I understand the basics of how the supercharger spinning can create boost.
What I don't understand is why it's only during acceleration or under load?
I've searched this forum and google and all I can find is very basic info.

Can somebody explain in plain English why boost isn't created at crusing speed?


Thanks for any answers!

 

In a word, bypass.

There is a valve the closes in direct opposition to the throttle opening. If the throttle isn't completely open, the bypass isn't closed, allowing the supercharger to be by-passed.

There is a GREAT CGI of the operation. Let me find it for you, hang on.

Here it is:
http://www.usol.com/~cable/Video/Ecotec2.mpg

 

http://www.superchargersonline.com/faq.asp

Great find....forgot who orginally found it though, but i wont take the credit for it.

 

That's a GOOD movie :-)

Thanks for the info. I had a feeling there was some
type of valve but this is my first supercharged car so I wasn't sure.
My friend at work was trying to tell me it had to do with difference
in air pressure potential...or something like that...now I'll have
to show him this movie!

Now my next question is.....

Is the bypass valve in the supercharger the same as the blow off valve
in a turbocharger? From what I was reading it sounds like the bov is used to
keep the turbo from stalling when you let off the gas and the throttle closes.
That supercharger video makes it look like when you close the throttle, then
it just bypasses the supercharger.

 

Two completely different things. A supercharger is driven by the engine, so it is turns at whatever speed the engine turns. The by-pass valve allows the engine to run at less-then-WOT without the supercharger making boost, thereby making the engine manageable to drive.

The turbo is run by exhaust gas velocity. It doesn't need a bypass valve. Remember that a bypass valve is intergral to the operation of the throttle. Since there are low amounts of exhaust gas while operating at cruise speeds, the turbo simply doesn't spool up enough to produce boost. Therefor the engine remains manageble.

A Blow Off valve is used to vent the pressure being made by a turbo AFTER you stop accelerating. If you stop holding WOT, the turbo still has enertia spinning it. Theres no belt like on the supercharger to slow it down. So it continues to produce boost when you no longer want it to for a short moment. That boost is vented off by the BOV.

 

ok, im a fucknut if u will. what does 'WOT' mean

 

Wide Open Throttle

 

thanks

 

Thanks for all the info, now it makes perfect sense :-)
and I'm even more amazed at how it all works LOL