Today I did some experiments. With the original heads with 32x24 soloprop it took 3470rpm (well the intake lines leaving the crackcase was smoothened). With the new head, the soloprop pitch was accidently 25", it took 3600 rpm. So it looks like it is the torque that was increased. Also the throttle respond is much better now and the lower cylinders keeps on firing a even running at low rpm's for longer periods. All in all, the engine is breathing better now. Almost forgot, the low rpm was 550 that it was able to keep. But now I must decide if I can use such a high pitch, It will unload to over 5000rpm so my corsair will fly very fast... With a 2-blade MenzS 32x20" it flew 250kmh.