What exactly goes into creating the sound that a car makes?

[Jasruler]

I'm confused.


For example, the McMerc SLR V8 sounds like a Spitfire's Merlin, which was a 12 cylinder engine, with that very bassey stacatto growl, whereas a Ferrari F430 V8 sings/screams an uninterupted sound, almost like a four-cylinder would... so It can't just be the number of cylinders... I...


I don't understand.

[AutoMX]

much of the sound comes from the timing. ferraris use valiable cam timing like the newer hondas which use their system called vtec, and nissan toyota etc all have their own new systems. variable cam timing allows for higher revs and usually give the car a high pitch whine. you also must consider the exhaust size, setup, and location, as well as the type of intake and other factors like engine aspiration.

the SLR has mufflers in the front behind the front wheels, and has a specially designed exhaust system to perform as well as sound right. ferraris have huge exhausts, about 5 feet long, and 2 feet wide, which helps to create the sound. I almost bought one for $2.48 but the guy selling it accidentally had it thrown away.

[Z Draci]

I'm not a fluid dynamics physicist so I don't know for sure. I'll try to explain it in a very simple way . . . I'll T R Y!

I do know that the exhaust note has a lot to do with the sonic pulses coming from each exhaust valve. When an exhaust valve opens, it releases a pulse. Equal length headers synchronize these pulses so each one travels in equal distances between each other. Since a vacuum is created behind each pulse, the following pulse is actually pulled along. (Are you guys following all this?)

Anyways, these exhaust pulses are altered in pitch through resonators and mufflers down the exhaust pipe. Stock mufflers have chambers which are designed so that each pulse cancels out each others' sound. (A negative wave hits a positive wave and they both equal zero.) Ferrari has a whole team of sound engineers who tune the exhaust note through specially designed resonators and mufflers. The design possibilities are endless like those of a musical instrument.

What you hear out of a car is very rapid pulses. Those pulses are so high in frequency that it sounds like one continuous roar. Other variables for the exhaust note include: bore/stroke, number of exhaust valves, exhaust pipe size, natural/forced induction, fuel delivery, etc.

I think the unique sound of the SLR and the 5.5 litre supercharged AMG engines comes more from the intake rather than the exhaust. Some car makers have engineered airboxes to silence intake noises. If you take those airboxes out, you can hear the pulses from the intake valve side. The SLR has a very loud supercharger "whine" and the pulsating intake charge.

I have twin SU carburettors on my car. If they aren't tuned right, they will backfire flames out of the intake airstacks! Cars like mine will make good noises out of both intake and exhaust sides of the engine.

Don't forget about the mechanical whine from the gearbox too. My rear diff literally sits right besides me. It makes a remarkable race carish whine on deccelration.

[fbc]

Interesting stuff - great learning this sort of thing

[bone]

Originally Posted by Z Draci

I'm not a fluid dynamics physicist so I don't know for sure. I'll try to explain it in a very simple way . . . I'll T R Y!

I do know that the exhaust note has a lot to do with the sonic pulses coming from each exhaust valve. When an exhaust valve opens, it releases a pulse. Equal length headers synchronize these pulses so each one travels in equal distances between each other. Since a vacuum is created behind each pulse, the following pulse is actually pulled along. (Are you guys following all this?)

great explanation, couldn't have done it better myself

but i'll add sth irrelevant

anyone ever looked at a 2-stroke exhaust? if it's a high performance engine, or just any 2-stroke engine you want to get power out, you'll see the exhaust making a hugh turn right behind the combustion chamber, or the combustion chamber itself will be odly shaped.
they also create a vaccuum, which sucks unburned mixture out of the cylinder into the exhaust (since there are no valves, only ports=holes). but since the exhaust makes a turn, the soundwave reflects, and pushes the mixture now in the exhaust, back into the cylinder, resulting in about twice the amount of mixture reachable than without such an exhaust. resulting in much more power (and half the mpg)

i love 2-stroke

[Leppy]

Originally Posted by Z Draci

I'm not a fluid dynamics physicist so I don't know for sure. I'll try to explain it in a very simple way . . . I'll T R Y!

I do know that the exhaust note has a lot to do with the sonic pulses coming from each exhaust valve. When an exhaust valve opens, it releases a pulse. Equal length headers synchronize these pulses so each one travels in equal distances between each other. Since a vacuum is created behind each pulse, the following pulse is actually pulled along. (Are you guys following all this?)

Anyways, these exhaust pulses are altered in pitch through resonators and mufflers down the exhaust pipe. Stock mufflers have chambers which are designed so that each pulse cancels out each others' sound. (A negative wave hits a positive wave and they both equal zero.) Ferrari has a whole team of sound engineers who tune the exhaust note through specially designed resonators and mufflers. The design possibilities are endless like those of a musical instrument.

What you hear out of a car is very rapid pulses. Those pulses are so high in frequency that it sounds like one continuous roar. Other variables for the exhaust note include: bore/stroke, number of exhaust valves, exhaust pipe size, natural/forced induction, fuel delivery, etc.

I think the unique sound of the SLR and the 5.5 litre supercharged AMG engines comes more from the intake rather than the exhaust. Some car makers have engineered airboxes to silence intake noises. If you take those airboxes out, you can hear the pulses from the intake valve side. The SLR has a very loud supercharger "whine" and the pulsating intake charge.

I have twin SU carburettors on my car. If they aren't tuned right, they will backfire flames out of the intake airstacks! Cars like mine will make good noises out of both intake and exhaust sides of the engine.

Don't forget about the mechanical whine from the gearbox too. My rear diff literally sits right besides me. It makes a remarkable race carish whine on deccelration.

That explanation is fairly good mate... nice work... takes me back to 2 semesters ago (fluid mechanics).

As for your carbies... man thats a good way to get an airbox fire haha

[Redliner]

OK, ok, I know it´s a CAR forum, but the same thing goes for motorcycles....it´s fun to try and tell apart different makes and models by sound only....and that´s harder, because almost ALL sportbikes are dohc 16 valve inline four, but it´s fun to see the difference because of engine size, if it´s air or water cooled.
I´ll stop the off-topic now.

[kem]

I had never given much thought to how a exhaust sound is created, until one day a biker was out front of my house waiting for the light... with the exhaust I could easily hear how its timed to the pistons & valves firing, a kinda 1-2-1-2-1-2, etc... as he gave it a slight rev the 1-2's got closer together, and as he finally took off at the green light and the engine reved the 1-2's got closer and closer together until they finally became almost a constant hum...