afterfire or backfire?

JB1 · 03-09-2010, 08:43 PM

I have read through the thread but have not seen the answer to the question: what does cause the burble and gurgle? So I'll take a stab: As far as I know, the flames are unburned fuel getting into the exhaust and igniting/burning in the exhaust instead, resulting in popping/burbling noises. This is more present with high powered turbo engines due to running rich and the fact that the turbine housing and wheel get nice and hot and help to ignite the unburnt fuel. I had a friend with a Lotus Esprit turbo, carburetor + turbo= big flames and lots of popping on deceleration. I also once owned a car with a engine with carburetor myself, that car was running rich, lots of popping and burbling. At some point the popping turned into big explosions in the exhaust, getting big enough to blow a hole in the middle muffler

the muffler just split open like a coke can that had a lit firecracker inserted...

The other reason for burble is air being sucked into the engine, through the exhaust and exhaust valves on deceleration when the throttle is closed. Because there is no ignition and expansion of fuel and air on the 3rd stroke (or power stroke) there will be a slight vacuum in the cylinder when the piston reaches the end of the stroke. So when the exhaust valves open (to let the not present exhaust gasses out), air from the exhaust will be sucked in, resulting in a popping/burbling sound.

This is all AFAIK, please correct me if I'm wrong...

RCZ · 03-09-2010, 11:50 PM

Quote:

Originally Posted by JB1

I have read through the thread but have not seen the answer to the question: what does cause the burble and gurgle? So I'll take a stab: As far as I know, the flames are unburned fuel getting into the exhaust and igniting/burning in the exhaust instead, resulting in popping/burbling noises. This is more present with high powered turbo engines due to running rich and the fact that the turbine housing and wheel get nice and hot and help to ignite the unburnt fuel.

This is all AFAIK, please correct me if I'm wrong...

Bingo.

Chriz · 03-10-2010, 12:10 AM

Sometimes I wish the Z had more "burble" too. Someone I know owns a r32 with an aftermarket exhaust and it sound awesome.

Kind of like this but not as loud.

JB1 · 03-10-2010, 12:24 AM

Quote:

Originally Posted by Chriz

Sometimes I wish the Z had more "burble" too. Someone I know owns a r32 with an aftermarket exhaust and it sound awesome.
Kind of like this but not as loud.

Nice Lamo doors... Ah well, guess it's OK as VW owns Lamborghini...

BTW, that's loud...

03-09-2010, 08:43 PM	#1 (permalink)
JB1 Track Member Join Date: Mar 2009 Location: Chicagoland Posts: 748 Drives: 09 Nissan 370Z sold Rep Power: 18	I have read through the thread but have not seen the answer to the question: what does cause the burble and gurgle? So I'll take a stab: As far as I know, the flames are unburned fuel getting into the exhaust and igniting/burning in the exhaust instead, resulting in popping/burbling noises. This is more present with high powered turbo engines due to running rich and the fact that the turbine housing and wheel get nice and hot and help to ignite the unburnt fuel. I had a friend with a Lotus Esprit turbo, carburetor + turbo= big flames and lots of popping on deceleration. I also once owned a car with a engine with carburetor myself, that car was running rich, lots of popping and burbling. At some point the popping turned into big explosions in the exhaust, getting big enough to blow a hole in the middle muffler the muffler just split open like a coke can that had a lit firecracker inserted... The other reason for burble is air being sucked into the engine, through the exhaust and exhaust valves on deceleration when the throttle is closed. Because there is no ignition and expansion of fuel and air on the 3rd stroke (or power stroke) there will be a slight vacuum in the cylinder when the piston reaches the end of the stroke. So when the exhaust valves open (to let the not present exhaust gasses out), air from the exhaust will be sucked in, resulting in a popping/burbling sound. This is all AFAIK, please correct me if I'm wrong... __________________ Black Fangs // Black rear Valance // Berk CBE // COBB post MAF tubes // K&N drop in filters // Setrab Oil Cooler // Stillen Sway bars // Z1 SS brake lines // Stillen brake cooling kit // Harness bar // Last edited by JB1; 03-09-2010 at 08:53 PM.

03-10-2010, 12:10 AM	#3 (permalink)
Chriz Track Member Join Date: Dec 2009 Location: Houston TX Posts: 626 Drives: '10 370z PW 7AT Rep Power: 17	Sometimes I wish the Z had more "burble" too. Someone I know owns a r32 with an aftermarket exhaust and it sound awesome. Kind of like this but not as loud. __________________ PW 7AT w/Sports Pkg Hook Em!