spend your money on a mass-air conversion kit first.
I think you would gain maybe 10 ponies max with just the intake swap. Dont forget to remove the restrictive factory air cleaner, air silencer, and air box, or else you wont get any more air into the intake in the first place. You should also get a 65mm Throttle body if you do this intake swap.
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1993 GT/AOD
'93 Mustang GT