Mazdaspeed3, Quieter exhaust than stock?

[northmiler89]

drone will always be worse in a wagon/hatchback.

 

[Ziggo]

I have studied this brr on deceleration sound and I believe the variable valve timing shifts to its most aggressive setting to increase pumping losses and increase engine braking. I believe it is similar to a Jacobs Engine Brake that holds the intake valves open to increase engine braking. If you will notice, the brr sound is associated with increased drag from the engine and does not happen immediately after throttle lift, there is a very slight delay.

Is the variable valve timing something that can be monitored with a Dash Hawk?

This is purely my theory based on observation and I have nothing concrete to back this up. I invite criticism in the name of enlightenment.
-enganear

A jacobs engine brake (jake brake) functions by opening an exhaust valve near the top of the compression stroke effectivly firing the cylinder into the exhaust and thus removing the potential for work to be done.(and making a ton of noise) The valve then closes forcing the piston to create a vaccum in the cylinder(usually no more than 40psi) until the exhaust valve opens again, making the engine do negative work on the power stroke and braking through the transmission. This is only necessary on disel engines since they have no throttle plate to "suck" against and increase pumping losses.

Agressive valve timing keeps the exhaust valves open longer/opens intake valves earlier. In either case it increases the volumetric efficiency of the engine and reduces pumping losses. Not exactly ideal engine braking

My motorcycle makes the same sound and its valve timing is not variable (but is very agressive). I would guess that the sound is a vibration created by the pressure difference when the intake valves are opened into a heavy vaccum in the intake, while the exhaust valves are still open to a positive pressure exhaust system causing the flow to reverse, or at least creating a strange pressure wave. The effect is that the "brr" sound goes down in frequency with the engine speed which is very noticible when going from 8k to 1k on the motorcycle.

I will use the same disclaimer as the above enganear, lest somone take my thoughts for physical law and sue me(an engineers greatest fear)

 

[Ziggo]

After some more thought I don't like that reason for the "brr" sound either. The motorcycle has a separate throttle for each carb/cylinder, so there really shouldn't be much of a vaccum before the valve opens. Assuming the sound is caused by the same thing in both cases it pretty much eliminates the heavy vaccum reason. I still suspect it has something to do with the valve overlap though.

 

[Sierra117]

I want more snap, crackle, and popping sounds!!!!

Trust me, you'll get it. I'm on my stock downpipe and stock midpipe (but not for long, midpipe gets shipped Friday!) with the cats, and on my Corksport at idle, I can hear little pops and such. Even had a few real loud pops and possible backfires when lifting after being in second or third pretty hard.