Factory cars backfire, the only difference is the catalytic converter, resonated sections of the exhaust, and muffler dampen the sound and resulting flame. Combine a car running a little rich with a straight through 3 inch exhaust with a canister style muffler and you'll get flames.

My old ka-t car ran a little rich and used to shoot huge flames out of my hks hi power with a megan racing straight test pipe.

I switched to a resonated test pipe and my rsr exhaust (conventional style muffler), low popping no flames.

I put a stock catalytic converter on the car with the rsr exhaust and what do you know... no flames and barely audible popping.

My STOCK ka used to pop a flame out of the tail pipe with a straight through test pipe, hotshot header and my old Apexi N1 exhaust.

On a turbocharged car you're making the car go rich - lean - rich - lean by modulating the throttle open/ closed. Recirculation of the bov on maf equipped cars also have a lot to do with it. On ANY sr or ka car running a rom tuned ecu if you drive in a high gear at low throttle basically on the threshold of boost and release the throttle the car should pop because you're loading it with fuel and purging it by releasing the air through the bov.