the distance you travel with the boat you can get away with less gas with the 4-stroke which might help offset some of the weight difference. 

The boat is rigged with two batteries and charger under the rear deck already plus I had 2 people and a bunch of other stuff onboard so wasn't a huge jump in overall package weight so to speak. 

I do remember the motor I had on this boat prior to the 4-stroke was an 18hp 2-stroke nissan, which weighed I think ~75lbs and was decent on gas. Still pushed the boat about 26.5 alone and about 21ish I think with 2 people. If I didn't make long runs and was looking for the absolute ultimate shallow-water setup, that's the motor I'd look to put on this hull. I do remember that the boat was absolutely ridiculously light with that setup. Maybe that sorta motor and a jackplate and you'd have a helluva shallow water setup.

Probably be able to pole it with a flexi-straw. 

-T


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## mark_gardner (Mar 18, 2009)

i have poled my mud minnow with both motors and i honestly could'nt tell the difference, like tom said, to offset the extra weight of the four stroke bring less gas


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## TomFL (Oct 2, 2007)

Bob, I'm going to run the 2-stroke tonight a bit so I'll tell you what I'll do. 

I'll measure the draft as the boat sits with the 2-stroke, and when I put the 4-stroke back on it I'll measure the draft then as well and post the difference. 

Worth a shot and then you'll know for sure. 

-T


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## Frank_Sebastian (Oct 15, 2007)

You fellows are beginning to sound like racers now and it worries me a little. Something like "never underestimate the power of the dark side" comes to mind.

Best regards,
Frank_S


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## deerfly (Mar 10, 2007)

For a non technical comparison I think the results are about as expected. Brett summed it up pretty well too. 

Me, I disagree on the point of 54lbs being inconsequential. Especially in a small skiff context. The way I look at it is that amounts to roughly 9 gallons of gas or about 7-8 more gallons than I'd need on an average outing. 

54lbs is apprx 6.5 gallons of water or apprx 2 day's survival ration for 3 people or 4 more gallons of water than I'd need, again on an average outing. 

54lbs works out to about 6 gallons of extra beer for Curtiss.  

If you're a trolling motor junky you've lost what could have been an extra group 27 battery in that 4 stroke crank case, which is like carrying two batteries when you can only ever use one. I can very quickly think of many more instances where having an extra battery is more useful than having 55lbs of cast iron on board. 

So while 54lbs doesn't seem like a lot, its still dead weight that I would otherwise not have on board or could add to my USCG rated loading capacity for other things like camping gear, etc. And "things" that can be moved around to better distribute the weight too. No choice but the transom with the motor. 

IMO that much weight for an extra mpg or two or a few decibels of noise reduction over a 2 stroke is not worth it to me. I'd rather haul the extra gas on those few trips per year where needing it may be factor and even there I think the actual MPG differences between 2 stroke DFI and 4 strokes is far less than most people think. 4 stroke quietness as well as no need for oil in the gas is irrefutable tho.


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## B.Lee (Apr 29, 2008)

Deerfly has some good points, but a few missed ones too.

1. that extra 54lbs isn't just dead weight, it's dead weight hanging off the transom. Probably more the 54lbs effectively considering leverage.

2. All the extra weight comparables mentionedd can be moved around to balance the boat, the engine weight can't. (kinda related to #1)

3. You can't go buy a new 2-stroke Mercury, so the arguement is moot. [smiley=1-doh.gif] [smiley=1-sillyface.gif]


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## Brett (Jul 16, 2008)

54 lbs on a balanced load 16' 'noe would make a 1/4 inch difference in draft.


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## TomFL (Oct 2, 2007)

Y'all have brought up some good points on both sides. 

Well here's my thoughts having run them both on the same hull. 

1) You don't have to mix oil with the 4-stroke. You can decide whether this is a big deal to you or not. 

2) The 4-stroke gets much better fuel mileage. Published reports available from Nissan are as follows: 

2-stroke 25hp : 3.3 gal/hr, when factored into a 31mph speed delivers ~9.4mpg.

4-stroke (non-EFI motor mind you): 2.3 gal/hr, when factored into a 31mph speed delivers ~13.5 mpg. With the 4-stroke EFI Merc I have personally covered 46 _GPS and Google-Earth measured_ miles on less than 3 gallons of fuel with LOTS of stop and go running. That's more than 15mpg. 

1 gallon of gas weighs ~6.5 lbs. 

So figure on carrying 50% more weight in fuel to cover the same ground with the 2-stroke. Figure the 4-stroke is about a 35lb penalty when fuel is factored in. 

3) The 4-stroke is a lot quieter. This can be good or bad given your choice of excitement. 

4) The 24v trolling motor comparison is a good point. The 24v motor alone is easily 10lbs heavier than the 12v motor. Factor in another 43lbs for the group 24 battery and you're right about the same weight difference as the 4 vs 2 stroke. But, the 4-stroke weight is over the transom, the widest part of the boat. So you wanna put your batteries up front to balance the weight? Well what happens when you stand in the bow while fishing? Now you've got 2 batteries, a heavy 24v trolling motor and your butt all on the pointy end. 

Here's my thoughts: They both have a great following, and good points to each of them. They both do the job very well, are basically evenly matched in speed. Fuel mileage can be a moot point if you fish 2 miles from the dock. Just depends on what you'd like to hang out back. 

I will check draft figures with a ruler in the next few days. 

-T


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## deerfly (Mar 10, 2007)

b.lee I did mention weight distribution in my post. 

"And "things" that can be moved around to better distribute the weight too. No choice but the transom with the motor. "

Tom, i'd have to dig around some and don't have time right now, but I thought the 2 stroke DFI mpg numbers were more comparable to 4 strokes like the Tohatsu TLDI engines. Even yami's recent DFI motors of since 2006 or so are better than carbed equiv.

Are those nissan figures from fuel injected 2 strokes or carbs? There is a much bigger delta between carbed 2 smokes vs 4 stroke injected or other wise. 2 smoke firing on every stroke still delivers HP quicker.. 

"1 gallon of gas weighs ~6.5 lbs." my bad, I rounded up to 7 from poor memory, so I stand corrected 8.3 gallons of gas or 7.3 more than I'd usually need.


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## deerfly (Mar 10, 2007)

> 54 lbs on a balanced load 16' 'noe would make a 1/4 inch difference in draft.



right, but the engine can't be balanced without moving it into the cockpit via sponsons or a mullet boat type thingy amidships or more forward still. 

A tiller 4 stk is exponentially worse with a fat guy sitting in front of it at the stern.


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## TomFL (Oct 2, 2007)

> > 54 lbs on a balanced load 16' 'noe would make a 1/4 inch difference in draft.
> 
> 
> 
> ...


Too funny... 

Deerfly, the MPG #'s I listed for the 2-stroke is not for TLDI, although larger TLDI motors are listed on there: http://nissanmarine.com/tech_talk/gas_mileage.html

-T


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## lemaymiami (Feb 9, 2007)

Looks like i started another small discussion... The only reason that I asked is that the micro I'd like to own eventually (with two still in college it's a ways off) wouldn't have any trolling motor or any live well. It would just be a poling skiff with enough motor to cover some ground out of Flamingo or Everglades City. It would never have more than two aboard and will need to get up skinny... I'm kind of addicted to poling for fish and keep three pushpoles ready to go. It would be nice to actually push something light for a change....


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