Superchargers - How they work, what types there are and more!

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  1. Superchargers - How they work, what types there are and more! 
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    Superchargers are driven continuously while the motor runs, like a fan or air conditioner unit, and they run at a fixed ratio to the engine rpm, delivering the same curve of boost regardless of the engine's natural aspiration, so they normally impose their own characteristics on the vehicle's breathability. But some of them can deliver instant boost practically from idle, which is held to be the great differentiator between the turbo and the supercharger..Superchargers give a much more Linear power curve, but is hte potential for big hp the same?...well, No in a word!

    Here's the lowdown on the different types of supercharger:

    There are essentially two ddifferent types of supercharger and the first, a centrifugal supercharger, is an air pump driven directly from the crank, injecting air it has ALREADY compressed. It delivers exponentially increasing boost as rpm increases.

    Some like to think of the centrifugal supercharger and the turbocharger as the same thing except with the compressor wheel being powered by different means. The centrifugal does experience lag at the lower end of the rev range as with a turbo

    Centrifugal superchargers aim for max boost at the high end of the rev range. A centrifugal supercharger is basically the same type of pump as the compressor side of a turbocharger, but it is mechanically driven off the crankshaft instead of by exhaust gas as with a turbocharger. Internal gearing then steps up the spin speed of the compressor wheel, and gives a distinctive whistling sound, that most drivers enjoy hearing, but the centri SC is basicallyt pretty damn noisy for a daily driver.

    The centrifugal's type of compressor - like the turbo's - is efficient only at high rpm. Because all superchargers by definition are under continual drive from the crank (i.e. with no comparable turbocharger wastegate system to cut the drive), design decisions set the limits to how much internally to gear-up (or overdrive) the spooling:
    The centrifugal aims for high-end boost and in consequence gives almost no boost at low rpm.

    Although centrifugal superchargers build boost relative to engine rpm: boost builds exponentially in the upper half of the powerband - generally they start boosting around 2000 to 3000 rpm, and attain full boost at max rpm - i.e. the quoted maximum boost of a centrifugal happens at redline.

    Enthusiasts say that in situations where they demand performance from their vehicle, they spend most time in the mid to high rpm ranges.

    Best applications of centrifugals

    The centrifugal is good for lightweight, manual transmission vehicles (you can downshift for a higher rpm) , and is popular with muscle cars that have plenty of low-end torque already in NA form (naturally aspirated), but they're not so good for heavier vehicles under load or towing, or automatic transmissions - in these cases a positive displacement supercharger is much more suitable.

    This positive displacement aspect brigns us on to the......

    Roots Blower - essentially a positive displacement air mover
    The roots-type supercharger is a positive displacement system referred to as a blower since it doesn't compress air directly, but simply moves it quickly. It employs 2 or 3 counter-rotating lobes to scoop a fixed amount of air from the outside and deliver it into the intake manifold. Unlike the compressors of the turbocharger and the centrifugal supercharger, which deliver exponentially greater boost with increased rpm and which are not designed to perform at lower rpm, a positive displacement supercharger pumps a fixed amount of air for every revolution, and delivers instant boost even at low rpm.

    Since positive displacement superchargers are both continually under drive and also delivering boost at all rpm an intake bypass system is used in street applications to divert airflow and prevent overboosting.

    The roots type supercharger is based on the very efficient air moving principles of positive displacement, but loses supercharging efficiency for several reasons, and primarily because it doesn't compress the air directly.

    High heat from turbulence
    The blower delivers more and more air rapidly into the intake manifold, where it compresses from the addition of increasingly more air. The turbulence of uncompressed air entering the compressed environment - with associated backflows - creates heat, the great negative factor of supercharging.

    The adiabatic efficiency of a roots type supercharger is only in the 40%-60% range. Furthermore, while the other compressors tend to gain efficiencies at higher rpm, the roots tends to experience decreased efficiencies as boost levels rise or for sustained maximum output periods.

    A positive displacement supercharger has great advantages in lower end delivery - more power at lower rpm equals less strain on the engine.

    The roots type blower is inherently noisy, largely from the gearing required to run the rotors. It is a very simple supercharger, and moves a great volume of air very easily. The roots blower has always been very popular, but is now yielding some ground to the twin screw.

    The history of the Roots blower extends from 1859, predating supercharger history - positive displacement is an air pumping invention
    Last edited by Boostist; 06-04-2007 at 01:35.
     
     

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    Now it gets more complicate still though!! because you have to split it between NON-positive displacement compressors, positive displacement NON-compressors, and the twin screw positive displacement compressor.


    The twin-screw supercharger is a positive displacement air pump driven directly from the crank, injecting air it has ALREADY compressed. It delivers linearly increasing boost as rpm increases. The twin screw delivers full boost at low rpm, like the Roots SC, but also delivers compressed air, like the centrifugal and the turbo.

    Twin Screw Superchargermoves fixed amounts of air per revolution, like the roots type blower. however, unlike the roots, which is only an air delivery system, the twin screw supercharger is also a compressor.

    The counter rotating lobes and chambers of the twin screw are designed for a screw-like tapering effect which runs its intake air into a smaller space for output, thus compressing it. The rotors have very close tolerances yet never touch. Compressed air is delivered into the compression environment of the intake manifold with very little leakage or energy loss.

    Because of the increased mechanical efficiencies of the superior design, the output air temperatures of the twin screw positive displacement supercharger are radically improved from the roots type. The Whipple twin screw quotes adiabatic efficiency of 70%-80% range across the whole powerband.

    As with the roots, since the supercharger is under continual drive, and since it delivers boost practically from idle, overboosting is prevented by the use of an intake bypass system, which allows the engine to breathe normally at cruising or idle: the bypass closes on throttle use, delivering full boost.

    Full boost by 2000 rpm!
    The twin screw supercharger creates boost the instant the throttle is touched, and generally reaches full boost by 2000 to 2400 rpm. Full boost is then available all the way to the engines redline. A positive displacement compressor is ideal for street performance cars and is well suited to many motors in the BMW stable... (both I6 and V8)

    The twin screw compressor is especially useful at high altitude, where physics dictates that all engines wil lose power due to the lower oxygen content available.

    The TS is essentially silent, producing maybe only 10% more engine noise (and it sounds like a whisper basically so is not intrusive)

    It has a low profile and will not take up too much underbonnet space. Of all the forced induction systems, the twin screw compressor supercharger is quite possibly the BEST one to pick if you decide you have to go linear power, zero lag...on your forced induction BMW.

    Just be sure to research the different types of supercharger kits before you buy because as with anything, there are good ones and there are bad ones :

    Supercharger kits review thread coming up shortly.





    main supercharger information source: http://www.coloradocobras.com
     
     

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    Brilliant write up dude.
    thanks
     
     

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    Great write up their boostist
    Anywhere closer to the SC kit review thread?

    im going turbo myself but have a good friend with a 3.2 evo who is very hot on getting it supercharged.

    With teh lack of 'ANYTHING' FI BMW in the UK market we are gonna go it alone but i would love to hear peoples thoughts on these...

    Now wheres moresvm3? ..... I think hes supercharging his /M iirc
     
     

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    Quote Originally Posted by stevem3 View Post
    Great write up their boostist
    Anywhere closer to the SC kit review thread?

    im going turbo myself but have a good friend with a 3.2 evo who is very hot on getting it supercharged.

    With teh lack of 'ANYTHING' FI BMW in the UK market we are gonna go it alone but i would love to hear peoples thoughts on these...

    Now wheres moresvm3? ..... I think hes supercharging his /M iirc
    I am away from home for the next month or so with work, will do some more when I get home
     
     

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    the only problem ive seen with supercharging the euro motors is the motor outflows the blower at high rpm

    ive seen many supercharged M's and they all share the same problem
    usually they make significantly less HP at high rpm when compared to a turbo'd version

    otherwise theyre great
    seen stock cars make good numbers and run great for a long time
    as long as its tuned right and treated right it'll treat you right
     
     

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    Quote Originally Posted by topshotta02 View Post
    the only problem ive seen with supercharging the euro motors is the motor outflows the blower at high rpm

    ive seen many supercharged M's and they all share the same problem
    usually they make significantly less HP at high rpm when compared to a turbo'd version

    otherwise theyre great
    seen stock cars make good numbers and run great for a long time
    as long as its tuned right and treated right it'll treat you right
    that is why I am using a twin screw blower off a 3.2L AMG merc, designed to run 14psi, I will only be running ~ 8psi
     
     

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    should make for a very fun car
     
     

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    Indeed, it should have a wicked torque curve :
     
     

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    I wonder what sort of numbers an M3 with that blower would put out?

    Whats the reckoning chaps? 450whp?


    Should be a superbly driveable car with that charger on though. Just make sure you attend to intercooling sufficiently well Alan...as inlet charge heat is your enemey as you know Im sure!
     
     

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