Having an argument with a coworker here as to why subarus make that pulsing/rumbling exhaust note.
We disagree on the cause of it.
I say it's entirely due to the exhaust manifold design, having uneven length runners, causing pulses to run in together and exiting the tip in that uneven burble sound.
He says it's due to the engine's design, being a flat 4, and the firing order causing a half resonance effect. He sent me this link to back up his argument: http://www.doudna.com/Subaru/
Now riddle me this. Rumbly subarus only run a single exhaust, not a dual exhaust, right?
The exhaust note of a subaru is heard at the exhaust tip, right? You don't hear the sound of it up at the manifolds as it's coming out of the engine.
What this means, is that you're hearing all four exhaust pulses coming out in the sequence that causes the subaru exhaust burble. What makes them come out in that order?
The only POSSIBLE REASON for it, is the exhaust runners being uneven, making the pulses from one side have to travel further than the other side, and them running in together to the turbo, before coming out the back.
Here's a quote from that article:
What the author of this article has done, is attempted to separate one cylinder bank from the other, to describe exhaust note. /facepalm
In terms of exhaust note, this is retarded because the vehicles do not run a dual exhaust system. Therefore, it's not [fire, fire, wait, wait] while the other side exhausts [wait, wait, fire, fire].
The engine as a whole, produces exhaust pulses like this: [fire, fire, fire, fire]. It fires one cylinder after another, evenly. It's irrelevant what side is firing, since the exhaust runners all come together to a single point before entering the turbo. It's an even series of combustion events, as even as any i4.
What this means, is the only possible way for the pulses to be uneven like this, is what's between the exhaust ports, and the merge point into the turbo. i.e. what does the exhaust pipe see coming into it?
What we have, ladies & gentlemen, is uneven length exhaust runners.
This is reinforced by the fact that all new subarus as of like 2005 or whenever, no longer have that sound... they have an even, flat exhaust note like an evo or a silvia, due to a new manifold design being in place.
Lastly, this effect is confirmed in my own original exhaust system on the V8... I made some headers for it that didn't have even length runners, and this my exhaust pulses ran together and created an unusual sounding exhaust note, not entirely V8 sounding, but more like 2x angry WRXes.
We disagree on the cause of it.
I say it's entirely due to the exhaust manifold design, having uneven length runners, causing pulses to run in together and exiting the tip in that uneven burble sound.
He says it's due to the engine's design, being a flat 4, and the firing order causing a half resonance effect. He sent me this link to back up his argument: http://www.doudna.com/Subaru/
Now riddle me this. Rumbly subarus only run a single exhaust, not a dual exhaust, right?
The exhaust note of a subaru is heard at the exhaust tip, right? You don't hear the sound of it up at the manifolds as it's coming out of the engine.
What this means, is that you're hearing all four exhaust pulses coming out in the sequence that causes the subaru exhaust burble. What makes them come out in that order?
The only POSSIBLE REASON for it, is the exhaust runners being uneven, making the pulses from one side have to travel further than the other side, and them running in together to the turbo, before coming out the back.
Here's a quote from that article:
In terms of exhaust note, this is retarded because the vehicles do not run a dual exhaust system. Therefore, it's not [fire, fire, wait, wait] while the other side exhausts [wait, wait, fire, fire].
The engine as a whole, produces exhaust pulses like this: [fire, fire, fire, fire]. It fires one cylinder after another, evenly. It's irrelevant what side is firing, since the exhaust runners all come together to a single point before entering the turbo. It's an even series of combustion events, as even as any i4.
What this means, is the only possible way for the pulses to be uneven like this, is what's between the exhaust ports, and the merge point into the turbo. i.e. what does the exhaust pipe see coming into it?
What we have, ladies & gentlemen, is uneven length exhaust runners.
This is reinforced by the fact that all new subarus as of like 2005 or whenever, no longer have that sound... they have an even, flat exhaust note like an evo or a silvia, due to a new manifold design being in place.
Lastly, this effect is confirmed in my own original exhaust system on the V8... I made some headers for it that didn't have even length runners, and this my exhaust pulses ran together and created an unusual sounding exhaust note, not entirely V8 sounding, but more like 2x angry WRXes.