You runnin nitrous Pete?
The only way to tune the motor is to plug chop @ the end of run , this will tell you what the motor wants , if your changing the octane rating or heat range on plugs then this will require pulling or adding spark lead.
No reason to add or pull timing above 3000 rpm (na) , unless you wanna risk totaling the motor or runnin slower
the motor does'nt see below 3000rpm , that's why you've locked the timing out.
If there are gains to be had by adding/pulling timing above 3000rpm on a na run then the motors not set up correctly to start with.
nitrous run motors have to pull timing due to increased cylinder pressures/heat & faster burn rate , to avoid detonation/preignition.
The motor wanted another 2/3* of spark lead & fattening up , i take it you leaned the motor the previous time @ the Nats due to the air quality bein poop..................did you pull the plugs after the next run @ take a look?
The MSD6 digital is a two step controller , the purple & blue wires are usually grounded to the nitrous solinoids , so when the solinoids are activated the box will pull timing to whatever is set on the soft touch. . The digi 6 box is normally used for nitrous/boosted applications or when running a trans brake , NA motors don't use the step retard facility for timing control above 28/3000 rpm , although the start retard function is useful when your running locked out timing , i like the anti theft device on em too
40* spark advance? maybe bleeding off too much cylinder pressure , try backing off the lash next time out.
