Plug gap depends on your coil, plug wires, TFI, etc etc, just gab them to where spark isn't being blown out. Also running a cat TAKES power away because it creates back pressure (not a ton, but it is created)
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The sad thing is, with 15 PSI, straight back exhaust, and a bobs log, it still feels slow...
Maybe 20PSI, new computer, new 3" VAM, and some porting will make it faster
It seems weird to me that you are running 20lbs but don't know what plug gap or how an exhaust system works. I don't mean it as a put down. those questions are kind of rookie questions however 20lbs in not rookie numbers. You bought the car set up already?
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97 Cobra-03 Cobra t56 and alum DS, SPEC111 clutch, FRPP 4:10,T&J Performance Forged 4v(8.9:1), Manley rods, Novi 2000 w/ Fast Track A/A I/C, Barry Grant Fuel syst., BBK longtubes and H-pipe, MSD ignition, Detroit True Track, Magnaflows, 315 NT01's on 17 x 11's, KB BAS, SCT tune and about a million other things. 575 RWHP. Going into the shop this winter, looking for 650 RWHP.
.028 maybe need. A free flowing exhaust is extrememly important. I am running 3" pipe and 3" dynomax ultraflow. I need to go to 3" elbow off turbo and 3" downpipe. I tried looking it up memory serves me that fuel pressure is 39 with vac hose off. Fuel regulator should build one psi for every one psi of boost.
Need to know plug gap and timing if im running 20 pounds 
