Rolly Polly Physics... WAS Re: battery relocation question

[amalventano@sc.rr.com (Allyn)]

    this one is a tough call, i'd say it depends on your driving style and
the changes you're willing to make to it. placing the battery in the rear
will change handling characteristics as far as weight distribution goes.
placing in center will lower your polar moment of inertia, which will speed
up your turn-in rotational acceleration. this may be a bad thing if you are
used to your cars rotational response in turns.
    as a side note, why not drop the battery weight by like #20-#30? go
here:
http://www.stealth316.com/2-dynabatt.htm
dont jump on the dyna-batt, as that page points out that the 'real' model of
that battery is actually cheaper.
    i've been looking at polar moments alot lately, as i must minimise it as
much as humanly possible in the twin, while keeping 2 huge hunks of metal at
the front/rear of the car.
Al

----- Original Message -----
From: "Jason Adams" <roclist@accessconsulting.ca>
To: <haygood@aemail4u.com>; "Drew Teague" <roccnroll@hotmail.com>;
<rocco_crossing@hotmail.com>; <scirocco-l@scirocco.org>
Sent: Wednesday, February 26, 2003 2:58 PM
Subject: Rolly Polly Physics... WAS Re: battery relocation question


> I meant, "no matter how" as lower the c.g. if you can by whatever means,
> i.e. remove sunroof, remove headliner, swap glass to plexi, sit yer fat
ass
> lower in the car, and if you can mount the battery lower than the stock
> position.  All of these actions will lower the c.g. of the car, whether
it's
> practical, noticable, I won't say. I'm just talking hypothetically here.
I
> haven't said anything about altering the first moment of inertia here,
which
> would also occur with any of the afore mentioned actions.  Is it good for
> this? I don't know. What would be better? Placing the battery as far back
to
> help weight distribution, or closest to c.g. / c.m. to minimize rotational
> inertia.  This is an important question for me, not saying I know the
> answer, as my ice racer experiences large moments as I swing it through
the
> twisties on the track.  Insight from knowelegable folks is most welcome.
> I'm inclined to mount the battery at the front of the spare tire well
> (compromise between lowering cm and lowering rotational inertia) is this
> correct? However if I wish to lower the rotational inertia more would it
be
> better to place the battery between the rear shock towers, (closer to the
> yaw axis).  Or does this stuff matter at all because we are only messing
> with a small percentage of the total mass. BTW, in attempts to lighten /
> decrease rotational inertia (yaw axis) i have removed the bumpers.
>
> Ain't Newtonian mechanics fun....
>
> Jason Adams
> Fahrvergnugen Forever! ;)
> 84 rocco 16v
> 93 320i
> 98 Z71
>
> ----- Original Message -----
> From: "Haygood" <haygood@aemail4u.com>
> To: "Jason Adams" <roclist@accessconsulting.ca>; "Drew Teague"
> <roccnroll@hotmail.com>; <haygood@aemail4u.com>;
> <rocco_crossing@hotmail.com>; <scirocco-l@scirocco.org>
> Sent: Wednesday, February 26, 2003 10:19 AM
> Subject: Re: battery relocation question
>
>
> > So I'm sure it's not what you meant by "no matter how", but lowering the
> C.G. or changing the weight distribution by adding weight is NEVER a good
> thing.  Only mention it because I went ten rounds with some "engineers" in
> school about this.  Finally won the arguement on the skidpad.
> >
> > So yeah, lower is better, and further back is better.  Which one wins is
a
> good question.  Only reason I didn't use the spare tire well was because I
> keep a spare tire there.  Seemed like a good reason at the time. :)
> >
> > I'm a big fan of balancing weight distribution front-to-rear.  Maybe too
> much of one, but we may never know.  I kinda figure that compared to real
> sports cars, our cars are really far off on front/rear W.D, and not so bad
> on C.G. height.  Just an opinion really.  Within the year I plan to recess
> my battery into the trunk floor at the rear of the trunk, so I'll have
both
> accomplished before too long.
> >
> > BH
> >
> > --- "Jason Adams" <roclist@accessconsulting.ca> wrote:
> > >I would expect that lowering the c.g. of the car is good no matter how
> it's
> > >done, that being said the lower the battery, the better...
> > >
> > >
> > >Jason Adams
> > >Fahrvergnugen Forever! ;)
> > >84 rocco 16v
> > >93 320i
> > >98 Z71
> > >
> > >----- Original Message -----
> > >From: "Drew Teague" <roccnroll@hotmail.com>
> > >To: <haygood@aemail4u.com>; <roclist@accessconsulting.ca>;
> > ><rocco_crossing@hotmail.com>; <scirocco-l@scirocco.org>
> > >Sent: Tuesday, February 25, 2003 8:57 AM
> > >Subject: Re: battery relocation question
> > >
> > >
> > >> Just a quick question after reading this:  Would handling be better
> with
> > >the
> > >> weight closer to the ground (i.e. spare tire well) or farther back to
> > >> distribute the weight a bit more evenly?  Not having had much
> experience
> > >> with all this, I would imagine getting it closer to the ground would
> > >reduce
> > >> roll a bit, which I would think would be optimal.
> > >>
> > >> ...My $.02
> > >>
> > >> Drew
> > >>
> > >> **Drew Teague**
> > >> Harrisburg, PA
> > >>
> > >> `84 8v Rocco --  "Bruise"
> > >> `85 BMW 318
> > >>
> > >>
> > >>
> > >>
> > >>
> > >> >From: Haygood <haygood@aemail4u.com>
> > >> >Reply-To: haygood@aemail4u.com
> > >> >To: "Jason Adams" <roclist@accessconsulting.ca>,"Rhett Farnum"
> > >> ><rocco_crossing@hotmail.com>, scirocco-l@scirocco.org
> > >> >Subject: Re: battery relocation question
> > >> >Date: Tue, 25 Feb 2003 08:22:26 -0800 (PST)
> > >> >
> > >> >Deep cycle means you can discharge it more without killing it.  They
> are
> > >> >used for things like trolling motors on boats that do a lot of work
> > >between
> > >> >charges.  You don't need that.  You want gell cell.
> > >> >
> > >> >As for mounting position, don't just worry about countering your
> weight.
> > >> >These cars have over 60% of there weight on the front end.  Counter
> that!
> > >> >Put the batt as far back as you can get it.  The whole "centered
over
> the
> > >> >rear axle" thing is a mystery to me as well.  Sounds nice, but from
an
> > >> >engineering standpoint there is nothing magical about that area.
> > >> >
> > >> >The downside of placing it further back is that the further from the
> CG
> > >you
> > >> >place things, the harder it is to rotate the car in a turn.  If, for
> > >> >example, your car's weight distribution starts out at 65% front and
> 35%
> > >> >rear, you are 15% away from the ideal of 50/50 (which is itself
> > >debateably
> > >> >ideal, but go with it).  Basic numbers I ran a while back (so they
may
> > >have
> > >> >lost accuracy with time :) ), suggested that putting the batt behind
> the
> > >> >rear seat would make you something like 62/37, and putting it in the
> rear
> > >> >of the trunk did something like 60 or 61/whatever.  Keep in mind
that
> a
> > >> >difference of "1" there is huge because we are only "15" away from
the
> > >> >ideal.
> > >> >
> > >> >So there is an incentive to move it far back.
> > >> >
> > >> >As for the increased rotational inertia, that batt., when in the
rear
> of
> > >> >the trunk, is no further from the rear axle than it was from the
front
> > >> >axle.  The inertia gain is probably small compared to the inertia of
> the
> > >> >whole car, which is dominated by the engine hanging out in front of
> the
> > >> >front axle.  The increase in rotational inertia (really it's the
first
> > >> >moment of inertia we are talking about, to be tech-ish), would hurt
> you
> > >in
> > >> >transitions, but then the improved weight distribution would help
you
> in
> > >> >transitions as well as the rest of the turns.  Prolly close either
> way,
> > >and
> > >> >either way is better than stock, but getting the battery further
back
> > >than
> > >> >the rear seat is prolly a very good idea.
> > >> >
> > >> >HTH.
> > >> >
> > >> >Brian
> > >> >
> > >> >
> > >> > >----- Original Message -----
> > >> > >From: "Rhett Farnum" <rocco_crossing@hotmail.com>
> > >> > >To: <scirocco-l@scirocco.org>
> > >> > >Sent: Monday, February 24, 2003 2:17 PM
> > >> > >Subject: Re: battery relocation question
> > >> > >
> > >> > >
> > >> > >>
> > >> > >> So, is a dry cell the same as a deep cycle? Or are they
different
> and
> > >> >what
> > >> > >> is the best to run in our cars.
> > >> > >>
> > >> > >> ALSO, I am thinking of putting my bettery where the back
passenger
> > >seat
> > >> > >> would be inorder to counter my wieght and balance the car better
> > >while
> > >> > >> autoXing. What would be the best way to attach the box and where
> to
> > >run
> > >> > >the
> > >> > >> vent?
> > >> > >>
> > >> > >>
> > >> > >> Peace Out,
> > >> > >> Rhett
> > >> > >> Rocco_crossing
> > >> > >> '83 Rocco (autocross ready, 20 days till season opener)
> > >> > >> '92 Olds Cutlass Ciera (DD)
> > >> > >>
> > >> > >>
> > >> > >>
> > >> > >>
> > >> > >>
> > >> > >> >From: "Josh20V" <mkii@nycap.rr.com>
> > >> > >> >To: <scirocco-l@scirocco.org>
> > >> > >> >Subject: Re: battery relocation question
> > >> > >> >Date: Mon, 24 Feb 2003 16:35:06 -0500
> > >> > >> >
> > >> > >> >just as a side note, this is the one Im going with.
> > >> > >> >
> > >> > >> >http://www.jshouseofeuro.com/images/stinger.jpg
> > >> > >> >
> > >> > >> >Its a Stinger brand dry cell.
> > >> > >> >
> > >> > >> >24.9 lbs / 5" H x 6-9/16" W x 6-7/8" D
> > >> > >> >
> > >> > >> >Josh Able
> > >> > >> >www.JsHouseOfEuro.com
> > >> > >> >BrandNew Eurobumpers in stock
> > >> > >> >check out the forums!
> > >> > >> >----- Original Message -----
> > >> > >> >From: "Vince Royer" <vince@performancecarstereo.com>
> > >> > >> >To: "Joe Doty" <Joe.Doty@lcnetwork.com>; "Ryan H"
> > ><rhock99@epix.net>;
> > >> > >> ><scirocco-l@scirocco.org>
> > >> > >> >Sent: Friday, February 14, 2003 7:21 PM
> > >> > >> >Subject: RE: battery relocation question
> > >> > >> >
> > >> > >> >
> > >> > >> > > Just a note on all this battery stuff.  Here's my take:
> > >> > >> > >
> > >> > >> > > I wanted to get the weight of the battery right between the
2
> > >> >wheels
> > >> > >and
> > >> > >> >as
> > >> > >> > > low as possible to lower the center of gravity.  In the
future
> I
> > >> >think
> > >> > >I
> > >> > >> > > will cut out the well and make my own, but I'll wait for the
> > >stereo
> > >> > >work
> > >> > >> >to
> > >> > >> > > start that.  For now I dropped the battery box down into the
> > >wheel
> > >> > >well
> > >> > >> >as
> > >> > >> > > far forward as possible and scewed it down.
> > >> > >> > >
> > >> > >> > > I'm using 1/0 phoenix gold power cable, through a 350 amp
> circuit
> > >> > >> >breaker.
> > >> > >> > > I have a distribution block up front sending 4 AWG to the
> Starter
> > >&
> > >> >4
> > >> > >> >AWG
> > >> > >> >to
> > >> > >> > > the Alternator.  I used the battery I had, it has a vent
hose
> > >which
> > >> >I
> > >> > >> >routed
> > >> > >> > > out the bottom.
> > >> > >> > >
> > >> > >> > > I also have another neat trick.  I recently had my car
stolen
> and
> > >> > >really
> > >> > >> > > don't want it happening again. If a theif cuts your battery
> > >cable,
> > >> > >alarm
> > >> > >> > > goes bye-bye.  So I ran a second 8 gauge cable from the
> battery
> > >> > >directly
> > >> > >> > > into the main power input from the fusebox.  That way I was
> able
> > >to
> > >> > >> > > eleminate the old corroded wire coming through the firewall.
> > >> >Suddenly
> > >> > >> >all
> > >> > >> > > my electronic devices performed better - like all the
> > >> >bulbs/wipers/fan
> > >> > >> >etc.
> > >> > >> > > I guess I freed up some electrons, but the biggest thing I
> gained
> > >> >was
> > >> > >> >the
> > >> > >> > > security.  Now there is no way of disabling the alarm from
> > >outside
> > >> >the
> > >> > >> >car.
> > >> > >> > >
> > >> > >> > > Cheers!
> > >> > >> > >
> > >> > >> > > Vince
> > >> > >> > >
> > >> > >> > >
> > >> > >> > >
> > >> > >> > > -----Original Message-----
> > >> > >> > > From: scirocco-l-admin@scirocco.org
> > >> > >> > > [mailto:scirocco-l-admin@scirocco.org]On Behalf Of Joe Doty
> > >> > >> > > Sent: Friday, February 14, 2003 2:29 PM
> > >> > >> > > To: Ryan H; scirocco-l@scirocco.org
> > >> > >> > > Subject: RE: battery relocation question
> > >> > >> > >
> > >> > >> > >
> > >> > >> > > I used a bench vise.  Worked great!
> > >> > >> > >
> > >> > >> > > Joe Doty
> > >> > >> > > IT/Development
> > >> > >> > > joe@lcnetwork.com
> > >> > >> > >
> > >> > >> > > > -----Original Message-----
> > >> > >> > > > From: Ryan H [mailto:rhock99@epix.net]
> > >> > >> > > > Sent: Friday, February 14, 2003 1:30 PM
> > >> > >> > > > To: scirocco-l@scirocco.org
> > >> > >> > > > Subject: Re: battery relocation question
> > >> > >> > > >
> > >> > >> > > > All this battery talk brings about an interesting question
> of
> > >> >mine:
> > >> > >I
> > >> > >> > > > bought the cheapo Summit kit, what kinda tool should I use
> to
> > >> >crimp
> > >> > >> > > the
> > >> > >> > > > end connectors (battery terminal connections are
pre-crimped
> > >> > >already)?
> > >> > >> > > I
> > >> > >> > > > don't think my trusty wire cutter/crimper will work for 2
> gauge
> > >> > >wire.
> > >> > >> > > ;)
> > >> > >> > > >
> > >> > >> > > >
> > >> > >> > > > _______________________________________________
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> > >> > >> > >
> > >> > >> > > _______________________________________________
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> > >> > >> > >
> > >> > >> > > _______________________________________________
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> > >> > >> >
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