Solid info?...
well i backfire all the time, both cracker pops and the deep pop, in first 2nd 3rd and 4th
Im running a straight through with no cat.
Pops/backfire is natural, dont worry, its better to run a bit rich then lean. Unless your detonating, coil failure etc and u lose power then u worry, otherwise keep driving hard and ignore the pops.
your mechanic said dont worry unless your backfiring. ??? all skylines backfire its natural...
what mods are you running? is it stock?