There's a great philosophical (spelling?) question for all you engine gurus.
Why? My shee is 350cc and puts out 50hp at the crank (to Yamaha), and actually 38 at the rear wheels, let's give a generous 15% loss or clutch/gearbox and you ed up with 45hp at the crank. My sled's a 436cc and puts out 97hp!!!!! 90cc and twice the power!
What's the deal? I want a 80hp banshee engine, will I have to adapt a clutch and gearbox to a Rotax engine to make it roost?
Someone give me a clue! The temp factor can't be enough...and the sled has the single stock pipe, not event aftermarket twinpipes.
Anyone know? Not really that I want to make my shee faster...but why such a difference?

 

i think it is becuase of the way the motor set-up differs and the difference in clutches

maybe or maybe not it is only my opinion

good luck

 

Sleds need more power becuase snow is like sand and robs power badly. If you had that power in a quad you would kill yourself. i mean i have a piped and slightly ported motor in my banshee and its real fast. if they came faster than that from the factory atvs would be banned.

 

The narrower a engines target power curve can be the higher the peak will be. It's the old addage of you can't have killer bottom end with killer top end as well. But...with snowmobiles with a CVT (constant variable transmission), the power spread can be narrower. I'll speak of what I know more of, mountain sleds, most sleds don't engage until around 4000 RPM and target RPM is ususally between 7700 and 8000 for most stock sleds.

Alot of sleds have powervalves(or some variant thereof) also. This enables the engine to have a decent exhuast duration at lower RPM's but as RPM's build the valve opens and the exhaust duration becomes greater which will make the better power figures at it's target peak power RPM.

Now back to our friend the CVT. It also looses alot of power as well from belt slippage and also the entire drive system on a sled is VERY heavy (primary & secondary clutch, jackshaft, chain, gears, drive axle, and the heaviest the track itself!!!). In comparasion a sled has alot more parasitic affect on the HP numbers.


The temp factor does help, mine-shaft air makes good HP. But you're right it isn't THE factor involved. The biggest contributor would be the narrower ALLOWED spread of power that will enable a similar sized engine to create higher power.

 

My friends jet ski has around 130-140hp but he only hits 60mph on the water, only!!!!!! 60mph on the water is fast, but you would think that much hp would produce more speed, i guess it takes less hp for our quads to get moving.

 

Hydro-drag is greater than any other type when dealing with motorsports. PWC's are pretty interesting creatures. They lack a transmission of ANY sort and therefore are peculiar to set-up and modify. It takes a tad more knowledge and real world experience to really get them to scream. I had a GSX Limited a few years back and it would do around 68 on perfectly flat water, I ate it hard once at that speed. That sucks.

 

Do you know somwhere I could see dyno charts of sled and quad engines (torque and hp)?

I know that quads don't need as much hp as sleds do (or pwc), but I'd like to know HOW they achieved such power besides the powervalves (that do help a lot).
Comparative compression ratios, piston/rods/crank weight, carb sizes (well, I can find this one myself)...I could fit my sled carbs on the shee (44mm instead of 28...eheh).
I had figures sleds need MORE power to get moving...a lot more!!! ahah

 

Here's an idea for you Zorro:

You could replace your 28mm carbs by buying my 34mm and someone elses. There are bound to be other Sport/Scrambler owners that have gone to the 39mm one and have one lying around.

Would this work?? More power??

 

Its simply the way that the motor is built. Sleds mainly need more horespower because of there tracks (hugh contact patch) compared to a quads tires (small contact patch) If your looking for why the motor actually has more power (not the reasoning, but the tech aspect) there are lots of reasons.. Carb size, RAVE Valves, Rotary intake valves, high tech ignition systems with awsome timingcurves (thinking of putting one on my banshee ) dome shape, ect. ect. ect. Sledding is alot more popular and therefore the technology has advanced extremely fast for them, whereas most quads havent changed in the last 10 years! And as far as the displacement 90cc on any two stroke can make a big difference!