Im honestly not sure of the increase just the 1.6 rockers themselfs made. Trying to compare a tired hipo 273 with ring end gaps @ .080 of an inch & 1.5 stock rockers to a fresh hipo 273 is night & day as it is. id guess i was losen 20-30 h.p. in blow by alone! But i will say this little 273 would put my o.e. 318 in my old 76 dart to shame,even after it was rebuilt & had the common bolt on goddies hands down! (R.I.P little 318!) Killed that 318 due to oil slosh back becouse we all know smallblock center sump pans had '0' baffleing in them & good hard accelration keept all oil away from pickup & fryed every bearing & crank in the bottom end! almost killed the 340 that replaced it too! until i wised up with a better pan. I made baffles in the 273 pan but looks bone stock from the outside! crafty eh?:D