Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: yo_marc on August 02, 2011, 10:49:53 AM
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Is there a consensus on what to use for a clearance when setting the 'squish' on a motor?
In my V8 experience, IIRC, it'd be around .040" for a tight street motor - and anything over .055 or so is boo-hiss.
Do those specs carry over to a 250cc mx motor?
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Have a read of this.
http://toostroke.blogspot.com/2007/12/squish-bands.html (http://toostroke.blogspot.com/2007/12/squish-bands.html)
http://polariswatercraft.com.au/basictwostroketuning.htm (http://polariswatercraft.com.au/basictwostroketuning.htm)
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That's interesting... (that first link). I'd say that's the first of heard of anyone being 'against' a squish-band cylinder head. I'd love to look into that some more, just for the theory of it.
I've heard it said by some that hi-performance engine tuners who are looking to get every last bit of power out of their motor get excited when the head (squish band or area) leaves witness marks on the piston. I would imagine a setup that tight would leave very little unburned mixture/gases behind.
I'm looking to setup the proper squish on my RM's motor. I've heard that many stock bikes come loose from the factory -- and a loose squish makes the bike harder to tune and leaves power on the table. I'm just a tinkerer, so I wanna check it out...
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I definitely would not want the piston ramming into the cylinder head!(The rod would not live very long).
I recently set up a friend's 011 Gas Gas 250 - slightly more then 1/2MM (.024) squish and 200PSI cranking pressure (his specs).I'm personally much more concerned with the compression ratio and the type of fuel required to feed that motor then,say, squish for example.
My friend is still not 100% happy with the Gasser's motor and he is presently experimenting with different carbs and intake tract lengths.My own personal observation is that the reed cage assy appears small though I would suspect the Gas Gas designers went that route for a reason. ;D
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I recently set up a friend's 011 Gas Gas 250 - 1MM (.024) squish and 200PSI cranking pressure (his specs).I'm personally much more concerned with the compression ratio and the type of fuel required to feed that motor then,say, squish for example.
Most people over here set the squish first and then machine the combustion chamber in the head to bring the compression back down to the required specs.
Although there is nothing wrong with the smell of AVGAS in the morning. ;)
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About 1.00mm would be ideal for a 250, squish width would depend a lot on useage. NO engines run 0.5mm squish that is just insane, doubling that will be much more sensible.
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I thought .5MM was a bit tight myself.The Gas Gas owner's plan was to vary squish between .5 and 1MM (head gasket adjustment) and see how the engine responds.This same guy has a 330 HP turbo charged (dynoed wheel HP) VR6 Corrado so I'm used to his experimenting.