What an IO is best at

[RotaryRacer]

Re: What an IO is best at

Can we add in torque vs horsepower to the conversation now?

What really gets the boat out of the hole? Torque or horsepower?

Does the amount of torque the engine creates even matter? Isn't the limiting factor how well that torque is turned into forward propulsion. Doesn't a single prop I/O have about the same prop characteristics as the comparable OB?

Aren't horsepower and torque related by the simple equation: P=(t x RPM)/5252 ?


Doesn't a 2 stroke create twice the torque/power than a equivalent 4 stroke per rev?

What kind of oil is best?






All kidding aside, I really don't have anything wrong with I/Os. I totally get the swimplatform & sunpad argument and can agree with it. Every boat/motor is a compromise. Each person sets their own priorities and decides what is best for them. I/Os have obviously been a family favorite for years for all the reasons discussed in this thread.

I think I'll shut up now.

 

[RotaryRacer]

Re: What an IO is best at

Bah.
The only glowing "sunset" I want to see from the rear of my I/O is the two balls of fire from the nitro I'm burning.
And I like my engine inside the boat for easy polishin'

Where's the sunpad?

 

[redneck joe]

Re: What an IO is best at

on top of the intake. Small people only, but it works...

 

[chambers1517]

Re: What an IO is best at

Torque is all about displacement. A small displacement OB can make equal HP but not torque. Torgue is the key to strong acceleration.

 

[H20Rat]

Re: What an IO is best at

Torque is all about displacement. A small displacement OB can make equal HP but not torque. Torgue is the key to strong acceleration.

And to go along with that, 2 strokes actually put out far MORE torque if you compare equal displacement engines!

 

[thumpar]

Re: What an IO is best at

And to go along with that, 2 strokes actually put out far MORE torque if you compare equal displacement engines!

Their curve is much different though. I have had many 2 stroke dirtbikes and love them but you have to hit the powerband to get all the power out of them.

 

[H20Rat]

Re: What an IO is best at

Their curve is much different though. I have had many 2 stroke dirtbikes and love them but you have to hit the powerband to get all the power out of them.

not counting specialty engines, they aren't much different. The conventional myth has always said that, dyno graphs show the truth. Again, make sure you check my key point... EQUAL displacement, not equal horsepower. If you have 2 engines of equal displacement, the 2 stroke will have more horserpower, as well as more torque almost entirely throughout the rpm range.

one example are my snowmobiles. 1 is a 700cc 2 stroke. Puts out about 140 horse, and peak torque is around 7000 rpm. the other snowmobile is a 1049cc 4 stroke, also about 140 horse. That engine has to spin at least 9000rpm to get decent torque, and likes to live above 10,000. Redline is 12000.

Anyway, just an example dyno graph of a 450cc 2 vs 4 stroke. This isn't unusual, the 2 stroke is higher than the 4 on almost every single point for both torque and HP. At the very high end, 4 strokes will outperform a 2 stroke, if they have a valve train that can keep up. (see my snowmobile example above) Without the valves and lacking a high rpm tuned exhaust, 2 strokes tend to become very inefficient at high rpm.

 

[thumpar]

Re: What an IO is best at

You are comparing small engines with same single piston displacement. I would bet my V8 has more low end torque and different curve than a 250HP 2 stroke OB.

 

[RotaryRacer]

Re: What an IO is best at

His point is that equal DISPLACEMENT gives 2 stroke the advantage...across the board.

The largest 2-stroke OB on the market today is the Evinrude 300 HP. It is spec'd to make 300HP @ 5500 rpm. It only displaces 3.4 liters as a 90 degree V6.

Of course a V8 iron block 4-stroke will make more torque?

BUT again the equation is simple. If we assume peak torque and HP is at about the same speed, lets calculate torque: t=(300*5252)/5500 ==> 286 lb ft of torque.

This from a complete package weight of ONLY 528 lbs. How much does a 300 HP sterndrive weigh from pulley to prop?

Power gets work done. When there is less mass to accelerate you need less power to do it. When you have 2-stroke the revs come easy and you start making power quicker than a 4-stroke.

Long live the 2-stroke outboard.

 

[dan02gt]

Re: What an IO is best at

I think I'm going to put one of these on the back of my next boat and call it a day:

Seven Marine | Home

What can be better than a supercharged Chevy LS V8 in a outboard. Of course the cost is insane.

 

[hungupthespikes]

Re: What an IO is best at

Don't forget the Seven Marine, 557 hp, Supercharged GM small block, OUTBOARD!
At 1100 lbs. it is a little heavy.

 

[RotaryRacer]

Re: What an IO is best at

And the only application the Seven makes sense in, is when you are debating between 4-350 HP motors or 3-557 HP motors.

The only advantage it has is when you are looking at multi engine setup where the drag in the water from more engines is the only real savings...at around $75k each, the boat you are putting this much power on is beyond the realm of this discussion.

 

[bajaunderground]

Re: What an IO is best at

The only advantage it has is when you are looking at multi engine setup where the drag in the water from more engines is the only real savings...at around $75k each, the boat you are putting this much power on is beyond the realm of this discussion.

And I suspect the pocket book for most on iboats as well?

 

[dan02gt]

Re: What an IO is best at

And the only application the Seven makes sense in, is when you are debating between 4-350 HP motors or 3-557 HP motors.

The only advantage it has is when you are looking at multi engine setup where the drag in the water from more engines is the only real savings...at around $75k each, the boat you are putting this much power on is beyond the realm of this discussion.

Rotary, What's with all this logic and reasoning? Everyone knows that Sevens are about saying I have more money than you. Oh and I think I will hang 3 off the back of my next boat, lol.

 

[coolbri70]

Re: What an IO is best at

:dejection:toss up between freezing and rusting:noidea: or perhaps being heavyop2:

 

[hungupthespikes]

Re: What an IO is best at

How much does a 300 HP sterndrive weigh from pulley to prop?

Big block with a Bravo I is just under 1200 lbs. But that's 400 hp or more.

The 350 Mag. with Alpha, 300 hp. is just under 950 lbs., but then for a 100 lbs. you can add a lot of ponies, and a lot less than 26 grand (Evinrude 2 stroke/300hp) for a second motor.

Yea, I like the 2 strokes for lots of reasons. But I'll take the big block IO for the three hour cruise to the Islands. They just seem to ride a lot better in a chop.

huts

 

[redneck joe]

Re: What an IO is best at

I want more charts. Charts make an argument better.

 

[Fun Times]

Re: What an IO is best at

I want more charts. Charts make an argument better.


:

Wait a minute here, there's an argument up in here?:focus: We can't have any of that going on you know.:mod:

Scott, Don't go eating up all the popcorn, guess i'll be needing some of that as well.opcorn:

 

[airdvr1227]

Re: What an IO is best at

I think both have their place. Biggest difference being if you have to replace them. Replacing an OB is so much more expensive.

 

[JoLin]

Re: What an IO is best at

I want more charts. Charts make an argument better.

They're the ONLY way to learn the truth! opcorn:

35 Extremely Funny Graphs and Charts | Bored Panda