Backfiring-Is it bad?
 

Rousch Stage 3
Kooks Longtube headers
No cats
Kooks H-pipe
Magnaflow axlebacks
Backfires quite often when gearing down and on decal. Is it bad for the motor?

Is it backfiring or is unburnt fuel igniting in the exhaust? Ignition in the exhaust system is fairly normal to a degree, and will be heard much more readily with all those mods.

Now backfiring in the intake manifold would be a much different issue.

What tune are you running and I assume you got an updated tune once the headers were installed.
More than likely its a conservative tune or a little rich and without cats plus hot exhaust can make for some loud pops.

Car has a JDM Custom tune which was done at the same time as the stage3 and exhaust. Bought the car this way and I'm not familiar with how tunes on these mustangs work. Crossed over from diesel trucks. maybe I should get an updated tune?

Hmmm, I guess it would be popping in the exhaust

It happens stock, too. But with a fairly conservative exhaust it's difficult to pick up.

With a tune it'll happen more as it changes how the motor decelerates. Typically there is a "lag" when the motor starts to decel, this allows the fuel that was just sprayed from the injectors to actually make it through the motor and get burnt before hitting the exhaust. This doesn't do anything good performance wise, and it's often eliminated or reduced with a tune. When this happens that unburnt fuel gets dumped into the exhaust, where it has a chance to burn...hence the "pop".

You'll notice this is VERY prominent on old carbureted vehicles. They have no such feature to burn the fuel in the engine, so lots of pops when decelerating.

The car runs awesome, dyno'd at 614 and gets 1mpg better than my stock 13 did. I'd prefer not to change anything I was just worried that the backfiring(popping) was bad for the engine

That's fairly normal. Any modded/blown car, esp with no cats will have some degree of backfiring. I have it, and I love it when it does upon slight decel. :)

FYI, I also have JDM as my tune and I love it/them. Nick is fantastic. You bought yours that way?

I have a non-tune CAI and GT500 axlebacks. The popping and gurgling is very noticeable and music to my ears.

It's practically non-existent in very cold weather though. But the denser air makes it more responsive so it's a good trade off in the winter.