Bore size and power

[Rcannon]

If an average 80 makes 20 hp
If an average 125 makes 32
Why doesnt the 250 make 64 hp

Do the engines get less efficient as they get larger? I am not sure if this is the correct forum to ask this in, so sorry if I did not choose correctly.

 

[Studboy]

I think that they get less efficient because of more friction and rotating mass but also with the larger engines they usually go for a lower RPM peak and a wider smoother powerband...can you imagine a 250 with a powerband like an 80? :)

 

[Studboy]

ooops....I meant reciprocating mass.

 

[bclapham]

so if a 125 uses a 36mm carb, why does a 250 not need a 72mm one?;)

 

[Studboy]

They are obviously not using twice the air.

 

[atc3434`]

The amount of power increase with an increase in displacement is a curve, it gradually peaks out. A single cylinder can only make so much horsepower. Thats why a twin cylinder engine makes roughly 20% more power than a single cylinder engine of the same displacement. You can only go so big before reciporcating mass gets to big, and the volumetric effeciency goes downhill. Thats why a Rotax 600cc two stroke triple can make 160hp, while a single cylinder 600cc two stroke would be hard to get over 70hp. BTW, those 600cc Rotax triples are one badass motor... friends got one in a Skidoo Mach III. WOW... pin the throttle, tach edges up to about 9500rpm, skis are in the air till about 70, and your doing 130 before you know whats going on. What a ride!!!

 

[Rcannon]

Thanks you guys. I wondered about this today. I was testing the little cr 80 and again was shocked at the power of this little bike. A 250 ported like that would be scary!