Beating High Gas Prices Using Simple Aerodynamics (Home Improvement Store Edition) 

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12:20 Funny you mention the aerodynamics of that Mercedes, it's the EQS which is their first all-electric model. To help maximize the range they designed it to have the best coefficient of drag of any production car on the market at 0.20, so your callout was spot on

You should do coast-down tests. It is a very accurate and repeatable indication of drag. Certainly will be more accurate than depending on the vagaries of a fuel pump and the fueling/venting system on a car. Heck, the reason the gas pump clicks off on a modern car is more about the EPA-mandated evaporative control system on the tank and less about the fuel level in the tank. I bet you'd always get different fuel amounts pumped in just as a matter of course, even with all else held equal.

By sealing the underfloor, you reduced drag from turbulence but also created downforce (as you said it felt more planted) and thus more rolling resistance.

I love how you tried to make the car more fuel efficient and accidentally created a dirt cheap mod for more downforce on your car at the same time.

by increasing the length of the tail you increased surface area which means the air is attached to the body for a longer period of time. You would need to probably find a balance between the first tail and the second one to find your optimal length to curve ratio; i.e. find how much you can curve the tail before the air separates and that is a good as you can make it

When your gas tank is empty, it's full of gas.

Great video, and 17% is an amazing result for a car thats already quite aerodynamic stock. I have a Mercedes with air supension that lowers about an inch at 75mph, ive also lowered the car another inch. Now the car is more efficient at 80mph than it is at 60mph when the supension rises. It makes a huge difference overall, even the topspeed is higher.

Your experiments are done at a non controlled environment. This implies that changes in the wind speed , different temperatures, non exact driving or speeds can affect and alter the final results, being what we could say unexpected results. Very good on your part to try this out! It's the first time I see one of your videos and was fantastic! Keep it up :)

A Bluetooth OBD reader (~$10 Amazon) and an app like torque would likely be much more accurate for fuel economy numbers. Great videos, hope you continue this series!

I would love to see this become a regular series! You could also look into tire rolling resistance, and as side mirror regulations are changed, the effect of replacing them with cameras. I second the idea of finding a long downhill slope and doing a rolling comparison. This way you could compare different cars, even compare gas and electric cars! Could be an annual event :⁠-⁠)

You should try using a OBD monitor to measure real-time fuel consumption. In order to maintain a consistent weight you would still have to fill up before each test, but it would eliminate any noise in the data caused an inconstant fuel station pump.

You could always buy some Flow-vis (short for Flow Visualisation) is a paint-like substance used for aerodynamic testing during practice sessions in Formula One. A high-contrast luminous colour, it is applied to an area of the car - e.g. one side of the front wing. (Or make some at home!!)

if you dont trust the gas station, you can always fill up some petrol cans and get a very exact amount inside your car. loved this 2 videos! here in germany we have so many rules, you will never find out something like this by your own :(

You can still make the underside more aerodynamic just a matter of what you’re comfortable with. Some Miata race cars use ABS plastic sheets underneath to really smooth things out underneath. Off road race truck teams with bigger budgets take that into consideration and throw a giant metal skid underneath the cab. Also 15 degree departure angle for the bottom if I remember correctly with diffusers

I would also look at your turbulence under the tail, and have a look with tufts. It may be wise to add some vertical diffuser elements to the tail underside

I'd like to see this done on something super inefficient like a lifted silverado 😂

The original: It scooped up from the bottom more. The top part didn't rake down so sharply and the sides 'boat tailed' in sharper converging at a point just below the taillight level. Even, fully enclosed transparent wing mirror fairings? Maybe? Love these uploads btw :)

I would advise you too look at the viewing angles for the lamps to ensure the vehicle is still compliant. I dough it is! Further to this I know the rear overhang would be illegal in Australia as it can only be 60% of wheel base. Fuel consumption test are difficult to quantify unless you can weigh the fuel tank before and after test and ensure the comparison tests are done under the exact same conditions.

I think one of the reasons why the tail *seems* less efficient (but might not be) is the combined effect of the underbody bypass and the tail. The previous tail might have reacted better to the previous body kit, but this one might benefit more from the smoother airflow coming from the new system

Super interesting. I did some tests on a 3 tonne truck a few yars ago with an inflatable tail - inflated by the stagnation of the air at a duct on the top of the body. I didn't have very good metrology but thought that I had reduced the drag by about 5%. The inflatable idea was that when it was stopped the tail would deflate and have bungee cord in it that would collapse it down to a short length for parking. I had to rent the truck for the testing so I ran out of time and energy but I think it would work well. People often put stuff on the front of vehicles to aid aerodynamics - we have a thing called NoseCone in Australia but it is really at the wrong end IMHO. Avoiding the separateion of the boundary layer on the rear is waaaay more important than making the front rounded...

Another tip is to tape over all the panel lines and shut lines on the front of the car. People do this on racetracks to reduce drag a bit

Keeping your RPMs below 1800 will help a bunch. My 2022 has manual shift mode. When I get above 50 mph, I shift to manual and put it in 7th gear. BAM!!! 42+MPG with a bone stock Impreza wagon. Even @ 70 mph

I do the same thing with my bikes. Round tubes are terrible in the wind. Adding some foam and tape to the trailing edges reduces drag by 10x.

When flying, after polishing our small aircraft (115 Horsepower) We can expect around a 5-knot increase in it's cruise speed at 25 Liters per hour. This represents around a 4% increase in cruising speed. It would be interesting to see what would happen if you smoothed the rear material and polished the car. Also, perhaps putting the fuel units in L/100km as well as MPG might help appeal to a wider audience.

The commentary toward is probably more spot-on that you would expect. I'm the guy that typically doesn't refuel until the reserve light comes on, and I get to know my cars fairly well as I drive them and pay attention to things like fuel dispensed. There are some gas stations I simply avoid because they'll consistently dispense almost 10% more fuel than others in the area. In cars where I know when I'm almost completely empty, just how much should be filled, going over a certain amount is pretty obvious. I had one car with a 12 gallon tank that would typically take 12-12.5 when the computers range was in the single-digit miles remaining. On gas station would routinely dispense 13.5. Another gas station never dispensed more than 12.5. Unless you have some calibratable way to measure the fuel, I would recommend either only using one pump at one station, or doing multiple runs using different stations and averaging all the results together in hopes of reducing the significance of that particular mode of variance.

have you standardized vehicle weight, and tire pressure? Tire pressure can have a massive effect on efficiency. also added weight from more material at the back axle could be to blame. I would suggest adding lightness and trying to see how far you can slope the read down before you hit turbulence, as a shorter tail would also reduce weight, and improve axle balance.

Maybe add clear plastic tapered teardrop shaped covers on the mirrors aswell? See if that really gives you 5%

Great simple experiments, well summarized. To monitor realtime data, and collect data on vehicle performance; you could invest in an On-Board Diagnostic (OBD) dongle. This would allow realtime monitoring and collection of data on a mobile device (via wifi, or bluetooth). Data parameters available varies a bit by make, model and year, but often can view realtime fuel consumption, or estimate quantity remaining, as well as odometer readings. Logging would allow export to a spreadsheet for some fun maths. BTW: did you do a calibration check on tire pressure? This an often overlooked item and can make ~5% efficiency difference. Varies with temperature and seasons, so is worth checking once a month, or prior to efficiency runs.

I have an FA24, ambient temperature makes a huge difference. In the summer when I am driving in 70-75F in the morning and 85F in the afternoon, I see ~30-31mpg. Now in the fall, morning temps around 45F and afternoon temps around 60F, I am seeing 35-36MPG. Same route, no traffic, trying to average 35mph or 50mph on the backroads mileage is always about the same over 3-4 tanks, leaving me to believe it is ambient temp, or if the additives package has changed in the gas. On another note, I had a pickup truck that I put a downward wedge cap on to do a fluid dynamics paper on (emulating a couple that were already done), that alone improved efficiency about 10-15% on a regular basis.

Just wanted to share my mileage tests by saying when filling up the gas tank the only way I could think of to keep consistent was filling up neck so I could not put another drop in. So that worked for me, but some cars might have problems with smog systems. I was not testing pollution effects so my mileage worked just fine. I was able to get 27.6 mpg in my F150 but if doing a full tank to empty don't drink to much, it's a long drive.

**Looking at a car with a 6 foot aluminized foam tail** - "Car looks incredibly plain now..."

Legal or not, it could also be that the cops who followed you decided that they just didn't want to know; "No, nope, to close to end of shift/next break, etc...."

I think some of the efficiency losses may be because of side winds. Perhaps a shorter tail section would reduce drag in a cross wind. Also, may as well leave the back portion of the tail section off so that there's a clear view of the existing license plate holder. I think such a design is called a "partial cam back." (Not my words) it may be the side wind and driveability solution as it would be shorter and (perhaps) still have most of the efficiency gains. Very interested in this as a series. Kinda hoping for a more final version, perhaps made from fibre glass laid over an existing test piece. Also, may as well test the pointy front. I hear it's kinda bad, but have no numbers to tell exactly how bad.

Before the back addition, the curves helped with the airflow. You could try angling it more towards the bottom, so only the area with the license plate is flat and nothing else, and even that could be slightly angled (something like 15 degrees or less).

Filling in the rear of the tail surely hurt you a bit. The plate cover is a large surface for the low pressure wake to act upon. Remember that it's pressure region's acting on a moving body itself that contribute to drag! Having the tail hollow the first time around meant that realistically only the edges of the foam were subject to wake forces, with the gradient increasing to probably around atmospheric when you reach the body. With such a better optimized curve on the tail, you had way higher velocities at the bluff cutoff, so every square cm had an even more severe pressure drop to contend with vs the former. If you cant get a point (which you probably can't achieve efficiently anyways) find a way to leave her hollow!

I had a 2014 subaru impreza sedan cvt that i used for my 1hr commute that got a consistent 36.9 mpg, i now have a 2010 honda fit manual trans that gets 38.1 and am in the process of k24 swapping a 2011 honda crz in hopes to achieve 40 plus mpg with some tuning, this video was great to watch!!

Im guessing that the variance in the results from the gas pump come from the mechanism of the stop valve in the nozzle. Since its purely mechanical, it might not always fill to the same point each time. Ive noticed on my car that sometimes the amount it fills will be off by a half gallon or so when i fill the tank from the same mark. Awesome video though!

I hope these vids start seeing more traffic man, such good content, and you do enough work to justify it! Love your content, which i found thru Daniel's channel. Love all of your ekrano-esque creations btw, such a cool phenomena that seemingly NO ONE is taking commercial advantage of, yet, you and Daniel are making a whole series of interesting ground effect vehicles in a relatively short time frame JUST for the appreciation of physics and to 'feel' that effect! Theres so much intersting phenomena to behold, and all the micro details of each design can make or break the entire character of the flight... so cool! Keep up the awesome work buddy! Cheers from HTX

I could imagine that the new tail causes more drag, because the back area, where the numberplate sits is substantialy bigger. Without directly changing its size again, you could try to angle the surface at maybe 45 degree, effectively creating more of a tip, instead of a big rear stub. Do you have something like discord for better exchange of ideas?

Aerocivic (ex)owner here, as well as owner of one of the highest fuel economy Insights on the road (100mpg+). Happy to see you continuing to experiment.

my idea for the gas pump issue is the different grades of fuel, ie the ethanol content during the climate shifts throughout the year.

This is a really cool series! Maybe one day if this makes enough you could try to find a cheap and already teardrop-ish car and try to make it insanely light and efficient. Also the Mercedes was an EQS, the new electric one that I remember seeing in videos s year or two ago, but it seems they haven't gotten very popular, so that's a cool car spot!

Love these videos, it’d be great if you keep producing more. But don’t feel pressured to produce videos quickly and rapidly, take your time

i agree with your last comment about the pump not being as accurate when shutting off, you can get around that by using a fuel cell instead and measure by weight

A simpler test that will eliminate the most errors is a down hill coasting test. Others have mentioned it. And it can be done in other forms. Dead stop from exactly the same place on the same hill under the same weather conditions and simply monitor the top speed and coasting distance. Do this 10 times with the regular car to establish average deviation. If your aero works well the top speed will increase as well as total coasting distance. I bet the car in it's stock form will fluctuate +-3% or more so an increase of 17% without knowing the average deviation is more likely 10-14% in actual improvement. That's still very good. So keep going. Make sure all things are kept equal. Tire pressure, weight in the vehicle, weather especially wind conditions. If the wind or traffic turbulence fluctuates the air +- 3% that's not helping get good data. stay away from dirt it will very the rolling resistance, stay away from testing in traffic and avoid stops and starts in the test, that puts the engine in the worst efficiency rpm range and can easily be effected by the driver, also avoid turns as they induce turning drag and are also effected by the driver. Go straight down a hill and only measure coasting top speed and distance and a more clear picture should come from that. Good work keep it up.

*Cybaru

To accurately measure the gas consumption you gotta add a new little fuel tank attached to the fuel pump of your car and measure how many liters or gallons of fuel you use... I learned it from Joseph Newman

I might suggest using an OBD reader to get your air-fuel ratio while doing these tests, it's possible your car had richened it out for one reason or another causing more fuel consumption. Cars actively manage all of the conditions that make the car run and could be doing one thing or another to make catalytic converters heat up or cool down or a bunch of other things. I think averages from a set of tests using one variation for another would be a better indicator. Love the videos, 18% is incredible.

I know I am late to the party, but - do you know with certainty that when the pump at the gas station cuts off, it is always accurate ie. what about foaming, or more precisely, the splashing that trips the trigger? It only needs a single splash to cover the 'trip hole' in the mechanism, and you could be quite a way out... Just a thought. (I used to work on such mechanisms, and they are far from precision mechanisms. I reckon you would have to do, maybe, three runs and average them out (-:)~

Removing the skirting introduced more drag, than the ever-so-slight increase in efficiency of the new tail could hope to compensate for. The ground effect between the chassis of the car and the road, is ~30% of the total drag of a modern car! You were definitely on the right track, when you tried to address turbulence underneath the car. Another thing to address, (I'm sure you thought of this) is tire rolling resistance. Tire pressures make a big difference. When a car becomes this efficient, tire inflation pressure becomes a greater percentage of overall drag, in that it greatly influences rolling resistance. Ambient temperature also makes a difference. A cold tire on a cold road on a cold day has much more resistance, than the same tire at the same inflation pressure, on a hot summer day.

That Mercedes was an EQS. It’s an electric production vehicle and it’s the most aerodynamic production vehicle with a drag coefficient of 0.20

I think it's very likely you fill up to a different point every time. You'd probably need a more accurate sensor in your fuel tank, or a transparent hose that makes the fill status very clear. I've found for my 50l fuel tank, that filling from empty till the click, then letting it really settle and filling again till the click gives me am extra 3l of fuel. I've been tracking my fuel consumption for aound 50000km, 2500l of Diesel, and sometimes for no reason my sonsuption goes up by like 5%, even though I commute the same long route every day.

There's a video of a german guy who made his car more aero. It's called "massive drag reduction for family car" and he went up to 55mpg in the end on a way sleeker design. But he also started with an efficient car to begin with.

First off, great work on this. Hopefully your testing is consistent enough and over enough miles to make up for any driving or environmental differences. I also would recommend pulling the gas pump lever until it clicks a second time. As for the aero, I helped design the SAE supermileage car that went on to hold the US made car record of 3013 mpg. After several iterations of the car, we found rounding the edges on the features helped . Doing this on the edges of your tail and the rear of your tail would help, but is certainly tough to do with your materials. A 17% improvement is really good. You also have to considering that roughly half of your energy is going into rolling resistance, so really you probably improved the air drag by ~30%. I would see if you can make any "easy" improvements to the underside of the car. Also, make sure your tires are pumped up to near their max (read the sidewall, it probably says 44 psi or 52 psi max, so go to maybe 2 psi shy of that when it is cold. I have a 100 mile commute and I tracked fuel economy religiously with various variables. I found 1 mph faster in average speed would make my fuel economy go down by 0.8 mpg in a 2013 Mini Cooper S with the full factory GP aero kit (under tray and wing). EPA was 36 mpg highway I believe and I normally would get 40-42 on a nice day, with my record being 47.2 mpg when drafting a truck the one day that was driving particularly slow. I've generally found my best fuel economy in a vehicle I can get is about 40% better than the EPA rating.

When I am passed by a semi on the freeway in my RV I feel pressure first against it pushing me away and then towards it sucking me in behind. Those admirers of the car that stay next to it will have an affect on air pressure in front.

Really cool process in finding a airodynamic solution

I too really enjoyed this. Aero & efficiency are always on my mind.

Why not go full Ricer mode, add the stickers and the sponsors and don’t forget add colors. Red means fast and Green for efficiency , don’t ask me how the color works just Ricer science.

What i think what this video is when clicking on the video: A guy upgrading a car with high quality materials What it actually was: a guy upgrading his car with cardboard, styrofoam and duc(k) tape You did this very good!

To get beyond 18%, here is a suggestion. Some air will flow underneath the car even you put an air skirt in the front. Starting from the rear bumper, you can taper the underside of your tail addition. The angle of the taper is gentle. See 2000 Honda Insight or Chevy EV1.

There are so many variables with testing fuel economy. Two bigs ones, are the energy density of the fuel, and the octane rating. Both of these are legally allowed, from batch to batch, to vary by up to 6% for energy density and 4% for octane. Temperature of the fuel can also effect it's overall density and the temperature in the gas station tank can vary according to how long it has been siting. All of these can have large effect on economy.

you can check mileage with the onboard computer. drive say 80mph on a level road in a high gear. Use the same gear to compare. do several runs and note the windspeed and air temperature each time for every setup. If you get better mileage in worse or equal conditions then the better efficiency is confirmed. Onboard fuel metering has about 0.5% accuracy and can be offset if the tire size is not nominal but the tire size doesn’t affect the test obviously if all tests are done on the same tires and pressure (check pressure each time). The fuel metering can be adjusted through obd if offset but you don’t need that either since all tests are using the same calibration Note the computer mpg average over say 0.5miles. Each run on the same road preferably

Rear defuser the turbulence created by the ground effect adds drag so you need to channel and speed up the air going out of the back

it was a Mercedes EQS - we have them in UK a lot - soap bar shape is one of the most efficient drag ratio vehicles

I randomly discovered the 1st video, so excited to part 2!

The reason for fuel burn marks is how warm the engine is from start and how gunked up your stuff is. Internal airflow is majorly affected by air density. I live at 6k alt, and I go to 3k alt to enter a city. I notice the difference between both altitudes in every vehicle I drive. Morning is different than mid day in how cool an engine runs.

While you eliminate one variable by using the same gas pump you still have the issue of the automatic shutoff. It will never be consistent. You have a couple of options. 1. Drain the tank completely. Not sure if there is a drain plug on the tank or not. Once it is drained put a measured amount of gas in the tank. Then run the car until the fuel is exhausted. Then put gas in the tank, start the car so until the fuel lines are primed then drain the tank again and refill with the same measured amount of gas. Repeat drive with the aerodynamic changes. Another option is to put a small tank and pump in the trunk and move the fuel lines. Either way you need to know precisely how much fuel you put in and then run until empty.

Yo yo yo!!! - Please find a secluded hill and try out rolling in neutral. If you can’t rely on your pedal or gas pump input then just see how far your car rolls (with you in it of course) from top to bottom!!!! Your results should overhaul anything gas mileage might tell you since you know for a fact one is more air efficient

There is a point where increasing the length of the tail to prevent separation is going to have more total drag due to viscous effects, than just having separated flow.

It's critical that the front of the car is as smooth as possible to help maintain laminar flow so to that end it would be advisable to ensure that the front lights and grill area as well as the wiper blade area be as smooth and sleek as possible. this should yield significant gains.

The racing stripes are everything!

I am suprisded that the officer didn't say anything about you license plate light being blue, because in Claifornia, which I think is where you are located, that is illegal. Super awesome video and great areodynamics and engineering!

To get the most accurate data you should fill a Jerry can with a specific amount that way you can eliminate the pump errors. Then either run it till it quits and measure time or have a set time and check how much you have left, the first is probably more accurate than the second unless your tank is split

I’m getting a vw type 3 squareback, and I’m going to do something similar to see how well it can do. I’m going to use magnets from old pizza toppers to help hold it onto the car and make it removable. I’m going to use plastic so I can still see out my back window. And do side skirts, and maybe wheel skirts on the back wheel if I can. I’m going to do my best to paint and style it to match. Mostly for my 100mile drive to and from work (twice a month) to see if I can get the mpg around 32-35. Wish me luck.

That Mercedes you mentioned was a EQS. An sort of electric version of the S-Class. The car has a drag coefficient of 0.20.

my first thought watching this was pressure at the pump fluctuating giving you different fill-up results. i had a wrangler that would click pumps off early from the gas's bubbly "head" in the filler neck. i imagine even the same pump has varying pressure dependent on a range of variables. you might be able to use calibrated vehicle scales to measure weight pre/post trip. or do the inverse and run til empty ...

Your new tail is less efficient because ot the vortices created at the edges were the upper surface and the side surface meets. This is beacause your tapering angle is larger at the top surface than at the sides, creating two vortices similar to airplane tip vortices and these cause the excess drag. You can even see these vortices even at low speed in your smoke test at 11:42. Other input is that seapation is usually just a bubble, the airflow closes up after the bubble so it is not necesserily as big of effect as one might think. (Taillight covers are not so crutial.) So even if you have some separtation but if you manage to taper the tail of the car more your wake region can actually be smaller. As for the wheel arches you do not have to fully close them you can merely make the gaps smaller.

12:25 Mercedes EQS. Their flagship EV and the production car with the lowest drag coefficient ever.

If you want to avoid the complication of the tail light cutouts and potentially unwanted cop attention, I'm sure there's a trailer wiring harness available for that car. Then you could just plug in a second set of tail lights on the end of the tail fairing itself.

there are fairly cheap fuel push drains that you could install in the bottom of the tank and drain the fuel, like those used on airplanes

Fuel pump stops when substantial amount of bubbles reach the top of the gas line, the vacuum tube in the pistol is very sensitive there. I usually wait for the bubble level to go down and can pour in another liter (for an actual full tank), so each time it can be 2-3% random depending on the temperature, humidity and atmospheric pressure, so refilling until the pistol fires is a bit random. The MOST accurate would be filling it with a jerry can (metal one) and have some sort of a physical dip stick in the tube and still, you might get a difference because your cars tank is plastic and can expand/contract. Too much work to calculate the remaining 3% is you ask me. Cars with direct injection (piezoelectric injectors) know VERY precisely how much fuel was dumped depending on the RPM of the camshafts - performance of the fuel pump, as the fuel pump gasflow is knows for a given rpm and for how many milliseconds was the injector open. My car (Hyundai with a G3LC engine) gets a more precise reading than me filling the gas tank.

Couple of foam panels on the roof and walls will Help your echo problem super cheap egg crate stuff

The skirts you put on the front and sides simulate the function of a diffuser (shielding air flowing below the car from the sides and accelerating it at the rear, by opening up the way the air can move). A diffuser is used in Motorsport and notorious for creating heaps of downforce and comparably low drag. And I think here is the problem with the new tail. The 90° angle at the end is too aggressive and you get turbulent air and drag. Put your stripes beside the licence plate. If you gradually slope up the bottom of the tail as well, it should work much better. Nice video and crazy interesting thanks 😅

When your improvement is going to detach suddenly at 90 mph and everybody panically braking being scared of it will bump each other in disorder, you'll discover a russian saying "Кроилово ведет к попадалову" which means "Hacking workarounds are usually the shortest ways to face a big loss". Easiest way to get even 20 per cent MPG growth is just a gentle handling with your gas. Good luck!

For testing I would recommend measuring instant mpg, not trip mpg, and at as high of speed as possible to make the differences more apparent. If you can do 90+mph on that lake bed that would be much better. Calculating based off a trip introduces so many variables, not least of which is the driver. You might drive more cautiously with the tail, thus improving MPG.

Great work, and brilliant imagination, to figure out such cool ways to make your car so much more aerodynamically efficent.

Dimpling flat surfaces ( like a golf ball) helps keep air from sticking to the surfaces, In not sure how practical it would be to do on the parts you added but it does make a difference to the point that some advanced race engines have this aero trick in their intake systems

Sealing that underfloor even partially will still help As well a front splitter will also help over just that chin, also when building make sure it extends past the front firewall or from that front firewall to about 30mm past the front air dam Also a much better test for aero drag would be coast downs rather than long drives due to variability Also “vortex generators” are a fickle beast and mostly useless without complex cfd work You’d get much better results from sealing panel gaps Ana worrying about tire pressure and equalizing them

Interesting you mentioned the car felt more 'grippier' on the road with the initial test of the side skirts/front splitter. Maybe you realized this, but you DID make your car grippier. Not sure if you're familiar with the 'ground effect' phenomenon seen in race cars, but by blocking off the underside of the car you're creating a low pressure zone that effectively sucks the car to the ground. The neat thing is, there is little drag so it's a fairly aerodynamic process. If you're curious, check out the Lotus 78, a Formula 1 racecar from, well, 1978.

Best fuel efficient mod on any CVT Subaru Is changing that fluid if old, the thing will regain a couple of MPG, also new spark plugs, the new NGK ruthemium plugs gave me about 1-1.7mg extra. PS: I also own a 8th gen Civic automatic. You can get 40mpg pretty easily with no mods, I can imagine you could get quite a bit more out of it, it's a 1.8 liter 140hp engine, powerful enough and stock aero seems pretty good.

your difference can be result of many things including fuel density, air temp, type of driving attempted ( sprint or easy acceleration ) , etc. usually 10% improvement isn't considered unless it's having a significant quantity impact. For ex 10% of 1ml vs 10% of 1000 ml.

Yes use obd meter regardless of amount in tank will give very accurate reading. I have improve my driving with obd meter achieving 26km per litre. Over the manufacturer claim of 19km per litre.

After watching these two videos I decided to design a car based off of what you said in concerns to why auto companies aren't making cars more efficient. After making a sketch I commissioned a 3D model and had it tested in a wind tunnel simulation up to mach 1.01 (775mph) where it was stable. While looking into a few other things concerning vehicle manufacturing I learned that America has a strict law about fuel efficiency based off of the footprint of the vehicle (makes no sense). It's measured from wheel center to center, and if the vehicle deviates from a chart the Feds made, manufactures get fined $10 per 1/2" out of tolerance. And to get REALLY good aerodynamics, cars would have to be way outside of that chart tolerance. So the car I designed would have an additional charge of roughly $500 or more to the manufacture because it was to aerodynamic if I'm understanding that law correctly.

You can probably gain 20% efficiency by doing nothing more than planning your trips more carefully, avoiding unnecessary trips, and saving a bunch of time in the process. You can probably gain 10% around town simply by modifying the way you drive: accelerating more slowly, and driving more smoothly, and with a manual, ensure the engine goes into over-run more frequently, when the ECU cuts the gas completely. Avoid using the brakes unless absolutely necessary. The skirts make a huge difference, and so does smoothing the underbody: the two nicest things which also improve handling substantially, but more to the point, they don't look stupid. :)

Basically the EQS is your roll model of aerodinamics, it was just passing by to salute your efforts.

The problem I found with the newer imprezas for MPG is that they're overweight and underpowered, so you end up using more gas because you're pushing the engine more. 140hp is not enough to move 3,100lbs efficiently. This is why my WRX was able to do 38mpg or why the corvette is able to do 30-35mpg. Although both weigh more then the impreza, both have a considerably higher amount of power. Meaning that the engines are understressed when you are driving.

replace the mirrors with cameras, get slightly skinner and lighter wheels, remove roof racks (wouldn't have to weld shut you can just use a plastic filler cap), tape off the rear door handles, tape off portions of the front grill if you can without overheating. that's all the recommendations I have to improve mpg. still a 17.9% isn't bad at all. the Crosstrek has a 15.9gal tank and 34mpg highway. With these modifications and an increase of 17.9% will yield a 51.9mpg Highway coupled with a 15.9 tank means this car could theoretically travel 825mi on a single tank

Now all you need is a Vtech sticker to increase the HP.

I think the decreased efficency is because the backend where the license plate is atached is much bigger than on the first version and therefore causes way more turbulences.