Compression numbers for 2.2 wbx?

[tsombrero1]

Should compression numbers for a wbx with the 2.2 upgrade be higher, lower, or the same as for a 2.1?

I would have thought higher, but my recent 2.2 is showing 125/135/110/125 with a cold engine (would warming it up make that much difference?)
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Tennessee Sombrero

1988 Westy, Syncro-nated
2003 Aprilia Caponord (now with Jif)
Atari 2600
1970 Earthbound Humanoid

[tencentlife]

It depends on which pistons were in your old engine vs. which ones are in the 2.2. Going from OEM German pistons, which give 8.66:1 CR, to GW's 2.2 pistons, you should have higher CR of 8.98:1.

Take the psi ratings in the book with a grain of salt. There are many variables, temp and altitude among them. The rated numbers are for sea level. If you're over 4000 ft. you'll see a substantial drop, more if you go higher. If the engine has only 1 or 2 thousand miles on the rings and cylinders, it may not have achieved full compression yet. How you break in the engine has much to do with how well the rings and cylinders mate up.

At minimum, test compression at operating temp. The aluminum pistons expand quite a bit relative to the cast iron cylinders, and don't reach the optimal size relationship until the engine is well warmed up.

Piston speed has a serious effect. Make sure your battery has a good charge, and remove all plugs so you get better and smoother cranking speed. Ground out the dizzy center wire while testing. Hold the throttle open as well, to reduce restriction of inlet air.

To get the most accurate test of all, you would actually run the engine, testing one cylinder at a time with a screw-in adapter for the gauge. Remove one plug at a time, ground out its wire, and read the gauge with the engine idling. Then shut off, reassemble, and move to the next cylinder.