[(F5)]

OK my bike is an '07 EC300. The principles will remain the same, but I can't tell you where other models may have altered in spec.

3 years ago I bought it & I fired a new piston in it 2 ago. I sadly onl get to ride this bike once a month on average. When I measured it I was a bit surprised, but its taken me till now to do something about it as time has been tight & racebikes take priority over perfectly serviceable playbikes.

Compression ratio was about 12.5:1, which is easy on a 300, esp a square one at 72/72 (maybe new ones grew 0.5 with a quick google). The squish clearance was a mammoth 2mm.

Squish areas have long been used to reduce risk of detonation by creating a thin boundary layer of cool gas that doesn't burn & promotes good cooling to the piston from the cool head.

Also by reducing the spark lead (Length the flame has to travel from the sparkplug) and thus combustion time. As a point the piston is not driven down by an explosion, the spark ignites & burns the fuel to increase the pressure; Boyles law in a fixed volume, except the fixed volume, has a piston on one side that is pushed to create a bigger volume, reducing pressure as it does so.

On top of that it increases the MSV but I'll get to that later.

Any space in the squish is a lost batch of combustible gas. Of course you need to have some space as the clearance gets used up at high revs. But as long as it never touches, you're sweet.

Manufacturers always leave this gap huge so if they get a batch of long rods, tall pistons & short barrels, there is still a gap. However if you just shave the head to reduce this to a decent gap the compression ratio always seems to go too high, so its a bit of a faff.

The queer thing is my bike had a 4*(degree) difference between the piston & the head squish area. This increases the area of unburnt gas which the flame can't effectively get to and decreases the pressure that the mixture is squished & squirted into the burning part of the chamber.

As the piston squishes the last bit of area of a mixture (that has sparked a few degrees earlier) & flame is propagating, increasing pressure, the mixture burn efficiency can be affected by the turbulence smashing the fuel into smaller particles supposedly increasing surface area, though I struggle with that, but helping mix the gas for sure. Anyhoo the speed that this mixture is squirted out of the squish area can be calculated & is called the Maximum squish velocity. the idea is that a certain MSV will suit your application, ours being dirtbike type power at comparatively low revs.

There is software to calculate this, however some uber tuners have started to poopoo this as it ignores the fact that the volume in this squish area decreases as the engine revs higher so the numbers are false. Either way the numbers give a reasonable indication of where you should head. People moved to Mota and then to EngMod, but I can't be with the $400 & considerable time investment to learn to drive it rather than monkey enter some data & get peanuts results.

This aside a dirtbike running somewhere around 50% of chamber area to squish area with a close gap & reasonable compression should be in the ballpark so I might not give a rats. I've lost my sw on this PC so I'll try find it at home & give it a bash for giggles.