afterfire or backfire?

JB1 · 03-09-2010, 09:43 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...

theDreamer · 03-09-2010, 09:44 PM

Sounds right JB1, the same burble noise happens with a co-workers Mustang and it is unburned fuel, but once the system warms up it goes away.

bluestyle55 · 03-09-2010, 10:06 PM

Quote:

Originally Posted by RCZ

I wish my Z gurgled more, its awesome when it does.

Hehe, I used to spit flames out of the STI. Check it out when I brake for the right hander. Lots of chirping BOV, I miss that car.

YouTube - Passing and being passed.

I use to have an 07 STi....I do miss that car sometimes. In a perfect world were I had more money I would own my Z and a STi

JB1 · 03-09-2010, 10:15 PM

Quote:

Originally Posted by theDreamer

Sounds right JB1, the same burble noise happens with a co-workers Mustang and it is unburned fuel, but once the system warms up it goes away.

Interesting that it goes away when the car warms up. With the carburetor cars I referred to it became worse (or better

) when the systems warmed up. Especially the Lotus, that really came alive when warmed up and driven "in anger"...

RCZ · 03-10-2010, 12:50 AM

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, 01:10 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, 01:24 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, 09:43 PM	#31 (permalink)
JB1 Track Member Join Date: Mar 2009 Location: Chicagoland Posts: 748 Drives: 09 Nissan 370Z sold Rep Power: 17	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 09:53 PM.

03-09-2010, 09:44 PM	#32 (permalink)
theDreamer A True Z Fanatic Join Date: Feb 2009 Location: Texas Posts: 30,879 Drives: 370z Rep Power: 4210	Sounds right JB1, the same burble noise happens with a co-workers Mustang and it is unburned fuel, but once the system warms up it goes away. __________________ theDreamer's Z // Fast Intentions // Uprev // GTM // HKS // TEIN theDreamer's Silvia // URAS // GREDDY Houston Zs // Facebook // Twitter // Instagram

03-10-2010, 01:10 AM	#36 (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!