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Old 02-23-2011, 01:41 AM   #1 (permalink)
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Planet Express Ship - '94 Geo Prizm LSI
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94 Prizm 1.6L 4A-FE 5-spd manual

I've had the car since October 2009, and its been my first car with a manual gearbox. I've put on over 25,000 miles since I acquired the car. My average F/E has been 34.52 mpg over that time with many tanks coming in around 37mpg but some lower. I currently have a highly variable commute as half the year I've been interning someplace where I've got a 106 mile daily commute and therefore have needed to refill the tank every two or three days to ensure I'm not caught short. The other half of the year currently gets spent commuting to university, and usually involves less driving, but also worse fuel economy, particularly in winter.

I've seen as high as just above 40 mpg but the alternator wasn't working properly at that time, the next highest I have achieved is 38-39 at 70 mph

I'm wondering what simple things can I do to improve on these baseline numbers. I'm trying to think of a way to seal some of the gaps in the body panels. I already try and coast in neutral with the engine running, or engine brake where possible to extend the time under way without using the brakes, however this isn't always possible around town here.

My mileage didn't seem to improve much if at all by slowing down to 65 from 70 mph (just around 3000 rpm). I can improve the results marginally off the cruise control with a light foot, but its usually not by much given the fact that with a manual the cruise can't really rev the car up and down as much or change gear as an automatic would have.

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Old 02-23-2011, 02:46 AM   #2 (permalink)
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Hi Hubert
I am new here myself,
and just learning
what i learned to day was that full smooth wheel covers have been tested to give 4% or so better mileage
http://ecomodder.com/forum/showthrea...-6-a-4368.html
that would give you another 1.5 mpg i think
they use pizza pans but im going to try the ones below shown..

http://ecomodder.com/forum/showthrea...ion-16179.html



apparently there are no quick and easy big jumps to be had ,, just many baby steps..
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Old 02-23-2011, 01:02 PM   #3 (permalink)
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Planet Express Ship - '94 Geo Prizm LSI
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The car has alloy wheels, so I'm not sure how the normal hub caps from a steel wheel would work, I could see some how modifying a pizza plate or other disk shaped metal object but then there is a question of how to mount them in such a way as to be easily removable when necessary, but not come off under the normal loading exerted while driving. This could also affect brake fade quite badly if you cut off the air flow across the wheel (which reduces drag) it can cause the heat from braking to remain soaked into the brake components reducing their effectiveness in an emergency situation.

I've been trying to shift to as high a gear as soon as possible, however in low speed situations rather than trying to over shoot then coast down I've been gearing down in the wintertime to assist the brakes should I need to stop on ice or snow, this I feel probably isn't the best technique for f/e however.

Since having changed locations at least once in the time I've had the car the new route to campus takes longer and involves nominally more highway cruising than before (albeit only 2-4 miles instead of the steady state 40-50 miles driven on the work rotation).

I'm wondering if I had enough time before classes to try and run this portion at closer to 2000-2500 rpm (which in this car is between 45 and 60ish) rather than accelerating up to 70 or trying to keep pace with traffic, although sometimes the right lane is going slow enough for it not to matter.

The car is OBD1 and has a toyota engine, ecm, and manual gearbox, therefore the scangauge won't work with it as far as I know, and I'm not confident enough yet with my wiring skills to tackle the opensource versions yet either, so I've been trying to make my metrics based on distance covered and fuel used based upon fillup logs, but recently I've noticed too much variation in the point in which one pump at one station clicks off relative to another elsewhere.

Apart from when I first learned to drive with a manual gearbox and my mileage was only 29 for the first tank it has never dropped below this except under certain winter conditions with short commutes when the car can never achieve normal operating temperature before setting off
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Old 02-23-2011, 04:10 PM   #4 (permalink)
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your questions about the wheel covers are valid .

look at my machine in the garage . i think the smoothie full moons will fit up nicely and may not look to shabby , what do you think.

there are strings i have seen where folks with the instantaneous MPG read outs have tested var. stratagem acceleration what not , sorry i can not link you to them.
a chart for your power plant is helpful
as you see my vehicle has no electronics , save a condenser in the points ignition.

a valuable informative and inexpensive tool/instrument to install is a vacuum gauge that detects intake manifold vacuum .

22$ from jcwhitney + 8$ install/tube kit
install is easy enough
then adjust ones throttle application in reference to that gage. on intake sensing the higher the reading in INHG the less application thus increase FE

full throttle [WOT :wide open throttle] one sees 0 [ZERO] on the gage . a more economical application 10 INHG .. even better 15 INHG . at full off throttle 20-25 INHG should be seen.
imagine a route requires on ramp to high speed divided motorway 4 miles to an off ramp.
on ramp merge see heavy power application to merge [5-10 INGH] use the proper methodology to shift up to top cog. when merged in high gear apply moderate application [15 INHG] at a level to continue to gain speed until the coast point to the off ramp is reached .. if that is 70MPH why not. the important thing for safety is to use proper merging to the motor way , if that requires WOT to match traffic speed that is what you must do no matter the effect on FE. once the motorway is attained as long as you are in excess of Minimum speed and in acceleration thats OK .
at the coast point reduce throttle application to such an extent that as you reach the off ramp you are at ramp speed , this might not be full off throttle just a reduction of application seeing perhaps 17-18 INHG

does that make any sense and appear to be proper methodology ?

w/o any o2 sensor and all that jazz i use a EGT[exhaust gas temp] to get an idea of the conditions in the combustion chamber. .. 1250 F would be an efficient and moderate application . 1300F getting in the power zone , 1400-1500 , heavy power poor FE . 1600 Do not exceed ..
on reduction of power the EGT falls immediate ..this is a more expensive instrument which i am just learning to use


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Old 02-23-2011, 11:31 PM   #5 (permalink)
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Greater vacuum means that the engine is under a higher load (ie is choked down more), the greater the differential in pressure the more negative work performed by the cycle in order to draw in the required amount of air. Engines operate best/most efficiently (at least under acceleration) when they are un-throttled and operating near their peak torque value. This is not a likely value for steady state cruising when you do want to try and have the least air coming in as possible so that if the car is running properly at the stoichiometric ratio of air to gasoline (about 14.7:1).

The whole point of a downsized engine is to allow it to be operated nearer to wide open throttle/ the more efficient point in these curves. I've been trying to find one for the 4a-fe, but have only found the 5h-fe which isn't going to be the same.

In one of my hybrid and electric vehicle courses at university I've played around with data for a hypothetical Fusion extended range electric vehicle powered by a honda insight 1.0L 3 cyl but in order to do the evaluations in matlab it required square data so some of the data was outside the actual performance of the engine just to fill in the matrix, so plotting the wot values is critical to see where those points lie.

I know that when the engine is cold its probably better to leave it in gear because as soon as it gets taken out of gear the car shoots back up to its fast idle for warming up/emissions, where as in gear it might be at that speed, but sometimes I can actually be running it smoothly below 1500 but above 1k in gear (although I fear this may be lugging the car's engine abit)
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Old 02-24-2011, 02:32 AM   #6 (permalink)
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Old Yellar - '79 MGB Tourer Drop-Hood Coupé
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i cant shift gears fast enough to operate at WOT in the lower gears i spend most of my time at cruise .

the greater the pressure differential the faster the charge velocity and better mixing
since at a given road speed gear combination speed the piston will continue to cycle at the same rate drawing less air and fuel mixture into the cylinder , i think when operating at 17 INHG manifold indicated and the valves close the air/fuel mix in the chamber will be at LESS THAN ambient until the compression cycle starts, i've never seen any data on the pumping losses to the energy cycle , so while the engine may not be operating as efficiently IE: converting a larger proportion of fuel energy into motion the net effect will be to burn less fuel / mile .

when you speak of downsized engines you are not speaking of either my or your machine , your 1600CC is rated at 105 HP my 1800CC rated at 62 bHP

that is unless your machine weighs 4000 Lbs

i would like a light weight carbonfiber air body 2+2 tare wight 500 gross 1000, 250- 500 CC superturbocharged and lots of gears , umm like 25 ,burn multi fuel : , when you pulled a grade it might pull down to 25-35 MPH but on the downgrade and on the flats fly..


there is a difference in language here.. you say that when the throttle plate is nearly closed the engine is under load.. old drivers think that when the throttle plate opens you are applying load to engine IE applying power to the gear train
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Old 02-24-2011, 11:58 AM   #7 (permalink)
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By downsizing I refer to newer vehicles, from the sub 1L 2 cylinder twin air engine being put in the new Fiats replacing a range of 1.2-1.4L engines to the 1.4L turbocharged engine in the cuze replacing a 1.8L na engine, as well as the turbocharged 2.0L ecoboost engine placed as an available option in the 4000+lb unitbody Explorer.

There are at least four critical efficiencies in the otto cycle engine:
η0=f(ηv ,ηc ,ηth,ηm ) (overall efficiency)
ηv – Volumetric Efficiency
ηc – Combustion Efficiency
ηth – Thermal Efficiency
ηm – Mechanical Efficiency

ηv=actuall mass flowrate of air / the theoretical massflow rate of an ideal engine of a given displacement
Therefore:
ηv= actual massflow rate of air/ (density*displacement*rpm)/(Z) Z is 2 for 4 stroke engines 1 for 2 stroke engines.

Direct injection as compared to port fuel injection can improve VE by around 8%
Gaseous fuels ( e.g. H2) displace more than liquid fuels

The pumping losses increase at part open throttle, (hence the greater vacuum pressure ie pressure differential). Yes by increasing the power output can be considered as one type of loading, that's speeding up the rate of combustion and reducing the pumping losses proportionally to how far open the throttle is. Most common rail diesels and some direct injected gasoline engines are eliminating the throttle plate and their "gas" pedal controls the rate of fuel injection directly rather than indirectly though the quantity of air inducted into the engine.
This can be seen in the chart I attached (it is however a bit fuzzy because the original pdf was too large)
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Old 02-24-2011, 05:16 PM   #8 (permalink)
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Old Yellar - '79 MGB Tourer Drop-Hood Coupé
Sports Cars
90 day: 25.83 mpg (US)

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theory, formula and charts/graphs can be illuminating , i would need to look at the language associated to understand.

i always liked the Classic fiat cinquecento, 21 bhp 1957-1975

the new units put out a *little* more

0.9 L (875 cc) TwinAir 85 PS (63 kW; 84 hp) @5500 3.6 L/100 km (78 mpg-imp; 65 mpg-US)


my unit is all analog 1950's technology ..

i am about to embark on quite the "Mad Scientist" or perhaps 1950's *souped up*
trial. i fitted a metered slow feed device to the intake manifold , when throttle application is decreased the feed rate increases ..feed various mixes in and see what happens , could be i melt a hole in the piston , could be a measurable effect or none.

run trials with light top oil , water /methanol mixes, top fuels [methanol/nitromethane 20%]...,, they way i go full trials will take 1000 miles .. i wonder wht will happen
but this is your introductory string and as a newboy myself feel bad about monopolizing it with my stuff the proper subject it to improve your mileage,
i do know the Vacuum gage when coupled with my analog SU HIF44 provides good info, , unsure about a fuel injected w/ computer controle
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Old 02-27-2011, 01:01 AM   #9 (permalink)
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The engine does have over 216k miles on it, and seems to occasionally go through a quart between oil changes, (sometimes when pushed slightly passed 3000 miles, but other times when I watched it every day on the days I was running 100 miles a day and did not notice the level drop on the dipstick for 2000 miles, or even past 3000 miles. I'm not sure what the state of the damage is or isn't, but I was really lucky to find this one when I did, even with the rust creeping in, the floor pan was pretty much solid, the engine runs well I think, although given I didn't test drive too many others I'm not 100% sure. If you can even find one its getting harder and harder to locate a good one for less than 2 grand, so I guess I'll try and take care of the one I've got.

I wasn't looking to get too crazy with the aero mods, at least not right away, just looking to see if my driving technique is working and maybe some small things that might make some difference in the longevity of the car and the fuel consumed. (I am not too terribly concerned about the absolute fuel consumption reduction for the sake of a cleaner planet, but rather looking to do my small part to not use more than I need to commute to be able to afford to go places, and do things like visit the amusement parks and ride those exciting rides more often with less direct expense and consumption to get there).
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Old 02-27-2011, 03:31 AM   #10 (permalink)
Smooth Operator
 
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Old Yellar - '79 MGB Tourer Drop-Hood Coupé
Sports Cars
90 day: 25.83 mpg (US)

Old Brown Ford - '91 Ford Bronco Custom

MAGNUM - '05 DODGE MAGNUM SXT
Thanks: 9
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thats good oil usage , i put in a pint motor oil every refueling usually and that is considered acceptable. with modern motor oils there are those who will go quite further between oil changes than the traditional . when i was a commuter traditional intervals would have required oil change every other month and i thought that excessive.
with a 32 year old machine like mine attention to rust issues are given,i repaired floor pans with stage 3 rust using hot lead , not the perfect solution but adequate .

i put a lot of miles on machines with power to weight of about 250 lbs/HP & 70 lbs/Lb torque , operating machinery like that will teach you the value of momentum and timing which i think is the essence . those types of ratio would put the new 84 Hp Fiat engine in front of 21,000 lbs, and the power in front of a generic 2+2 airbody of est 2800 lbs gross of 11 HP.They need to work on the torque though.
ratio like that would increase the time at WOT but i doubt the rate of acceleration would be acceptable to even the strictest of eco-driver

we have to drive whats available though and do the best we can with what we have.

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