By adding Header, intake and cat-back does it make your fuel economy better or worst???? Also is there anything else that add hp and increases fuel economy???

 

ill say this: more horsepower=less fuel economy.
cold air intakes do help, but not really that much. if u want to add power and still have good gas mileage, get a fuel pressure regulator or something like it, it will help.

 

Technically those things should help your fuel economy because they help your engine breathe better, but since most people dont buy performance parts for fuel economy, the gas mileage does not increase, and sometimes go down because people like to go faster with these parts. I'd be interested to see the differences in gas mileage for the same car before and after installing performance parts but with normal daily driving.

 

there is a difference between gas mileage/fuel economy and efficiency. Yes, installing those mods will likely improve efficiency (and also emissions) because of the increased/efficient air flow. But, this does not translate into better gas mileage. These mods will undoubtedly hurt gas mileage.

To repeat what has already been posted... For these mods, more power = more gas burned.

 

it all depends on how you drive. if you drive EXACTLY the same as you did before (you wont), then its possible to increase your fuel economy. technically, those items dont introduce more air into the cylinder (they do, but thats not really where the power comes from, its too small of an amount to matter much) the power comes from reduced parasitic losses. the engine doesnt use as much power to pull air in and push exhaust out. the problem starts when you hear the growl of an intake. its very addictive, and you will be getting on it to hear it a lot more.

 

Yeah I agree, if you get a cold air intake then you won't drive the same. Even if you did the mileage won't go up that much and you'll basically have just wasted some time. its up to you man but its not really worth it to me.

 

actually no. you aren't getting most of the power from "improving" inefficiencies from the engine. The power does come from getting more air into the system. The engine isn't going to be more efficient because you are suddenly reducing restrictions in the air flow. the amount of "power" the engine uses to "pull" air into the system is a constant (mostly). the parasitic losses you are talking about is not in the restrictions to air flow it is in the moving parts of the engine. ie friction from crank, piston against cylinder, etc.

The engine "pulls" air into the cylinders through a vacuum that is generated as the piston cycles. This cycle will happen the same way everytime no matter if you have stock air box or CAI. So, by reducing the restrictions for air flow, you are able to get more air into the cylinder on that same stroke. This stroke will not suddenly become easier without air flow restrictions.. simply put.. the losses due to friction are many magnitudes larger than losses due to turbulent air flow.

Simply adding a K&N filter (not even talking CAI) you can easily get 30% (and higher) increase in air flow into the system. from chemistry we know that fuel must burn with oxygen and air is only like 22% oxygen. So a 30% increase in air flow means a 6.6% increase in oxygen. Now, I don't remember exactly but the oxygen required to burn gasoline is something like 12 to 1. This means that same 6.6% increase in oxygen will allow the engine to burn about 0.55% more fuel. Of course this is assuming stiochiometric (sp?) ratios.. this increase in fuel means more energy is released when it is burned, thus increasing power.

So unless you are setting up to run super duper lean, you will increase fuel consumption.

Edit: Also, when I was talking about effciency in my previous post, I was referring to volumetric efficiency.. not engine efficiency.

 

nope. sorry, i dont mean to be argumentative, but i have to point out a few flaws. first and most obvious is your math. if you increase airflow by 30% then all of the gas contents will go up roughly 30%. not 6.6. and (not being a smartass, just FYI) the stochiometric ratio is 14.7:1.

and if you remove restrictions in the exhaust, how would that increase air flow into the engine.and if you increased the airflow into the engine by 30%, (assuming fuel requirements and such are met) then power would increase by roughly 30%. and as for your theory of the lower restriction intakes not being why you get more power, try closing off your intake and see how well it runs. it will run like crap. because of the vacuum resistence on the piston going down. imagine a straw full of water. if you cover the top with a finger, the downward movement stops. if you let off the "resistance" of your finger, the water will drop easily.

i do definately agree that you lose more power from the moving parts, thats easy.

and the extra air coming into the engine is very slightly higher. its only higher because of density being higher due to the less vacuum pressure during the intake stroke. the difference is miniscule.

 

The Numbers
Fuel is burns only with oxygen which is only about 22% of air. You cannot add more fuel to the mixture because it won't burn. So the increase in the amount of OXYGEN into the system is only 22% of the 30% (.22 x 30) = 6.6%. The rest of the air is usually treated as Nitrogen which combines to produce NOx after combustion.

From chemistry, to burn hydrocarbons the chemical equation is

CxHy + zO2 = aH20 + bCO2

CxHy = hydrocarbon (gasoline). I'm not sure what x and y are for gasoline (don't feel like looking it up).
zO2 = oxygen. where z = the ratio of CxHy to O2. (z depends on x and y)
H20 = water and CO2 = carbon dioxide. Basic by products of burning hydrocarbons.

Based on this, any fuel that is burned is solely dependent on the amount of oxygen is available. Since Air is not 100% oxygen, you cannot say 30% increase in air will equal 30% increase in required fuel. In addition, there is the z factor that must be taken into consideration. It takes much more O2 to burn 1 HC. So, the 6.6% increase in O2 is then divided by the z factor which then results in the % increase of HC's that can be burned.

Exhuast
removing restrictions in the exhaust reduce the back pressure in the system and allows exhuast gases to escape easier. Every bit of exhaust gas still left in the system takes up space for fresh air. Because the exhuast gases do not contain any more oxygen (u've burned it all), this is a total waste of space. The exhuast gases mostly consist of CO2 and NOx but NO O2.

Intake Suction
The reason why your car runs "like crap" when you close off your intake is simply because your car is "choking". It is not getting enough air to burn fuel. If your car is unable to burn fuel, it does not produce power. It has nothing to do with vacuum resistance.

The straw example doesn't really apply. If you deprived your engine of air (like in your straw example), the engine would only work until all the oxygen is consumed. It stops because you are depriving the engine of a required combustible not because the vacuum is not allowing the engine to turn over.

Now, lets assume the engine can actually run without oxygen... the vacuum would not stop the engine because the power of the engine is much stronger than air pressure. The air that is already in the system after combustion (CO2 and NOx) would simply expand and compress as the engine turns. In the case of your straw, the only other force in the system is the air on the open end of the straw. So you see, atmospheric air pressure vs atmostpheric air pressure will obviously yield an equilibrium. In the case of the engine, it is atmostpheric (maybe a little higher) air pressure against a controlled explosion inside the combustion chamber. The explosion easily generates pressure 100's of times greater than atmospheric pressure.

Air Density
extra air going into the engine is not "slightly" higher and is not due to the vacuum creating more dense air.

ok.. check this out http://knfilters.com/facts.htm and scroll down to stock replacement filters section. The 2 graphs show an increase in air flow of 38% for flat panel filters and 61% for round filters. Ever car is different but this gives you the general range.. which is not "miniscule". My original 30% was actually pretty far off compared to the round filter.

Next, a vacuum only affects air density in a CLOSED space. Since your engine has an air intake (and exhaust), the vacuum does not increase or decrease density. What DOES change density is the temperature of the air. This is the other part of cold air intakes, to gather lower temperature air. The objective again, is to increase the amount of oxygen that the engine recieves so it can burn more fuel.

this post is getting long but it is a fun conversation. i am enjoying it.

 

ok. air flow is completely different than the volume of air getting into the engine. if the air going into a 1.8L engine is at 14.7 psi(i know im simplifying this, but the point is unaffected) then it cannot increase the volume of air without forced induction. the filters are able to flow a higher cfm, but that doesnt matter as long as the cfm of the stock filter is proportional to the volume the engine needs. the engine wil not take in more air than its own volume unless the density is increased.

ahh, but there IS another force at work. the force of gravity. and yes, it may still spin, but under what power? if the engine keep expanding and compressing the air inside, it will take more power than (lets go to the other extreme) spinning the same pistons on the same crank in the same cylinders with NO compression. and yes, the force of the one piston driven down by the force of the combustion is WAY higher than the resistance of the air being pulled in, thats why it runs. if it took more force to pull the air in than the combustion is making, then it wouldnt work. take that straw and suck air through it. then put a piece of cloth over the end and suck through it again. its a little harder huh. the same as your engine pulling air through a paper filter.

yes, that is the point of CAI, but it is colder compared to a SRI. not stock. look at the intake placement of a stock intake, it usually comes from outside of the engine bay, or some source of cooler air.

and im not arguing the chemistry (of which i have no formal training, but im well versed in the principles), but the math is wrong. if you have 100ccs of air, then (yes im approximating) 22ccs will be oxygen. then if you add 30%, which =30ccs of air, that adds 6.6 ccs of oxygen, right? thats 6.6% of the original air, not the original OXYGEN, of which it adds 30%. you said yourself that, basically, the rest of the gas doesnt matter, it will be ejected unaffected by the engine. so the only part you should measure the new oxygen against, is the old oxygen for your percentage.