In the 60's and 70's TF and FC ran motors of all makes...The 392H (& Donovan 417) and later 426H proved to BE the motors to lead the pack for several reasons: as mentioned, with more and more nitro being used in the 60's/70's they stayed together better/longer than the others; the chrysler hemispherical combustion chamber design was the best, particularly in blower application. As side note- the hemi was competitive in the early years of PS, but later with rpms above 8500 and in normally aspirated motors... in PS the Hemi was inefficent. BUT with a blower attached- NOTHING could touch the Hemi and it's combustion design. Fast forward 10 or so years when no other motor would would even try to compete in FT/FC, NHRA deemed the Hemi was king! and made it the standard.