2-3% per point of compression. Some people claim 4% per point, but I've found that is a stretch and often not accurate.

0.5 point = 1-1.5% power. 180hp-0.75% = 178.65hp.

180hp- 0.8 point *3% = 175.68hp.

On the top end, compression isn't worth as much as you think. But it seems to help torque more if you don't adjust the ignition timing curve.

increases in power from compression is not a linear function. As compression gets higher there are diminishing returns.
We also have the issue with our engines layout, particularly with a single plug. As the dome gets more intrusive into the combustion chamber it block flame propagation to the far side of the chamber furthest from the plug. This is one of the reasons that twin plugging 911 engines as compression is raised is common. Adding the second plug helps as the piston dome intrudes into combustion chamber by starting flame propagation in two locations. This allows more complete and shorter time burn time. This shorter time also why twin plug engines do not need as much ignition advance for peak power.

john

Hello everyone - I am building a 2.4 with 2.2 pistons and wonder if anyone has the dome volume for a Mahle 2.2E piston?

Thanks