Ok guys, I need some hard evidence. I'm about ready to spend some money, so this is a serious question: Does a cold air intake and a free-flowing aftermarket muffler help mileage? Or, is just a claim from the manufacturers to get us to buy their wares?

Does anybody have first hand knowledge of before and after mileage tests on their vehicle using a cold air intake and a flowmaster, Magnaflow, etc. muffler???

Thanks, Jag

 

The stock intake is already free flowing, and making it more free flowing should have no effect on fuel economy. So are known to decrease fuel economy, in contrast to the manufacturers claims. A freer flowing muffler can sometimes help, but in practice, if you are doing these changes for fuel economy, it makes almost no difference. Performance mufflers tend to make you drive more aggressively because you will respond to the sound with more throttle. It does depend on the vehicle though. So if you leave your question vague, the answer is that neither will help fuel economy. If you are specific about a vehicle, the answer might be different.

 

When it comes to intake and exhaust it helps to think of the pistons as air pumps(not much of a stretch really). As the piston moves down it creates a vacuum and draws air in. This vacuum resists the piston's downward travel and causes it to work harder. Then on the exhaust stroke the piston is shoving the air out. If it can't get out fast enough it compresses and resists the piston's upward travel. The better flowing the intake and exhaust the less resistance there is and this is where any gains are made in HP and/or fuel economy, but this isn't a hard and fast rule and you can go too far. Auto companies spend lots of time and money developing their cars and fuel mileage is a big area of competition. However they also balance it with performance and comfort. People usually want quiet vehicles so there is some small room for improvement for those willing(or wanting) to listen to a louder exhaust.

I don't have specific first-hand knowledge with any company because I've never had the money to plunk down, maybe a google search can provide more info. Obviously they can't make false claims by saying their product will give you better mileage when it won't but if you read close you'll see a lot of times they say something more like it CAN make an improvement and making generalized statements so read the claims/descriptions carefully. Larger big-name companies will better develop and test their products so they might not be total BS. If you do get a new intake get a true cold-air intake that's completely sealed off from the rest of the engine compartment. A better flowing exhaust sucking in hot air thin air from the engine bay can end up being a wash and because there's not a ton of room for improvement you want all the help you can get.

 

Thats not really true. A lot of people try to look at engines as simple air pumps, and to look at the simple diagrams they were taught in school as fact.

In reality, the engines use a complex set of timing designs to move more air more efficiently than a simple pump mechanism.

1. Lets start at the intake stroke. The piston is sucking in the mixture, but the air that is flowing in has already been set in motion by another force that I will have to come back to.

2. The piston moves upward to compress the mixture. Interesting thing to note, the intake valve has not yet closed. If the intake valve closed the moment the piston reached the bottom of the first stage, it would not take advantage of the velocity of the incoming air. By delaying the closing slightly, it allows more air to get into the engine. The intake valve closes sometime after the compression stroke begins. As the mixture compressed and reaches the center position, the spark plug fires. This is so that the flame front has time to propagate by the time the next stage begins.

3. The burning mixture begins pushing down on the piston transferring its power to the rods, on through the crankshaft, through the transmission, driveshafts, differentials, and on to the wheels. Before the piston reaches the end of this power stroke, the exhaust valve opens. It opens a lot sooner than you might think. This allows the expanding gases to start propelling themselves out of the cylinder. By the time the piston reaches the end of this stroke, the cylinder will be mostly vacuum.

4. Contrary to popular belief, the piston never pushes exhaust out of the cylinder. The exhaust propels itself out of the cylinder before this stage even begins. There will still be some exhaust in the cylinder, but the speed and velocity of the exhaust that has already left creates a vacuum in the remaining mixture which helps pull the piston upwards. This is a very efficient design, because it prevents the power and inertia of the engine from having to be wasted on this task when waste energy from the exhaust itself can be used for that task. The vacuum that is produces is so complete and effective that before the exhaust stage ends, the intake valve opens. The low pressure in the cylinder and upper exhaust draws some of the fresh air mixture into the cylinder. This gets the intake mixture in motion to that it wants to flow into the cylinder instead of having to be pulled in. This whole design is to maximize the volumetric efficiency of the engine.

So as you can see, thinking of an engine as an air pump is not entirely true. Yes, it moves a lot of air, but it actually moves more air than it appears it should on first glance, largely because an engine uses a complex dance of valve timing. Have you wondered how engineers keep getting more power out of engines? Well now you know a large part of it.

It is absolutely true that you can in theory improve things, but how much affect it will have on fuel economy is a different question. The maximum fuel economy point of an engine operation is under light throttle, low RPM conditions. Under these conditions, the throttle plate is restricting the incoming air, so how free flowing the intake is is irrelevant, and much of the same could be said of the exhaust. In fact, in an ideal world, you would actually want an exhaust that could change its size. Under light throttle operation, most exhaust systems are actually too large in certain parts. A smaller size close to the engine would allow greater velocities, which would in turn create greater vacuum during the exhaust and overlap phases. However this would create backpressure as RPM and throttle increased, limiting power. Since a variable sized exhaust has not yet bee developed, manufacturers choose a happy medium pipe size, so that you get the best of both worlds with as few tradeoffs as possible. Improved head designs and valve configurations, along with technologies like variable valve timing, allow the engine to operate nearer to peak efficiency under more conditions.

Among the things you can control or change, a larger freer flowing intake will have almost no positive effect on fuel economy. However it it can more efficiently flow more colder air, the user can use less throttle because the air will be more dense, and the computer can use more timing advance, which allows it to use the fuel more efficiently. So if properly designed, a good cold air intake can yield a slight improvement in fuel efficiency if it can help get more colder air to the engine.

On the exhaust side, freer flowing mufflers can help increase fuel economy, if they are properly sized. All to many people upgrade the size of the pipe, and this can improve performance, and can decrease fuel consumption under acceleration and heavy throttle, but can sometimes decrease fuel efficiency under light throttle and cruising conditions. If fuel economy is your goal, the stock pipe is more than sufficiently sized, all that needs to be changed is the muffler itself. The best type is a straight through type muffler with sound absorbing material. Baffled and chambered mufflers are designed to create noise, but often slow down the exhaust as it passes through, an effect that is not desirable from a fuel economy or performance standpoint.

As far as the other exhaust components, headers, particularly long tube and triple-y types are very effective at maximizing the efficiency of the exhaust scavenging effect. Whether they improve fuel economy can be a mixed issue. In many cases they can, but in some instances they can create over scavenging, where the vacuum effect is so strong that during the overlap phase, they cause an excessive amount of the fresh fuel air mixture to be drawn through the cylinder and into the exhaust.

High flow cats can help improve both performance and fuel economy, but it has to be understood what a high flow cat really is. Most cats sold as high flow cats are nothing more than ordinary cats. They have little or no benefits over the factory cats, since their internal structure has similar density and cross section to the factory unit. If anything, their smaller cases might make them louder, but the actual airflow through them is the same or slightly less than the factory unit. Real high flow cats on the other hand use lower density cell structures and increased precious metal loadings. This allows them to flow more freely while still giving the same level of efficiency as a standard converter. The benefits are still more conducive to performance gains than fuel economy, but they will not inhibit fuel economy. On engines that have valve and cam timing profiles designed to factor in converters, they can maintain fuel economy better than a straight pipe. They can also prevent over scavenging. Since they burn unspent fuel in the exhaust, while this is an issue of controversy, I belief that this effect increases the velocity of exhaust, which can help increase volumetric efficiency, especially at low RPM.

All said and done, I believe that you can improve on the factory design. But if fuel economy is your goal, that is a very fine line. Many performance mods will offer little or no improvement to fuel economy, or can decrease it. Make sure you have a good grasp on the effects any change will have, and realize that some mods will cost a lot more than fuel. Take headers for example. A good header can cost upwards for $600 for the headers alone, and extra for installation and/or modifications that need to be made to accommodate them. Headers that have large collectors will increase top end performance, but could harm fuel economy, so select headers that are more cleverly designed. You can buy a lot of fuel for the money you could sink into these types of upgrades.

 

Unfortunately Fuel Economy is a bag of worms. There are way to many variable thats why K&N doesn't guarrantee a fuel economy increase, However there are many users that have seen increases in economy if you would like to see the testimonial click on the link below.

K&N Customer Feedback

Simply put there are many factors that conrtibute to it thats why most people refer to the engine as an air pump in its simplist form. In the Quote below its stated that the "throttle plate is restricting the air flow coming in therefore a free flowing intake is irrelevent." Well thats not entirely true the factory intake system not only reduce the restriction which allows the engine to draw in air with less effort (picture a marathon runner with a coffee straw in his or her mouth) the intake system straightens out the air flow and removes the turbulence. These factors allow the enigne to increase its Volumetric Efficiency. Ultlimately the intake system makes its biggest improvements in performance underload at WOT.

At the end of the day if you drive with your foot to the floor don't expect an increase in MPG. If a K&N system is made for your vehicle give it a try you have nothing to loose and everything to gain.

It is absolutely true that you can in theory improve things, but how much affect it will have on fuel economy is a different question. The maximum fuel economy point of an engine operation is under light throttle, low RPM conditions. Under these conditions, the throttle plate is restricting the incoming air, so how free flowing the intake is is irrelevant, and much of the same could be said of the exhaust.

 

Factory intakes are restrictive at the expense of flow for noise reduction reasons. Same for the exhaust system.

 

Not even close to factual.

 

In 2005 I changed the intake and exhaust on my wife's 2004 Jeep. She drives the same 170 miles every week, taking the same route every day.

I don't remember the intake manufacturer but the exhaust is a magnaflow. There was not any measurable difference in fuel mileage over several years of use. I put the factory intake back on last year, same mileage.

It does sound better though

 

I can only tell you what actually happened with my cituation. I too needed to increase fuel mileage. After doing EXTENSIVE research and after listening to numerous sound videos, I decided against a flowmaster/magnaflow baffle type muffler. I went with a straight through muffler called the "torpedo pack" made by AP exhaust technologies. At best I got 10.8 MPG pulling my equipment. After the exhaust change I have checked my fuel mileage three different times. The lowest MPG I've gotten was 13.8. I have gotten up to 14.7 MPG. I have done NOTHING else to the truck. By the way my truck is a 1996 F150 with a 5.8. It has 137,000 miles.

 

See, thats not a factual statement, because for starters, a Magnaflow is not a baffle type, it is a straight through muffler, so the results should have been the same as the AP unit. Secondly, just because you saw an increase in economy does not state why an increase happened. You may have been getting 10.8 mpg because something was actually wrong with your stock muffler, and it was either rotting apart, or was partially plugged. Even at that, I had my '97 Aerostar, was getting 16 - 18 mpg most of the time. Found that the factory cat had been hit and was breaking apart and was internally plugged. After replacing it (I already had a free flowing catback system) with true high flow cats, my fuel economy didn't increase at all. The old one was definitely plugged, had pieces lodges sideways in the pipe, and in the rear cat. One would certainly think this would severely affect the fuel economy, but it didn't. Average fuel economy after having it repaired, measured over a lot more than just three tanks, is 16.8 under the same conditions.

I'm not saying you aren't getting better gas mileage, I'm saying that other factors might be contributing that you might not be taking into consideration, especially as right around this time, your local gas stations might be transitioning from winter mix to summer mix fuel, and that could also cause a significant increase in gas mileage.

 

This all falls into the same category as spark plug claims. Remember those Split Fire commercials when people were touting about the drastic change in performance and mileage. Well DUH.........they probably needed plugs anyhow and ANY plug would have likely improved the situation. Since they got Split Fires............that was the reason(ya, whatever).

A motor is an air pump, BUT it uses a lot of variables to perform better(like you mentioned). The easier air gets IN or OUT the better it will perform within a RPM range. That is what you need to determine.

If you drive it slow/easy, then likely there is no need to change what the factory built.

 

Sorry folks, I didn't read all the above design criteria for exhaust systems because while I'm sure they have great info - I did my homework already and I opted out of the refresher course. I have a turbodiesel and I'm light on the funpedal. I went bigger exhaust and ended up with a 5% increase in fuel economy with city/hwy driving (from 16.3 MPG to 17 MPG). I still don't have my highway fuel economy yet - it takes a big trip to get those, but mine was 19.5 MPG before the upgrade. My real gain was more power when I push the testost-o-meter (turboboost gauge) to the right and lower Exhaust Gas Temperatures. As it goes with any exhaust system; if you have restrictions, replace the offending component and you will see some form of performance gain. Will it pay for itself in coin? Maybe - not always in fuel, sometimes in less wear on the engine because of reduced heat. Better sound is always alluring, but you must decide for yourself if this is why you open the wallet.

 

Your statement is both true and false. The reason is because you are opening a new can of worms. When you go from a naturally aspirated engine to a forced induction (yes turbochargers are a type of forced induction) then the way the airflow behaves totally changes, and the way the engine reacts to changes in the intake and exhaust are totally different from the way a naturally aspirated engine does.

On a naturally aspirated engine, a larger intake and exhaust will often do little or nothing, because often the most restrictive part of the system is the heads, and just because you have increased the flow potential of other parts doesn't mean the engine can flow more air, and in turn more power. In fact, sometimes the opposite happens. Engines rely on a principle known as natural induction, which is a function of velocity and inertia in the intake and exhaust. It works on the principles that any object in motion tends to stay in motion, and that the faster that object is, the more resistant i will be to changes in that speed. The gases in the intake and exhaust have speed and mass. They are designed to move at a speed sufficient to maintain a certain velocity and that in turn, when combined with a carefully calibrated cam timing, is intended to maximize the engines volumetric efficiency under a lotos differing conditions, but specifically at low to mid rpm when you do most of your driving. If you increase the diameter, you decrease the velocity which in turn decreases the volumetric efficiency at lower rpm. So the engine has to run at a higher rpm to achieve the same velocity to achieve the same level of volumetric efficiency, but a the same time the higher rpm means more friction and less overall efficiency. This is why vehicles with oversized intakes and exhaust might see an increase in peak horsepower, but often loose low end torque. You disrupt one part of the carefully calibrated and designed system on a stock vehicle, and you alter the power band. Sometimes if for the best, sometimes its for the worst, each model is different, and that needs to be left up to the discretion of the individual.

In a turbocharged application, the forced induction behaves differently. While there is always so degree of lag, as a turbo spools up, it produces boost, which overcomes the principles of natural induction. The more air the turbo can take in, and the more exhaust you can get out, the more efficiently the setup works, so intakes and exhausts are excellent upgrades on turbocharged vehicles. Will fuel efficiency necessarily follow? Depends. On a gasoline engine, less so. The fuel efficient turbo vehicles like the Ecoboost V6 get their efficiency for advanced technologies like direct injection, variable valve timing, etc. Also the engine is a small displacement, allowing it to be a small efficient engine when it needs to be. The idea is that the turbo can deliver enough power on demand that a small efficient engine can be asked to do the work of a much larger less efficient engine.

But at the end of the day, gasoline engines have to try to maintain a certain fuel to air ratio to run correctly, this is where you experience again while true, does not apply to everyone. Your example is a diesel engine that does NOT have to maintain a specific fuel to air ratio. By increasing the efficiency of the turbo, you increase airflow, which in turn gets more air into the engine. This in turn probably leans out the mixture more than normal, while simultaneously increasing the combustion efficiency, resulting in an increase in power and economy. For any given throttle position you get better efficiency and use less fuel. On a gasoline powered engine, if you increase airflow, you must also increase fuel accordingly. In addition, as airflow increases, and efficient increases, the heat also increases. A gasoline engine often has to add additional fuel under load to prevent detonation, so they run even richer under boost and heavy throttle that they do under cruise and light throttle. So increases in airflow often do not result in increased economy, and sometimes even result in decreases.

Hopefully that can help clarify some things, not trying to argue, just saying your not comparing apples to apples. Turbocharged versus naturally aspirated is not an equal comparison, and diesel versus gasoline not an equal comparison. They work differently, and the behave differently when modified.

And I do totally agree with you on the fact that often savings can be in something other than fuel. In a turbocharged engine, larger exhaust in particular often results in lower EGT temps and lower cylinder head temps. This is beneficial for engine life, oil life, and puts less strain on the cooling system, belts, hoses, etc. Savings on those things, and improved reliability can go a long way. If the turbo runs cooler, the seals in it will last longer too. Not sure how many have experienced the pain of having turbo replaced or rebuilt, but its an experience best avoided. Larger intake rarely helps with operating temps, though in some situations, a larger intake helps the turbo run more efficiently, which can help the turbo run cooler, and that reduces heat, and improves fuel economy.

I have several vehicles with performance exhaust. My '97 Aerostar is running a customer made y-pipe with real high flow cats (not the lame regular cats that many people think are high flow), and a larger but reasonably sized catback system with twin tailpipes coming out of a single muffler. Does it increase performance. I don't have any dyno results, but I can tell it performs much better than the stock setup by the kind of loads I can haul. My intake on said vehicle is stock. But did I see any economy gains? None whatsoever. The vehicle gets the same kind of gas mileage that it would without an exhaust system. I need the added power for work.

I also have a 1987 Thunderbird Turbocoupe. It has a 3" turbo back exhaust system that splits into dual 2.5" mufflers and tailpipes. It also has a larger cold air intake and increased boost. Does it get better performance than stock. Absolutely yes. Does it get better gas mileage? No, it gets about the same as a stock one would. I have managed to get it in the mid 20s on highway trips, it averages in the upper teens. That care is currently having the engine rebuilt, so I may get different results after the rebuilt motor gets put back in. At the end of the day, both vehicles are gasoline powered, and they need to add fuel in relation to the amount of air they flow. Thats pretty much just the way it is.

 

I have been putting intake exhaust and programmers on all the vehicles I have owned but this is the first truck I have noticed an increase in fuel mileage. On my 06 f250 6.0 it added about 4-5 mpg highway

 

I have found on my 250 the single largest thing that contributes to my gas mileage is my right foot. I have a custom y pipe, no cat, and a magnaflow exhaust. I average around 10.5 mpg. 99 percent of my driving is all done in town though. I work 12 minutes from my job, and there is no high way driving involved.

When my overhead computer worked, it said I was getting 12.6 mpg. It was a little optimistic though. I have had tanks of gas where I have gotten 11 mpg, and I have had tanks where I have gotten 10.2 mpg.

As others have stated, once you get a louder exhaust you tend to have a heavier foot.

2004 F250 Crew Cab 5.4 with 3.73 Gears and 285/75/16 BFG ATKO's.
Drop in K&N, Tuned by 5 Star Tuning, exhaust mods listed above.