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squish clearance vs squish velocity?

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I have bought a new sx250 17 cylinderhead from vhm. And the squish is 1.6mm but everything I read about it, everyone writes it must be between 1-1.3mm ... So is squish velocity more important?

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You should run the spec exactly as given by VHM and not worry about their squish figures. If you compare your insert to your standard head you will see the differences. You have a choice of inserts for different terrain as well. They are the European leaders in 2 stroke head research and development. We run them on our mx 125s and always use their specs. We also use their deck height tool for total accuracy - well as much as a mix of gaskets allows. Bob.

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 msv -maximum squish velocity is beyond the average back yard hack, confirm with the head builder the optimum squish gap for you and go ride.

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It's beyond us all I would imagine. VHM give a deck height for each model of bike (which may vary from KTMs figures), and a resultant squish figure for optimal performance and to match how the respective inset is cut by them. As I suggested stick with their deck height, the squish will then be exactly as they say and your insert will be shaped to match these figures. We run 12 degree VHM pistons in our race bike and they need a positive deck height of 0.5mm but obviously the insert is cut to suit. VHM is a top rate company and will only sell you products that enhance your engine.

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Yes, but I still wonder when most tuners say 1-1.3mm at 250cc and 0.7-1mm at 125cc and vhm have 1mm on 125s

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 Drop VHM an email - I have found them to be extremely helpful and respond quickly - and I'm sure they will explain it to you. I am also pretty sure they will know more than 'most tuners'. The KTM factory 125s in Europe did run VHM heads and cranks. Not sure currently to be fair. Bob.

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I've done a lot of work with squish gap (and area and chamber shape) on Yamaha Blasters and Chinese bicycle engines(don't laugh!). I found the performance "bell-curves" in a certain range for a certain area/angle/chamber shape. I'm sure VHM has done the work to find the sweet spot...

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Edited by sbest

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I Got This mail from vhm
Most people think high compression and  tighter squish is more power.
But with the KTM 250SX is not.
When KTM changed the powervalve ( I think is was 2012) we switched from squish 1.40mm to 1.60mm
All tested on a stock bike.
If you tune it can be different

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I'd say either go all balls out and either give to a tuner who's going to port it, match everything up and cut the standard head to suit or just buy the vhm one and have done with it. 

Me personally,  well I just through my cylinder head in a lathe . Set it at 1.3 squish as a quick experiment really just to see if it would fix the jetting issues (which it did) it also gave more power throughout the rev range too. Totally different bike. I'd highly recommend getting it done.

The only real reason I went for 1.3 is my last few motors were set the same and the compression ratio still wasn't crazy high. Still runs fine on 95 Ron with no pinging although I usually run 98.

Who knows, the vhm head at 1.6 might give more power but I'm too poor (tight) to shell out the money to find out ;)

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My 0.02c on the debate is that my under standing of head squish is .

1: that if you just set the squish it cleans up the bottom end and makes jetting easier but raises the compression which kills top end 

2: if you set the squish and machine the dome as well it cleans up the bottom end , makes jetting easier and still allows lower compression to help over rev

3: if you widen the squish as discribed above then the bottom end will be terrible but top end and over rev will be good

my conclusion would be that unless you can keep the motor singing high in the rpms then the VHM head would be a waste and you would probably benefit more from the squish band and dome machined and take the advantage of a crisp bottom end and good drive out of corners ( option 2 )

could be wrong 

Edited by kxrob

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