Hi,
You have mismatch in your system somewhere.
My '87 put out 244 rwhp with only mufflers and ported stock heads,timing at 13*. @ 4,500 rpm.
That said, my '91 pulled hard to 5,300 rpm with the B303 cam so I think you have an over restricted exhaust, I would go to 1 5/8" shorty headers, 2 1/2" 'S' pipe and a better sidepipe, they can choke down 50 HP. Bump your static fuel pressure up to 42 PSI, timing to 12* with your compression, 180* thermostat, plugs set at .044 .
Good Luck,
Perry.
