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Facts and Myths About MPG's

13K views 67 replies 26 participants last post by  07CobaltGirl 
#1 ·
Dimples on a car does increase highway fuel economy
Drafting within 200 feet of a large truck does increase fuel economy
Driving with the tailgate down (not on cobalts :blink1:) decreases MPG
Electric superchargers have not been proven to help fuel economy
Those tornado or vortex things that go in the intake line do not increase MPG
Those "chips" that retune the IAT to 30 degrees decrease fuel economy
Anything claiming to increase your MPG by more than 3 is false
Vortex generators do not help mpg's on a cobalt at least
Gas treatment, fuel injector cleaners, things like that do help fuel economy but not immediately, more in the long run by keeping the engine cleaner
From what I have found using a scan gauge II auto computer that reads gallon per hour of fuel used, I have found that idling in neutral uses .1 GPH less fuel than drive
Coasting on a highway in 5th gear will read 0.00 GPH at roughly 2500 RPM depending on speed, but in neutral it will read .3-.4 GPH at less than 1200 RPM.
An intake and exhaust will usually increase MPG and HP and are pretty much the only two items that can legitametly increase both MPG and HP at the same time. The only reason the factory gives you shitty intakes and exhausts are to keep the cars quiet.
Underinflated tires can greatly decrease MPG so keep them inflated.
Low rolling resistance tires increases fuel economy
Weight reduction mods increase fuel economy
Streamlining a car increases aerodynamics and usually helps
From what i've found, is that using the AC at idle increases GPH by .1-.15 no matter what setting it is on.
Higher octance gas usually increases MPG but mostly on the highway
Magnetic fuel Ionizer things are garbage


Some other things that don't hurt MPG but some people claim that they increase MPG but these aren't really proven are tint (less strain on the AC), lowering the car (better aerodynamics), certain designs of spoilers, synthetic oil vs regular oil, higher performance battery and alternator (less gas to spin the alternator if it runs better),

The biggest ways to increase MPG are simply change your driving habits. That can be a new thread though.
 
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#2 ·
oh one more myth
water for gas which is simply shooting HHO into the intake line by creating electolysis in a mason jar full of water and baking soda to create the gas then sending a line to the intake. I want to try this and see for myself if it increases MPG but I haven't seen any claims saying it hurts mpg but then again I haven't seen any credible claims saying it helps MPG either
 
#4 ·
nice post...
 
#8 ·
The a/c results are from what my own mileage test showed. And mythbusters the first episode they filled up the tanks on their two trucks and simply drove to see which one outlasted the other, the truck with the taillgate up outlasted because with the tail gate up it allows for a vortex to be created just behind the window of the cabin and it shoots air over the tail gate, lowering the tail gate destroys that air flow. The best option though on a truck is a tonneau cover
 
#12 ·
see guys, alot of these things are simple comon sense, and some take a little thinking but thats it.

for example, it's obvious that staying behind a large truck (100 feet or under) will increase mpg because you have no more air pushing against your car. like driving behind a snow plow, so your car won't have to push the snow. "that one took a little thinking....lol"

it's also obvious that things that say, "increase mpg by 10 instantly!!" is fake, no matter what it is. If it is 3 mpg and under your fine.

Also very obvious that heavy weight will decrease mpg; don't drive with your trunk full of crap.

I heard that the best tires/rims are best to get is the doughnuts in your trunk!!lol id rather keep the looks then save the mpg...
 
#13 ·
Higher psi in your tires will reduce the amount of contact patch you have with the ground. This decreases friction and increases mpg. Narrower tires will accomplish the same thing.

Optimum psi? Well, that will vary depending on where you live and how you drive. During the winter I would run higher psi in Florida than Michigan because Florida is not going to get snow anytime soon. You really have to experiment with your psi to get the ride and mpg you are looking for.

NOTE: DO NOT EXCEED THE MAX. PSI PRINTED ON THE SIDE OF THE TIRE!!!! Yes, it can blow up, and yes, you can get someone killed.

Running on donuts instead of regular tires will get you higher mpg in town, but not hwy. Yeah, I tried it, just not on the balt. The reason for this is that out on the hwy you will have the wheels will have to spin a lot faster to maintain hwy speed. This will chew up anything you save. Anyway, it's not a good idea to use them even in town due to their limited life span.
 
#16 ·
wow will I can't believe you rolled on donuts lol, never thought of that. and good post about the tire pressure safety too. While working at my job, I have run into some cars that had as high as 80 psi in the tires and were limited to 50 psi!!!!! talk about stupid!!!

Camo, I'm thinking about trying to get some hail damage or maybe just use a ball peen hammer to get the dimple effect, what do you think? lol
 
#24 ·
in theory it would work, but I think it's just too small of a difference for it to be measured at all.
 
#26 ·
the waxing and claying thing. in theory it should get you better MPG because the car is smoother and has less drag. but, in reality it is probably too small of a difference to be able to measure better mileage from it. make sense now?
 
#27 ·
i wasn't sure if you were talking about that or dimpling, dimpling got a 3 mpg difference which I think is significant, they dirty vs clean car yeah not noticeable at all, in theory yes but little specs of dirt aren't going to catch enough wind to seriously create enough drag
 
#29 ·
Not to sound like Mr. Webster or anything, but they call it the "boundary layer effect". Have you ever noticed that if you drive your car when it's covered in dust it is still covered in dust when you are done, but a slight wind can move the dust? When you are driving air is smashed against the car where it forms a layer of slow moving air that sticks to the car. The oncoming wind glides over this boundary layer as it travels over the car. One of the biggest mpg losses is boundary layer separation. If the rake on the back of the car is too much the wind will break from the boundary layer and create turbulence in the airstream. This turbulence generates a vacuum which pulls on the car from behind reducing your mpg.

This is one of the biggest reasons that the Honda Insight and Toyota Prius look the same. It's the best shape for keeping the boundary layer in tact. It's also part of the reason I wanted the Coupe Cobalt.

Wow... That is more words than I have ever said at one time before...
 
#32 ·
First off, man up, that's not cold at all :laugh:. Come talk to me when you get -50F days.

Yes, cold weather does affect MPG. Cars account for the air they take in based on volume. The same volume of air will not be the same density depending on its temperature. Air is much denser when it's cold, so it stands to reason that a car takes in more air in the winter. To account for the denser charge the engine compensates by firing in more fuel. This is why you get more power and less efficiency in colder temperatures.

Colder regions also use winter blends of gasoline which are much less efficient than summer blends.
 
#34 ·
Dimples on a car does increase highway fuel economy
Drafting within 200 feet of a large truck does increase fuel economy
Driving with the tailgate down (not on cobalts :blink1:) decreases MPG
Electric superchargers have not been proven to help fuel economy
Those tornado or vortex things that go in the intake line do not increase MPG
Those "chips" that retune the IAT to 30 degrees decrease fuel economy
Anything claiming to increase your MPG by more than 3 is false
Vortex generators do not help mpg's on a cobalt at least
Gas treatment, fuel injector cleaners, things like that do help fuel economy but not immediately, more in the long run by keeping the engine cleaner
From what I have found using a scan gauge II auto computer that reads gallon per hour of fuel used, I have found that idling in neutral uses .1 GPH less fuel than drive
Coasting on a highway in 5th gear will read 0.00 GPH at roughly 2500 RPM depending on speed, but in neutral it will read .3-.4 GPH at less than 1200 RPM.
An intake and exhaust will usually increase MPG and HP and are pretty much the only two items that can legitametly increase both MPG and HP at the same time. The only reason the factory gives you shitty intakes and exhausts are to keep the cars quiet.
Underinflated tires can greatly decrease MPG so keep them inflated.
Low rolling resistance tires increases fuel economy
Weight reduction mods increase fuel economy
Streamlining a car increases aerodynamics and usually helps
From what i've found, is that using the AC at idle increases GPH by .1-.15 no matter what setting it is on.
Higher octance gas usually increases MPG but mostly on the highway
Magnetic fuel Ionizer things are garbage


Some other things that don't hurt MPG but some people claim that they increase MPG but these aren't really proven are tint (less strain on the AC), lowering the car (better aerodynamics), certain designs of spoilers, synthetic oil vs regular oil, higher performance battery and alternator (less gas to spin the alternator if it runs better),

The biggest ways to increase MPG are simply change your driving habits. That can be a new thread though.
ahh I need my gas to stop spinning the alternator! lulz, anything that is driven by a belt or your crank will release power and possibly increase MPG if upgraded to something lighter or something that spins easier..

oh yeah another thing that decreases MPG... fat friends
 
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