I have mine set to 10 degrees and it's running pretty strong. I'm not sure that's the best for my L98 though. I've been so busy chasing down codes and replacing parts this year that I haven't had too much time to try anything else.
6 degrees at idle ,and 38 degrees total by about 3000rpm is about correct if everything else is dialed in, Ive seen more than one corvette destroy pistons due to detonation when the ignition timing got to far advanced, keep firmly in mind that about 80% of the detonation an engine sees can occur without the driver being able to hear it! yet it can and will damage the engine
I recently had a friend scan my 87 Coupe and the scanner read an ignition timing of 25 degrees at idle!!! . The car starts well and accelerates nicely but I doubt the timing is really what the scanner read.
the correct ignition timing at IDLE must be set useing the correct CHEVY procedure, and that includes doing it by the chevy manual. and the TPS sensor must first be correctly adjusted ( it is mandatory that you disconect the EST (electric spark timing) connector located near the brake boosterin order to bypass the computer timing mode, if you leave it connected the computer will add timing automatically to correct the ignition advance