What is the ideal cylinder head squish for an 04 CR250?


7 replies to this topic
  • Jsabowabo

Posted February 06, 2012 - 09:45 PM

#1

So on the recommendation of everyone here I pulled the head on my 04 CR250, followed the directions on RB-Designs webpage (had to buy thicker solder, .092 or so) and got three measurements.

They all came out to .054 at the end of the solder. I'm not sure if I just got lucky, because most guys seem to report they have .070 or more stock. Previous owner may have had it done already, who knows?

I emailed RB-Designs to ask what the ideal squish is but so far they just replied that they could help. I don't want to spend $100 for them to set the head to .050, which is almost nothing.

Does anyone know what is ideal squish for 91 pump gas on these bikes? It's stock aside from pipe, VF3 reeds.

  • APBT

Posted February 07, 2012 - 06:54 AM

#2

The bikes with the biggest squish problem are the '05-'07 which changed from the older flat top piston to the newer dome piston design. I have 2 of these and both measured over 0.080" stock squish clearance. Most properly set squish clearances are around 0.045" for a 250 engine.
One thing to remember is that there is much more than just setting the squish clearance. The width of the squish, taper angle, dome design, head volume and resulting compression ratio all are critical factors as well.

Edited by APBT, February 07, 2012 - 06:55 AM.


  • Crazyced

Posted February 07, 2012 - 07:30 AM

#3

I just got my head back from RB-Designs. I have yet to install it though. I will report back.

  • JJRace

Posted February 07, 2012 - 09:06 AM

#4

I had RB do our 02 125 head. came back great! Fired the bike up, and you could tell it ran on the stand better. smoother, less bog. I am anxious to ride it to see the difference.

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  • jar944

Posted February 07, 2012 - 09:30 AM

#5

The width of the squish, taper angle, dome design, head volume and resulting compression ratio all are critical factors as well.


People dont seem to understand that.

OP, there is no ideal squish clearance for 91 octane. There is however an ideal squish clearance of about .9-1.1 mm

The squish band width, angle and bowl may (or may not) need modified to run on 91.

  • Jsabowabo

Posted February 07, 2012 - 03:37 PM

#6

Interesting. I thought the whole point was just to get the squish down to around .050 without raising the compression ratio. The whole premise of the mod is that Honda screwed the pooch on the squish clearance, necessitating decking the head to reduce clearance. Of course of that is all that's done, you raise compression.

The other things you described, like head porting seems like more than just setting the squish and keeping the same compression ratio.

Bottom line for me is it worth $100, when the squish is already at a near optimal level from the factory? At this point it sounds like head porting, not setting the squish.

  • APBT

Posted February 07, 2012 - 05:44 PM

#7

If you are worried about the $100, you could try an '05-'07 base gasket which is thinner than the '02-'04. These base gaskets retail for about $9 and will reduce your squish clearance but also obviously increase the compression ratio.
One thing about RB Designs: He does terrific work. Very precise, high quality machining. He will set the squish to optimal clearance based upon what fuel you will be using. He also adjusts squish taper, width, maximum squish velocity, dome shape and volume to your engine and fuel spec.

Edited by APBT, February 07, 2012 - 05:47 PM.


  • dmcca

Posted February 08, 2012 - 03:12 AM

#8

Interesting. I thought the whole point was just to get the squish down to around .050 without raising the compression ratio. The whole premise of the mod is that Honda screwed the pooch on the squish clearance, necessitating decking the head to reduce clearance. Of course of that is all that's done, you raise compression.

The other things you described, like head porting seems like more than just setting the squish and keeping the same compression ratio.

Bottom line for me is it worth $100, when the squish is already at a near optimal level from the factory? At this point it sounds like head porting, not setting the squish.


Honda isnt the only one, i dont know if a single production bike that has a proper squish clearance/band. They have to be large to compensate for machining tolerances. Like anything in life there are good head designs and bad head designs... the 05-07 not only has a large squish but is also a crappy design.

Most people blow money on bling, pipes, jetting kits, etc when the first thing they should do is get the head set up to suit their riding, fuels, altitude, etc.





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