2002 CR125 Raise Compression?

[DIRT-RIDER]

I have a a 2002 CR125 same motor in 1998-2002 bikes. I want to go high compression maybe like a 13:1- 14:1. I want what everyone wants MORE POWER! There are some heads that are shaved like .031 on ****. Is .031 enough to raise me to a 13:1. I am willing to run VP race fuel. How much should i shave my head if i buy a new one? Would my jetting need to be richened or leaned? Thankyou in advance :)

 

[Rcannon]

I asked a similar question a few weeks ago and had very few responses.

I ended up having a local hop-up shop mill .010 off of the head. I now know why many did not respond. Its very difficult to know how your bike is going to respond. Anything can change the outcome. Altitude, jetting, gas, etc.

Common sence said my bike would gain low end. If anything , the opposite was true. I gained top end. Low end felt similar. I am thrilled with the change, but....

My bike needs to start reading the forum. Then it would know the proper way to act. Try and find someone on the know who can do the work for you. Chances are they have milled a 2002 cr allready and will know the correct specs to use. I recommend Eric.

 

[bikepilot]

you are confusing 4-stroke engine mods with 2-stroke mods. You do not want 13:1 on a two stroke. Frankly, you will be much better off letting someone who knows what they are doing set up your motor. Shipp your cylinder/head/pv's off to your favorite engine guy (Varner, Eric, Pro Circut or whatever) and talk to them about how much you can spend, what your class limitations are and what you want out of your motor. Let them decide what mods will fit in your budget and will give you the performance you want. If you tell them you want 13:1 they will probably just laugh.

Assumeing you are racing MX, you will have to stay under 134cc's and your best bet would be to have it bored to 134cc, ported to suit your riding style and the compression set to take advantage of race gas.

good luck

 

[usgpru27]

You dont want to just mill the head. You are milling off the outer squish band. You need to have the head milled and reprofiled to the lower compression. I have been looking at the Phathead set up. It is very simular to the VHM set up. I will be getting blanks and getting them cut to the volume and squish band I require for the riding I do.

 

[Rcannon]

You dont want to just mill the head. You are milling off the outer squish band. You need to have the head milled and reprofiled to the lower compression. I have been looking at the Phathead set up. It is very simular to the VHM set up. I will be getting blanks and getting them cut to the volume and squish band I require for the riding I do.

Your exactly right. This is what my local guy did to my head. There is more to it than just milling.

 

[usgpru27]

Rcannon,Didnt mean to imply that you had. Sorry. Just wanted to clarify because MANY shops will do this and give some poor guy a hell of a time trying to figure our the problems.

 

[Jaybird]

If you want more compression and HP for cheap, simply add more oil and jet it properly.

I'd suggest ~20:1 ratio.