I have a 1993 chevy z71 5.7 litre. Fresh rebuild, with New vortec heads. Running stock throttle body,on Edelbrock 4 bbl. manifold,with adapter plate. my issue MAY be the camshaft chosen. Speed Pro CS-274. Problem is... if I set the timing as called for 0 degrees with spout disconnected,the truck almost doesn't run. Backfires thru t-body terrible,especially trying to accelerate. If the timing is bumped to 18-21 degrees the truck is now driveable,but it aint right.Using a Moates tuner,we ALWAYS see the knock retard trying to remove about 18 degrees no matter what I do or set timing.The ecm is#16168625. We have replaced everything in ignition system,moved the disributer a dozen times...I am missing SOMETHING..