70 2- stroke or 60 four stroke?

[dearl]

I have been trying to make up my mind on what motor I want to put on my boat, and I still have not made up my mind.There is not that much diffrence in the price, but I am looking at the performance side of things. I want the most top end I can get, but I still want to watch the weight. The 70 horse weighs in at 228 but the 60 weighs in at 247 not much there, the 70 is 52 cubic inches, while the 60 horse is 61 cubic inches. The 70 is a 3 cylinder, while the 60 is a 4 cylinder and is fuel injected. Looking at all this am I to beleive the 60 four stroke will out perform the 70 2 -stroke? I can't stop thinking about the cubic inches and cylinder diffrence, any ideas?

 

[ben2go]

I would go with 4 stroke.Better fuel economy.Lakes in my area have banned 2 strokes.It could happen in your area also.

 

[Quackrstackr]

The 4 stroke is 10 fewer hp but even equal hp 4 strokes do not perform as well as 2 strokes. As you noted, the 4 strokes have to be larger to attempt to approach the same hp but in your particular case, it still didn't get there.

If performance is your goal, you will definitely want the 2 stroke (less weight plus 10 more hp at the top end where you will want it).

If fuel mileage is your concern, 4 stroke hands down unless the 2 stroke is injected.

 

[bassboy1]

Horsepower is Horsepower. Period. A 2 and 4 stroke of the same hp both have the same ability to turn the same prop. The 2 stroke in your case, is 10 more hp, so even if all else was equal, you have more power there. Also, the 2 stroke is lighter, which is more advantageous. The 4 stroke has more displacement, but as Quack mentioned, the 4 stroke needs that extra displacement to crank out the same power as the two stroke. If both were 70s, you could bet that both of them would be pumping out 70 hp at the prop. The two stroke would still be lighter, and have less displacement, but the power at the prop, where it matters would be the same. Torque might be a little different, and acceleration probably would, but the top end power would equal out. Horsepower is horsepower, no matter how many strokes it has.

 

[Loggerhead Mike]

if you want top end you want the 2stroke. 4strokes have a wider powerband, alot more bottom end to get you on plane and going quicker, but it wont turn as many rpm's as the 2banger.

I'd personally get the 4stroke and a fancy prop to go with it for the speed. 19lbs isnt enough to notice a difference in eather motor in my own openion

 

[taxidermist]

Yes the weight difference can mean top end speed!!! Try that with a full tank of fuel verse a 1/4 tank of fuel with my 90HP Johnson three people and a full tank is 42 MPH with just me and 1/4 tank I can hook 53mph. so yes weight can mean big mph. This is up lake on Taneycomo at Branson MO. downlake empty I can boost 56 mph solo. Yes this lake has a lot of current when thee COE is generating electricity.

I have a 22 ft river jon tin boat. had a 9.9 Merc 2 stroke in 30 river miles of fishing I wold use over 5 gallons of mixed fuel.
I went to a 25HP Yamaha 4stroke and loved the speed, fuel economy was about 2.5 gallon on the same trip. At low river levels the 25 was just to big for the boat.
So I bought a 15HP Merc 4 stroke, about 100lbs lighter than the 25hp but 50 heavier that the 9.9 Merc.

Speed is good with the 15HP, running 7 generators last weekend, we ran 15 miles in 45 minutes against the current up river. Thats pretty close to 20mph. and the rerunning of certain fish holding area, wife and I used .8 thats right less than one gallon of gas.

Three weekends ago a buddy and I ran 30 miles up river against 5 generators and used 1.4 gallons of gas.

So as you can see the 4 stroke is sure better on fuel use.

Now depending on the boats rating for HP you want as close to the max as you can afford. Its better to have enough power, than to little!!

My Lake boat is rated for 120hp and it has a 90HP on it. I sure wish I had a 2 stroke 115 or 125hp onit!! the 90hp does good on fuel for a two stroke.

Thats my take on the differences.
John

 

[Quackrstackr]

56mph gps'd with a 90? :shock:

What hull and prop are you running?

 

[taxidermist]

Lowe 170. I dont know the prop, its a SS three blade with cupped edges and all the stuff. It scootes pretty good if there no load, runs like a pad boat. The insurance company and I had a fight over the motor, they said the boat was not rated for a 90. I had to have my agent take a pic of the plate that says its rated for a 120HP. Then the home office called Lowe to confirm the rating. The dealer said a larger motor would not push the boat much faster. I would like to try it!!! Its the first black Johnson outboard I have seen.

John

 

[Quackrstackr]

Is that a gps speed or speedo speed?

If that rig hits 56 on a gps with a 90, you have one of the faster 90hp tin rigs that I have ever heard of and I am extremely envious. I have a pad boat with no carpet and I can't get 56. I really need to spend some $ and tweak mine in. I know I have several mph sitting on the table but need to change props and play with the setup.

 

[seif5034]

56mph with a 90 is very impressive. My father in law has a Lowe with a 115 and it runs about 70mph

 

[Quackrstackr]

56mph with a 90 is very impressive. My father in law has a Lowe with a 115 and it runs about 70mph

70 with a 115???

There are bass boats out there with 225's on them that do well to hit 70. :lol:

 

[bassboy1]

56mph with a 90 is very impressive. My father in law has a Lowe with a 115 and it runs about 70mph

I'm sorry, but that is not possible. For a 115 to go 70, it has to be turning a 29 pitch prop, if you allow for any slippage. If you use a more realistic slippage number, a 30p would be closer to right. (I used gear ratio and RPM of a 2000 Johnson 115, but other brands will be close). Most 115s can't turn more than 17 pitch or so, even on rather light boats. Most 250s, unless they are on a really light boat can barely turn a 27p.