What's the duration @ .050 with your Z-303 cam?? The mighty demon is a step up from the speed demon. Anyways check to see what your jet sizes are but 76/83 would be optimum for the 650 Demon carbs. Sounds like you got a good combo.

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347 Stroker/XE284H(284/296 dur, 240/246 dur @ .050), BG 650 VS Speed Demon, Ported Victor Jr intake, Jack Roush World Jr Heads (ported from 180cc to [B]195cc[/B])(upgraded to 2.02/1.60 valves) 260cfm/190cfm @ .550 lift, 11:1 comp... 450-475HP