spridgets
[Top] [All Lists]

Re: Power to weight ratio

To: "Steven Fooshee" <sfooshee@clubrx.org>
Subject: Re: Power to weight ratio
Date: Thu, 20 Dec 2001 16:17:37 -0500
Cc: <spridgets@autox.team.net>
References: <110.a76ab1e.295385f2@aol.com> <3C223208.72E8FBFE@clubrx.org> <01aa01c1898c$5c0458a0$6601a8c0@ascutney> <3C22475E.E5FD82BA@clubrx.org>
Well the point of the original suggestion was to increase acceleration by
reducing weight, and the equivalent increase of total engine power. What I
was saying is that HP/weight ratio is rather superfluous, because
acceleration is a function of torque, as you so aptly agreed.

So if your Spridget engine originally put out 60 lb/ft of torque (??) at
3500 RPM your Torque/weight ratio was .0308 lb/ft per pound (assuming a 1600
pound car with a 350 pound person in it). Are you suggesting that for every
pound the person loses it is the equivalent of adding .0308 lb/ft of torque
to the engine? If so, then to add the equivalent of 1 lb/ft of torque you
would need to lose about 32.5 pounds. This makes some sense, but it sounds
kind of fishy if you solve it for another set of criteria - say you have the
same car with the same person and you had a B/O/P 3.5 (weighs about the same
as a 1275) in there with 150 lb/ft of torque. Now you have .0769 lb/ft per
pound and would only need to lose 13 pounds to gain the equivalent of 1
lb/ft of torque.

I have no idea as to the real answer - maybe there isn't one. Maybe it's
like the "how long is a piece of string?" question.

The "up a hill" problem is a combination of Torque and HP. HP to overcome
the resistance of the speed, and Torque to overcome the "acceleration" of
gravity (that's the definition of gravity - 9.8 m/s/s).

<dnw>
1972 Midget
1998 Safari
1999 9-3
1964 (Me)

----- Original Message -----
From "Steven Fooshee" <sfooshee at clubrx.org>
Cc: <spridgets@autox.team.net>
Sent: Thursday, December 20, 2001 3:17 PM
Subject: Re: Power to weight ratio


> David N Waldmann wrote:
> >
> > I think you're confused.
>
> Nope, sorry. :)
> >
> > Power to weight ratio can and will be anything, as you showed in your
> > example.
> >
> > What was being asked/suggested is a formula or statement that says "for
> > every ____ pounds removed or added it is the equivilent of 1 HP"
(actually
> > should be lb/ft, as the "midget racer" expressed).
>
> Right, I wasn't referring to the validity of the thought that power =
> acceleration (torque makes the world go 'round, y'know :). But saying X
> lb. = Y bhp is *exactly* the power to weight ratio. So gaining 1 bhp has
> the *exact* effect as losing 26.667 lb. of weight on the p/w ratio. As
> to the 40 billion variables that determine how the power, torque,
> gearing, and weight effect the acceleration of the car is a matter WAY
> over the simple (and genuinely meaningless, as you said) ratio that all
> the magazines like to list.
>
> >
> > HP is what determines your speed, because HP is an expression of
> > time/distance work. It makes no difference how heavy your car is if you
are
> > trying to make it go 120 MPH (well, actually you do increase the rolling
> > resistance very slightly), the only forces you have to overcome are wind
> > resistance and rolling resistance.
> >
> > However, Torque, expressed as lbs/ft, describes a weight/distance work,
and
> > will therefore determine how _long_ it will take you to get to 120 MPH,
or
> > how fast you can go up a hill (adding the overcoming of gravity to the
> > wind/rolling resistance force).
>
> I'm pretty sure the "up a hill" example would be determination of
> power. I'd have to think about it, maybe even read. . . Fizzix was a
> while back. :)
>
> --
> ~
> '94 FZR-600: Wants a brain.
> '90 GS-500E: Wants a heart.
> 'LXIX Sprite: Wants courage.
> '93 B-2200: Wants to go home.
> '87 RX-7 TII: Please ignore what's behind the curtain.
> Getting caught is the mother of invention.

///  unsubscribe/change address requests to majordomo@autox.team.net  or try
///  http://www.team.net/mailman/listinfo
///  Archives at http://www.team.net/cgi-bin/wilma/spridgets


<Prev in Thread] Current Thread [Next in Thread>