At 12:31 PM 11/14/2000 +0930, eric@erickson.on.net wrote:
>....
>Yep, the 'econoguage' or 'economy guage' was a big thing for a while here.
My '86 .... has one of these with markings for 'POWER' and 'ECONOMY'....
>
>Why couldn't they just call it a 'vacuum' guage and calibrate it properly
....
Oh, this is going to be fun! This topic is perfectly suited to this list,
covering a multitude of interests that should encompass every subscriber
here. Those with no sense of humor may "delete now". Those with
absolutely no electrical comprehension may delete now. Technical geeks may
warm up the printers. Long time list members should grab a beer, put on a
Jethro Tull or Pink Floyd album, and browse through names in the list
address book while reading this message. And WARNING, this memo could be a
real time waster if not deleted immediately. Did I cover all the
disclaimer requirements?
I'll get right to the meat of the matter ("obligatory LBC content" thread,
or at least "list" content). I guess this can be appropriate for this list
(staying on topic or not thread), as we spend a lot of time chatting about
changing final drive ratios and installing OD's (noise, economy, cost,
comfort, and durability threads), at least partly in the interest of fuel
economy (ficticious cost savings thread), and also the function and
calibration of dashboard instruments ("wobbly/misguided needle" thread).
For those of us who can figure out how to delete or ignore the unnecessary
verbage ("don't copy the whole message in the response" thread), this can
be a very informative tech article ("useable content" thread).
I once had a real fuel economy gauge that actually worked (contrary to the
"laws of Lucas" thread), and worked well (reliability/accuracy thread), and
I miss it, sort of (don't make them like they used to thread), as I lost it
when the car was vandalized (unlocked parking thread). This was no vacuum
gauge (current thread), and I actually paid good money for it as an after
market accessory (J.C.Whitney plug) in early 1975 (good old days thread),
about $50 then as I recall (inflation thread), just around the time of the
"first" oil embargo (fuel shortage/prices thread) and the beginning of that
silly 55 MPH national speed limit in the U.S. (ficticious politics thread).
I had just dumped a kit car (DPO and fake car threads) and was in between
MGAs (no LBC content because I didn't have one at the time), needed
something automotive to fiddle with (car addiction thread), and as usual,
thought this gadget might be appropriate technology at the time (snake oil
thread, but not snake oil). I wasn't interrested in the "power" range
(cams and carbs thread) or the shift points (current thread), but was
commuting 600 miles a week at the time (reliability and distance driving
threads), so I had some interest in determining the most economical highway
cruising speed (torque curve thread), regardless of the speed limit
(flaunting the law in the interrest of comon sense thread). Given the
opportunity I might buy another one today just as an interresting toy
(models and gadgets thread), but I haven't seen them in years (obsolete,
obscure, and unavailability thread).
The design and function of the instrument is interresting and quite simple
(much like our LBCs), as well as accurate (oh ye of little faith thread).
It has a round analog gauge (days of old thread) that gives a direct
readout in Miles per Gallon (too logical for today's society thread). It
is (was) available in two dial ranges, 0-30 MPG for the gas hogs (SUV
thread) and 0-60 for the economy cars (jellybean appliances thread), and is
intended to have the readout somewhere in mid dial for constant speed
cruising (aircraft in the movies thread). For the state of technology at
the time ("who wants computers in the cars" thread) everything is analog
(car instruments thread), nothing digital (computer problems thread). The
two essential signal inputs are fuel flow rate (obstructions and spillage
threads) and ground speed (cops and speedmeters threads), both of which
should be measured in a linear fashion for simplicity (more of the good old
days). The electrical function was to be a simple analog division, ground
speed rate (miles/hour) divided by fuel flow rate (gallons/hour) yielding
the economy ratio (miles/gallon). Simple math, even by today's standards
(poor schools thread).
The ground speed signal is generated (litterally) by a small permanent
magnet generator (generator thread) mounted on the back of the speedometer
(odd threaded connector thread) and driven by the speedometer cable (wobbly
needle thread). This generates a voltage (bad connections thread) which is
directly proportional to the ground speed (tire size and gear ratio
thread). As this doesn't require much current (dim bulb and dead batteries
thread) the generator is very small (generator vs alternator thread), about
the size of a large shotgun shell (gun lobby thread).
The fuel flow rate signal is created using a photoresistor (Princess Di
thread and bad/insensitive jokes thread) with a small light bulb
("dim-bulb" thread), and a little round ball on a spring (political change
of mind thread) mounted in the flexible fuel hose (hope it doesn't leak
thread) between the body and the engine (warm and cozy thread). As the
fuel flows past the ball it physically displaces the ball against the
spring (detents and carb balancer threads) with a distance that is
proportional to the flow rate. With the light source on one side of the
ball and the photoresistor on the other side (armrest in the middle
discourages intercourse thread), the position of the ball regulates the
amount of light (daylight savings time thread) getting to the
photoresistor, creating a resistance that is proportional to the fuel flow
rate (law of proportional reactions thread). The linearity of this device
is controled by the shape of the light passage apperature (small windscreen
thread). And of course this simple little device will not work on newer
cars (engineered to screw up simplicity thread) with excess flow fuel
supply systems (overpressure fuel pump thread) where the unconsumed portion
of the fuel flow is returned to the fuel tank (leaky check valve in fuel
pump thread).
The dash instrument is internally not much more than a simple galvanometer
(volt meter thread), where the indicator needle rotates proportional to the
variable voltage provided (faulty regulator thread), except that there is
some sort of current limiting circuit (faulty fuses thread) intended to
prevent the needle from hitting the hard peg at the top end of the scale
(non linear instruments thread) when the input signals want to drive it to
infinity (no ground on the fuel tank thread).
Now you simply wire these three devices in series in any order you like
(simple wiring diagrams thread), except to pay attention to the polarity of
the generator (pos/neg earth thread), and you have a functional instrument
(not yet calibrated). The small light bulb in the flow sensor is powered
from any ignition supply circuit (ignition switch thread), and no other
outside electrical connection is required, except for the instrument dash
lamp (dim bulbs and rheostats thread). Because the signal circuit is a
closed loop and not conducting current from any outside source (jumper
cables thread), any single point in the circuit can be shorted to the
chassis of the car (frayed wiring thread) with no functional effect. For
instance, one wire on the (instrument) generator can be connected to earth
at the back of the dash (good ground we hope), and one wire on the
photoresistor can be connected to earth in the engine bay (another good
ground we hope), and the chassis of the car will complete the circuit
(missing ground strap on the engine thread), eliminating the need for a
ground return wire (more bad grounds thread).
To calibrate the instrument (calibration thread) there is included in the
kit a small peg with a shoulder (plastic nail) with a precisely controlled
length (post war precision mechining thread). This peg is to be inserted
into one end of the flow sensor (fool the inspector thread) and taped into
place without installing the device in the fuel line (disconnected fuel
cut-off valve thread). This positions the small ball against the spring
(oil pressure relief valve thread) such as to provide the exact position
that would be attained with a fuel flow rate of two gallons per hour (slow
sipping econobox thread) for the high mileage unit, or 4 gallons per hour
(gas guzzling SUVs thread) for the low mileage unit (also tach reads double
RPMs thread). You then take the car for a drive and observe the position
of the instrument indicator needle (keep one eye on the road thread) as
compared to the speedometer reading (rashly assuming the speedo is correct
thread). With the flow rate sensor locked to a fixed flow rate (won't go
over 40 MPH thread), the MPG meter needle will move in linear fashion in
unison with the speedometer needle (tach same as speedo in top gear thread)
as the small generator creates a voltage proportional to the speed
(sticking voltage regulator thread). At 60 mph you want the new instrument
to indicate exactly 30 MPG, at 40 MPH exactly 20 MPG, etc, high mileage
unit example (wishful thinking thread). On the back of the MPG meter you
can adjust a tiny potentiometer (electric tach calibration thread) to
attain the desired reading on the gauge (lie as much as you like thread).
Electrically here the potentiometer is just shunting a portion of the
voltage/current around the galvanometer (ampmeter thread) to compensate for
variations in speedo cable drive speed in different cars (OD conversion
thread), so that you get the desired voltage/current for the dash
instrument regardless of the cable drive ratio (speedo conversion thread).
Once the dash instrument is calibrated you just remove the plastic peg and
install the flow sensor in the fuel line with hose clamps (emergency fuel
pump thread), and you're finished with the installation ("when is the
restoration finished" thread).
In operation this MPG meter has almost instantaneous reaction (bouncy MGA
fuel gauge thread) to changes in throttle modulation, as fast as the fuel
flow will change at the entrance to the carburetor (leaky float valve
thread). The instrument reading during accelleration goes very low, and
during decelleration goes very high, much like the vacuum operated
"power/economy" gauge (current thread sidebar). As such it is very
interresting to watch while you modulate the throttle (how far into the
"power" range thread), and anyone can achieve 59 MPG for a short moment
simply by lifting the foot fully off the throttle at speed (impress the
passenger thread), but that yields very little useful information about
fuel economy, because those conditions are short term and transient (like
some folks interest in this thread). The only practical use for this type
of indication is simply to discourage you from tromping so hard on the
throttle ("loud pedal" thread), which is why the power/economy gauges do
not have numbered calibrations on the face (late model MGB temperature
gauge thread), and why they are so easily supplanted by an idiot light
theory of stupid drivers thread). In fact the idiot light may be better
suited to that cause (some useful idiot lights thread) because it can also
be keyed to engine speed as well as vacuum level (distributor spark advance
thread), and so actually encourage you to use higher throttle settings at
slower engine speeds (tough on the bottom end thread) to keep the engine
torque closer to the power curve where the thermal efficiency is best
(power curve thread).
The real practical use of this MPG instrument comes at constant cruising
speed on the highway (does anybody really do that thread). Here you get a
readout of your exact fuel economy in realtime (appropriate computer terms
thread). As long as you continue at a constant speed in fixed conditions
(depends on the police population thread) the instantaneous MPG indication
is the same as the long distance average MPG result (useful information
thread again, finally). Perhaps the most important information gleaned
here can be the optimum cruising speed for best fuel economy (is this the
real world thread). As different camshafts yeild optimum torque at
different engine speeds (power purchase thread), various cars are also
geared to yield optimum fuel economy (remove two pistons thread) at
different ground speeds. When the national 55 MPH speed limit was imposed
(the not so good old days thread) it was widely advertised that Chrysler
corporation immediately started bulding their "49 MPH cars" (misleading
advertising thread), meaning that they were geared and tuned to optimize
the government mandated Corporate Average Fuel Economy (government
interference thread) in a lower average speed range than was previously
practiced (changing times thread). Unfortunately (depending on your point
of view thread) my 1975 Mustang-II was built to earlier practices (good old
days thread), so it turned out to get the best fuel economy at a constant
62 MPH (try explaining that one in traffic court thread), which is exactly
what I wanted to know.
The next thing you can learn from instantaneous MPG readings is what
happens to fuel consumption (sometimes more is better thread) when you hit
an upgrade and press the throttle a little more to maintain speed going up
hill (not letting the SUV pass you thread). With just a little practice
and a short learning curve you might watch ahead more (defensive driving
thread) and accellerate slightly before getting to the upgrade, so that you
can negotiate the hill at a reasonable but decreasing speed (depending on
who's in the rear view mirror thread) without pressing so hard on the
throttle. This is contrary to what a cruise control unit (lazy driver
thread) will do with the throttle modulation, but can in fact achieve
better fuel economy (prove it to me thread). Another bit of useful
information is what happens when you drive in a strong headwind (I didn't
know we were in Kansas thread) or tailwind (why did the chicken fall down
thread), and the optimum speed for best fuel economy changes, possibly
being a large change in either direction (back in traffic court again thread).
But IMHO the coup de grace on this list (foreign language thread, but only
if you don't speak French) would be to tabulate the real (without prejudice
thread) MPG effect at various speeds with and without overdrive engaged (OD
thread is obvious), and with a few different final drive ratios installed
in your MG (most desireable mod's and models of MG thread). Similarly one
could take the initiative to map differences in MPG related to various high
performance engine components, free flow exhaust, etc (more power = less
throttle = better economy thread), and maybe even investigate the theory of
incremental and cumulative fuel economy improvements through the use of
economy improving gadgets (snake oil ads thread) to the point of less than
zero fuel consumption and having to drain the fual tank occasionally
(useless jokes, endless run-on sentences, and overconsumption of bandwidth
threads). One might even aspire to the grand objective of finally
discerning the optimum cost-vs-benefit combination of components for
lifetime minumal operational cost of your MGB (this is the mgs list isn't
it?). One might also retire and grow old gracefully (old farts thread)
while attempting to achieve some minimal economic benefit (offset by other
important social benefits thread) for a dubious number of disinterrested
owners of useless old junk cars (flame suit thread). Then again, one might
also benefit by getting some sleep (dangerous drivers thread) rather than
sitting up all night corresponding on a mailing list (internet addiction
thread).
Zzzzzzzzzzzz.......,
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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