The squish band is a cut in the combustion chamber that's at the same angle as the crown of the piston, how it works basically is you set up your engine so there's very little clearance between the piston crown and this "band" cut in the combustion chamber, typically a good squish clearance is 0.25mm up to about 1mm and it loses its effect quickly if the clearance is more than about 1mm. Basically what this does is keep the combustion and flame front at the center of the piston crown keeping it away from the edges of the crown where detonation can occur. Having a tight squish band basically let's you get away with considerably more compression before the threat of detonation becomes a problem. Other benefits are the ability to run lower octane fuels, more timing advance, and more compression without the worry of detonation. There are still limits tho and the tighter the squish clearance the more effective it becomes.
You can set it too tight and the piston may hit the head after the engine warms up or if a bearing gives out (this will cause more problems than just the piston hitting the head tho if a bearing goes at high rpm), and it can still detonate if the compression is too high, octane is too low, or too much timing advance is set, but this does let you get away with more so it's possible to exploit this in order to make more power.
not all engines will benefit from a squish band and it does depend on how the engine is set up to some extent, but for the most part, a squish band can be a good thing on these little engines.
This is why some builders are against ramping pistons since it also gives a passage for the flame front to the edge of the piston where detonation occurs. You can get away with some ramping with a squish band but not much, typically keeping the ramps depth 1mm or less won't disrupt a squish band too badly on a street engine with moderate compression, but on a race engine that depends on a tight squish clearance it could completely negate the benefits of having a squish band when all the engines tolerances are right on the edge for max performance. That's why you may have seen some of my earlier posts mention to ramp a piston to see how another mm would effect the performance, then cut that amount off the exhaust roof and replace the ramped piston with one that's un cut, this is to preserve the squish band and compression ratio for max performance. Basically you cut the piston to experiment, then cut the port when it works and put the un cut piston in once you get the porting dialed in... this is for max performance or race engines, ramped pistons can stay in on lower performance engines to give them more power or port duration, but won't bring home any wins at the track, but it will offer a street engine some nice performance gains without having to cut on the cylinder.
You can set it too tight and the piston may hit the head after the engine warms up or if a bearing gives out (this will cause more problems than just the piston hitting the head tho if a bearing goes at high rpm), and it can still detonate if the compression is too high, octane is too low, or too much timing advance is set, but this does let you get away with more so it's possible to exploit this in order to make more power.
not all engines will benefit from a squish band and it does depend on how the engine is set up to some extent, but for the most part, a squish band can be a good thing on these little engines.
This is why some builders are against ramping pistons since it also gives a passage for the flame front to the edge of the piston where detonation occurs. You can get away with some ramping with a squish band but not much, typically keeping the ramps depth 1mm or less won't disrupt a squish band too badly on a street engine with moderate compression, but on a race engine that depends on a tight squish clearance it could completely negate the benefits of having a squish band when all the engines tolerances are right on the edge for max performance. That's why you may have seen some of my earlier posts mention to ramp a piston to see how another mm would effect the performance, then cut that amount off the exhaust roof and replace the ramped piston with one that's un cut, this is to preserve the squish band and compression ratio for max performance. Basically you cut the piston to experiment, then cut the port when it works and put the un cut piston in once you get the porting dialed in... this is for max performance or race engines, ramped pistons can stay in on lower performance engines to give them more power or port duration, but won't bring home any wins at the track, but it will offer a street engine some nice performance gains without having to cut on the cylinder.
