Instructables

How to Become a Hypermiler

Step 10: Aerodynamics and Modification

Aerodynamics are important to a car. It's hard to make a car better aerodynamically - but it's very easy to make it worse.

*Blocking your grille has proven to be effective - just remember that your radiator (and grille opening) were designed for the worst case cooling scenario. So monitor your engine temps and adjust your grille opening accordingly.
  • Fold your mirrors. If you can, fold your rear view mirrors in. Just be sure to stay in compliance with local laws.
  • Belly Pan - A significant amount of resistance comes from the open areas under your car. Covering them with corroplast or some other material can reduce your drag coefficient (Cd)
  • Wheel skirts - covering your wheel wells to keep your cars body one contiguous object can help
  • Air Dam - see image, if you car doesn't have one already, this can help
  • Always Drive with your windows up

The best thing you can do to help your aero resistance is to slow down. Resistance goes up with the cube of your velocity (holding everything else equal).
 
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M0HIZ1 year ago
Correction: air resistance/drag goes up as the velocity squared, not cubed.
Outlander6 years ago
No real pay off here. My old 87 Oldsmobile cutlass achieved 21-23mpg highway with a carbed 5.0L V8. This is one of the most non-aerodynamic cars ever made, but! A new V8 dodge charger only gets 17-18mpg. Something most likely a lot more "aerodynamic" than an old square 4000 pound muscle car, but yet it achieves even less fuel mileage. One the of the most aerodynamic cars, the smooth looking mid-late 90's camaros only achieved 24-28mpg. Aerodynamics has very little to do with MPG unless one is planning on driving 200 MPH. Sorry to be a negative Nancy, but it's true.
Aerodynamics don't matter until 200mph!? Try riding your bike behind a semi and then against the open air.
LMAO but true. that's why bike racers on Tour de France wear those helmets and not a block shaped one
trebuchet03 (author)  Outlander6 years ago
Once 4000 pounds of car is no longer accelerating (say you've stopped at your cruising speed of 70mph), it takes no additional force to move the mass of your car EXCEPT that of resistance forces coming from: 1) Rolling Resistance 2) Aero Resistance Ride a bike on a windy day and tell me that aerodynamics doesn't matter. You're comparing different cars, with different power trains and making a link to aerodynamics. That is what's known as a fallacy ;)
Not true again. an 87 olds cutlass vin 9, and some vin y's used the 4 speed overdrive 200-4R. Every single GM car has used the 200-4R and 700-R4(a less efficient but tougher trans.) since the late 80's up until the early 2000's The 4L60 and 80's are nothing more than an electronically controlled 700-R4. As for the engines, not much has changed, still 5.0L, 5.7L 90deg roller V-8. The fuel, electronics and induction has changed over the years, but still the same. Simply look at the EPA rated MPG figures for each. There is no major change, or difference. On some models there has been a change for the worse. As with the 4.6L ford. The fuel economy has dropped since going from the 5.0L going to the "modular" 4.6L. No real positive change. hope that makes some sense for you.
So, basically you're saying that if electronic engine control really makes milage better, or at least wasn't just an unnecessary complication, then a more aerodynamic car should not have lower rated milage, am I reading you right? Two things have changed: engine control and car shape. So assuming that the new engine control is better, it must be the car shape causing the lower milage. But since we know from experience that wind resistance does actually matter, we may have just proved that most electronic engine management is all smoke and mirrors. Another possibility is that you're quoting sports cars, which are generally tuned for downforce. Of course, downforce gives you more grip, but robs your straightaway speeds and fuel economy, which is especially obvious in stock car racing. I do know, though, that my dad's '93 Olds Cutlass gets embarrassingly close to a brand-new Milan's milage, with more than 120,000 hard miles on it's clock. There's something amiss there from a technology standpoint.
jimmytvf3 years ago
the side skirts and the belly pan are true, but i won't let the engine overheat for blocking the grille. The engine before the fuel. That's the first law of efficient hypermiling. Close the mirrors is even more unaerodynamic, are more flat sided than the rounded edge mirrors as if, and you'll may be fined too
trebuchet03 (author)  jimmytvf3 years ago
Cooling systems are extremely overbuilt to hand a scenario that includes driving through a desert (45C+ with very low humidity) under high loads (heavily loaded car, a/c on, windows down, etc. etc.).

If those are the conditions you always drive in - you potentially can't afford to cover. Otherwise, if you're driving in 20C weather - the thermostat is going to stay mostly closed to reduce coolant throughput.

From a heat transfer standpoint - you want to keep the engine at a relatively static temperature over a dynamic range of environments. In hot conditions, you'll need high airflow and high coolant flow. In "normal" conditions you can either have lower airflow or lower coolant flow. In cold conditions, you want both lower airflow AND lower coolant flow. Unless you're in that desert/high load class - you don't need 100% efficacy (mind you, that's not efficiency).
i'm talking about traffic jams that the engine in idle needs some refrigeration and if you block the air intake of the fan, the car overheats, because there's no other kind of air running through it. In highways, you're not idling, youre often running at 3000 rpm, and it generates even more heat, and if you block the air intake, the air coming through the radiator wouldn't be enough to cool the engine as designed. combine that with a fan that recirculates hot air through the engine. combine that with daily driving like running a/c and carrying people on your car like children and the daily shopping. That's not extreme conditions (the desert is), is daily driving
trebuchet03 (author)  jimmytvf3 years ago
If you're in a traffic jam.... There's no airflow anyway ;)

"youre often running at 3000 rpm, and it generates even more heat, and if you block the air intake, the air coming through the radiator wouldn't be enough to cool the engine as designed."

Firstly, heat generated is independent of RPM. Heat and load are correlated. It's a minor caveat - yes, on the highway, you will have more load than when idling.

Secondly - my earlier post stands. The cooling system is way overbuilt to handle desert conditions running all of these accessories (a/c, carrying people, cargo, etc.).  If you're not in a hot climate - you don't need all of the cooling capacity that the factory installs.

I operated my cars in South Florida where temperatures would frequent 35C - I had no problems. My car warmed up faster and temperatures leveled off around 95C (within the operational zone of specified by the mfr - in my case, Volkswagen)

I, among others, have not had issue. Blocking off the front of the car does not hermetically seal off the entire system ;) You still have some flow ;) As I said in the instructions - monitor your coolant temperature and adjust accordingly :)
"If you're in a traffic jam.... There's no airflow anyway ;)"

yes, but you force the fan to push more air than expected. The air cavities are designed to make a correct air flowing.

"Firstly, heat generated is independent of RPM. Heat and load are correlated. It's a minor caveat - yes, on the highway, you will have more load than when idling."

no. at more RPM, the more strokes you make, more explosions in the cam. that's why injection cutting was invented, to prevent overheating due the high RPM (yes you won't cut injection all the time, i'm talking about an emergency issue) and is more dangerous 3000 rpm when idling than on the highway (you have the fresh air that cools the engine to run properly)

"Secondly - my earlier post stands. The cooling system is way overbuilt to handle desert conditions running all of these accessories (a/c, carrying people, cargo, etc.). If you're not in a hot climate - you don't need all of the cooling capacity that the factory installs."

not so overbuilt as you think. people that live in the desert usually have issues of that. If you see tv show Extreme Trucking, all the grilles are blocked up to keep some warm inside. too much warm will be harmful for the engine

"I operated my cars in South Florida where temperatures would frequent 35C - I had no problems. My car warmed up faster and temperatures leveled off around 95C (within the operational zone of specified by the mfr - in my case, Volkswagen)"

you say 95C? 100C is the temperature of boiling water!. Agree with the coolant could handle 120C but is better have a little margin. That's why coolant is designed this way. the perfect temperature is around 80-85C

"I, among others, have not had issue. Blocking off the front of the car does not hermetically seal off the entire system ;) You still have some flow ;) As I said in the instructions - monitor your coolant temperature and adjust accordingly :)"

agree, but all of this will harm your engine. maybe not today, maybe not tomorrow, but the engine is not designed to handle this. sometimes is better spend a little more fuel that a brand new block
neffk3 years ago

Driving slowly should be the emphasis here. Folding in your mirrors may make you feel cool, but I doubt you could even measure the difference in fuel usage due to that. In fact, maybe you should try to measure.

http://www.youtube.com/watch?v=GC6FbiiTSec
crispy0105 years ago
Two words: pressure drag. The low pressure zone that forms behind moving vehicles is where most of your drag comes from. This low pressure zone is easily seen behind tractor-trailers on the highways on rainy days - look for the curling vortices of mist forming behind the trailer. The larger the low pressure zone behind your car is, the more your drag. However, without doing some serious body modifications or constructing very large items to attach to the back of your car (which are probably not street legal), there's not much you can do about it. If possible, buy a car with a contracting body, such as a Pruis or Honda Insight. A car body which narrows towards the aft will help reduce the size and severity of the low pressure zone.
trebuchet03 (author)  crispy0105 years ago
However, without doing some serious body modifications or constructing very large items to attach to the back of your car...

Which is why boat tailing wasn't mentioned ;)
One Link........ http://autos.aol.com/article/boat-tail-boosts-mpg/
what kind of pontiac is that??? looks like a two door hatchback cavalier
hellinabox4 years ago
It would prove additionally fruitful to lower the car and install stiffer suspension. A lot of performance modifications will improve gas mileage as well.
Very true!  I lowered my Astro van 3" and got an increase of 2.5 mpg or 10%.  This was my single biggest milage improvement.  I don't know if a more aerodynamic car would see the same benefit but it sure worked on my Astro
vandal11384 years ago
And best of all, chicks dig cardboard cutouts on geo metros!
rimshot6 years ago
I've heard of people using aluminum siding panels under the car to smooth airflow under there. I drive a Honda Insight (www.insightcentral.net) which has excellent areodynamic features. It has removable panels on the underbelly.
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