How far can you shave the head before...

[nouseforaname90]

How far can you shave and R's head before you have to run race gas? I figure that if you shave the head, you definately need to run higher octane gas anyway.. but how far until you need to run race gas? I found a guys with a nice R head that has been shaved.. all he knows is that is has been shaved so that you "get 19cc's more". WTF? Would that require race gas (100+ octane) or could I run 98 octane pump gas?
Thanks

[nate b]

I think you would want to bolt the head on and check your compression ratio and squish to know for sure

[Billy Golightly]

Well...19cc's more would mean there is more volume in the head dome. And unless they trimmed a ton off of the bottom the cylinder, it also means lower compression. Trimming right off the bottom of the head isn't the best way to get compression. It is the easiest though.

[nouseforaname90]

So.. that means? lol
What are the disadvantages of running a shaved head?

[85 250sx]

whats it equal out to when you run a CR head gasket? you can still run pump gas with that cant you?

[Billy Golightly]

If you cut off the bottom without redoming it your moving the distance from the top of the piston to the outer ring of the head (called the sqish band) closer together which can be bad if it gets to close. Theres a certain range its suppose to be in, I dont remember it off hand, I'd have to consult one of my books. And in addition to that your also putting the spark plug closer to the piston which creates more heat on the top of it which in turn makes detonation occur easier.

[Ordo]

You can pull it down to .035" but that is extremely low and with rod stretch and other variables you could find yourself in trouble. I'd set it at .040" and you be safe. Set your piston up just before TDC. Put a piece of solder on the piston to where it runs from the exhaust side to the intake. Use a small piece of masking tape to hold it in place so that way you don' t drop it down into a transfer, exhaust or intake port. The reason for this, you want to eliminate any rocking of the piston and get an accurate measurement. Put the gasket and head on and torque it to spec. Make sure the plug is out. Run it up by hand, pull it apart and check the thickness at the thinnest point on both ends. You could pull it up through plug hole but you might get false measurements if it gets twisted or bent wrong.
About the shaving the bottom of the head. You can take some off the bottom without having to rechamber the head (up to .004"). But there are different angles and widths to consider when chambering. Squish area and angle should be a consideration when building an engine but is over looked far to often. And the dome on pistons can vary slightly from manufacture, cast, forged and over-bores.

[nouseforaname90]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=280000358803&ih=018&sspagename=STRK%3AMEWA%3AIT

This is the head I was referring to.
What do you think? What does it mean by "Shaved down to 19cc"?

[metalm0]

If you are worried about the whole thing and want a new head. Go to this site http://www.2strokeheads.com/Custom-Yamaha-Suzuki-and-Honda-ATV-Performance-Heads.html The guy is a fellow cr500 rider that is on another forum I am on and he'll answer everything for you. Plus they are really cool looking...

[nouseforaname90]

Well I bought that head off of eBay, I just wanted to be informed as to what octane I had to run, etc etc. I figured someone might know, but I'll talk to the guy that is selling it to me and see how much it is shaved.
And how much do those heads cost from that guy?

[metalm0]

Well I am not sure about the 250r but for my cr500 it is 325 bucks... I mean its cool looking since well its billet and its chrome but they have a different chamber design so it produces more power than milling the head and all.