How do manufacturers map in exhaust bangs and crackles?
Discussion
The only way I know of producing a bang form an internal combustion engine is by igniting fuel.
Therefore it stands to reason that to do what you say would require fuel & spark/heat when it is not really required.
I find it hard to believe that in these days of emissions/fuel efficiency, that a mainstream manufacturer would actively seek to do this.
Therefore it stands to reason that to do what you say would require fuel & spark/heat when it is not really required.
I find it hard to believe that in these days of emissions/fuel efficiency, that a mainstream manufacturer would actively seek to do this.
burbles and pops are tuned in with a lean mixture and retarded timing.
FWIW I have a switch in cabin to flick between normal and yobbo, for when I'm in the mood. On the yobbo map the ignition retards to 10deg BTDC during overrun conditions. Fuelling around that area I aim for 15:1.
It's been like that for 18 months and the CAT is absolutely fine - (visual inspection).
Overly rich mixtures will cause bangs and those will destroy a CAT very quickly - along with any baffles in the exhaust.
FWIW I have a switch in cabin to flick between normal and yobbo, for when I'm in the mood. On the yobbo map the ignition retards to 10deg BTDC during overrun conditions. Fuelling around that area I aim for 15:1.
It's been like that for 18 months and the CAT is absolutely fine - (visual inspection).
Overly rich mixtures will cause bangs and those will destroy a CAT very quickly - along with any baffles in the exhaust.
It's generally as a result in the difference in torque controller paths caused by the requirement for different torque reduction / re-instatment events.
On a low load "non sporty" gear shift for example, the system has time to reduce flywheel torque slowly (say 500ms reduction period) as so the slow "air path" can be used (ie, shutting the throttle, and then cutting fuel). (no pops and bangs)
On a high load "sporty" gear shift, where you want the shift even to be all done in say 100ms, the torque controller uses it's "fast path" which is the ignition angle controller (because this can be done on a firing event based raster, and control flywheel torque much much quicker than waiting for the throttle to shut and the plenum to empty of air. This is done by extremely retarding the ignition angle, at a constant AFR, so the fuel is still burnt, but hasn't time to be expanded by the piston (which would normally extract work from the fuel and produce torque). This results in a large fuel mass being burn't in the exhaust manifold, with the resultant snap crackle and pop. Often the makes the car sound "flat" or "soft" and is heard as a sort of waffle or warble in the exhaust note.
This is not the same as proper Antilag on a turbo competition car, where air bypasses the cylinder and burns the fuel in the exhaust pre turbine, which is pretty uncontrolled and very aggressive, sounding like gunfire!
The advantage of using spark retard to cut torque rapidly is that the torque can be re-instated equally rapidly, and because the average exhaust AFR is still close to target, the catalyst oxygen storage content isn't massively changed and so conversion efficiency is maintained
On a low load "non sporty" gear shift for example, the system has time to reduce flywheel torque slowly (say 500ms reduction period) as so the slow "air path" can be used (ie, shutting the throttle, and then cutting fuel). (no pops and bangs)
On a high load "sporty" gear shift, where you want the shift even to be all done in say 100ms, the torque controller uses it's "fast path" which is the ignition angle controller (because this can be done on a firing event based raster, and control flywheel torque much much quicker than waiting for the throttle to shut and the plenum to empty of air. This is done by extremely retarding the ignition angle, at a constant AFR, so the fuel is still burnt, but hasn't time to be expanded by the piston (which would normally extract work from the fuel and produce torque). This results in a large fuel mass being burn't in the exhaust manifold, with the resultant snap crackle and pop. Often the makes the car sound "flat" or "soft" and is heard as a sort of waffle or warble in the exhaust note.
This is not the same as proper Antilag on a turbo competition car, where air bypasses the cylinder and burns the fuel in the exhaust pre turbine, which is pretty uncontrolled and very aggressive, sounding like gunfire!
The advantage of using spark retard to cut torque rapidly is that the torque can be re-instated equally rapidly, and because the average exhaust AFR is still close to target, the catalyst oxygen storage content isn't massively changed and so conversion efficiency is maintained
Mine crackles and spits more with afr around 16 it seems and does it more during the warm up cycle before the afr drops to 15 or less, so it's less fuel that is involved it would appear, and is louder with no cat, and also has that flat symptom just off idle, and very light throttle under 2k, pops only 2-3k usually.
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