Supercharger \'off\' switch?

[m1tch]

Hi everyone,

Really random question but would it even be possible to turn a supercharger \'off\'? As in having a sort of clutch arrangement on the nose pulley much like the air con pulley that can be disconnected etc? I know that some OEM superchargers have a divert valve so that this can be done for certain applications as I am guessing if you stop a supercharger its pretty much a solid block of metal covering the intake lol

[TiddlesRX7]

Mad Max springs to mind

[Prof]

Why would you want to turn it off ?

[Kenji]

The old style blowers use a clutch, they can be switched off (as demonstrated in the aforementioned MadMax movie).
The belt will still turn, but the charger wheel will rotate free of the internals.
It will however, be a massive obstruction in the flow, but given that chargers that big usually require quite some engine power to begin with, it won;t really be a problem.
 
To give an example, the blowers used on Top Fuel dragsters give an output of 4000 bhp or more. To turn the blower over however, will require around 1400 bhp on the engine alone.
So input 1400 bhp : output 4000+ bhp.
On a streetcar, turning off the charger will result in engine power alone, minus some obstruction bhp\'s.
 
More modern chargers don;t have the clutch, so can\'t be switched off.

[m1tch]

Ah ok, was just wondering, always wondered if you could drive one \'off boost\' but it seems not lol

yay for train supercharger:

http://www.youtube.com/watch?v=v0qeYd5gcnQ

[Ricco_04]

Possably talking a pos but I was sure that some applications have an \'automatic\' clutch. Example :  if your just crusing down the motorway then it dis-enguages, when you put your foot down it re-enguages again.

We get so much exhaust gas I would have turbo was a more efficient / better option?

[jackaleks]

i always thought that the point of roots/screw blowers was that you have a constant positive pressure going into the engine?

also, SC rotaries are definite win!

[Grant Monkhouse]

The answer is yes. A few years ago in Max Power the main feature car was a 350z that was being developed by nismo that incorporated an electromagnetic supercharger pulpy system. This was to maintain the fuel economy of the the na engine and when wanted the hp could be increased by the flip of a switch.

Obviously the car ran different maps on the system for when the charger was on/off. The hp increase wasn\'t huge but it was more than enough to make it a spirited drive. I think it was in the range of 50-80 hp but I may be wrong.

[m1tch]

Why would it have to run different maps? You can run a turbo II map on an EGI, its just that the EGI won\'t ever need the fueling table for the fueling on boost lol

[jackaleks]

Why would it have to run different maps? You can run a turbo II map on an EGI, its just that the EGI won\'t ever need the fueling table for the fueling on boost lol

you could probably find a map that would be middle ground for both FI and NA, but having two maps would probably be more efficient i guess...

totally pointless imo! if you\'re going to put a blower on a car it\'s because you want massive torques and throttle response, not an economical cruise to work :Hammer

[m1tch]

A turbo car off boost is NA....

[B.Martin]

A turbo car off boost is NA....

It\'s not quite the same though as most turbo charged engines are designed to run low compression, so when they are \'off boost\' they are generally quite un-amazing lol.

Not sure if this has any relevance but it might make me sound like I know what I\'m talking about :Hammer

[DrDan]

Electro-magnetic clutch, details of how it works, here:
http://en.wikipedia.org/wiki/Electromagnetic_clutch
 
Used a lot in air-conditioning compressors; also has been used on the Mercedes SLK supercharger. But you do need to then have a way to bypass the stopped SC
 
Also, some (Eaton) superchargers have a bypass mechanism built in, see here: http://www.capa.com.au/eaton.htm about 3/4 of the way down the page. Works quite well in my other motor
 
DrDan.