why are saw motors so weak????

[drmiller100]

my 800 cc snowmobile motor came from teh factory with 150 horsepower.

My 80 cc saw motor came from teh factory with 6.3 horsepower. The math doesn't make sense.

How come saw motors are so inherently weak???? Diminishing return and 2 stroke theory says small motors shoudl make a lot more horsepowre then they do.

Anyone know how much horsepower they get from teh hotsaws for racing??? 20 for a 5 cubic inch reasonable, or is that high?????

Thoughts????

 

[talon1189]

my 800 cc snowmobile motor came from teh factory with 150 horsepower.

My 80 cc saw motor came from teh factory with 6.3 horsepower. The math doesn't make sense.

How come saw motors are so inherently weak???? Diminishing return and 2 stroke theory says small motors shoudl make a lot more horsepowre then they do.

Anyone know how much horsepower they get from teh hotsaws for racing??? 20 for a 5 cubic inch reasonable, or is that high?????

Thoughts????

How many pistons does your snow mobile have? Most chainsaws only have 1 >>>>>>>>>>>>>>>>>>>Talon

 

[chowdozer]

my 800 cc snowmobile motor came from teh factory with 150 horsepower.

My 80 cc saw motor came from teh factory with 6.3 horsepower. The math doesn't make sense.

How come saw motors are so inherently weak???? Diminishing return and 2 stroke theory says small motors shoudl make a lot more horsepowre then they do.

Anyone know how much horsepower they get from teh hotsaws for racing??? 20 for a 5 cubic inch reasonable, or is that high?????

Thoughts????

Doess your snomobile have a tuned pipe? How about your saw?

 

[Lakeside53]

Will your snowmobile last 2000 hours? What's it's power to weight?

Life is full of compromises..

 

[ciscoguy01]

Engines

Think of it like a diesel and a gasoline engine. Only not quite.

 

[drmiller100]

Will your snowmobile last 2000 hours? What's it's power to weight?

Life is full of compromises..

yes, 1 horsepower to 5 pounds.

I my saw is 6 horsepower to 295 pounds.


I sit on my chainsaw, and all it does is agitate my hemeroids.

 

[litefoot]

High output equals high temps. High temps require increased air flow across the cylinder (i.e. a moving motorcycle) or closed-system liquid cooling (a radiator). I don't think I could swing my saw fast enough to meet the requirements of the former scenario nor would I want to carry the extra weight of the latter.

A detuned (as compared to a snowmobile) weight-manageable saw will do just fine. But that's a dang good question.

 

[blis]

the biggest thing that chainsaws miss is the proper EXHAUST, since theres no room for expansion chambers and such... The other reason is that we cant use huge carbs (21mm in 50cc) in saws becouse they need to work longer than 15mins on tankfull...

 

[Justsaws]

Saw engines are "weak" because people do not want to carry a snowmobile engine around the woods all day. It would remind them to much of the past.

 

[Sprig]

yes, 1 horsepower to 5 pounds.

I my saw is 6 horsepower to 295 pounds.


I sit on my chainsaw, and all it does is agitate my hemeroids.

lol, u obviously have confused yer washin' machine wit da saw, nm, same hp no doubt

 

[Sprig]

Saw engines are "weak" because people do not want to carry a snowmobile engine around the woods all day. It would remind them to much of the past.

Yup, when we use to carry skidoo engines around, but then, really far back in the olden days, we got the kids to carry um. :yoyo: :yoyo:

 

[timberwolf]

A stock 5 cubic inch saw putting out 5 hp is giving 1 hp/in3, your sled at 50 cubic inches and 150 hp = 3hp/in3.

Add a pipe and some port work to the saw to put it on the same level and it will be in the 10-12 hp range.

The sled still has a couple advantages, rotory or read induction, this allows longer or non symetrical intake timing and would boost a saws output another 10-30% over piston porting. Also many sleds puting out high hp are EFI this would add some HP to a saw also.

Some claims of 80 cc saws pushing close to 30 hp have been discussed, that would put the saw at 6 hp/in3, nearly twice that of the sled. Ok, a bit of nitro was involved.

 

[PES+]

Yes

The increased volume is what we used to call "stuffing" with the reeds you get more fuel air mix into the case and back pressure shuts the reeds a form of supercharging if you think about it. It was the reason for the why no more reeds thread.

And thank you for pointing out that saws even in stock trim are not that far off in comparison to any other two stroke. Personally I have seen some really silly snowmobile designs. My wifes brother has a Cat 900 and try starting that @ 30 below It almost breaks the starter rope just getting the pistons to start to move
There was good reason for multiple cylinders in snowmobiles but now it is a status symbol and a show of machismo to own a machine that Hercules has a hard time starting.
My other favorite from Cat is the 700 good motor but 7MPG to my eye just hook up a long hose to the nearest gas pump and ride oye.....

Now the 900 gets better mileage not by much but it does.....so does it not stand to reason that the 700 is dumping fuel out the pipe and wasting it?

 

[MS-310]

Water cooled to air cooled makes a big diff.

 

[timberwolf]

Can't an air cooled engine put out just as much HP, just not for as long as a water cooled engine? Though agreed that water cooling can allow an engine to run under sustained load at a higher specific output.

With a race saw running 5 seconds or less would there be any amount of heat transfer into the water? Could it even cause problems with the piston heating very fast and the jug kept cool by water?

Some of the fastest drag sleds I have seen were freeairs.

 

[PES+]

Not as big as you might think

Not really but it does allow a more constant operating state which can be easier to tune predictably we thought that was the answer in ancient kart days and made water cooled heads to cut detonation sure it did that but guess what?....long term the detonation returned. .......head too cool....... carbon on the head........... lower squish.......
quick stop.
pushing off the track

 

[MS-310]

Can't an air cooled engine put out just as much HP, just not for as long as a water cooled engine? Though agreed that water cooling can allow an engine to run under sustained load at a higher specific output.

With a race saw running 5 seconds or less would there be any amount of heat transfer into the water? Could it even cause problems with the piston heating very fast and the jug kept cool by water?

Some of the fastest drag sleds I have seen were freeairs.

Yes I do agree but I was thinking of stock engines and so on. My fathers old drag car was filled with sand, ( plus running on methanol). Its just a better idea, anyways very true timberwolf.

 

[smokechase II]

perspective

Shouldn't you be asking: "Why is my snowmobile engine so heavy?"

Do you need that much horsepower? Especially when with a lighter sled you could get out of tree wells easier. Indeed, with a one of them great snowmobile motors being made interchangeable it could have cut down that tree faster and you'd have avoided the tree well altogether. This being a secondary method to the preferred one of cutting down trees with a snowmobile. Locally we seem to prefer targeting them head on despite the fact that trees, with a very poor horsepower/weight ratio, usually win.

Expense is also a factor. Carb vs fuel induction etc.

Honestly, most modern saws are such a gift of technology; I'd suggest that Rule #1 should apply. Don't complain when you should be saying thanks.

 

[PES+]

That too

It depends on the intended use
No the heat would not make it to the water until after the race was over and in some ways that would be worse no? what happens then in the next race?

 

[oldsaw]

Litefoot nailed it...heat, but some other guys brought up the weight issue as well as anticipated lifespan.

Liquid cooling lets you run the engine hotter, allows more little "hop-ups", and if you overheat the design, you add more cooling capacity. A couple of pounds here or there on a snowmobile is no big deal, especially today when they have HUGE engines.

Turn it around. A couple of pounds here or there on a saw is a big deal to someone who is going to use it all day. Complexity is also a bad thing on something that takes the abuse of a saw. Say a radiator leak...very bad.

It's a tradeoff between simplicity, light weight, reliability, and durability. A snowmobile can sacrifice weight and simplicity, and durability has different meaning.

Mark