Actual test results for HP vs pressure.

[mark kibort <mkibort@xxxxxxxxxxxxxx>]

Message text written by INTERNET:bmw@domain.elided
>From: Joel Marion <zeitguy@domain.elided>
Subject: Re: Eram
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Joel, we just got back from the dy=
no
last week and did a few tests.  the 911 produced 200 hp on the dyno off t=
he
street
totally stock.  We then attached the eRAM to the airbox, leaving the
internal filter
inplace, and did a dyno run.   =

We measured a peak difference of close to 10 HP at 6300 rpm.   we did a
little test =

after ward with the eram running off a separate battery and their was no
differenc.
(you know, just .5 hp spikes up and down along the same curve.
IT WORKS ON A 911, WE ARE TESTING A M3 THIS WEEK.    =

As far as your analysis goes below, yes, I understand that the 400 watts
electrical
need to be replaced by the alternator , and by the way they are
traditionally more
efficient than motors of the same size, but the belt has some losses.   s=
o
, call it 1 hp like you  did.
Now the fun stuff.   .5psi increase in air density , if you work it thru
gas law results in a 3.3% change in =

air pressure which usually crosses to HP. we measured the air box for
vacuum at 6000 rpm and =

found a .25 to .4 psi vaccum.  We then connected the fan to the air box a=
nd
did a run again.
.5psi was measured as a pressure in the air box.  our net is in the range=

of 1 psi.    1 psi is close to =

7% change in air density.   Ignoring heating, this usually converts over =
to
HP.   You are absolutely right
on your analysis below.    If it was a total boost of .4psi then it could=

be 5 hp.   dont forget we measured
.5psi increase in the airbox above the .5 psi vacuum in the airbox. =

(slightly less, but not much)  =

Anyway we have tested 3 vehicles now.
928 v8  9 hp
911 6     9.5hp
honda civic  4 hp

We have the dyno runs on the web site if you are interested in pictures o=
f
the event.
no funny stuff, just run the car with , and then without, and then repeat=
.


Am I dense (pun intended) or would driving the car forward create this
kind of air pressure much more cheaply?

> - --- those not interested in E*ram talk can skip the rest of the post
- ---
>
>
> About the infamous e*ram, unless you have your A/C at max, your 500W
> high beams on, your rear window defroster on and your megawatt stereo
> blasting at 130 dB spl, etc, etc, if it only draws 30 A of current, the=
n
> the alternator will be powering it since it has enough capacity.  30A a=
t
> 14 volts is roughly 420 watts, which is about 1/2 horsepower.  So
> depending on the efficiency of the alternator, the power lost driving
> the alternator while the e*ram is running is about 1 hp (assuming about=

> 50% alternator efficiency).
>
> If the E*ram is capable of a 5hp increase on a 200hp engine (that's a
> 2.5% increase) then it means that the manifold pressure is being
> increased by roughly the same percentage, or ~0.35 psi, plus 0.05 psi
> more to account for the increased alternator drag.  So for the E*ram to=

> work it must be capable of boosting the intake pressure by at least 0.1=

> psi (for a net gain of 0) to about 0.40 psi (for a 5 hp gain in a 200 h=
p
> engine).  Just food for thought (and assuming it only draws 30A of
> current).  I'll let somebody else decide whether it really is capable o=
f
> these kind of boost pressures or if a hampster-powered unit would work
> better.
>
> Luis Marques
> '97 328i<

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