So the speedo is that far off? I swear the damn thing said 78. at 4800 rpm. Sorry for the ignorance but what is prop slip?
I don't know all the calculations for prop slip and all that. If you do a search you should find it. What I do know is you may be mistaken about your RPM or you got a bum deal and paid for an HO and only got a 496 Mag. Max RPM on the 496 Mag is 4800 whereas the HO max RPM is 5300 I believe.