It's mill'en time!!! (head milling that is....)

[250r'en +TCB]

Hey guys!

Alright basically for those of you who arn't familiar with my 85R the mods are listed in my sig. I know stock compression of a 250r is 8.5:1........right? The company I got my 310cc kit from says you should run 100 octane fuel with a 20:1 mixture. I run 32:1 honda racing synthetic and when I fill up the gas can I mix 110 octane leaded with 93 octane street gas, 50/50. So about 103 octane........

Now my machine is geared for top end speed, so much so that you could not even think about shifting into 6th gear unless you had a wide open flat expance (aka frozen lake ). To help you get what we're talking about, my R is as fast a a stock R in 4th gear (maybe low 5th...). So in the next week while I'm waiting for my tires I'm going to buy and MSD ignition system http://www.msdpowersports.com/atv_hondatrx250r.html and I'm gonna mill my head down, which is where I need help!!

How much should I mill off my head? I can run 100% 110 leaded Cam II racing fuel with a 32:1 mix....... So as far as compression goes where does that leave me for a ratio and how much do I mill to get there????

Any other input you guys want to throw in I'm all ears!!!

Thanks, -Devin

[MTS]

You May find that you will loose some top end power, cutting the head down, you will have to measure the squish as it sits, the quick method would be taking a piece of solder, put a 90 degree bend in it, stick it in the plug hole so it sits in the squish area, then turning the motor over once to squish it, measure it, and go from there, they have a tendency to very from head to head, stock or not, mass production isn't exactly perfect every time, .75 mm on a 250 is pushing it,

[250r'en +TCB]

so lets say i just wanted to gain a little, not go crazy milling.... would I be safe taking like .015 off? I really just have no idea how much I can/should go!!

help me out

[toocheaptosmoke]

Idealy I think you want to get the squish band set right first, (say .050) then reshape the dome to get the compression back down to a reasonable level if it's too high.

[BigGreenMachine]

You may want to contact Ronnie on here.


Ideally if your going to be running wide open you may want to stick with stock compression or even lower it.