[MustGT98allday]

So I was just wondering how many people actually know why a supercharger whines? I know im gonna get some funny and crazy answers but im extremely bored.
its also going to kinda be ruined once someone gets the right answer but lets see how many posts before the right answer

[wannabeimportkiller]

[WickedSnake00]

Originally Posted by MustGT98allday So I was just wondering how many people actually know why a supercharger whines? I know im gonna get some funny and crazy answers but im extremely bored. its also going to kinda be ruined once someone gets the right answer but lets see how many posts before the right answer

Well sound is nothing but compression waves in air. What is a supercharger (or turbo for that matter) doing? It's using a series of blades or screws to compress air, causing a localized, attached oblique compression wave. I can only assume at those high radial velocities, the incident compression (shock) wave, is basically similar to that of a supersonic aircraft. Higher RPM = higher oscillation of said wave, higher pitch. Of course there's also the possibility of the compression waves generating a standing wave or pulses in the intake system, as well as resonance frequencies. That might also create choked flow and blah blah blah...


...did the Mech Engineer just ruin all the fun with the graduate compressible flow course he took?

[SWEET2KSTANG]

the flux capacitor gets going at hyper sonic speed, then the what-cha-macallit sends the dew hickey surging twice the speed of sound, which requires the cleaning of your k&n, but you can only make more power from it if you run rusted out shitty flowmasters

[sharkbait]

Pretty sure its just the gears inside of the blower whining under load. There straight cut i believe

[GMoney98]

i have a headache after reading this thread. i know i wish had a supercharger

[WickedSnake00]

Originally Posted by sharkbait Pretty sure its just the gears inside of the blower whining under load. There straight cut i believe

I'm not sure if that's true...

Most MD/HD diesel engines feature a front gear train (for accesories such as air compressors, sometimes hydraulic pumps) with straight cut gears, and they don't whine like an S/C.

I also do not want to think of the complexities of interacting oblique shockwaves in four dimensions, especially with frictional losses, heat addition, and reflections. Makes me want to

[wheelsjz]

I also have a headache from reading this thread haha.

[MustGT98allday]

good try wicked snake
props to sharkbait. Its because the gears are straight cut. Thats why trannys have helical gears (slant cut) because they are quieter and cars are built on customer preference.
to the others who dont give a fuck and wanna trash this thread stop being sourpusses and go read up on your auto books!!!

[bigjohnstud4200]

Originally Posted by sharkbait Pretty sure its just the gears inside of the blower whining under load. There straight cut i believe

+1, plus it add to the BADASS FACTOR!

[MustGT98allday]

sorry for the stupid thread i guess. I thought this was a tech section. My bad

[WickedSnake00]

Originally Posted by MustGT98allday good try wicked snake props to sharkbait. Its because the gears are straight cut. Thats why trannys have helical gears (slant cut) because they are quieter and cars are built on customer preference. to the others who dont give a fuck and wanna trash this thread stop being sourpusses and go read up on your auto books!!!

Hmm. Now you've got me puzzled. I don't get any of that noise out of the multitude of straight cut gears in diesels.

Not to mention my assumption also had to do with the method of compression. Turbochargers and centris have similar compressor geometry, and create more of a hiss than a whine. Twin screws have, well, two screw shaped rotors, and produce that distinct whine. This is also present in industrial screw type compressors. My guess would have assumed the whine would have to do with the shock wave geometry in the twin screw, as it has two rotating elements, with a stationary housing, as opposed to the centri geometry.

Also think about turbines/jet engines. They have a nasty whine to them, is that due to gearing as well? I throw that out there, because those are more the basis of my applied compressible flow knowledge.

And I wouldn't discount the possibility of harmonics. PD blowers have two rotating elements, which can create a beat pattern of harmonics, similar to the beat pattern of two jet engines.

Of course I'm mostly just throwing all of this out there.

Does anyone have a definitive answer?

[MustGT98allday]

ok well its very hard to argue with that type of knowledge. now im no diesel mecahnic but how fast are those gears in the diesel your talking about because with the spur gears (straight cut) the faster they spin the better or more pronounced the whine is.
also that statement about the jet engines does interest me now. Im not sure what they are composed of.
Its sounding to me like we both have got some truth in the question. If you think about the spur cut gears you will get a whine whether in s/c trannys or diffs and of course in the supercharger they spin extremely fast therefore creating that high pitched whine.
however like youv been saying with the compression waves that is what the supercharger is doing (taking in air and compressing it down) as well as jet engines.
im a little too tired right this second so im gonna say BOTH

[bigjohnstud4200]

A jet engine is spinning way faster than a supercharger. I have nothing to back this, but even on a slant cut gear, if you get the revs high enough, you're going to get whine. As far as jet engines go, I've sat in the wheel well of F-16 and F-15 and with a set of internal ear plugs and ear covers, the noise is INCREDIBLY loud, even at idle.

[98BAGT]

straight cut gears are exactly why most reverse gears whine

[MustGT98allday]

Originally Posted by 98BAGT straight cut gears are exactly why most reverse gears whine

exaclty!

[sharkbait]

Its most deffinitally the straight cut gears and not the method of compression. I can spin my blower to 6k rpm when at under 1/4 throttle and have it stay completely silent.

Once you start adding air they start whining. The whine is a distinct gear whine though

[tfofkyle]

Originally Posted by sharkbait Pretty sure its just the gears inside of the blower whining under load. There straight cut i believe

youre thinking of a centrifugal blower. blower whine (a la eaton, roots, screw, etc) is caused by compressed air from the rotor lobes creating a small "pop" as it exits - or - a whine/scream in this case as rpms build. wicked had a rather good technical explanation.

if we were talking about centrifugals to begin with - my apologies. then it does have to do with the straight cut gears. although wicked is also right - when you hear a helical cut gearset centrifugal - the compressed air hisses as it exits the impeller wheel and enters the air intake stream.

would just like to point out that its generally accepted that centrifugals *whistle*, roots blowers *whine*, and twin screws *scream* differences are caused by case size, rotor lobe angle differences, numbers, sizes, etc.

[WickedSnake00]

Originally Posted by tfofkyle youre thinking of a centrifugal blower. blower whine (a la eaton, roots, screw, etc) is caused by compressed air from the rotor lobes creating a small "pop" as it exits - or - a whine/scream in this case as rpms build. wicked had a rather good technical explanation. if we were talking about centrifugals to begin with - my apologies. then it does have to do with the straight cut gears. although wicked is also right - when you hear a helical cut gearset centrifugal - the compressed air hisses as it exits the impeller wheel and enters the air intake stream. would just like to point out that its generally accepted that centrifugals *whistle*, roots blowers *whine*, and twin screws *scream* differences are caused by case size, rotor lobe angle differences, numbers, sizes, etc.

So you mean I was...

...right? How the hell did that happen?

Also I meant to bring up the difference in sounds between Eatons/Whipples/Kenne Bells. Think about it, they all have characteristic sounds to them, and it does vary greatly upon displacement. It couldn't possibly be simply a matter of gears. The true variation is in geometry.

The big point would be in comparing displacements (and efficiencies.) If you notice, the blower with the loudest whine is the old KB 2.2. This was a small displacement blower, relatively old, so relatively inefficient. Intuition would lead you believe that small displacement means higher frequency in relation to shock wave motion, thus higher pitch whine. Compare that to either the new KB 2.8L, or the Eaton TVS. The 2.8/TVS are much larger and newer, and thus much quieter due to increased displacement, as well as improved efficiencies. Remember, noise is energy, and the more noise you make, the more energy is being expended NOT compressing the intake charge.

It's almost ironic that people will pay a premium for the 2.2L just for the whine. As much as I love the whine, I like power better. I guess some people think sound is a very important mod, just like those that love their LM1's.