Im having a problem with detnation in my 400. i will give u a run down of the motor. i picked it up for $1600 the bill owed at the the shop. the motor has between parts and shop work $6000 into it.
10.5 to 1 comp, complete head work ported polished valve job milled,
large cam ( dont have the specs off hand), oil restickters, harland sharp roller rockers,
electrical: msd 6al, msd coil, accel dist, 8.8 plug wires, new 145 amp alt, elec water pump
timing 12 init and 36 full adv.
detnation dont start till it gets to about 150, runs at about 170. and mostly it only happens at holding speeds. this is also running 94 octane
iv tried hotter pugs and gapped them to .55 still the same
Any ideas would be very helpfull