[jusdorange]

ok something I've always wondered

what exactly makes an engine note? for example, when you're hearing a NA V8 engine , what produces the noise you hear? the pistons moving?

[doug piston]

Detonation. When the fuel goes "BOOM"

[xDrive35i]

Among many other things, it's a combination of intake type/size, how the engine is cooled, the shape and running pattern of the cylinders (V-6, inline-6, W12, etc), and the tuning of the exhaust. Sometimes turbochargers muffle the intake, trading mechanical noise for a deep but raspy exhaust note. Usually, more cylinders means smoother sound, but it also means smoother operation. Inline-sixes (like BMWs) have a distinct, turbine-like intake noise, transmitting little to no vibration. That's why you hear of "silken-smooth V-12s," because they are effectively two inline-sixes running alongside each other.

[DocB]

I thought it was squirrel farts.

[300hp]

Thanks for this post. In addition to the engine how does the exhaust play into the sound. How is it that we get burbles on our N55s. My g37 never had that. What happens back there. How come MPE does a better job than the stock exhaust. I have been meaning to ask this for a while. Please no you tube videos. I just want the guys who know what's going on to impart their knowledge upon us.

[Halsifer]

Originally Posted by 300hp

Thanks for this post. In addition to the engine how does the exhaust play into the sound. How is it that we get burbles on our N55s. My g37 never had that. What happens back there. How come MPE does a better job than the stock exhaust. I have been meaning to ask this for a while. Please no you tube videos. I just want the guys who know what's going on to impart their knowledge upon us.

+1

From what I heard (and this is only what I heard), apparently it comes from extremely small droplets of fuel being let into the exhaust system, being lit and creating some type of gurgling sound and the grunt shift noise... I'm not sure how much I believe it though, since it was told to me like 2 years ago. Lol

I also assume MPE does a better job mainly because they allow a higher flow of the exhaust air, giving the effect of more burbling sounds coming through, even though it may be the same amount produced. That's just my guess though.

Anyways, that's what I 'heard'. If anyone can shine some light on that, I would be very interested as well.

[HighlandPete]

Originally Posted by jusdorange

ok something I've always wondered

what exactly makes an engine note? for example, when you're hearing a NA V8 engine , what produces the noise you hear? the pistons moving?

xDrive35i gives a very good explanation, are you also referring to why we have a particular sound, like the "burble" of the NA V8?

The actual crankshaft configuration of any engine design, has a big part in the recognised 'beat' of that engine type. From the layout we get the firing sequence and exhaust pulses which, according to how managed, give us our sound track. The burble of the typical V8 is due to having a cross-plane (two-plane) crankshaft configuration. A flat-plane (single plane) V8 has a different sound, more like two 4-cylinder engines coupled together.

BMW's in-line 'six' with 120-degree power strokes has excellent dynamic balance and even torque pulses, allows good exhaust tuning. Hence why we love them.

HighlandPete