Ok....here's the story...I have a 1997 ITR and just had the machine shop install JE 11:1 compression pistons with rods...also i had them machine the head for Skunk high compression valves, springs, and retainers...installed everything...the car starts but it backfires at idle...also it hesitates to rev but once it gets to 2000 rpm it doesnt backfire or hesitate to rev but once i release and immediately tap the accelerator it backfires...at times i had the rpms steady at 1500 it didnt backfire but i would hear a knock inside the engine and the rpms would drop and black smoke would come from exhaust...i have no stand alone ecm or upgraded injectors...please help...