a possible way to improve mpg

It's true that when you "open up" the air intake system of a vehicle you get more power, due in fact that an increase in air will register with the computer and more fuel will be delivered to maintain the correct air/fuel ratio. Does this principle hold true the other way around? If you were to restrict the amount of air flow, would the computer deliver less gas to keep the air/fuel ratio correct, thus using less gas per mile. I thought of this the other day. The only part of it I can't understand is if this is true then why would a partially clogged air filter hurt fuel mileage. It is to my understanding that all newer vehicles have a preset air/fuel ratio that the computer must maintain. If you were to restrict air, will the computer not adjust the fuel to maintain this? Just wondering. Let me know what you think.

that is how your throttle works.

My question doesn't pertain to the throttle. Yes the throttle allows you, the driver, to control the amount of air that enters the motor, the computer regulating the air/fuel ratio delivering more gas, thus accelerating the vehicle. Anyone else have any theories.

there is a minimum amount of airflow that is required for the vehicle to remain operational. through testing at the manufacturer, they've deduced that amount, and that tells them what diameter the throttle body should be, and the intake tube. so restricting airflow will actually starve the engine of air and fuel, making it run worse and you will get worse gas mileage.

If you were to go out to your truck, take off the itnake tube, start it up, and stick something larger in diameter than the throttle body over the intake, you'd note that there is quite a decrease in functioning and it will be more likely to stop running.

so, don't downsize your intake. up-sizing your intake will actually help your efficiency believe it or not. it's not the mass airflow sensor that adjusts the amount of fuel entering the vehicle, it's more the throttle position sensor which does this.

btw, cold air = better gas mileage. it compresses better

I quote from a study done on this topic:

Driving with a dirty air filter in modern engines doesn't have a significant impact on fuel economy, as it did with older engines. While fuel economy didn't change, however, power output did. Both cars accelerated much more slowly with a dirty air cleaner. We drove both vehicles with their air cleaners restricted and found little difference in gas mileage with either engine. That's because modern engines use computers to precisely control the air/fuel ratio, depending on the amount of air coming in through the filter. Reducing airflow, therefore, caused the engines to automatically reduce the amount of fuel being used.

Hope that clears things up for you.

yes, but it requires more fuel to get more power out of restricted engines.

so you essentially rob yourself of horsepower, resulting in more gas used to get to speed.

If you were to go out to your truck, take off the itnake tube, start it up, and stick something larger in diameter than the throttle body over the intake, you'd note that there is quite a decrease in functioning and it will be more likely to stop running.

I don't know that I can agree with you on this. It would basically be like unrestricted air flow. This would allow the engine to basically get as much air that will fit through the opening of the throttle body. The only thing that I could think that would kill the engine would be in the process of disconnecting the intake tube you would disconnect the mass air flow sensor as well. Another point is I know the mass air flow sensor doesn't adjust the amount of fuel, but instead it carefully measures the amount of air flowing past it so that the computer can adjust the amount of fuel the engine needs to maintain the right ratio. Do you see what I'm saying. It would work in theory, but I want to know why it doesn't work.

the more work an engine has to do to get air the worse MPG think about a K&N less restriction and better MPG. put one straw in your mouth and seal your lips around it then go run as far as you can. then do it with out the straw. which one is more work per step? you have to work alot harder to breathe when your air supply is restricted.

It is simple physics. It requires a certain amount of energy to move something. That amount of energy will never, ever, ever change. That is it. Given the current setup of the entire driveline, the weight, tires, and engine of the XJ, nothing you will ever do will significantly change acceleration or gas miledge, except to make both worse (with the exception of major engine work-supercharger, stroking, etc). With this said, keep your vehicle well maintained and stock. I have a flowmaster and a cone air intake with a throttle body spacer, among other mods. My girlfriend's completely stock XJ is at least as quick and gets slightly better miledge. All of that crap is marketing garbage.

Driving with a dirty air filter in modern engines doesn't have a significant impact on fuel economy, as it did with older engines. While fuel economy didn't change, however, power output did. Both cars accelerated much more slowly with a dirty air cleaner. We drove both vehicles with their air cleaners restricted and found little difference in gas mileage with either engine. That's because modern engines use computers to precisely control the air/fuel ratio, depending on the amount of air coming in through the filter. Reducing airflow, therefore, caused the engines to automatically reduce the amount of fuel being used.

Click to expand...

Did nobody read that? Studies found that in newer engines, there was LITTLE difference in MPG because the computer keeps the air/fuel ratio the same. The difference was in power output. So you do not benefit in any way with having a dirty air filter or smaller intake cause instead of getting better MPG, the only thing you are doing is robbing your engine of its power that it normally has. I can see where your thinking comes from, but it will not improve your MPG.

Yes, what you speak of is true. But we're talking about an automobile not a boulder sitting on the edge of a hill. I quess a good comparison would be baking a cake. Your making a cake with 1/2 lb of butter,1/2 cup of flower, 2 eggs, "I'm not a cook". You want to make half of that serving size, so it would be 1/4 lb of butter, 1/4 cup of flower, 1 egg. Your just reducing the ratio to get the same product but a smaller size. In the case of the vehicle youd get less horsepower, less torque, but better fuel mileage.

so basically your saying theoretically it works but in actuallity it won't work. I just want to know why that is why I originally posted.

Regarding K&N filters providing less restriction upon an intake stroke consider the vavle opening size which is far less than any intake tube. Manufacturers allow for variances with a maixmum at sea level and maximum air density otherwise the computer would not be able to compensate for altitude etc and the engine would run to lean or rich and out of range. Many of the new cars and FI bikes these days cant even take a simple change to a K&N without a remap of the FI parameters if its even capable of compensating for the extra air, if not overly lean conditions exist and things start to burn. Choke off air and more throttle is needed to increase air again with more fuel as the other way not enough energy was produced to move the vehicle. Then consider a Diesel engine which uses no throttle butterfly, the air intake is the same on every stroke, the throttle position regulates fuel flow only. Theres no such thing as to lean or rich this way, only at some point to much fuel to physically burn and thats when the black smoke starts and high EGT`s. Like mentioned every quick fix for better fuel economy is a marketing scam. Go visit a Summit catalog and find some headers,mufflers,ignition,cam,intake,synthetic oil,Cold air intake etc all stating to give up to 10% better mileage. I throw it on my 83 chevy pu and I guarantee the 9mpg wont go to 15+ mpg, and it not just cause I have my foot in it all the time now from the extra power. More power is easy to obtain, better mileage for the most part isnt impossible, but nearly.
Just some things to ponder.

ok well while were on the subject of fuel mileage, "I hate to hijack my own thread", has anyone ever thought about mounting an electric motor and routing a belt from it to the ac compressor. I don't know if any car company currently or has ever done this, but I think that it is a good idea, and I don't think it will be long before you start to see it on the market. It would basically bypass the motor having to turn the compressor and allow you to enjoy as much ac as you wanted without hurting your mpg.

fspell220 said:

Yes, what you speak of is true. But we're talking about an automobile not a boulder sitting on the edge of a hill. I quess a good comparison would be baking a cake. Your making a cake with 1/2 lb of butter,1/2 cup of flower, 2 eggs, "I'm not a cook". You want to make half of that serving size, so it would be 1/4 lb of butter, 1/4 cup of flower, 1 egg. Your just reducing the ratio to get the same product but a smaller size. In the case of the vehicle youd get less horsepower, less torque, but better fuel mileage.

Click to expand...

Yep just like your throttle that what it does. its simple look and how your butterfly works sometime it restricts the air flow when you let up on the throttle and the computer compensates for this by putting in less fuel. resulting in less HP, torque, = less work done. but also less RPMs resulting in less distance traveled. I sugest a class in physics for ya. you end up with half a cake because you used half the products. that is not saving gas that is the same. you have to make two cakes to get the whole thing. now when cars get around 60 mph there is an increased amount of friction from air and it is not a constant thing it increases much faster at hight speeds.

Oh and the electric AC forget it once again it is all work and you engine (gas user) will turn that compressor some how. if its electric then the alternator will have to pull it. and then your jeep weighs more and you loose mpg with that.

fspell220 said:

If you were to go out to your truck, take off the itnake tube, start it up, and stick something larger in diameter than the throttle body over the intake, you'd note that there is quite a decrease in functioning and it will be more likely to stop running

Click to expand...

.

I don't know that I can agree with you on this. It would basically be like unrestricted air flow. This would allow the engine to basically get as much air that will fit through the opening of the throttle body. The only thing that I could think that would kill the engine would be in the process of disconnecting the intake tube you would disconnect the mass air flow sensor as well. Another point is I know the mass air flow sensor doesn't adjust the amount of fuel, but instead it carefully measures the amount of air flowing past it so that the computer can adjust the amount of fuel the engine needs to maintain the right ratio. Do you see what I'm saying. It would work in theory, but I want to know why it doesn't work.

Click to expand...

I said COVER the throttle body. that results in NO air getting in. it proves the theory that less/no air means running improperly. that's the exact same thing that a dirty air filter does, and the same thing that a smaller intake would do.

"studies show less horsepower, but same gas mileage..." now, think about that statement.
the common person, if they experienced less power than normal out of their vehicle, woudl be inclined to increase the pressure on the gas pedal so that they accelerate more rapidly. the result is lower gas mlieage due to the higher consumption of fuel associated with the simple act of stepping on the gas. Do any of you remember the 2.8 v6 that was used in 85 and 86 cherokees and comanches? notice that in a small car, with fuel injection, they're OK engines? put them in a truck/suv, and carbeurate them with a piece of shit carb (thus limiting airflow as well as efficiency), and you now have an under-powered engine in an "oversized" vehicle for that power output. end result, WORSE GAS MILEAGE.

so to state plainly, YOU WILL GET WORSE GAS MILEAGE IF YOU RESTRICT THE AMOUNT OF AIRFLOW INTO YOUR VEHICLE TO A POINT WHERE IT IS LESS THAN STOCK AIRFLOW.

I really am not trying to be an ass, but it needs to be made clear that restricting airflow is robbing the engine of everything you could name. i.e. horsepower, torque, economy, longevity (yes, that would be affected to since you have to rev higher to get to speed).

bottom line, don't do what you were thinking of. it's wrong.

sorry if I missunderstood you. now that you say "cover" your quote makes sense now about the engine cutting out and what-not. By-the-way, I don't know if you realize it or not but your caps lock key intermittently keeps sticking. Thanks for the advice.

if you care about fuel economy, buy a honda. my jeep gets 10-12 mpg and i don't care. i don't expect it to get bad a$$ mileage.

fspell220 said:

I'm trying to explain this as simple as I can. Basically it won't work now that I've thought of it more. I thought of the friction from air or (the drag coefficient) and the friction coefficient of the tires on asphalt. Alot of people will never get anywhere in this life if they never attempt to try. By-the-way, physicals was pretty easy for me, the hard part is trying to apply it to an aspect. Anyways, thanks for the input, I just wanted to get some second opinions on the subject.

Click to expand...

Well I am glad physicals are easy for you. I guess that means you can run pretty far with that straw in your mouth. Turn your head and cough!