First let me say your all on crack!!!
At this time there is NO 4stroke r/c engine that will out run a 2stroke. The technology of todays r/c 4stroke engines is way behind that of ALL r/c 2stroke engines. Even the cheap RTR engines are way ahead of todays r/c 4stroke engines.
If you were to compare a .12 sport engine (Fantom .12 for instance) to a .26 4stroke engine (OS Surpass .26 car engine), first you would get a max rpm difference of around 17,500 rpm. The .12 2stroke would have a max rpm of say 32,500 and the .26 4stroke would have a max rpm of 16,000. So gearing would definitly have a crucial role in comparing.
The 4stroke makes 1 power stroke per 2 rev. of the crank where the 2stroke makes 1 power stroke per rev of the crank.
4strokes make more torque on their power stroke due to the fact that the combustion pressure acts on the piston all the way down the power stroke. 2strokes on the other hand let the combustion pressure excape the cylinder around 2/3'ds the way down, and out the exhaust port. To make matters worse on the 2 stroke, the piston is fighting secondary(crankcase) compression at this time.
Your average 2stroke has a 85deg. power phase duration, where
your average 4stroke has a 155deg. power phase duration.
However the 2stroke gets to make a power stroke every rev. so that bumps the 2strokes power phase duration to 170deg., 10% more than the 4 stroke.
That said, you would need to double the displacement of your 4stroke to mathmaticaly equal the power of a 2 stroke.
Now to correct a few statements:
4 strokes run much hotter than 2 strokes. Always. (Remember the Kyosho Super 10 four, is required a fan driven off the crank to keep it cool).
There are no 4 strokes capable of 30,000 rpm. Valve float limits this physically.
A 2 stroke will wind out alot quicker due to the drastically reduced rotating mass compared to a 4 stroke.
The 4 stroke will NOT have twice the top end of a 2stroke, valve float prevents a 4 stroke from having rpm capabilities anywhere near a 2 stroke.
A modern r/c 2 stroke has the luxury of taking advantage of tuned pipes which makes them way more volumetrically efficient than a 4 stroke could ever hope to be.
Compare a 125cc 2 stroke mx bike with a 125cc 4stroke bike. 2stroke= 38hp, 4stroke =15hp.
Until very recently technology of 4 stroke singles has been in the stone ages. In the last 3 years 4 stroke single technology in the mx field has improved enough that 250cc 4strokes are now able to compete with 125cc 2 strokes. And that took F1 type technology to accomplish!
I challenge anyone to compare a .12 2 stroke to a .26 4 stroke on a dyno and show me how a .26 4 stroke could possibly make more power.
BK
Factory Honda mechanic for Mike LaRocco
Designer of the X-Dyno for Xtreme r/c magazine
http://www.nitrodynesystems.com