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Old 03-31-2020, 11:17 AM
Velocimetry Velocimetry is offline
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Default GX390 Combustion Chamber

Does anyone know (measured or calculated), what is the combustion chamber volume of a Stock Honda GX 390 engine?

This is the volume/ space where the combustion happens, when the piston is at the TDC.

It can also be called as a Clearance Volume.
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Old 03-31-2020, 12:32 PM
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KartFab KartFab is offline
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stock gx 390 has a dished piston approximately 6-8 cc's of volume added to combustion chamber vs flat top (guess)
piston sits approximately 0.005" to .010" in the hole at TDC
head gasket is 0.050"
combustion chamber volume is approximately 41cc's

all else the same, you can mill about .050-.080" from the head and still run on premium pump gas.

Also, you dont run into spark plug hitting the piston issues on a big block like you do on small blocks. as the spark plug is "recessed" more into the head due to a larger combustion chamber, even after milling.
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