FE550E Vs. the FE650E ?

Md4stone said:

It makes sense that the short stroke same bore engine will gain rpm faster, even at 87% of the capacity. The shorter distance the piston has to travel gets it back to the power stroke faster at any rpm. Should also be capable of much higher red line, given that other factors such as valve size and porting is equal. Which brings up an interesting aspect of all naturally aspirated engines:

Horsepower is a direct result of an engines ability to flow gasses through it, measured in cft/sec (cubic feet per second).

The higher this number is, the more hp will result. Has little to do with the displacement of an engine, other than larger displacement engines generally are able to flow more, as more cylinders are added etc. But the easiest way to gain horsepower is to increase the size of the carb or FI throttle bodies, enlarge the valves, enlarge, straighten, and polish the intake and exhaust ports, tune the exhaust manifold/pipes/silencer to "extract" exhaust gas.

Rev limits are a result of more factors than just piston speed in ft/sec, a lot of that has to do with the limits of any valve trains design. But with improvement in engineering an engine to be able to achieve higher rpm without valve float etc, an engine with the ability to flow "x" amount of gas with a smaller displacement will rev to the exact rpm where it is moving the same amount of gas through it that a larger displacement engine with the same ability to flow "x" amount of gas at lower rpm, and making maximum equal power at different rpm's. So if the 550 could rev about 1000-1500 rpm higher, it would probably make about the same max horsepower as the 628.

This should help to explain some of the reason why your 550 feels faster in certain regards. You would have to gear them exactly the same to get a real comparison though. The lower gearing of the 550 should give it an advantage until top speeds are reached. The 650 is making more hp because the rev limiter for both engines is the same.


Sent from my iPhone using Tapatalk

Click to expand...

pollo said:

My official Supermoto review .
I rode the FS650 and FS550 back to back today. The 650 geared at 16/40 and the 550
geared at 15/38. So close enough ratio with the 650 slightly taller at 2.5 to the 2.53.
Both bikes like their gearing.
Its a run for the money at the start with the 650 edging it off bottom until the 550 gains
on it and steps out with a massive blast in the middle. I cant say it's a lot faster there but
faster is what it feels like. And without the vibration.
The 650 is fun everywhere with its linear bottom to top thrust.
The 550 can be a handful off road with its race attitude ( depending on gearing too), but I think it really shines as a Supermoto.
Can't wait to get more time on it.

pollo

Click to expand...