2 stroke question.

[Mike S.]

While at work today, I was telling a buddy of mine about how I can run my boat across the lake wide open and not have to let out of it. He looked at me with a puzzled look, and then asked if it was a 2 stroke. I said yes. He then asks me why an outboard can do that, but a dirt bike or snowmobile can't.  I really don't know. So, do any of you?  If you watched the Classic last year, some of those guys ran for hours at full throttle to fish for 2 hours, and run back. What makes an outboard be able to do that?

[bigmojet]

 I know carburated sleds need to be properly jetted for the altitudes and temps you ride in. If you get outside the range your setup for and you run the throttle pinned for extended times you run the risk of to much air and not enuff fuel or lube in a 2 strokes case and could burn up motor.

[Mike S.]

Right. But even a fuel injected sled can't continuously be ran at full throttle. My F7 was efi, and in a long haul, it would start to lose power. My ZR800, ZL600, and my Thundercat were all the same. But my boat, that's a different story. The boat never stumbles, and only loses speed if the jackplate or trim get too high. I have never even thought about this until today when my buddy asked me about it.   You can't jump on a 2 stroke dirt bike or quad and run it as long and hard as you want. If so, boom. So why are outboards different? It's not a matter of life or death for an answer, but I was just curious as to what responses I would get.

[LGMOUTH]

I dont know the answer but maybe because it is water cooled. Just a thought.

[1javelin]

The technology involved would have something to do with it somehow.  I don't know how, but a new snowmobile will run you what, 6-10 grand for a decent to good one.  A new outboard will run you 13-25 grand, depending on model and horsepower.  There has to be a reason for this huge price difference, and it can't be just the lower unit and steering cables.  Sounds like an awesome question to post on a certain other bass boat site if you can't get an answer here.

1jav

[Waterfoul]

DISPLACEMENT, piston count, rpm, water cooled, they all add up to longevity.  How many cc's is the "average" snowmobile?  We'll say 700, or .7 liters.  How about the average bass boat motor?  My Merc 150 is 2.5 liters... that's 2500 cc's.  It's got 6 pistons versus a dirt bike (one or two cylinders) or a snowmobile (2 or 3 cylinders).

Imagine a 2.5 liter 150 horse power sled?  How about a dirt bike!!!

"There's no replacement for displacement"

I know a man who used to be the "fastest man on snow."  He's local, some of you may know him too.  His sled was powered by 2 Mercury outboard motor power heads.  Hmmm... wonder why??

[Mike S.]

Makes sense.

[motocross269]

Outboards are set to maximum RPMs by proper set up...A boat motor is usually set up to run less than 6000 RPMs....My MX bike runs close to twice that.....Max MX RPMs are set by my right hand/gearing and Clutch..
If I set my Race bike to run at Max RPMs of Around 9k I could hold it wide open across a lake...but I wouldn't have that quick build of power I need to clear a big double....So it is give and take....
An outboard motor and Snowmobile/MX engines are two different motors....Snowmobile engines can be setup for longevity and the long haul...I was part of a team that set an endurance record on snowmobiles running pretty much WFO on a mile oval track for 24 hours...So it can be done...

As far as no replacement for displacement that could be argued....There are some Stock Snowmobiles out now that are puting out 180HP..... ....My 300CC Motocross bike puts out around 65HP...So big HP can come in small displacements with the right technology...I do agree that more displacement does help with longevity....

[LAPORTE]

The biggest question is how do you keep the rotating mass together with out failure.
Like moto said it's all about RPM's.  most of us have rev limiters on our outboards.The water not letting the prop turn as fast as it wants is the reason we never hear the motor on the limiter doing its job.

LaPorte

[Waterfoul]

I've got a buddy who drag races outboard boats.  He regularly gets 400+ hp out of a 2.5 liter block spinning at or near 10,000 rpm.  BUT, he blows up a motor or two a year... minimum.  No rev limiter here... just put your foot down and steer to the end of the course, no matter what rpm you hit.

Rev limiters and proper propeller size does a LOT to save us from blowing up our outboards.

Oh, and his boat normally does the quarter mile in right around 10 seconds.  800 feet in about 6 seconds.  That's dang quick right there!!!

[bigjc]

The biggest question is how do you keep the rotating mass together with out failure.
Like moto said it's all about RPM's.  most of us have rev limiters on our outboards.The water not letting the prop turn as fast as it wants is the reason we never hear the motor on the limiter doing its job.

LaPorte

I am no expert, but in my opinion Ron has hit it on the nose here;  If you run your outboard in your drive way, even with water to the cooling intake, wide open for any length of time, it will come apart.  For that matter if you ran your boat in the lake with too small of a prop, it will implode. 

[Waterfoul]

I am no expert, but in my opinion Ron has hit it on the nose here;  If you run your outboard in your drive way, even with water to the cooling intake, wide open for any length of time, it will come apart.  For that matter if you ran your boat in the lake with too small of a prop, it will implode. 

More like EXOPLODE!!  I've seen my buddies blown motors and he actually has parts FLY OUT of and OFF the motor.  Chunks of block missing, pistons busted into pieces, rods cracked and sticking OUT of the block, cylinder heads with extra holes in them, etc... often his motors are un-rebuildable.  Wish I had his deep pockets!!

[Mike S.]

My old boss, when I used to build houses, had a 32 foot Skater. It had three Merc drag motors on it. The middle one was up higher on the boat than the other two. He said they had to be rebuilt after x amount of hours. I remember laughing and telling him that it must be nice to be rich.

I see the point about the outboards being limited by several factors on rpm's. My speed ran way harder. When you clutch a sled, you are trying to get it to stay in the optimum rpm range. And when you exceed that, it gets doggy and loses power.

This has been an interesting read. It was something I never have thought of before. I really don't have much experience tinkering with outboards. I have worked on and modified several snowmobile engines, and many 2 and 4 stroke bikes and quads. I have built several motors for my Nova when I used to drag race. Never had the desire to work on an outboard. Way too expensive to replace. I have checked in to some of the crazy performance packages and the different stages that are offered for boat motors. I will leave that to the rich man. I would like a ride in a modded bass boat, though.  Have any of you seen the video on YouTube of the yellow Bullet with the 345 Merc drag motor?  102 mph on the gps!  Belongs to an old man. Must have really deep pockets.