[two89w]

i have a 347 with quad 44 mm idf webers, comp cams 294s, dart snr's, 10.1 comp,1 3/4 headers, it hasnt been tuned yet but its backfiring out the exhaust and the carbies what could/would the problems be??
i have had it on the dyno for a power run it made 295rwhp/5700rpm and 355ftlbs torque,it started to lean out and ping,does anybody think that the 295rwhp figure is a bit ordinary(low)for such a combination?or am i expecting to much?