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View Full Version : 12.1 compression piston what kind of gas


kfx400isdashiz
07-07-2006, 09:31 AM
ok the ltz z400 is detuned from its daddy the drz400 dirt bike stock comression on the ltz is 11.1 and stock compression on the drz is 12.2.or 12.5 somthin if i were to put a 12.2.stock bore or a 12.2 440 bore piston in it would i be able to use high octane pump gas? and i know this is stupid but waht are valve shims?
Scro
07-07-2006, 09:36 AM
You should be OK using 93. If it was me, I would mix it 50/50 with 110, just to be on the safe side. A valve shim is used to adjust your valves.
rooster300ex
07-07-2006, 10:46 AM
Do a search there are all kinds of threads on this.
GPracer2500
07-07-2006, 01:46 PM
One option for increasing the compression is to use the cylinder base gasket from the DRZ (the E model, not the S or SM). That's where the difference in compression comes from between the two engines--the piston is identical. It's a lot less expensive and easier than replacing the piston.

The cam timing is retarded ever so slightly by doing this mod but it is not a problem in this instance.

Like was already mentioned, you'll be OK using premium pump fuel after doing this mod. A little extra octane won't hurt, but premium should be OK.

Actually, it's funny--just last night I started a thread in the DRZ section about this mod. Don't think anyone has replied yet.
kfx400isdashiz
07-07-2006, 01:55 PM
i might do that but would you recomend jsut slightly retarding the cam chain?
GPracer2500
07-07-2006, 02:20 PM
Originally posted by kfx400isdashiz
i might do that but would you recomend jsut slightly retarding the cam chain?

If you do the base gasket mod then you have no choice regarding the retarded cam timing. The thinner base gasket of the DRZ lowers the cylinder and head reletive to the crankcase. That's where the additional compression comes from. But since the cam chain remains the same length, when the "pulling side" of the cam chain goes tight the cams will be timed a little different than before. But it's a very small change and not a concern in this instance. I don't own a Z and haven't performed this mod myself but according to everything I've heard the cam timing is a non-issue. Many don't even mention the cam timing change when discussing the base gasket mod.