Rumours & facts, new models & prototypes discussion group: RE: 2 stroke/4 stroke HP ratio?
RE: 2 stroke/4 stroke HP ratio?
Andy said 2004-06-25 00:26:47
Er actually the ratio of two stroke to four stroke power output per cc is 2.5:1 on average.
For instance a humble old JAWA 350 two stroke puts out 28 BHP @ 5,250 RPM and 38 FT/Lbs. torque @ 3,800 RPM.
A Suzuki GT550A put out 52 BHP and 44 Ft/Lbs. Torque whilst the GS550M that replaced it only put out 38 BHP!!
A two stroke has power every rebolution of the cycle whilst a four stroke only has it evry other revolution plus it has to drag the piston up the cylinder to squeeze out the spent gases.
Another factor is that a two stoke can use super heated unburnt fuel gases bounced back into the cylinder block using the Kladen Principle (expansion chamber) to bosst the power up to 15%. However a four stroke doesn´t like back preasure especially at low RPM hence collector boxes VVT etc. to try and prevent it causing blow back through the carb on high lift, long duration camshaft engines.
Also blowing a head gasket on a two stroke is not such a pain in the **** as fixing it on a four stroke!!
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