Im trying to figure out my CR on my H22a, with stock pistons. Im running supertech flat faced valves supposedly a .2 bump. OEM single layer headgasket and the head was decked .004. My question is what does a stock h22a head CC at (it will be alitle different because of the decking but close) ? As well as a compressed sinlge layer HG ? Also what is a typical deck clearence on these ?

 

Typical OEM head gasket is 0.026" to 0.028" compressed that I've measured. You can probably come up with a good estimate from that value.

OEM H22 combustion chamber should cc right around 53.8ccs with stock valves.

I can't tell you about OEM deck clearance, sorry.

 

thanks man. ill try to find something on it.

 

Calculating CR is simple dude, all it is is the ratio of volume at TDC versus bottom dead center.

CC @ TDC =

Combustion chamber cc = 53.8cc

-

Flat Valves = 2cc

-

.004 deck = .604cc
^^To get that, take 8.7cm(bore)/2 to get r of the cc (4.35cm), square it, 18.9225cm^2, then multiply by pi to get 59.4467cm^2 surface area of the cc. Then convert .004" to cm (.01016cm) and multiply the surface area by deck height to get .604 cm^3 (cc)

-

Piston dome cc = -2cc (so you end up adding 2cc)

+

In the hole volume = .604cc
You're .004 in the hole with a stock setup (deck height - compression height - rod length- stroke/2 so 8.643 - 5.633 - 1.221 - 1.785 = .004" in hole)
Conveniently, this volume is the same as the amount you had decked off the head, so they cancel each other.

+

Head gasket cc = 1.308cc
I really have no idea here, but stock 3layer hgs are .026" fully compressed, so I'll ASSume the single layer is 1/3 of that so .00867". Then just do pi*r^2 * .0220218cm (converted from inches) to get 1.308cc

=

55.108 cc @ TDC

Now we need cc @ BDC. All we need to do is add the displacement of a single cylinder to the TDC cc since that volume is still there, and all that will be added is a single cylinder worth of displacement.

So, we will need bore surface area * stroke.


87mm bore = 8.7cm bore/2 = 4.35cm radius ^2 * pi = 59.4467cm^2 (again)
90.7mm stroke = 9.07cm stroke * 59.4467cm^2 = 502.902cc

502.902 + 55.108 = 558cc

558cc/55.108cc = 10.1255:1 CR

 

Now, that does seem a little low, so the piston dome CC might be wrong some....

I'd try to figure that out for sure and then just sub that into the calculation. I bet it's more like 10.4ish