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i just bought a 603 sealed crate to run this year.i wolud like any info anyone has on how i could possibly pull every bit out of this thing as far as areas i can play with. Im limited to only bolt on things basically, but i hear some guys are running a better valve spring?? we have no rule on fuel. the car is an asphalt late model that weighs 2900lbs, and usually turns around 6500rpm. i have a VDL 500cfm carb, and stepped 1 5/8 to 1/3/4 crossover headers.. possible idea on a good spark plug and timing? any help is much appreciated- thanks