[justwheels]

Originally Posted by lambdaplus

The characteristic thump of the bullet is due to almost 350cc (to 500cc) of air-fuel mixture being burnt! I'm sure everyone has felt the shock waves coming out of the bullet exhaust!

Apart from this, as Ajamt said, the induction and exhaust system along
with the poppet arrangement adds to the noise. The vrooom sound of the engine is due to the high speed valve operation, when the valves hit the beds at a frequency of 5000 rpm! Listen to the F1 engine revving at 18000 rpm! Its, as Russel Peter says, mindblasting!

With different engine configurations, it is possible to cancel out some unwanted "noise" by arranging the firing order\cylinder alignment differently. I'm sure you should've seen the Ferrari sound engineers, in Nat Geo's Mega Factories, fine tune the engine to make the required sound

Oh yes, that bullet thump of exhaust that hits you right on your face, I have had many instances with that.As you said that the vrooom sound is that of the valves hitting the beds, I always thought that vrooom was all because of the high speed gases rushing out of the muffler.The F1 vrooom is surely mindblasting.

Originally Posted by lambdaplus

Increasing back pressure is a strict no no for engine manufacturers! This directly leads to a decrease in volumetric efficiency since, the engine has to not only do work to take in fresh air-fuel mixture but also work hard to push out the exhaust gases, which will remain in the cylinder or, worse, enter the intake manifold! Hence, the power output is drastically reduced! No FE can be achieved by increasing exhaust back pressure!
Infact, reducing exhaust back pressure increases FE. If you have noticed, engines runs smoother and with more FE in hill stations. This is due to naturally reduced exhaust back pressure since the ambient air pressure is lesser due to high altitudes.

Thats what is my idea with back pressure. What I have read/understood till date that the muffler/silencer construction causes some amount of he back pressure as the exhaust flow is altered. Now if you had to make a near silent exhaust, the silencer would create massive back pressures for the engine and will take the FE for a ride.
Also, what would be the effect if we had a bigger exhaust outlet. I mean not just the small pipe, rather a bigger diameter and a larger outlet. I think even that can kill the sound as exhaust will come out with less restrictions.

Originally Posted by aargee

Not exactly; once the back pressure pushes the piston back to TDC, the job is done & there's no more pressure against which the piston has to be working. Hope you got the point.

Originally Posted by lambdaplus

Yes! Presense of back pressure causes a part of work generated by engine to be used to push out exhaust gases. Hence, reduced FE. If you can entirely or partly get rid of back pressure, you will get better FE. This means, you've to remove all or few of the components on the exhaust side. For example, removing the silencer will increases the sound of the engine but reduce the back pressure by a small amount.


Aargee, I din't understand your point of the back pressure pushing the piston to TDC. Can you please clarify?

@aargee : pls explain this point of back pressure pushing the piston to TDC. Even I did not get your point. Seems I am missing something.

[vsk2009]

Polo Petrol and A star have 3 cyl engine. But the engine noise of Polo is more like a disel. Does it mean that A star is better engineered than polo in noise deduction?

[NOS Power]

Originally Posted by vsk2009

Polo Petrol and A star have 3 cyl engine. But the engine noise of Polo is more like a disel. Does it mean that A star is better engineered than polo in noise deduction?

Not really. There are a lot of variables. For instance damping or sound deadening could be better. Also as you say that it sounds like a Diesel, it could be that the valve's might be having high lift or maybe that's how it is in cold condition.

There could be a variety of reasons, and since I haven't closely watched either can't comment. Will leave that for the experts.

[rxpaul]

I think the exhaust(muffler) has the most prominant influence on the sound. The Yamaha RX 100 mutants...the 135, etc sounded quite different as they had different mufflers. I once heard a Ind-Suzuki, which sounded just like the RX100. The owner had fitted the RX 100 exhaust.

The old BMW e36, which i once owned had a loud booming exhaust when idle and during acceleration, which used to progressively reduce at high speed...Wonderful.
The new BMWs do not have this, but the 6 series does (i think).

[aargee]

Originally Posted by lambdaplus

Aargee, I din't understand your point of the back pressure pushing the piston to TDC. Can you please clarify?

Originally Posted by justwheels

@aargee : pls explain this point of back pressure pushing the piston to TDC. Even I did not get your point. Seems I am missing something.

I guess I wrote something real bad, while I was keeping expansion chamber in my mind always. I intent to speak about the animation here on two strokes.

Originally Posted by rxpaul

I think the exhaust(muffler) has the most prominant influence on the sound.

+1; Say that the muffler ALSO has an influence in addition to the volume of the cylinder, firing sequence, cylinder arrangement, escaping gases, intake manifold.

[fuhrer]

Originally Posted by NOS Power

Now I have a question here. If you discount the intake and exhaust and just think about the engine, say the 1.3 MJD, there is still a difference in the noise it makes in 3 different cars. I am talking about the noise it makes at idle when one listens to it after opening the bonnet as sound from the inside could be due to damping and firewall related stuff. How does still it sound different, considering they are manufactured at the same engine plant and only have a different engine cover. Could it be that the different engine maps give it a distinction?

Originally Posted by justwheels

Thanks ajmat for the wonderful explanation! Well I could understand is that since most of the sounds are inherent to the engine assembly there isn't much that can be altered. Just one question, since MJD being a national engine, its made the same way, why is it that it still sounds different in the TATA or SUZUKI or FIAT. or may be I just feel so. I know the same engine is tuned differently in all these cars. Does the tuning also have an effect on the end sound.

Yes different tuning or mapping definitely changes a lot of characteristics of the engine, which indeed changes the noise of the engine. A slight alteration in the pressure of the CRDi or change in the valve timing, will change the engine tone.

This is why cars with tuning boxes such as Pete's sounds smoother than regular ones.

[D33-PAC]

Sup everyone,

I would like to know what determines how an engine sounds, if any of you can go in to specifics, it would be wonderful.

From my years of analyzing , the noise factor, in terms of what is loud, is decided by the exhaust system and the camshafts.


Does engine angle have anything to do with it? I understand it is how the exhaust gases pass through the engine that primarily gives the engine its characteristics .


Obviously, the CGT in the video sounds very high pitched , but the grunt in the engine and the motor-bike like revving ease is noticeable too, like a 1980's F1 car.

Now the revving ease can be determined by how light the pistons weigh, how easily the crankshaft rotates and etc. But this only determines how fast an engine can rev, so it's like measuring a cycle(I mean to say how fast an exercise can be completed).


But if I cammed, say, a Toyota Corolla, and put straight pipes on it, as in, it's just one pipe from each manifold to the end of the car. It will sound nothing like an FXX or a CGT.

I thought for a while that the number of pistons had something to do with it, but if you take the Bugatti's W16, it sounds nothing close to a V10 or a V12, the engine sounds very restrained and refined, like American muscle. Of course it's muffled, but without the muffler I doubt it would change much.


Lastly, does bore and stroke have a lot to do with it? If you notice closely, one can come to the conclusion that all super-cars and race cars(f1, gp2,etc)
have engines that need to rev high, so the bore is big, but the stroke is very short. The perfect contrast that exemplifies the relationship here between bore-stroke and noise is that diesel engines , are very slow sounding. This is obviously because they need to produce oodles of torque, hence the long stroke and short bore.



But if I had a V6, like that of a GT-R, no matter how much I tuned the engine, even if I found the lightest of pistons, and the best of cams, it will never, sound like an F1 engine, or will it rev like a Carrera GT. One can easily tell there is a lot of weight in parts that need to be rotated by hearing the lesser of the super-cars.



Here is a Porsche Carrera GT V10 with straight pipes, which happened to be cammed:

Porsche Carrera GT Ride in VRAlexander's CGT - YouTube

Notice that at 1:31 in the video above, when the driver downshifts, the change in the engine's tone is ridiculous. I think the driver heel-toe-shifted hence, raising the rev's unnaturally . But if I was to do the same in R8 V10 (say, a Le Mans edition), it would not sound similar.



One more thing, I don't know if any of you have heard an Aston Martin, but the V12's in Astons sound very, very different from the V12's in, a Murcielago. Besides the camshaft and bore/stroke, what else can be used to explain why it is this way?

[AlphaKilo]

Its a good topic you have brought out! I am too eager to hear from the experts. My thoughts, its the exhaust that causes the sound. Thats why an AMG sounds different to a Porsche or a M-BMW. The "exhaust note" as its technically called, is just a cosmetic thing and has got not much to do with the performance or the tuning of the engine.

[suhaas307]

From what I know, I can say that companies like Ferrari and Lamborghini generally tune their exhaust-systems in order to achieve such sounds. But tweaking the exhaust is just the half of it.

The engine has a lot to do with the sort of sound a car makes. For instance, Subarus and Porsches make a distinct thrum. These engines sound rough, unrefined and raw. And the exhaust, while silencing the 'noise', are tuned to produce the best acoustics and sounds extracted from the engine. This can be attributed to the boxer engines that power these cars. Boxer motors inherently sound like that.

Ferraris and Lamborghinis make engines that are generally naturally-aspirated, (and the cylinders are usually arranged in a 'V' pattern). Such engines tend to rev higher and louder than say, a Porsche 911 Turbo. Cars with engines that have forced-induction tend to hit the rev-limiter a lot earlier.

I'm not a technical expert, but this is my understanding on the sounds made by such cars.

Feel free to correct me, if I'm wrong.

[Sankar]

Originally Posted by D33-PAC

From my years of analyzing , the noise factor, in terms of what is loud, is decided by the exhaust system and the camshafts.

And then some too.. like compression ratio, firing order, crank angle, intake design etc..

The engine angle if you mean if its a 90degree vee or 60 degree vee or a flat 6 or an inline 6 also affects the engine sound, Is got to do with the crank angle (i think its called duration, i forgot).

[Guna]

Folks, I really like the sound of old premier padmini engines . Any idea what makes it sound so different?

[mayankk]

I would think, apart from just the exhausts, the revs(and how the engine gets there) would also help explain the "shout" from say a santro with a FFE, and the "scream" from a gallardo().

Cheaper thirlls can be got from a universal filter, giving out a belch when blipping, and the roar when hammering.

[D33-PAC]

Originally Posted by Sankar

And then some too.. like compression ratio, firing order, crank angle, intake design etc..

The engine angle if you mean if its a 90degree vee or 60 degree vee or a flat 6 or an inline 6 also affects the engine sound, Is got to do with the crank angle (i think its called duration, i forgot).

Yes that's exactly what I was talking about! Please do elaborate if you can, especially about the firing order and engine degree.

How does the degree of the V type affect the sound?

[alpha1]

There are Different sounds (noise in my opinion):

1. Cam/valve noise.
2. Piston noise.
2. Exhaust noise.

Added somewhere would be the changes in each due to the flywheel, clutch and gear assembly.

All the three are different and one cannot be compensated by the other.
And of course geometry of each component plays an important part in production of this noise.

[amit_mechengg]

Originally Posted by AlphaKilo

Its a good topic you have brought out! I am too eager to hear from the experts. My thoughts, its the exhaust that causes the sound. Thats why an AMG sounds different to a Porsche or a M-BMW. The "exhaust note" as its technically called, is just a cosmetic thing and has got not much to do with the performance or the tuning of the engine.

Not exactly. Its combination of many factors. The fluid dynamics of exhaust gases generated from the exhaust valves, their timing, flow rate, velocity and similar many factors.

A honda city cannot sound like AMG if you implant a AMG exhaust onto honda city.