Why do rally cars backfire?

[ugh]

Anyone? Someone told me that those blasts of fire from the exhaust are due to the brake pads being to hot... That isn't so rite?

 

[ThisIsMatt]

Brake pads? Exhaust? That guy been sucking on the exhaust?

Backfiring is from the engine exhaling hot gas that hasn't burned all the way. It comes in contact with something hot in the exhaust system and blows...

 

[kpxgq]

it is because race cars have no emmisions restricctions.. so they run with no cat convertor or muffler and the turbo cars esp run extremely rich and falmes come out the exhaust...


<a target=new class=ftalternatingbarlinklarge href="http://www.myevo.com/e6egmo.GIF">380 horsepower UK Ralliart Mitsubishi Lancer EVO 6 (4wheel drive turbo sedan)
... blowing flames</a>

 

[ugh]

Ahh.. Thanks. So in that case the combustion in rally cars are quite bad?

 

[Bozz]

All wrong on this answer

The loud popping you hear coming from the exhaust of rally cars on partial acceleration and deceleration is called the anti-lag system where fuel is squirted directly into the exhaust manifold before the turbo with the intention of keeping the turbo spinning at high speed so there isn't any turbo lag when the GO pedal is mashed to the firewall

<ex rally driver >

Cheers

 

[Bozz]

<< it is because race cars have no emmisions restricctions.. so they run with no cat convertor or muffler and the turbo cars esp run extremely rich and falmes come out the exhaust...


<a target=new class=ftalternatingbarlinklarge href="http://www.myevo.com/e6egmo.GIF">380 horsepower UK Ralliart Mitsubishi Lancer EVO 6 (4wheel drive turbo sedan)
... blowing flames</a> >>



Nope, while the computers can run the engine rich, this only happens when it starts detonating (pinging). Running any engine rich will cause carbon deposits inside the combustion chamber or on the piston crown so it is not in anybodies interest to do so.

Cheers

 

[puffpio]

bozz is right, the anti lag system is to keep the turbo spinning....(i believe the japanese call this a misfiring system)

I read somewhere about ALS system using a modified fuel injector to inject air? This is from a British rally car driver so he is trustworthy, but need more info

Also I heard the latest WRC cars don't exhibit the ALS squeaking noise anymore, any reason why?



<< All wrong on this answer The loud popping you hear coming from the exhaust of rally cars on partial acceleration and deceleration is called the anti-lag system where fuel is squirted directly into the exhaust manifold before the turbo with the intention of keeping the turbo spinning at high speed so there isn't any turbo lag when the GO pedal is mashed to the firewall <EX driver rally>Cheers >>

 

[trmiv]

Race cars without that system will shoot flames out the exhaust as well. It's just fuel that wasn't burnt in the combustion process being burned off at the exhaust. The small block chevy in my race car does that, and there is no anti-lag system on there.

 

[Bozz]

<< bozz is right, the anti lag system is to keep the turbo spinning....(i believe the japanese call this a misfiring system)

I read somewhere about ALS system using a modified fuel injector to inject air? This is from a British rally car driver so he is trustworthy, but need more info

Also I heard the latest WRC cars don't exhibit the ALS squeaking noise anymore, any reason why?

Yeah there is air as well, gotta make the lovely fuel combust with something

I dont know much about the latest world rally cars so perhaps someone a bit more knowledgeable than me could offer an explanation?

 

[lupohki]

Bang! Bang!

 

[MisterNi]

<< The loud popping you hear coming from the exhaust of rally cars on partial acceleration and deceleration is called the anti-lag system where fuel is squirted directly into the exhaust manifold before the turbo with the intention of keeping the turbo spinning at high speed so there isn't any turbo lag when the GO pedal is mashed to the firewall >>


Excellent Bozz! I didn't think anyone on this forum knew squat about modern cars. (Read any previous car thread if you doubt me) Sure showed me

 

[MrCraphead]

gawd, someone knows their stuff, very impressive.

 

[ugh]

Wow, didn't expect so many replies.. Heh... Thanks for the info dudes!

 

[Fausto]

I thought that the anti-lag worked by retarding the timing somewhat as the driver lifts his foot, thereby allowing some unburned fuel to get past the cylinder and then ignite upon hitting the hot side of the exhaust/turbo? I didn't think they actually had an "injector" to put fuel in there...

Fausto

 

[arcain]

(Not for rally cars but.. ) I was under the impression that some (many?) modern ECU controlled cars will run rich at WOT (I'm pretty sure mine does), and can shoot flames out the exhaust if the cats are removed. I've seen videos of RX7s shooting rather large flames under heavy acceleration.

 

[Masas]

so...where can i get this for my honda?

 

[Zenmervolt]

<<I was under the impression that some (many?) modern ECU controlled cars will run rich at WOT (I'm pretty sure mine does), and can shoot flames out the exhaust if the cats are removed.>>

As I understood things (which may well be wrong) the ECU does not run the car rich at WOT. However, since engines are decidedly not pollution tested at WOT, the ECU does optimise the fuel/air mixture for power and not for economy/pollution control. As Bozz said, running an engine rich is never a good thing. Too much fuel will foul the plugs and also seep past the piston rings diluting the oil.

ZV

 

[mAdD INDIAN]

Isn't running rich better than running lean? Because if you have less fuel, then you can damage the piston?

Also when under WOT, the ECU runs in an open loop, meaning it disregards all the parameters for fuel-efficineny and emissions.

 

[Cyberian]

<< I thought that the anti-lag worked by retarding the timing somewhat as the driver lifts his foot, thereby allowing some unburned fuel to get past the cylinder and then ignite upon hitting the hot side of the exhaust/turbo? I didn't think they actually had an "injector" to put fuel in there...

Fausto >>


That's what I thought. I also thought the mixture was enriched somewhat at the same time (throttle lift off).

 

[Bozz]

<< Isn't running rich better than running lean? Because if you have less fuel, then you can damage the piston?

Also when under WOT, the ECU runs in an open loop, meaning it disregards all the parameters for fuel-efficineny and emissions. >>



Out of the two worse case scenarios, yes running rich is better than running lean, running it rich will foul up your combustion chamber, running lean will cause the engine to ping(detonate, knock) and it can also cause the exhaust valve to burn out due to higher temperatures of a lean combustion.

The open loop running of the ECU is somewhat of a misnomer, some cars will ignore the o2 sensor at WOT while still monitoring the air mass meter and/or MAP sensor while the majority always stay in closed loop. Some engines do richen up the mixture even as much as 12:1 at WOT to reduce chance of pinging and reduce exhaust temperatures. This generally isnt harmful because the engine will not be at WOT for long periods of time at high revs.

Now many ECUs also lean out the mixture on cruising conditions, some can go as lean as 15.5:1 under very light load constant speed cruise. This is a common reason that engine control units need an input from the gearbox speed sensor. Reason for this is fuel economy and emissions, it varies with cars. The reason the exhaust valve is unlikely to burn up is the greatly reduced amount of gas that flows past it under these conditions.


Cyberian: Out of tune cars will richen the mixture on throttle lift off, it is what is called afterburning, or the popping you hear in the exhaust of manual dinosaurs rolling down a long hill in a low gear. EFI cars generally stop all supply of fuel when the throttle is closed and the engine is above approximately 2000-3000rpm, depending on engine and car.

Cheers