I'm not sure about the bigger ones but on the small engines (3-5 HP) they
don't give a specific compression--if the compression is enough to blow your
thumb out of the spark plug hole then it's enough to run the engine. Pretty
In general you can figure a compression ratio of from 7 to 9 for a
gasoline engine which is roughly 100 - 135 psi. For small engines the
lower end is more typical. As someone else I think noted, they'll run
down to about 60-80 psi, obviously losing power as there's lower
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