Building a 540 motor . 632 lift cam. How much HP can be gained by increasing compression from 8.2.1 to 9.2.1 . Long story but need to know .

~3.5% according to David Vizard's article.

Here's the article.

Once of the best primers written on the subject, imho.

With a 540 you need to get to 9.5 to 9.75 and you will gain a great torque increase. A good cam for that motor will roll off compression and make it seem like 8.5 due to the valve overlap and generally large cam profile. Torque makes a boat run, not HP. Put in a 120 Arizonia Speed thermostat, set your timing at 32-34.

I like compression, 8.2 is blower motor compression. What cam are you going to use?
Good Luck