I was looking for some 2 stroke info and this long string of posts came up. I think there is big value in reading this series of posts.

http://www.formula500.org/viewtopic.php?t=3177

Try this one on page 2 about 3 or 4 posts down.

Bill Smeal wrote:I was trying to compare factory advertised hp ratings between 2 stroke 600cc motors and 4 stroke sportbike motors. I could find a lot of info on the rotax---But couldn't find but one add for a yamaha 600cc.--spend over 4 hrs searching then gave up.

http://sportbikeguy.com/bikes/r6/timeline/r6tl2003.html

The above link was the only one I could find--It stated the hp rating at 123hp.

Problem there Bill is that it's sort of an "apples to oranges" type thing.

"all else being equal" a 2-stroke will normally make more power than a 4 as you're making power every crank revolution vs every other revolution... however, in the case of the bike engines they make up for that due to the fact they have 4 cylinders rather than 2 (so they have a power stroke every 180 deg) and they run at near twice the engine speed (HP is a function of torque & RPM).

However, no matter how close they come in HP per CC, they still have a ways to go in matching the 2-stroke's HP per pound performance... the 2-stoke is still the HP-to-weight ratio king... which is why the snowmobile industry refuses to let them die... 30-40 lbs one way or the other in a sled that only weighs 450 lbs total is HUGE... in a moden performance sled the rider is around 1/3 the total package weight... they've gotten THAT light.

Also, trying to calculate what kind of HP you're getting at the crank in a MC engine is something of a "guesstimate"... there's no where to measure except at the output of the gearbox... so even if you have a gear that's 1:1 (which some don't have) you still have to estimate the HP loss through the gearbox.

Now, even if the HP numbers are dead even with a 2-stroke... a well-tuned CVT will have an edge on the manual gearbox... as the CVT keeps the engine at its power peak 100% of the time you're on the gas... while the 4 stroke moves up & down the RPM band with gear changes.

So, a 120-125 HP MC engine may indeeed have a hard time keeping pace with a properly tuned 110-115HP 2-stroke... which in my mind is what you're seeing the result of with the MC engines yet to crack the best of the Rotax 500 times, even unrestricted.
- Dix