- Joined
- Dec 28, 2007
- Messages
- 8,232
- Car
- Volvo XC90 T8 Polestar c500bhp
Ok, AMG anoraks on.
A few of us have commented that whilst the M156 exhaust note is louder/fuller than the biturbo, at cold start our M157's seems even louder than the M156 at cold start.
Here's why, from:
William Vetter
Asst. Product Manager - AMG & Black Series
Exclusive Vehicles
Mercedes-Benz USA
It is all in the engine ignition timing and fuel delivery...
When you first start up the vehicle, the primary objectives are to get oil flowing and heat generating both in the engine and more importantly in the catalytic converter...
So when the engine first starts it is running far more fuel into the engine than would be needed when the engine starts warm...as well the timing retards so that combustion is incomplete in the cylinders...the net result is that this unburned fuel (or still burning fuel) is sent out into the exhaust and down into the catalytic converter where it quickly heats up the cat...
this change in timing and fuel load are why there is a different exhaust note...
after a short bit there is a good fuel load in the cat and the heat is building, it returns the timing to normal and reduces the fuel load...
for the folks that have the M157 engine, this start up exhaust note is far more pronounced....the goal of cat heat is the same but noise change is for a different reason...the reason is that a M157 engine on cold start is actually making the exhaust gasses bypass the turbo which makes the note much more pronounced...one the heat starts in the cat, it then closes the bypass and you can actually hear the turbo spool up and then the exhaust gets much quieter...
Now you know
.
A few of us have commented that whilst the M156 exhaust note is louder/fuller than the biturbo, at cold start our M157's seems even louder than the M156 at cold start.
Here's why, from:
William Vetter
Asst. Product Manager - AMG & Black Series
Exclusive Vehicles
Mercedes-Benz USA
It is all in the engine ignition timing and fuel delivery...
When you first start up the vehicle, the primary objectives are to get oil flowing and heat generating both in the engine and more importantly in the catalytic converter...
So when the engine first starts it is running far more fuel into the engine than would be needed when the engine starts warm...as well the timing retards so that combustion is incomplete in the cylinders...the net result is that this unburned fuel (or still burning fuel) is sent out into the exhaust and down into the catalytic converter where it quickly heats up the cat...
this change in timing and fuel load are why there is a different exhaust note...
after a short bit there is a good fuel load in the cat and the heat is building, it returns the timing to normal and reduces the fuel load...
for the folks that have the M157 engine, this start up exhaust note is far more pronounced....the goal of cat heat is the same but noise change is for a different reason...the reason is that a M157 engine on cold start is actually making the exhaust gasses bypass the turbo which makes the note much more pronounced...one the heat starts in the cat, it then closes the bypass and you can actually hear the turbo spool up and then the exhaust gets much quieter...
Now you know
.
