I was on the parkway heading home yesterday and i saw a WRX next to me and he rev'd pretty hard and there was a loud POP, followed by a blue flame. Well iam just wondering what causes that pop?

 

Turbos backfire sometimes.

 

too much fuel going into the exhaust...
once it exits the exhaust it combusts (goes pop)

sometimes called a backfire or mis fire but thats not true.
those you would hear and feel in the motor and never see coming from the exhaust...
that pop is just fuel loaded gases burning past the exhaust tip.

 

wish my car did that. LMAO

 

^^ smart guy

my magnaflow pops like hell but thats from the difference in backpressure i think

 

Can the tc back fire after intake, headers , s-pipe, catback? Not with the fire and all , just the POP.

 

my frends stock RX8 with HKS hi-power exhaust does it too. i thought it was pretty cool but im over it hahaha

 

if you hear it. it will.

some cars will "pop" more than others.

my focus was awesome. it poped all the time. sounded real mean. almost SRT-4 mean

 

i confirm that

 

my sr powered 240sx pops all the time. its a sign i'm running rich...aka wasting gas (i get 200 miles per tank ). gets annoying after awhile. extra attention for a cop to look at your exhaust, then hand you a fix it ticket.

 

boogers

 

im also in love with the popping.. its also reffered to as afterfire.. rotaries are more prone to it and flames =P.. but correct me if im wrong ....its mainly on turbo cars b/c of the the excess fuel built up inside the exhaust pipe like some one said..basically means your running rich...it may be a waste of fuel but damn does sound nasty!

 

turbo cars tend to run richer (and get that "pop") as a safeguard to avoid detonation under boost. oxygen sensor malfunction is a common cause for running rich on any car. running rich will burn out spark plugs faster (I change my 240's every 5000 miles just to be safe).

 

running rich for long periods can also ruin the cat.

 

I know that one for a fact.

 

now question.....was it an STi, or a basic WRX Impreza

 

as cool as the popping and flames and all that ____ is... any explosions/combustion of gases anywhere other than inside the engine itself is not good. if it happens long enough it will ruin your cat and your muffler . if the explosions are intense enough and could ultimately cause leaks in your exhaust or even break things loose...

 

lol. thats probably why i blew a chunk the turbo gasket (and one of the bolts that connects the turbo to the manifold). Now I have an 8 repair job ahead of me to replace $8 in parts.

 

My car spits fire all the time like that, it's from the fuel map I'm running right now. I also have no cat and 3" exhaust from the turbo back too, so that contributes to that also...

 

What you heard is the turbo bypass valve letting off some of the turbo compressed air pressure so as not to overpressurize the system and cause detonation. It's also called a turbo "pop-off" valve. These bypass vlaves are set to release the turbo pressure to bypass the cumbustion system at a certain PSI rating. The ensueing flame is caused by the rich mixture that results because there is less air going into the system when it is diverted out to the atmosphere by the bypass valve.

Chombi