Z900 head gasket thickness?

[12:1]

Hi all, 1st post. After the stock head gasket thickness. Part no. 11061-1214. Cometic sell a 74mm at .018" (0.4572mm) or 74mm at 0.27" (0.6858mm)
I can't find the Zds spec but motors similar seem to be 0.70mm. Just need some confirmation so I don't  turn it into a handgranade. Cheers.

[Zed62]

Are you worried about the change in compression ratio?  Or the ability of the gasket to "hold"?  Will a .009" difference in thicknes increase the the CR enough to matter?  Let's check...In fact you can calculate it.
  OK, looks like the Z900 has 11.8:1 CR.
Per cylinder the displacement is 948/4 cylinders = 237 cc per cylinder.  The clearance volume is therefore 237/11.8 = 20.08cc.  73.4mm bore has area of 230.59mm^2.  A cylinder Ø73.4mm x .229mm (.009") high (difference in volume between gaskets) has a volume of .967 cc.  So, 20.08 cc - 0.967 cc = 19.12 cc.  Almost there...
237/19.12 = 12.4:1.  New compression ratio.

Definately more than I thought.  Is 12.4:1 too high?  Dunno.  Also query valve clearance.... / timing???  I would make sure to stay stock myself.  YMMV

I was comparing the two numbers you know for sure.  Gives an idea of the effect of changing thicknes of gasket.

[12:1]

Thanks for the detailed reply, wasn't expecting that, well done. I have ordered the OEM HG but I was hoping for a marginal gain of around 12-12.2:1 with a Cometic. Still have no idea if the stock is 0.7mm
I am transplanting a z900 motor into my z900rs. The only RS remnant of the motor being retained will be the head.
Lighter crank, high compression pistons, 2mm higher lift cams. The rods and journals on both motors are the same, valves are the same. I am not even going to clay the motor. The engine numbers are only 90 apart.
Head swap, shim adjustment, new head gasket, 12000rpm hear I come. Will hopefully peak at 128bhp, the high compression head gasket would get me to 130bhp. That's all I want, nothing more.
Disappointed with the RS high ratio 1st gear, 10000rpm red line and pitiful peak power. Having the revs maxed out in 1st at the apex of a hairpin is not fun and second gear sucks at 3500rpm.
I still want it to look like a teddy bear, just not be one.

[Zed62]

Wow, that is quite a list of high performance mods.  Good luck!  Also my math in the above has a mistake; I neglected to consider the clearance volume itself in the CR.  That will definately alter the results a bit.

[12:1]

Got the oem head gasket. Part no 11004-0769. Does all Z900B and RS's. Thickness is 0.645mm, measured in 4 places, 0.636-0.645mm