Car Noise - Why not Induction?

[Alex_225]

I've wondered this for some time but why do manufacturers not enhance their induction noise rather than exhausts?

I've installed a few air filters over the years, and having recently installed a new air filter and heat shield in my Saab it sounds great but at idle and normal driving it sounds very subtle.

I appreciate manufacturers aren't going to whack this kind of thing on stock cars and they're not always suited but I've yet to experience a car that benefits hugely from the noise it can produce. My Twingo 133 actually comes with a bung at the bottom of the airbox you can remove to open up the noise but even then it's subtle.

I'm sure there's a valid reason, or I'm naïve but a genuine question!

[supacool1]

I suspect its to do with NVH. Some don't like roaring induction noise. There are certain resonances that will cut right through you. I know when we borrowed a S2000 to take to the 'ring and took the airbox lid off, the induction was other worldly. But after a short while it got so mind blowingly annoying we put it back.

[Leon R]

BMW did a pretty good job getting it right for the e92 M3.

[White-Noise]

I would guess your average Joe who wants a bit more noise knows what an exhaust does but no idea what induction noise is. If someone watches top gear or motorsport on TV they will hear the exhaust primarily so there is your market. That's my guess anyway but I like a good bit of induction noise!

[Hoofy]

Good question. As above, NVH.

I replaced mine in my TT and it does make it sound better. More "warbly" with gentle acceleration (it's a subtle change from the buzzy sound you normally get with a small 4 cylinder engine), and very angry and louder with heavy acceleration. You also get a bit of a whoosh with the accceleration and a hiss when you lift off (not a proper dump valve sound but it's noticeable). I've done the resonator "delete" on my stock exhaust so that sounds slightly more sporty but I didn't want the full sports exhaust sound that you get with many modified VAG cars. I suspect that if I got a proper sports exhaust system, it'd drown out the induction sound.

In terms of volume, it's easy to drown out the induction sound if the radio is on a reasonable volume, and cruising along a motorway at normal speeds, you wouldn't notice anything when maintaining speed. It's quite boring, really, but you probably don't want a loud noise if you're driving the length of the M4.

Anyway, a res "delete" in tandem with the air filter does make it sound more interesting without being annoying to others. I can creep home through my housing estate late at night without anyone noticing.

[Alex_225]

Thanks for the answers guys, I'm just intrigued. My Saab now sounds fantastic and I recall putting a cone filter on my first Clio 172 and that only ever sounded purposeful when you were on full throttle, normal driving it it didn't shout much.

I guess like exhausts, the sound could drone. I recall a girlfriend years ago who had a Clio 182 and had both back boxes replaced with custom ones. They sounded great but if you were in 4th at say 40mph so the revs were fairly low, the drone was really unbearable.

[Sycamore]

My 3.0 Z4 had a pipe that led into the cabin that sent in induction noise too I recall. I removed the bungs out of it for extra straight 6 goodness

[Hoofy]

Alex_225 said:

Thanks for the answers guys, I'm just intrigued. My Saab now sounds fantastic and I recall putting a cone filter on my first Clio 172 and that only ever sounded purposeful when you were on full throttle, normal driving it it didn't shout much.

I guess like exhausts, the sound could drone. I recall a girlfriend years ago who had a Clio 182 and had both back boxes replaced with custom ones. They sounded great but if you were in 4th at say 40mph so the revs were fairly low, the drone was really unbearable.

There is zero drone from my induction cone. I guess it's just not hitting the right frequencies to cause any drone. It's the cheapest Halfords one, in case you're wondering. I'm probably sucking in all the London dirt now that I think about it.

[Alex_225]

Sycamore said:

My 3.0 Z4 had a pipe that led into the cabin that sent in induction noise too I recall. I removed the bungs out of it for extra straight 6 goodness

I recall the original Focus ST did that as it sounded great from inside the cabin. Seems some manufacturers have put some focus on it.

I'm just really surprised how much it can open up the sound of even a mundane four cylinder, can only imagine how the V8 in my CL would sound with open filters for example.

Hoofy said:

There is zero drone from my induction cone. I guess it's just not hitting the right frequencies to cause any drone. It's the cheapest Halfords one, in case you're wondering. I'm probably sucking in all the London dirt now that I think about it.

I can't say I've noticed a drone from induction kits I've run. I've noticed a lot more turbo noise on my Saab but I've yet to do a long run with it on.

[Gericho]

I want selectable sound. I want it whisper quiet on the motorway and then loud at lower speeds.

[Debaser]

Alex_225 said:

I've wondered this for some time but why do manufacturers not enhance their induction noise rather than exhausts?

I've installed a few air filters over the years, and having recently installed a new air filter and heat shield in my Saab it sounds great but at idle and normal driving it sounds very subtle.

I appreciate manufacturers aren't going to whack this kind of thing on stock cars and they're not always suited but I've yet to experience a car that benefits hugely from the noise it can produce. My Twingo 133 actually comes with a bung at the bottom of the airbox you can remove to open up the noise but even then it's subtle.

I'm sure there's a valid reason, or I'm naïve but a genuine question!

Manufacturers spend a lot of time and money developing induction noise. Plenty come with a symposer to enhance the noise in the cabin.

[Hoofy]

Alex_225 said:

I can't say I've noticed a drone from induction kits I've run. I've noticed a lot more turbo noise on my Saab but I've yet to do a long run with it on.

Yeah - I love the turbo noise. I wish I could fit one on my Porsche but I don't think anyone makes one. I thought about fitting a K&N one but I can't figure out how to do it as easily as I did with my TT.

[Hoofy]

Gericho said:

I want selectable sound. I want it whisper quiet on the motorway and then loud at lower speeds.

That's pretty much the benefit of an induction cone filter - it's not noticeable when maintaining speed. You only notice the sucking/hissing when you accelerate... which is nice.

[aka_kerrly]

Hoofy said:

Gericho said:

I want selectable sound. I want it whisper quiet on the motorway and then loud at lower speeds.

That's pretty much the benefit of an induction cone filter - it's not noticeable when maintaining speed. You only notice the sucking/hissing when you accelerate... which is nice.

I'd say the ability to switch between having a standard sounding engine and a noisy animal is having a valved exhaust system more so than an induction kit

In general I spent too many years with rather loud exhausts which I thought was great, now I find that a good induction sound is considerably more desirable than a loud exhaust on the basis that a loud exhaust is always loud. The increased sound from an induction kit really makes itself known at high revs which is typically when you're in the mood for it!

Confession time - I have "swiss cheesed" the air box on nearly every car I have owned within hours of buying it

[Hoofy]

aka_kerrly said:

Hoofy said:

Gericho said:

I want selectable sound. I want it whisper quiet on the motorway and then loud at lower speeds.

That's pretty much the benefit of an induction cone filter - it's not noticeable when maintaining speed. You only notice the sucking/hissing when you accelerate... which is nice.

I'd say the ability to switch between having a standard sounding engine and a noisy animal is having a valved exhaust system more so than an induction kit

In general I spent too many years with rather loud exhausts which I thought was great, now I find that a good induction sound is considerably more desirable than a loud exhaust on the basis that a loud exhaust is always loud. The increased sound from an induction kit really makes itself known at high revs which is typically when you're in the mood for it!

Confession time - I have "swiss cheesed" the air box on nearly every car I have owned within hours of buying it

Yeah, a switch would be handy - it just costs more than the £15 cone and some elbow grease.

Re drilling the air box, I take it you do that on the other side of the engine intake?

[Huff]

...letting all that carefully -designed-out 'hot air in the engine bay' in, killing power...

[Pebbles167]

Sycamore said:

My 3.0 Z4 had a pipe that led into the cabin that sent in induction noise too I recall. I removed the bungs out of it for extra straight 6 goodness

Came to post this.

The noise it made was incredible. 5 minutes to remove 1 or 2 bits of foam depending on noise preferende. I'm not sure why it wasn't a more common feature. Well done to BMW.

I've often wondered how hard it would be to implement something similar into any other car DIY style.

[dvs_dave]

Many many cars have induction noise enhancement systems fitted. A pipe connected to the induction hose leading to a diaphragm in the bulkhead under the dash is exactly that. An induction noise enhancer.

[havoc]

aka_kerrly said:

Hoofy said:

Gericho said:

I want selectable sound. I want it whisper quiet on the motorway and then loud at lower speeds.

That's pretty much the benefit of an induction cone filter - it's not noticeable when maintaining speed. You only notice the sucking/hissing when you accelerate... which is nice.

I'd say the ability to switch between having a standard sounding engine and a noisy animal is having a valved exhaust system more so than an induction kit

I'd disagree. Induction noise is linked to throttle position as much as to rpm, as the volume is (broadly) proportionate to the airflow, and the airflow is determined both by rpm and by throttle opening.

...so if you're cruising at low-rpm, low throttle opening, you've automatically got low volume. Then your right foot operates the switch...

[philrs03]

There is not a single engine note (in my opinion) better than a screaming 2.something with hot cams and a set of ITB’s. Epic. Especially in a convertible!!! Now my MX5 is functioning properly, nothing makes me happier than an 8000rpm rev limit, tall hedges either side of the road, and the roof down. Driving pleasure at its finest.