am planning on adding the a z speed and marine "magnum" efi kit( flame arrestor, ecu re-calib.,adj. fuel reg. msd ignition) to my stock 1998 502efi, do i need to have the ecu re-calibrated again if i add an after market exhaust in the future?

Answer to your question is no. Save your money and just buy the adjustable fuel pressure regulator, use the remaining$950.00 for somthing worthwhile.

THe flame arester is good because it filters the air, the ECM recalibration helps clean up the soot on the transom.

I bought it and wouldn't do it again. Not worth the $$.