What makes the car loud on cold start?

[Owain55]

When you start the car, it runs noisily for the first 1-2 minutes. The idle rpm is slightly higher (as expected) but its more noisy than when warm at the same rpm. Its also louder while driving and you can hear it quieten down, it's like something is turning off. I was wondering what is it doing to make it that much louder?

Sorry for the dumb question.

Thanks,

[MikeFish]

The secondary air injection kicks in to keep emissions down by warming up the catalytic converter quickly.

[MikeFish]

Quote from a webpage:
With spark-ignition engines, the greatest pollution occurs on cold starting. Secondary-air systems have been successfully employed to reduce such cold starting emissions.

A “rich mixture” (λ<1), i.e. a mixture with excess fuel, is required for starting a cold spark-ignition engine.
Until the catalytic converter reaches operating temperature and Lambda control action starts to take effect, large quantities of carbon monoxide and unburnt hydrocarbons are produced.
To reduce the level of these pollutants, ambient air with a high oxygen content (“secondary-air”) is injected into the exhaust manifold directly downstream of the exhaust valves during the cold starting phase. This results in post-oxidation (“afterburning”) of the pollutants to form carbon dioxide and water.
The heat generated in this process additionally warms the catalytic converter and speeds up the onset of Lambda control action.

[James1984]

Ive removed all of my secondary air system, I am yet to start the car as still putting it all back together will it still be louder because of the additional fuel?

[MikeFish]

Ive removed all of my secondary air system, I am yet to start the car as still putting it all back together will it still be louder because of the additional fuel?

Just a guess but I think it will still be loud as there is different fuelling and timing (maybe?) involved too. MRC normally map out the cold start when doing remaps as most customers also have noisier exhausts so it makes them a little more neighbour friendly.

[James1984]

Ive removed all of my secondary air system, I am yet to start the car as still putting it all back together will it still be louder because of the additional fuel?

Just a guess but I think it will still be loud as there is different fuelling and timing (maybe?) involved too. MRC normally map out the cold start when doing remaps as most customers also have noisier exhausts so it makes them a little more neighbour friendly.

Probably still loud but running rich until I can get it mapped

[Owain55]

Quote from a webpage:
With spark-ignition engines, the greatest pollution occurs on cold starting. Secondary-air systems have been successfully employed to reduce such cold starting emissions.

A “rich mixture” (λ<1), i.e. a mixture with excess fuel, is required for starting a cold spark-ignition engine.
Until the catalytic converter reaches operating temperature and Lambda control action starts to take effect, large quantities of carbon monoxide and unburnt hydrocarbons are produced.
To reduce the level of these pollutants, ambient air with a high oxygen content (“secondary-air”) is injected into the exhaust manifold directly downstream of the exhaust valves during the cold starting phase. This results in post-oxidation (“afterburning”) of the pollutants to form carbon dioxide and water.
The heat generated in this process additionally warms the catalytic converter and speeds up the onset of Lambda control action.

Thanks Mike

[Owain55]

MRC normally map out the cold start when doing remaps as most customers also have noisier exhausts so it makes them a little more neighbour friendly.

Does that map stop the secondary air injection? I had seen it on their website, but just assumed it stopped the little rev of the engine on start-up.

[pule333]

Ive removed all of my secondary air system, I am yet to start the car as still putting it all back together will it still be louder because of the additional fuel?

Yes it still will be loud. Mine is.


Sent from my iPhone using Tapatalk

[James1984]

Ive removed all of my secondary air system, I am yet to start the car as still putting it all back together will it still be louder because of the additional fuel?

Yes it still will be loud. Mine is.


Sent from my iPhone using Tapatalk

Thanks! I think I will get mine mapped out, although I don’t mind it my car will be garages soon and not sure the neighbours would appreciate it bouncing off the walls.