496 too much timing?

Me and my brother just put a 496 in his s-10 mud drag pickup, I don't know the specs exactly of the motor, what I do know it has a solid flat-tappet cam with roller rockers on 781 casting heads that have the bigger valves. About 7 grand into the motor. Right know we have the initial timing at around 17 degrees, it seems to run fine, it starts fine. But it just seems high. We tried bringing it down but it just seemed like it wouldn't idle as good the response wasn't as good either. Would that high of timing hurt the power at all. He raced it a couple of times it runs really good. Just curious I guess. Thanks.

how much total timing .when is all the timming come in at ?