How do engines get their sound?

[bob6600]

In BMW's case an upgraded speaker system

 

[Charles Morgan]

I recall when I bought my first Porsche Boxster S that Porsche had a department devoted to tuning the sound of the car to provide maximum aural pleasure to the driver. Certainly the induction howl was right by my ear (mid engined) and highly enjoyable.

There are essentially three main categories of propulsion sound on a hydrocarbon powered car: - induction, being the sound of air being sucked into the engine; what I call reciprocation, being the sound of the mechanical engine movement of pistons and crank; and exhaust, being the sound of the gases being expelled from the engine to the outside.

Certainly all of these are capable of tuning - think of induction and exhaust as pipes similar to a large brass instrument, with their own frequencies and resonances. Indeed, some carburettors have intakes known as trumpets for precisely the reason above. Obviously as air intake grows in size so does the volume going through the induction system in a relatively smooth way, while the smoothness of reciprocation and exhaust notes is as much a product of revs and innate balance within the engine - hence the very different sounds produced by 4s, 6s and 8s (and multiples thereof).

I am much fonder of induction sounds which, fancifully I admit, sound closer to voice production than exhaust sounds which can be excessively loud and too low in the bass area. Hence so much sound insulation to regulate frequency as much for enjoyment as for noise control legislation.

 

[Charles Morgan]

A vid on Youtube I just found of the effect of changing trumpet length on induction sound. Different material too.

[YOUTUBE]MiAdjVWXOys[/YOUTUBE]

 

[leef44]

What's changed since TVR made cars? Regulations and shifting customer expectations mean that engines and even the rest of the must be designed differently in order to sell in any real volume.

And of course even then TVR didn't need to sell in any real volume, which would mean that even today they could take a different approach to the bigger manufacturers but that's risky: some win (eg Morgan) ans some lose (eg TVR).

But it still has the same basic exhaust structure as modern cars and silencer and catalytic converter. Passes MOT. So what regulation is holding back other manufacturers.

Also BMW M4 is just as loud as a TVR (at low speeds and half throttle).

 

[Druk]

Was at a meeting this morning and got chatting to what turned out to be another petrolhead who's just bought a brand new M4. He loves the car but the sound that emits from the exhaust is actually quite offensive and it's starting to take the gloss off the ownership quite quickly for him.

There's always the 'chuck in a diesel, connect it to a central cherry-bomb with 3" stainless tubing, top it off with a 3 1/2" Rangie straight-thru and give it a bit of welly down a Donny suburban street' option. Isn't that right Lee?








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[WDB124066]

My feeling is sound is mostly determined by the inlet and outlet port design in the head/s and the number of cylinders.
You can change it slightly with manifolding/plumbing and all manner of components as mentioned above but the basic sound of an engine lies in the port design and firing order of course.

The other big contrinbuter is the location of the balance pipe in V engines or even if you have one. That would be one exception where you can ruin the sound quite effectively.
Some engines sound carp no matter what you do to them or the inlet and outlet plumbing and some sound great no matter what you do too.

 

[TheFoX]

I love the sound the turbo makes when it sucks air in. It's not that loud but it is audible/

 

[Lotiman]

Turbocharged engines are notoriously difficult to get a decent exhaust sound from due to the attenuating effects of the turbo itself. Nevertheless, AMG do seem to manage it.

A flat plane crank in a naturally aspirated V8, as Ferrari traditionally used in the past, is best suited, in my mind anyway, to producing a spine tingling exhaust sound. You obviously need to design the exhaust system well to make the most of it, but it does give a very good starting point. Mind you, I do love the supercharger scream from my Loti. The Exige is the more raw car and less well attenuated so you can generally hear the supercharger from around 4500 rpm onwards. The Evora though has the best (and loudest) exhaust note, especially when the bypass valve is opened and, childish I know, but is very addictive when I seek out tunnels just for the thrill of hearing the noise it makes.

 

[PobodY]

Turbocharged engines are notoriously difficult to get a decent exhaust sound from due to the attenuating effects of the turbo itself.

I'm reasonably happy with mine:
https://www.youtube.com/watch?v=5SdEGNJo9aU

Raspy note with a gettle *pop* on gear change from an Nissan SR20DET.

 

[190]

Turbocharged engines are notoriously difficult to get a decent exhaust sound from due to the attenuating effects of the turbo itself. Nevertheless, AMG do seem to manage it.

Pity the F1 boys can't manage it.

 

[jfhuk]

I remember an article a few years back on the MGB apparently they spent more money on getting the right exhaust note, than they did on chassis development.

 

[Charles Morgan]

I remember an article a few years back on the MGB apparently they spent more money on getting the right exhaust note, than they did on chassis development.

Given the chassis is cart sprung and awful I can believe that, and that they spent next to nothing on the exhaust at the same time...

 

[Ted]

Lever shocks too iirc.

 

[Tim203]

Sadly as with most of these cars from the Leyland group, there was precious little new development ever, just raiding the existing parts bins for bits. Just look at the Marina! Still the MGB's weren't that bad on the corners.

 

[Tim203]

Isn't part of the story with TVR that they don't make enough cars to have to conform to EU legislation about exhaust noise?

Correct. We got a Sagaris through local TÜV test in 2004 in Germany. That was loud!

 

[leef44]

Turbocharged engines are notoriously difficult to get a decent exhaust sound from due to the attenuating effects of the turbo itself. Nevertheless, AMG do seem to manage it.

And Scoobys with their trademark warble