[justwheels]

Hello all,

@mods: pls merge/delete if found irrelevant and guide me to the correct place.

The question might be a it weird, but still is a question and I couldn't search for any thread regarding this, so I am starting a new thread.

We all have talked a lot about the smoothness of an engine vis-a-vis the sound and how the rattling of the erstwhile indica was hated to the smoothness of its japanese competition.

My question is,

1. What makes this characteristic sound. I am sure there aren't any loose parts in the engine, nor leaking gasses, so what is it?

2. The diesels sound different to petrols, is it just for their size/weight, or is something else?

3. Whats with the similarity between the TATA ACE engine sound and the NANO engine sound.(I bet they are quite similar-audibly).

4. Nano is a mere 130cc less than M800 (749cc exact), but the engine sound is horribly different.WHY?

5. Also, all three wheelers in India (like Force Minidor, Mahindra Gio, Ape "xxx" etc.) have the same characteristic sound (remember the SCI Vikram). Why so? Do they have something characteristically common among them? Is it anything to do with no. of cylinders?

Gurus, Pls help , I have been craving to get the answers! (sorry if the questions sound stupid, I was always taught to ask silly questions rather than none)

[Hashim]

Sound of engine depends much on where its mounted and the design of muffler and length of silencer. If you fit Nano engine in M800 but using silencer of 800 only, it will sound no more like Nano. Sound is damped in car chassis also.

Regarding 3 wheelers, they sound same because no matter what make, most part are identical.

[ajmat]

Many factors - lets trace the various paths.

Air induction - most cars this is damped heaviliy. If you have a k+N universal one, you will hear the hiss. Carb engines made a much more delightful noise. Seen an Alfa or was it a Ferrari with triple carbs - oh boy! Intake manifolds also play a part in the induction noise

Top engine - more parts means more music or noise - double overhead cams should make more interesting sounds. Belt driven cars are a little quiet. It all depends on tolerances and valve lifts. Pushrod enings generally sound harsh at high speeds

Bottom end - it really depends on bore stroke and number of cylinders. In line sixes are creamy, v8's brawny, v10's wail, 3 and 5 cyl have a slight uneven note. Large four cylinders are rough but some companies like Porsche and mitsubishi, added balanincing shafts to compenste for this.

Exhaust - this plays the biggest part both in terms of noise and tone - wider bore - more base but the manifold design is where the "tunes" happen

Turbo - It actually muffles the car, exempt for the hiss when the turbo come on

There could be more but these are from the top of my head.

Coming to Indian cars - Jap cars have tight tolerances and a lot of balancing of internal components hence the smoothness. Diesels, it is due to the high compression and preignition knocks which dissipate when engine warms up.

Those single cylinder engines - they are rough since it is a single cylinder engine, high compression, thumping away with nothing to balance it

[aargee]

Originally Posted by justwheels

1. What makes this characteristic sound. I am sure there aren't any loose parts in the engine, nor leaking gasses, so what is it?

Its the exhaust gases, firing & strokes that contributes mainly followed by the muffler. To give an idea, the sound that escapes from a single 250cc cylinder is different from twin 125CC cylinder; another example would be, the difference of a V shaped 4 cylinder & inline 4 cylinder.

Originally Posted by justwheels

2. The diesels sound different to petrols, is it just for their size/weight, or is something else?

Like I mentioned before, the sound of escaping gases. Diesel engines have higher compression ratio & hence the sounds more too

Originally Posted by justwheels

3. Whats with the similarity between the TATA ACE engine sound and the NANO engine sound.(I bet they are quite similar-audibly).

Tata ACE is a Diesel engine while Nano is petrol. Obviously they're different. I'm not sure how they're similar in sounds.

Originally Posted by justwheels

4. Nano is a mere 130cc less than M800 (749cc exact), but the engine sound is horribly different.WHY?

Firing sequence, cylinder size, quality of metal used, stroke cycles, volumes of gases escape all these make a lot of difference. To give you another example a HD's sounds is very much different from Triumph Bonneville. Both of them are 2 cylindered 800+CC engines, however, the alignment of HD is V, while Triumph is parallel twin.

Originally Posted by justwheels

5. Also, all three wheelers in India (like Force Minidor, Mahindra Gio, Ape "xxx" etc.) have the same characteristic sound (remember the SCI Vikram). Why so? Do they have something characteristically common among them? Is it anything to do with no. of cylinders?

Not sure on the above quoted vehicle's engine capacities, but yes, no: of cylinders does matter on the characteristic sound.

Note - most of my examples are quoted with motorcycles & not with cars; reason being that, we'd a similar discussion, but with motorcycle engins, that went all way upto mid of the night & continued next day morning about 3 months ago.

Originally Posted by justwheels

sorry if the questions sound stupid, I was always taught to ask silly questions rather than none

No; its a very interesting topic; I would be a regular visitor to this thread as & when it gets updated.

[akshay4587]

@Just wheels,Nano has a Twin cylinder air cooled engine,and M800 has a 3 cylinder,liquid cooled engine,hence the peculiar difference in sound,M800 sounds smooth,where as engine not of nano is gruff.

[NOS Power]

Another point to note is that improvements in efficiency leads to different sounds. One should note that the components used in the engine, mainly parts that are constantly in motion are the ones that make most of the sound. Good quality bearings, belts, pulleys etc. can make a difference in sound.

Also things like exhaust back pressure, engine oil lubrication system etc. also have direct impact.

[justwheels]

Originally Posted by Hashim

Sound of engine depends much on where its mounted and the design of muffler and length of silencer. If you fit Nano engine in M800 but using silencer of 800 only, it will sound no more like Nano. Sound is damped in car chassis also.

Regarding 3 wheelers, they sound same because no matter what make, most part are identical.

I very much understand the importance of the muffler/silencer in the sound. Just wonder if TATA could have done some mods to that for Nano. That sweet car surely deserves a better sound signature.

Originally Posted by ajmat

Many factors - lets trace the various paths.

Air induction - most cars this is damped heaviliy. If you have a k+N universal one, you will hear the hiss. Carb engines made a much more delightful noise. Seen an Alfa or was it a Ferrari with triple carbs - oh boy! Intake manifolds also play a part in the induction noise

Top engine - more parts means more music or noise - double overhead cams should make more interesting sounds. Belt driven cars are a little quiet. It all depends on tolerances and valve lifts. Pushrod enings generally sound harsh at high speeds

Bottom end - it really depends on bore stroke and number of cylinders. In line sixes are creamy, v8's brawny, v10's wail, 3 and 5 cyl have a slight uneven note. Large four cylinders are rough but some companies like Porsche and mitsubishi, added balanincing shafts to compenste for this.

Exhaust - this plays the biggest part both in terms of noise and tone - wider bore - more base but the manifold design is where the "tunes" happen

Turbo - It actually muffles the car, exempt for the hiss when the turbo come on

There could be more but these are from the top of my head.

Coming to Indian cars - Jap cars have tight tolerances and a lot of balancing of internal components hence the smoothness. Diesels, it is due to the high compression and preignition knocks which dissipate when engine warms up.

Those single cylinder engines - they are rough since it is a single cylinder engine, high compression, thumping away with nothing to balance it

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.

Originally Posted by NOS Power

Another point to note is that improvements in efficiency leads to different sounds. One should note that the components used in the engine, mainly parts that are constantly in motion are the ones that make most of the sound. Good quality bearings, belts, pulleys etc. can make a difference in sound.

Also things like exhaust back pressure, engine oil lubrication system etc. also have direct impact.

Exhaust back pressure is surely something that will have a massive effect on sound. For a family hatch / sedan, what do you think should be the priority of the manufacturer : a) decent sound from the muffler/silencer which could have an effect on the FE or b) let there be that extra decibel without any compromise on FE. This question is assuming that too much of silencing will increase back pressure effecting FE. Correct me if I am wrong.

[justwheels]

Sorry Mods for back to back posts, was confused with the multi quote option. Would take care in future!

@aargee : Thanks for that point to point reply. Well nice to see you all had a similar discussion involving bikes. Infact this question first came to my mind during the days of suzuki shogun / samurai. If you remember they had that typical sound, also the Yamaha Rx100. The newer bikes are 4 stroke so I can imagine a much smoother sound, as the Rx100 was 2 stroke, don't remember about the shogun/samurai.
And I did not want to compare TATA ACE and Nano, as i know they are two different engines, its just that they sound too similar. Many non petrol heads complain it to be an auto sound. Not good to hear that comment for that sweet car.
And thanks for the encouragement!!! Hope to learn more at TBHP.

[aargee]

Originally Posted by justwheels

The newer bikes are 4 stroke so I can imagine a much smoother sound, as the Rx100 was 2 stroke, don't remember about the shogun/samurai.

When you comapre 4 strokes & RX, there's a world of difference because RX/Shogun/Samurai are 2 strokes. For every 1 stroke in 4 strokes (TDC & BDC of piston), a two stroke makes 1.5 strokes!!!

So as discussed on the noise on exhaust gas escape, it would be faster on 2S compared to 4S; this also means, the noise on 2S will also be more than 4S. Oh!!! the noise factor being smooth on 4S is just a myth. Remember the last model of RX135 5 speed with catcon silencer? They make less noise than a typical RX & have almost the same noise as a 4S.

[NOS Power]

Originally Posted by justwheels

Exhaust back pressure is surely something that will have a massive effect on sound. For a family hatch / sedan, what do you think should be the priority of the manufacturer : a) decent sound from the muffler/silencer which could have an effect on the FE or b) let there be that extra decibel without any compromise on FE. This question is assuming that too much of silencing will increase back pressure effecting FE. Correct me if I am wrong.

I'll give you an example.
In the biking world, there is also a national engine. The Hero Honda 100 cc 4 stroke single which was used in atleast 5 different models. The engine was enlarged to 110cc to be used in the Splendor. After that all the lower end models had this 110cc engine. But, there was a difference in power, torque and most importantly FE. The Splendor initially had a normally loud exhaust, which was then later silenced by a lot, this lead to an increase in FE and a much more silent bike.

Another example is the Honda 150cc engine which does duty on 4 different bikes, the Unicorn, Hunk, CBZ Extreme, Achiever and Hunk. The engine has similar specs in the present Unicorn, CBZ Extreme and Hunk, but the Unicorn is the quietest of the lot, and it gives a bit more mileage than the other two.

The simple logic being that when back pressure is increased the engine runs leaner. The technicality behind this is not clear to me, if some experts can give a clear view on this.

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?

[aargee]

Originally Posted by NOS Power

The simple logic being that when back pressure is increased the engine runs leaner. The technicality behind this is not clear to me, if some experts can give a clear view on this.

IMO, increasing the back pressure only leads to increase in compression or less effort required by the crankshaft to move the piston(s). Running the engine leaner or richer is taken care by the intake systems; be it carb or FI.

So when the compression increases, I assume that less fuel is required to give the same level of output & the effort on crankshaft & pressure on connecting rod is less.

[lambdaplus]

Most of the engine noise is caused due to pressure waves created by sudden expansion of the burning air-fuel mixture. Hence Diesel is noisier than petrol, due to higher pressure changes caused by higher compression.

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

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.

[justwheels]

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?

To my opinion, the engine map should be playing a role here, as the BHP figures for said rpm are different for these cars. The strange part is that a more peppier swift is smoother audibly than a more balanced Vista. I feel some gurus can put some light on this?? Gurus

Originally Posted by NOS Power

I'll give you an example.
The simple logic being that when back pressure is increased the engine runs leaner. The technicality behind this is not clear to me, if some experts can give a clear view on this.

Originally Posted by aargee

IMO, increasing the back pressure only leads to increase in compression or less effort required by the crankshaft to move the piston(s). Running the engine leaner or richer is taken care by the intake systems; be it carb or FI.

So when the compression increases, I assume that less fuel is required to give the same level of output & the effort on crankshaft & pressure on connecting rod is less.

Now this needs clarification, as, if you increase the back pressure, the engine needs more power to push the exhaust gases out, that means it does more work and the exhaust gases travel out slowly. So this will eat away the FE. Therefore a much silent engine should have a lower FE (considering only the effect of muffler/silencer. Please correct me if I am wrong, but this should be plain physics.

[aargee]

Originally Posted by justwheels

Now this needs clarification, as, if you increase the back pressure, the engine needs more power to push the exhaust gases out, that means it does more work and the exhaust gases travel out slowly. So this will eat away the FE. Therefore a much silent engine should have a lower FE (considering only the effect of muffler/silencer. Please correct me if I am wrong, but this should be plain physics.

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.

[lambdaplus]

Originally Posted by justwheels

Now this needs clarification, as, if you increase the back pressure, the engine needs more power to push the exhaust gases out, that means it does more work and the exhaust gases travel out slowly. So this will eat away the FE. Therefore a much silent engine should have a lower FE (considering only the effect of muffler/silencer. Please correct me if I am wrong, but this should be plain physics.

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.

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.

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