Well, it's driven by the crankshaft, so I'm gonna go with rpm which is controlled by your throttle.

 

Your question doesn't quite make sense... it would be similar to asking, does the law kick in when a crime is committed or when an arrest is made?

Try this: HowStuffWorks "How Superchargers Work"

 

It kick in because of load


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It's load based and that's why there is a valve to let out the extra air not pushed to the motor based on the load amount.

 

The supercharger has a bypass valve, which opens and closes based upon engine vacuum.
Fuel economy would be reduced, if the supercharger was not bypassed under light throttle, which creates high engine vacuum. The bypass recirculates supercharger air output, back into the air input of the supercharger. When the bypass valve is open, you create little or no boost.
So, under light throttle, the throttle butterfly is nearly closed, a high vacuum is created, which opens the bypass valve. When you put your foot into the throttle, the throttle butterfly opens, causing a loss of intake vacuum, and closing the bypass valve on the supercharger, which then creates boost.
Disconnecting the vacuum line on the supercharger would cause it to create boost all the time, reducing your fuel economy.

 

Great summary. Does anyone know where the bypass valve is located? Mine whistles under heavy load, which drives me crazy. Looking for a fix, but I have been lazy so far.

 

And the prize goes to addertooth! Additionally, the Bypass also reduces superheating of the intake air under light load where the supercharger would be thrashing the same air against a closed throttle.

 

I have yet to purchase a Lotus yet so I might not understand the plumbing of this supercharger fully. I thought bypass valves were related to turbo engines and allowing the exhaust gas to exit the system without turning the turbo. Not sure how to bypass the supercharger as it is belt driven. My history with superchargers is on old V8s and the butterflies are before the supercharger compresses the air. This way under low throttle there is a small volume of air for the supercharger to compress. I understand the use of a blow off valve after the supercharger has compressed the air if the butterflies are after the supercharger and I’m guessing this is the setup here. Maybe my vocabulary is wrong?

 

Sorry I it's been a crazy morning I needed some levity.

I won't do it again I promise


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SupeSuperchargers are mechanically belt driven and provide proportional power increase as a function of engine RPM over a NA version of the engine up until the point of efficiency fall off at higher RPM’s due to thermal losses or to the point that the Bypass value opens to relieve pressure, this is similar in principal to a turbochargers blow off value. Lotus has set this valve at 0.5 bar (that is 1/2 nominal atmosphere or about 7 psi). This value also opens at low engine load, regardless of RPM to reduce amount of pressure developed and thus reduce the parasitic drag of turning the SC. As to boost, you are effectively creating boost all the time and at full throttle the engine is acting as an approximation of a 5L engine, along with its "great mileage". The advantage of a supercharger over a turbo is that it is always there in the lower RPM range, subject to engine load demand, whereas the turbo must both spool up and with long piping creates a lag. At the higher RPM’s most SC’s run out of steam, whereas the turbo is entering its prime as long as the engine can withstand it. The Turbo can also be driven to achieve better mileage by p***y footing the throttle to keep it off boost (yeah, like that will ever happen, my RX-& TT gets at 3 mpg on the track and has never gotten better than 15 on the road, other than a fake driving mileage test; no such luck with the SC, however mileage is still better than the 5L as rotating components are lighter, cylinder chambers about 10% smaller for better combustion and less need to have the foot in it compared the NA version as power is adequate with less.

 

Does it sound like this:

 

Bypass valve is in the supercharger itself, on the side opposite of the pulley (the intake side). Look for a diagram of a magnuson MP62 and it should all become clear.

 

Thx. I will check it out. I honestly can't tell if the whistling sound is normal or not. I am obsessed with finding out. It ruins the sound track under acceleration, but I seem to recall hearing it in some test videos. So, it might be a feature of the supercharger under high load.

 

A typical supercharger will make a whine under full throttle, this is normal (and to my ears sexy). I wouldn't describe the noise as a whistle.

 

I get that, and I like it as well, but I expect the pitch to change as the RPM's build. This sound comes on late in the rev range and the pitch doesn't change. It is literally like a switch gets thrown under a certain amount of load. If I gradually build the rev's, I generally don't hear it. I will try to get an audio today.


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