Basic Question Time: Why does the supercharger whine?

[Tigger, Eeyore & Roo]

Here's a basic question: why does the supercharger whine?

I'd always thought it was the belt whining, but last night while I was giving a friend a lift we were talking about it and realised that the supercharger can be pretty much silent at any engine speed; it's only when it's under load that it makes its glorious whining noise

For instance, the engine can sit at any constant engine speed (2, 3, 4 , 5 , 6,000 rpm) and the supercharger makes no noise. Put the gearbox into neutral and rev the engine to the rev line and, again, the supercharger makes no (or very little noise) noise. Yet, put the engine under load, accelerate hard and it whines like mad

Why is this?

Tigger.

[MINI-Bob]

Good question, i'd assume it has something to do with the volume of air being forced through.

[Tigger, Eeyore & Roo]

Okay, that means there's two of us who'd like to know!

Anyone?

Tigger.

[Nebdingo]

Its cos its female...

When I stand on the wife and press harder she makes the same noise!

*hides from the missus!

[Tigger, Eeyore & Roo]

I'm so glad I'm not in your shoes!

[MINI-Bob]

I've been thinking about this some more.

What sort of 'charger does the MCS have? Don't think it will make any difference as they all whine! But i don't know.

Does the 'charger have a clutch which only engages when on full throttle so in effect it's not engaged at at lighter throttle and therefore doesn't whine?

[Tigger, Eeyore & Roo]

No, the supercharger is "always on", but it only seems to whine loudly when under load

[MINI-Bob]

Agreed!

Hope someone knows the answer!

[richg40]

The Eaton supercharger whines because the two bladed shafts are driven by straight cut toothed gears.

[Loui]

Quote: Originally Posted by MINI-Bob (original)

I've been thinking about this some more.

What sort of 'charger does the MCS have? Don't think it will make any difference as they all whine! But i don't know.

Does the 'charger have a clutch which only engages when on full throttle so in effect it's not engaged at at lighter throttle and therefore doesn't whine?

Rotrex blowers dont whine

[MINI-Bob]

So the MINI has an Eaton blower, which has straight cut gears which creates the whine. Yes?

So why doesn't it whine at small throttle openings?

[richg40]

there is less pessure on the bladestherefore gears, just like a straight cut gearbox whines less on overrun.

[MINI-Bob]

Ok. That makes sense. Cheers

[Tigger, Eeyore & Roo]

I'll buy that as well. Thanks.

Tigger.

[r1_kde]

The superchargers whine because of the rotors meshing, as the tolerances are so close to ensure there is air pressure held, the rotors make a whine towards higer spreeds. Should you ever have the blower out of the car and turn by hand you will hear the sound of the rotors meshing. produces a sound like gears but it is the rotors just about touching, pre face lift should be louder at high speeds due to the lack of teflon coating.

Howstuffworks "Supercharger Basics"

Read the page, it helps with the basics.