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Joined: Wed Jul 02, 2008 7:51 am Posts: 1028 Location: Canberra, Australia
Hi,
Something that I have been wondering about lately is what exactly is RPM measuring? Is it the number of times the engine fires in a minute, the number of revolutions of the crank shaft per minute, the number of oscillations made by a single piston in a minute...and so on ?
My first guess is that it is measuring the crankshaft?
or if it is measuring piston movements, then the pistons in a v-twin idling at 1000rpm are oscillating twice as much as an inline-4 idling at 1000rpm.
And then there are two-strokes. Ahhh god my head hurts.
So, someone please enlighten me...
_________________ A bad tradesman blames his tools, but so does a good tradesman who owns shitty tools. Life is so confusing
Joined: Sun Nov 23, 2008 11:58 am Posts: 88 Location: Wiltshire, UK
I'm pretty sure it's the crankshaft revolutions. If it was something like piston movements the 'revolutions' in 'revolutions per minute' wouldn't really make much sense!
This also seems logical given the gearing: gearing is all about changing the crankshaft's revolutions into a smaller number of more powerful wheel revolutions, so knowing the crankshaft's RPM would be the one you're interested in for this.
Joined: Thu Jul 10, 2008 9:59 pm Posts: 120 Location: Peoria, IL, USA
A single RPM is one 360 degree revolution of the crankshaft. The GSX has a four stroke motor, meaning a power stroke only happens every other down stroke of a cylinder. In other words, for any given cylinder it takes two crankshaft rotations to go through a full cycle of suck-squeeze-bang-blow.
Because the GSX has a standard four cylinder motor, the two outside cylinders move together and the two inside cylinders move together. However, each of these pairs of cylinders are in opposite operations in terms of suck vs. bang. In this way the power strokes among the four cylinders are evenly spaced at 180 degrees of crankshaft rotation.
Therefore there are two ignition/explosions of fuel/air for every revolution of the crankshaft. To put it another way, while cruising down the road at 5000 RPMs, the motor is setting off 166 controlled explosions per second between your legs.
(If I screwed up any of my math in this, I apologize.)
Joined: Sun Oct 26, 2008 1:16 pm Posts: 158 Location: jackson, mi
Hickey dude,
Excellent description of rpm's in this 4 cylinder engine. It still boggles the mind how fast all that steel is moving inside of a gas piston engine and holds together for tens of thousands of miles.
(Imagine if we were all green freaks and had to ride electric motorcycles.
Hell no......... I want my 4 cylinder piston powered motor forever.....
no electric crap for me.) Maybe a hand drill
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) at an average piston speed of 74 kph 
