Re: electric supercharger response **Rob

["Rob Levinson" <always_coca-cola@xxxxxxx>]

Mark Kibort <mkibort@domain.elided> wrote some things about his "electric
supercharger" (which sounds like that recent Korean company's device).  I'm
not saying these are not worthwhile products, but I do take issue with a few
of his statements....

>Subject: electric supercharger response
>
>our tests on the dyno show 4 hp on a honda 4 banger and 9 hp on a porshce
>928 2 valve race car. These figures are on the ground!!!!  and e30 can put
>160 stock to 200 to the ground , and this should add the 3% no mater what
>you have done .  We have already done the tests.


        4hp might be hyper-important between identical race cars, but you
can gain/lose a 4hp "net effect" from the drag/loss of drag from properly
chosen tires and inflation of tires.  A recent Sport Compact Car article
showed that.

Brett Anderson (who knows a thing or two about cars) wrote:

>>It sounds like a cool idea, but it is quite easy for the Bosch alternator
>>in an E30 to drain over 5 hp from the engine when it is
>>under high load.  Therefore, chances are good that the electric
>>supercharger could actually cost power.
>>Now, if it could create 40 hp or more, that would be a fantastic upgrade.=


And then Mark responded with:


>the altenator doesnt work that way, I dont think.   when you start your car
>you drain 80  or more amps for a couple of seconds. this is a couple of hp.
>the altenator then takes a few minutes to recharge what was taken from
>thebattery.  thats why you have a battery, otherwise you would have a
>magnito.


    Actually, the alternator *does* work that way... it responds to load and
has to work harder when more devices are drawing electricity.  True, there
is a baseline drag even if no electrics (besides the ignition) are being
used - that's why Honda introduced a "two speed" alternator some years back.
    I'll give you a concrete example of how the alternator responds to load;
I have some electrical devices in my car that pull a lot of power.  As I
switch on my 85W low beams and then my 100W high beams, I can *hear* the
alternator working harder (from outside the car).  The alternator is at that
point dragging the engine so much that it drops the rpm a tad.  This is not
the iginition system being drained, it's strain on the engine just as if I
was letting out the clutch slightly.
    Also, at least in older BMWs, the alternator takes no part in starting
the car; in fact, it is specifically *not* generating significant power
until the car is revved over 2000rpm.  The battery is doing all the
starting, it has to - the alternator does not put out the peak amperage
required to spin a high-torque starter motor (the battery has 600 CCA - Cold
Cranking Amps, a lot more than a 90 or 130 amp alternator).



>anyway, the fan only works for about 7 to 10 seconds and is
>released  and so on.
>on the race track, no problem.  it is on for 40 seconds on a 2 minute lap
>at laguna seca.  On the street is on for an order of magnitude less.


        So you're saying this fan responds to... what?  RPM?  Airflow?
Vacuum?



>So , it works, and it will be tested further on midsize engines for
>comparison.
>40 hp would require 1.5 to 2 psi of boost , that would be  (if it could be
>done by an axial blower , which it cant)  6 hp to move 300 cfm at 1.5to 2
>psi .   this is just basic physics.     6 hp would be at 12 volts , well
>lets just say , 2 or 300 amps.   (after you factor all the inefficiencies=
>in)


            WHAT???  40hp from 1.5 to 2 psi of boost?  Hmmm... then my 10psi
turbocharger should make my car capable of producing, uh... 550hp!!!  Nice,
but I think a stroked and turbocharged 3.9 M5 has trouble coming anywhere
near that number (maybe only 475hp).  2psi of boost would do little more
than compensate for intake turbulence, maybe 5hp at best in a 3.0 liter
engine.  What are you talking about in the above statement?


>any comments.   It works and it is nice to have the extra 10 hp on the
>track because over time , it helps.
>besides, how many people on this list have spent 100 bucks on  plug wires,
>chips, air cleaners, cool air tubes , that at best provide less hp and
>maybe  none.    The electric ram air is a mass flow device and does work
>for obvios reasons.

        Once again, I'm not saying it doesn't work... but I'm not saying it
does anything significant.  And just to clarify, a set of $100 spark plug
wires is an excellent investment to replace old wires and will give a
tangible performance improvement.  A good chip (like a Jim C.) will also
give an honest hp improvement from 10hp to 50hp depending on application.
Real cool air tubes (not that neon monkey stuff on Hondas) that draw outside
air also give an improvement (Sport Compact Car did a test 1 year ago).

        A problem with your "blower" is that older cars (and E30 M3s fall
into this category) have an AFM, not a MAF.  The AFM doesn't know the air is
pressurized (has more mass) and will not adjust fuel properly.


- - Rob Levinson
'85 535i Turbo
'86 535i

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