balancing.

[jdbubb at ix.netcom.com (Dan Bubb)]

Well, I guess this is round three then.


----- Original Message -----
From: <mr.utility@highstream.net>

> Okay, round two...
>
> Quoting Dan Bubb <jdbubb@ix.netcom.com>:
>

> > >   As you are cruising on the highway, it takes less effort to stay at
a
> > >constant speed with a stock flywheel, because you have built-up
inertia...
> >
> > >Inertia is defined as the resistance to change it's present state of
> > >motion...  In this case, if the flywheel is spun at 4K, it is going to
> > resist
> > >a change in speed, either up or down, IF it has more weight to it, yes?
Then
> >
> > >that inertia will in fact save you more mpg, at a cost of mph...
> >
> > So, if I understand this correctly, greater inertia helps you to
maintain a
> > constant speed better and because of this your throttle is more constant
and
> > therefore you get better mileage?
>
> To be more specific, this should read ---"greater inertia helps you to
> maintain a constant speed more easily, and therefore if your throttle is
> constant, the inertia of a weighted flywheel will be higher than a
lilghtened
> flywheel, therefore more mpg."
>
>  Well, I can't argue with that but think
> > it's such a small change you're never going to be able to measure it.
>
> I did not say it was a huge drop, I just said that it would happen...
>
> The
> > flywheel may represent a significant amount of the rotational inertia of
the
> > engine, but not a significant amount of the inertia (both linear and
> > rotational) of the whole car, especially in the higher gears where the
engine
> > is only turning 3-3.5 times faster than the wheels.
>
> True, but the whole car does not push itself along, the engine does... And
if
> you improve the ability of the engine to maintain a given speed, then IF
it
> maintains a given speed, the efficiency is higher...

Well, that's it right there. You're assuming that constant speed provides
higher efficiency.
If you're really jacking in and out of the throttle then this is an
absolutely true statement.
Small throttle variations, where you're not provoking A/F enrichments, and
small speed variations are going to have small (really small) effects on
MPG. And making this small of a change in the overall inertia of the car
isn't going to make your speed that much more difficult to control. I'd look
elsewhere for your change in MPG


>BTW, the whole car does
> not have any rotational inertia to speak of, unless it is rolling end over
> end...  :-)

Cute! Tires, wheels, brakes rotors or drums, axles, CV's, gears......these
all have rotational inertia.
But, in the end it doesn't matter. Simple equations relate rotational
inertia to linear inertia for any mechanism so there is a sum total of a
car's inertia.

>
> > >From a purely physics point of view, baring frictional effects, if a
mass is
> > at a constant velocity (linear or rotational) it takes no energy to
maintain
> > that velocity.
>
> Do you engineer rockets or something?  We are on earth, where friction is
> king, and gravity its' gueen...  If that were true, I could coast from
> Oklahoma City, to Dallas without any trouble...  Even if I do not include
> friction, there is still gravity, prevailing winds, etc...  I am speaking
of a
> real world scenario here, or trying to...
>
> Clearly it takes less energy to accelerate a lighter mass, but
> > to maintain a constant speed requires no energy input so there is no
> > difference between a light flywheel and a heavy one.
>
> Ummm, like, what?!  We are talking about cars, not space ships...  It does
> take less energy to accelerate a lesser mass, which is why we are talking
> about all this mess...  To maintain a given speed DOES take energy, as
this is
> the real world we live in, not space...

Instead of just ridiculing the individual statements you need to read them
together.
It's necessary to start with simplified cases to teach the basics of physics
and then expand by adding additional factors.
Any physics book will tell you that a body in motion tends to stay in motion
and a body at rest tends to stay at rest. So,as I said ,"baring frictional
effects, if a mass is at a constant velocity (linear or rotational) it takes
no energy to maintain that velocity. No MPG difference here!
Now, we include the real world factors of friction. Bearing friction and
aerodynamic drag. A heavier flywheel has no advantage here either. There's
no way bearing friction is going to be less, but as I said it's
insignificant. No MPG difference here!

> > If you take into account frictional effects, bearing friction and
aerodynamic
> > drag, the lighter flywheel will have less bearing friction
(insignificant)
> > and the same aerodynamic drag (for all practical purposes), so, again,
there
> > is no practical difference between a light flywheel and a heavy one as
far as
> > energy input required to maintain speed and no difference in MPG.
> >
> WHAT!?!  Umm, no...  Take an 2.0 off the line in Wolfsburg today, drive
the
> snot out of it for 200K, and you will have a wear factor (what ever that
is),
> of 1.2 say...  Now, take an identical engine, under identical conditions
with
> the exception of a lightened flywheel, and you will have the SAME WEAR
> factor...  WHY!?!  Because both flywheels are balanced!  Neither will have
any
> effect on bearing wear!  The only way  there would be less bearing wear is
if
> the lightened flywheel magically removes the amount of bearing surface in
the
> engine, which it cannot do...  (screwy)

See, now you're taking statements out of context. I said nothing about
bearing wear! I said a heavier flywheel would involve more bearing FRICTION
and then pointed out it was an insignificant amount in this case.

>  Overall, I'd expect to see a slight increase in MPG from a lightened
flywheel
> > simply because you're accelerating less mass.
> >
> Depends...  What amount of time are you accelerating?  What amount of time
are
> you maintaining a given speed?  Answer these questions, and you will have
your
> answer, either way...

Yes, this is a primary point in relating MPG to a lightened flywheel (plus
the additional point made somewhere that with at lightened flywheel you may
be more inclined to be racy!) If you did a back to back test with the exact
same speeds and throttle pedal movement and no other changes to your, then
your drop in MPG may be relavent

>
> > >   Do you know how heavy a Diesel flywheel is in comparison to a gas
> > >flywheel?  Part of the reason is that they have a higher mpg is because
of
> > the
> > >higher inertia they have once up to speed...
> >
> > I disagree. Diesels get better mileage due to the higher energy content
of
> > diesel fuel and the more efficient diesel cycle. The heavier flywheel is
> > required because of the significantly higher CR of a diesel engine. More
> > energy/inertia is required to get the engine through the compression
stroke
> > and maintain decent idle quality doing so.
> >
> Re-read....  PART of the reason, not THE reason....  PART, say it with me,
> PART, Part, part....  There, I feel better...  :-)

I read, "Part of the reason...." And my response was, "I disagree." The
heavier flywheel makes no contribution to a diesel's fuel efficiency. Clear?

> > >  The reasons you cited for having weight on the flywheel are good
reasons
> > as
> > >well, but they are not the only ones...
> >
> > Sorry, your original statement that a heavy flywheel would increase
highway
> > fuel mileage implied that was the Primary reason for a heavy flywheel
which
> > is incorrect.
> >
> That is not what I said...  I said REDUCING the weight of the original
> flywheel would DECREASE your fuel mileage on the highway...  Patrick has
> agreed with my findings, he too has lost some mpg, at the gain of power...

No. Your original statement, long since snipped (not by me), said that the
heavy factory flywheel was there to increase MPG with no mention of other
effects. That implies, to me, that from your prespective that is the primary
reason the flywheel is heavy. You must have the original post somewhere.
Please repost.
Patrick's agreement is invalid since he changed to a 2.0 at the same time.

>
> > >David
> >
> > >PS  And while I read the Vortex quite a bit, I weigh that against
hands-on
> > >experience, as well as reading good technical sources (read that
> > >as 'accredited'), as well as long conversations with a good friend of
13
> > years
> > >who has been a mechanic for almost 40 years...  The one thing I will
promise
> >
> > >each and every one of you is if you can prove me wrong, I will admit
it,
> > >period...  I don't know it all, nor do I pretend to (hopefully) :-)  I
can
> > >only ask that if you do not agree/understand, please ask questions...
I
> > have
> > >not insulted anyone here, nor will I throw jabs at someone, even if I
> > >disagree, but especially if I do not understand...  I am here to learn,
and
> > to
> > >share.  I thought that was that this list was for...  Did I
misundestand?
> >
> > Ya know, I'm an engineer and I've spent way too much time thinking about
and
> > working on cars.
>
> An engineer of what?!?

Mechanical. BSME.

> Perhaps instead of thinking about cars, you should
> instead work on them , and experience a few things...  You seem a bit too
far
> removed from working on them daily, as I do...

Really? I'm a bit too far removed? Anybody want to chime in here?
I think I work on cars just the right amount. I don't have to work on cars,
I work on them when I want to which is pretty much most nights and weekends.
I've been working on cars since I was 14 and I'm sure to be way older than
you! I thnk it's a rash assumption on your part to assume that since I
disagree with you that I don't have much experience working on cars and I
can't imagine how my statements on the topic would be more valid if I was a
professional mechanic. After all, working on cars on a daily basis doesn't
give you a new insight every day. 90% of it is repeating the same old boring
 shit.

>And are you 'implying' that
> because you are an engineer, and I am not, that I am wrong?

No. I'm NOT implying or stating that because I'm an engineer and you are not
that you are wrong.
I'm simply stating that you are wrong!
You pointed out you were accredited. I pointed out I'm accredited.

>  I may only have
> two diplommas on my wall, but let's face it...  The most novel invetions
come
> from those who were not trained to 'know better'...

Unfounded opinion, but nicely said. Are you implying that because you're
untrained in physics or engineering that I'm wrong? ;^)

>  Maybe, I'm overly concerned about trying to help make the
> > Scirocco list technically correct and, hopefully, a huge step up on some
of
> > the laughable statements made on Vortex.
> >
>
> I applaud you on that, if that is what you are attempting to do...  I just
> hope that you are looking for the 'truth' in its broadest terms, and not
just
> in yours...
>
> > But, whatever.
> >
> >
> >
> No, not whatever...  I apologize if I seem heated, but you have 'implied'
that
> I am merely regurjitating what I have read on Vortex, which is not the
> case...  I am insulted by that, as I have not brought in any outside
comments
> into this discussion, as I don't know you, nor do you know me...    I ahve
not
> said, well, you suck, because your idea makes no sense...I have stuck to
the
> point here as much as I can, and I hope that you can do so as well...
Anyone
> can sling indirect insults if they do not understand, it takes someone of
real
> character to try to understand something that they initially do not agree
> with...
>
> Now, please stick to the point at hand, and I will not be insulted...

Well, I hope you're not insulted. I tried to respond in the same manner as
the statement at hand.

Dan