# 15 OR 20 HP.... IS THERE MUCH DIFFERENCE?



## randyo3629 (Jan 28, 2017)

been looking at new Tohatsu 15 & 20 hp tiller outboards. the brochure shows the internal engine specs to be identical... as in displacement. the gear ratio is the same. prop selection size is the same @ 6"-11.5"
the only difference is see is in the Max RPM range. 5000-6000 on the 15 hp and 5400-6100 on the 20 hp.
how could the additional 100 RPM make 5 hp difference?
what do they do to get the extra 5 hp?

seems to me that with the engines being basically identical, you make up for a difference in top speed with change in propeller pitch.
i also looked at the specs for their 8 & 9.8 hps motors....they are identical in every way.

this will be my first new engine. do you get to pick the pitch of the propeller? why the large range in prop sizes?
all else being equal, is it worth the extra $$ for 5 hp?
thanks.


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## Prowelder (Jan 28, 2017)

randyo3629 said:


> been looking at new Tohatsu 15 & 20 hp tiller outboards. the brochure shows the internal engine specs to be identical... as in displacement. the gear ratio is the same. prop selection size is the same @ 6"-11.5"
> the only difference is see is in the Max RPM range. 5000-6000 on the 15 hp and 5400-6100 on the 20 hp.
> how could the additional 100 RPM make 5 hp difference?
> what do they do to get the extra 5 hp?
> ...


I would look for a used motor and go for the higher horsepower. Faster is always more fun in my opinion. On the other hand if you have money for a brand new motor why not buy the 25 or 30?

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## mirroman (Jan 28, 2017)

Some engines like merc gain 5 hp by using a different carb, ie 10hp vs 15hp same specs different carb.


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## Prowelder (Jan 28, 2017)

mirroman said:


> Some engines like merc gain 5 hp by using a different carb, ie 10hp vs 15hp same specs different carb.


A lot of times it's more than just a carb. They usually have different Reeds also

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## richg99 (Jan 29, 2017)

I'd re-post your query on Microskiff.com Lots of Tohatsu motors are used on that site.

richg99


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## satx78247 (Jan 30, 2017)

randy03629,

IF it was me, I'd find a NICE pre-1960 Johnson/Evinrude/Gale 15-25 horse OB & replace the points/plugs/condensors/coils/water pump impeller & rebuild the carb. = It's been my experience that you can buy the motor & do all the things that I suggested for 250.oo or less on a Johnson Model FD-12 & have a BETTER OB, too.
(In point of fact, I own a 18HP electric-starting 1958 Johnson, for which I paid 40 bucks at garage sale & then spent 112.oo replacing all the things that I mentioned above for a total of <155 bucks. - It's been FINE on my 14 foot tin Lone Star open fisherman, that I paid 100.oo for, for over 3 years now & hasn't "missed a lick".)

just my OPINION, satx


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## turbotodd (Jan 30, 2017)

The 15 and 20 are the same engine. IIRC carb and CDI are different. But if you bought a 15 and decided to make it a 20, you'd have to buy the carb and CDI, which costs considerably more than just buying the 20 in the first place. So yes, it's worth the extra initial outlay to get the 20hp from the get-go. At least it would be to me.

The power difference between the 15 and 20. The 20 has more mid range and a lot more top end power. About the same from idle to, say, 3000 RPM. There is a difference down low but it's not a night & day difference like it is from 5000-6000. Top speed? The motors I tested were on a 1448 Lowe just a bare boat with me in it. 15hp was 19.6mph. Pulled 15, dropped the 20 on, and the 20 went 21.9mph. Not a huge difference. BUT we pulled the 20 and put that heavy old 25 on the same boat, about 20 minutes later I run it across the exact same water, and was 27.5 mph. But that is one heavy motor. I liked how smooth it runs. All Tohatsu/Mercury, BTW, and this was in 2013, FWIW. I didn't care for the 15/20hp. Little noisier than I liked which is counterproductive. You buy a 4 stroke for it's quiet operation.

I don't remember if they let you choose the pitch on the Tohatsu's or not. Yamaha, you get what comes on the motor unless the dealer is willing to trade the installed with whatever you want as long as the price is about the same. But generally speaking, on most Jon's, the Yamaha's factory installed prop is usually pretty close, with there being maybe 1 to 1.5 mph difference in a prop change, at the most. Sometimes people will re-power a rig, say pull a 40hp off and put a 25hp on, say a 1754, and that's when the factory installed prop is grossly "off". 

And lastly, having owned and mostly enjoyed having vintage old outboards in my past, I'd suggest going new. Old stuff has been out there for decades, and while they might be good motors, having a problem out in the middle of nowhere with no other boaters near and no cell signal in some cases, is not my idea of enjoyable fishin' trips. Actually I lost a friend of mine because of that. I had a 3.5hp Mercury, had it for a long time. Early 70's model. Guy I knew was looking for a motor to power his little 12' boat. I reluctantly sold him my old merc and he used it for several years. Ever since I've had it, which was my dad's from when his dad bought it new in the 70's, it was intermittently hard to start. He was out in the middle of a small local lake bream fishing when a "barbecue storm" rolled in. Before he could get the motor started, the swells swallowed up his little boat and he went under and drowned. His son was there with him and made it back to shore. They found his body several days later. Your chances of having an issue with a new motor are fewer than you would with an older well used motor.


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## bcbouy (Jan 30, 2017)

i had the same dillema,15 or 20.i also decided i wanted a power tilt/trim and electric start short shaft, so etec was out,merc as well.i ended up with the 25 tohatsu.weight difference was minimal.worth every penny.the dealer also swapped the prop for a different pitch so i could troll with it for no charge.i think i'm going back to buy it for a spare in the spring.and mirrrorman and prowelder,there's no carb,it's injected.i think it's all in the ecu tune,like modern cars/trucks,if only i had an outboard tuner.


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## scoobeb (Feb 2, 2017)

The 25hp merc and tohatsu are the same engine,same exact everything except the tiller,merc is built in and tohatsu is a shifter. Tohatsu actually makes all mercs up to 30hp,the difference is paint,decals and a whole lot of money. Tohatsu also used to make nissan (out of business ),makes evinrude 4 strokes also. Tohatsu is the biggest outboard manufacturer in the world.


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## scoobeb (Feb 2, 2017)

I can't believe a 20hp tohatsu only moved a 1448 Lowe jon boat 21mph,something is wrong there. Maybe gps was off possibly. My 20hp suzuki moves over 1000lbs total weight over 25mph,something is not right there. Boat is 320lbs,engine is 97lbs,me 300lbs,friend is over 200lbs,plus coolers,tackle,gas tank and a full pvc board floor in it,I get near 25-27mph depending on wind and conditions. My buddy has a 1648 semi v alumacraft jon boat,20hp tohatsu he gets 26.7mph also.

Huge difference in power between the 15 and 20. I went through this yrs ago and I'm glad I went with the 20hp. It's 25% more hp so yes it makes a big difference.


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## Prowelder (Feb 2, 2017)

turbotodd said:


> The 15 and 20 are the same engine. IIRC carb and CDI are different. But if you bought a 15 and decided to make it a 20, you'd have to buy the carb and CDI, which costs considerably more than just buying the 20 in the first place. So yes, it's worth the extra initial outlay to get the 20hp from the get-go. At least it would be to me.
> 
> The power difference between the 15 and 20. The 20 has more mid range and a lot more top end power. About the same from idle to, say, 3000 RPM. There is a difference down low but it's not a night & day difference like it is from 5000-6000. Top speed? The motors I tested were on a 1448 Lowe just a bare boat with me in it. 15hp was 19.6mph. Pulled 15, dropped the 20 on, and the 20 went 21.9mph. Not a huge difference. BUT we pulled the 20 and put that heavy old 25 on the same boat, about 20 minutes later I run it across the exact same water, and was 27.5 mph. But that is one heavy motor. I liked how smooth it runs. All Tohatsu/Mercury, BTW, and this was in 2013, FWIW. I didn't care for the 15/20hp. Little noisier than I liked which is counterproductive. You buy a 4 stroke for it's quiet operation.
> 
> ...


I am very sorry for your loss but this is one in a million chances. I'm not telling you to buy a 1970s motor. you can easily find something 2000 and up that is very reliable especially in the Yamaha and Hondas for way less than new. But like I said originally if you have the money to go new why not. If you're already planning on spending three grand what's an extra thousand dollars

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## bcbouy (Feb 2, 2017)

scoobeb said:


> I can't believe a 20hp tohatsu only moved a 1448 Lowe jon boat 21mph,something is wrong there. Maybe gps was off possibly. My 20hp suzuki moves over 1000lbs total weight over 25mph,something is not right there. Boat is 320lbs,engine is 97lbs,me 300lbs,friend is over 200lbs,plus coolers,tackle,gas tank and a full pvc board floor in it,I get near 25-27mph depending on wind and conditions. My buddy has a 1648 semi v alumacraft jon boat,20hp tohatsu he gets 26.7mph also.
> 
> Huge difference in power between the 15 and 20. I went through this yrs ago and I'm glad I went with the 20hp. It's 25% more hp so yes it makes a big difference.


my 25 moves my 1000 lb. v hull to a max 25 mph with a 9.9x12 prop.


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## scoobeb (Feb 2, 2017)

Wow,my 25hp 2 stroke merc with a 14 pitch prop moves my 1648 alumacraft loaded with 1000lbs total weight over 32mph,I thought it was wrong because that is insanely fast for a 25hp. I gps'd it again and again 3 different times and every time it was over 32mph so it was not a glitch or wrong. I even used 2 different gps's to confirm. My friend was in shock as well. With the stock 13 pitch prop it hit 30.5mph with 1000lbs of weight. By myself and just enough weight to stop the boat from porpoising I was at 34.6mph which was so fast I couldn't control the boat so I had to slow it down. I have never ran a 25hp 2 stroke merc with so much top end speed and power and I have bought and sold over 15 of them and none of them touched this particular engine in speed and power.


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## richg99 (Feb 2, 2017)

Scoobeb.....maybe it's a 40 with a 25 cowl??

Ha

richg99


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## scoobeb (Feb 2, 2017)

No sir it's a certified 25hp merc. believe me Richg99 i was floored\in disbelief myself as well as my buddy to that's why we measured the speed 3 times with a couple different gps apps on my phone and my hand held Garmin gps .With over a 1000lbs total weight i was at 32 mph,with 200lbs less which was one person i was at 34.4 mph.The boat was so fast my buddy said when i was doing laps around my lake he said the hull was barely touching the water,it was like gliding right over it. i have nothing to lie about as i gain nothing from doing so. Now i was using a 14 pitch prop not the standard 13 pitch and it was aluminum so i can't imagine how much faster it would go with a ss prop.

I can't explain the burst of power this engine has.I have bought and sold over 15 of these but they have been on the newer powerhead which is the mercosil power head,my power head is a nikasil power head which could make a difference i guess.Out of all 15 of them this one engine just seemed to have that extra mega power,not that all the other mercs were slouches but this engine has never been altered in anyway that i know.It has very,very low freshwater hrs on it and it was originally a 20hp and i switched out the carb with a newer 25hp merc.Even with the 20hp stock carb this thing was as fast as any 25hp merc i have ever ran,then i put the 25hp carb in it and i tell you what a difference in wot speed and the torque nearly throws you out of the back of the boat,lol. I just don't know anyway to explain it,it's a mystery to me.I just sold it today to because i went with a brand new 2017 20hp 4 stroke suzuki which i love to death.The best 20hp outboard on the market as far as technology advancement.Nothing is better,efi,it's only 97lbs,super quiet,better on gas due to the efi,the power out of this little engine is mind blowing to me.It will move my 1648 loaded down with 1000+lbs near 25-27mph,depending on wind and conditions. t hat is plenty fast for what i'm doing. i sold my merc which is a 93 by the way for $1800 today,worth every penny.As soon as he saw it in person he said wow it's nicer than i expected and ran better. i love the new suzuki 20 and 25hp 4 stroke engines.I also can't wait to see the new 25hp 4 stroke efi yamaha in person,looks like a really sweet and reasonably priced engine that has been a long time coming,honda is all that's left for a new efi 25hp and all the other manufacturers will eventually get the 20hp efi engines.The suzuki 20hp throttle response is instant and very touchy.


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## richg99 (Feb 3, 2017)

Sounds like you wound up with what you want, and that is all that is important.

Congratulations. richg99


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## scoobeb (Feb 3, 2017)

Absolutely, may not be the fastest engine but it runs like a sewing machine. Smooth quiet power. I can't rave enough about this 20hp 4 stroke suzuki, I just sold my 25hp merc to a guy and he couldn't be happier. With 3 full grown men on a 16ft gheenoe he was at 28mph,that is insane impressive. I will miss the power of that merc but the 20hp suzuki does well with 2 people it gets up near 25-27mph,I'm excited about it. I'm glad I went with the 20 over the 15hp also. Imo the 20hp is so much more powerful that the 15hp,torque ,torque,torque.


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