~~ Well Written Tuning Articles; Worth a read. . . ~~

TUNING, PERFORMANCE, AND HOW TO UNDERSTAND!!!!! - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum

I take NO Credit for this and although its written for autos, its very applicable here. I read and see nothing I can pick apart for being in error. Enjoy!


** PASTE ** NOTE: lower it refers to charts. These links are broken on the forum they came from.

The Great NY said:

MAZDA 6 SPECIFIC - HELP/TUNING/TROUBLESHOOTING THREAD


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NARROWBAND vs. WIDEBAND air/fuel meters and O2 Sensor Background:

O2 Sensors:

Most cars produced after the 1980s, and all since 1996, have at least one oxygen sensor. It is a part of the emissions control system and is also a part of the engine management system. Oxygen sensors help the engine run efficiently.
Different fuels have different stoichiometric values, e.g. methanol 6.4:1 and ethanol 9.0:1. Theoretically gasoline burns completely at an air to gasoline ratio of 14.7:1. This value is gasoline's "stoichiometric" value.

When the air-fuel-ratio (AFR) in the combustion chamber of your engine has less air than the stoichiometric value, then the AFR is said to be "rich," rich in fuel. If there is more air than stoichiometric, then the AFR is "lean," lean on fuel. The AFR variance indicates the deviation of the actual AFR from the theoretically required ratio for complete combustion. The value of this variance is represented by the Greek symbol called "lambda," and is calculated by dividing actual induced air mass by the theoretical air requirement.
Variations from the stoichiometric air-fuel ratio result in pollutants. Excess, unspent fuel in the combustion process results in hydrocarbons (HC) and carbon monoxide (CO). Excess air causes increased nitrogen oxides (NOx). Catalytic converters help reduce the HC, CO, and NOx emissions if the engine is operating around the stoichiometric AFR.

Oxygen sensors measure AFR post-combustion. They are positioned some distance down the the exhaust pipe in order to ensure that the sample they measure is representative of the AFR in the cylinders. Oxygen sensors can identify variations from the ideal AFR and tell the engine management system to adjust the ignition and injection processes accordingly. So what is the difference between narrowband and wideband O2 sensors?


Wideband O2 Sensors -- What is the difference from narrowband O2 sensors?

Narrowband O2 sensors are designed only to measure the stoichiometric air-fuel-ratio (AFR) for gasoline, i.e. 14.7:1. Wideband O2 sensors have a broader effective range of sensing. Narrowband sensors can only tell you when the AFR is 14.7:1. Although it can also tell you when you are richer or leaner, it cannot tell you by how much.
A wideband O2 sensor can. Designed to measure a broader range of AFR (9.65:1 to 20:1), Wideband O2 sensors are more effective instruments for tuning your engine. They can detect variations of the AFR better than stock narrowband O2 sensors. The result is that you can tune your engine and modify your management system according to your use and performance level. But who needs to measure a wide band of AFRs?



TUNING AIR/FUEL RATIOS AND TIMING:

Programmable engine management allows the selection of pretty well any air/fuel ratio and any ignition timing at any load and rev point. But what are the "right" settings that should be used? Here's a little guide to the settings that will give good results. Remember every car reacts differently to changes so this should just be used as a guide to get you in the ball park.
Before a programmable management system can be effectively tuned, the air/fuel ratio needs to be measured. The air/fuel ratio will need to vary in different conditions, and so the meter needs to be accurate across a wide range of ratios. While the oxygen sensor found in the factory management systems of all cars can determine rich/lean scenarios, it is not accurate enough to be used in the tuning of programmable management. Which was explained a lil more above with the types of O2 sensors.

A well-tuned engine used in normal road conditions has an air/fuel ratio that is constantly varying. At light loads, lean air/fuel ratios are used, while when the engine is required to develop substantial power, richer (ie lower number) air/fuel ratios are used.
Bosch state that most spark ignition engines develop their maximum power at air/fuel ratios of 12.5:1 - 14:1, maximum fuel economy at 16.2:1 - 17.6:1, and good load transitions from about 11:1 - 12.5:1. However, in practical applications, engine air/fuel ratios at maximum power are often richer than the quoted 12.5:1, especially in forced induction engines where the excess fuel is used to cool combustion and so prevent detonation.

There is no one air/fuel ratio where all emissions are minimised. At an air/fuel ratio of 14.7:1 oxides of nitrogen peak, while hydrocarbons and carbon monoxide (CO) increase substantially as the air/fuel ratio richens.



High Load

A naturally aspirated engine should run an air/fuel ratio of around 12 - 13:1 at peak torque. The exact air/fuel ratio can be determined by dyno testing, with the ratio selected on the basis of the one that gives best torque. Rich air/fuel ratios can be used to control detonation, and this is a strategy normally employed in forced induction engines. Thus, on a forced induction engine, the mixture should be substantially richer: 11.6 - 12.3:1 on a boosted turbo car and as rich as 11:1 on an engine converted to forced aspiration without being decompressed. As is also the case for ignition timing, the air/fuel ratio should vary with torque, rather than with power.

Most factory forced induction cars run very rich full load mixtures, with 10:1 being common. This is done for engine and cat converter safety reasons - in case an injector becomes slightly blocked, or the intake air temperature rises to very high levels. These cars will normally develop more power if leaned out. Note that emissions testing does not normally take place at full throttle, so full load emissions can be high without legal problems.
In the engine operating range from peak torque to peak power, a naturally aspirated engine should be slightly leaner at about 13:1, with the forced induction factory engine about 12:1 and an aftermarket supercharged engine staying at about 11:1.


Acceleration

During acceleration the engine requires a richer mixture than during steady-state running, with the extra fuel provided by acceleration enrichment. Under strong acceleration, the air/fuel ratio will typically drop 1 - 1.5 ratios from its static level. The amount of acceleration enrichment that is required is normally found by trial and error, and this is best done on the road rather than the dyno. The acceleration enrichment should be leaned out until a flat spot occurs, then just enough fuel to get rid of the flat spot should be added. This approach usually gives the sharpest response. Note that both over-rich or over-lean acceleration enrichment will result in flat spots, and that a greater amount of acceleration enrichment is needed at lower engine speeds than higher speeds.

Over-run/Deceleration

In road-going vehicles, deceleration enleanment is used to reduce emissions and improve fuel economy. This normally takes the form of injector shut-off, with the shut-off often occurring at mid-rpm (such as 3000-4000 rpm) and the injector operation re-starting at 1200-1800 rpm. High rpm injector shut-off can, in some cases, have the potential to cause a momentary lean condition.



IGNITION TIMING:

(Wikipedia Definition)

Ignition timing, in a spark ignition internal combustion engine, is the process of setting the time that a spark will occur in the combustion chamber (during the power stroke) relative to piston position and crankshaft angular velocity.

Setting the correct ignition timing is crucial in the performance of an engine. The ignition timing affects many variables including engine longevity, fuel economy, and engine power. Modern engines that are controlled by an engine control unit use a computer to control the timing throughout the engine's RPM range. Older engines that use mechanical spark distributors rely on inertia (by using rotating weights and springs) and manifold vacuum in order to set the ignition timing throughout the engine's RPM range. There are many factors that influence ignition timing. These include which type of ignition system is used, engine speed and load, which components are used in the ignition system, and the settings of the ignition system components. Usually, any major engine changes or upgrades will require a change to the ignition timing settings of the engine.


RULE OF THUMB:

A good rule of thumb to follow when taking a naturally aspirated vehicle into the realm of boost when it comes to timing is to retard the timing initially to safe yourself from experiencing knock/deto. Typically a globally accepted value of timing retard for boost is:
For every 1psi of boost added take away 1.5 degrees of timing. Keep in mind this amount of timing retard may vary (increase or decrease per PSI) depending on the motors starting compression. On the V6 motor of 10:2:1 compression I would recommend using 2 degrees retard per PSI of boost, 9:5:1 or 9:2:1 use 1.5 degrees of retard for each PSI of boost and 8's and below use 1 degree.

This rule of thumb is in no way gonna make the most power initially but it will generally run you motor safely while you dial in your AFR. Once you target afr is met. Begin dialing up the Timing advance a degree or two until you are not making anymore noticeable power or u begin to hear or feel ping/knock/deto then retard it 2 degrees and you should be good.

WEATHER CONDITIONS: (WOT Air Fuel Tuning)

Anyone who assumes that the tunes can be left alone once they have been set is sadly mistaken. An overnight change in weather conditions may prevent an engine from running or may put it at risk of some damage if adjustments aren't made to the fuel-mixture settings. While its highly uncommon, but has happened to not have a car start due to cold weather and etc. it can happen. Ignoring an engine's tuning needs compromises its ability to make horsepower and at time can lead to detrimental engine damage. In response to certain changes in weather, equipment and other variables, engines must be regularly retuned, or at the minimum have a couple different tunes for different weather and driving conditions.

Temperature:

Hot weather requires a leaner mixture setting; cold weather requires a richer setting. Most people assume the opposite because they treat the mixture adjustments like a thermostat.

IE- the temperture goes up, you add more fuel, the temperture goes down, you take away fuel. It is wrong to assume that colder weather requires a leaner setting to keep heat in the engine and vice versa.

Cold air is denser than hot air. The denser, colder air packs more oxygen into the engine, so going from hot weather to cold needs a commensurate increase of fuel to balance ratio of fuel-burning oxygen and the fuel itself. The opposite is true in hotter weather. Going from cold to hot weather requires a leaner mixture setting.

Humidity:

Humidity is the amount of moisture (water vapor) in the air. Moisture in the air takes up volume that would otherwise be occupied by fuel-burning oxygen. Less oxygen means less fuel is required to maintain a proper ratio of air and fuel. High humidity requires a leaner mixture setting than dry conditions.

Barometric pressure:

A barometer measures the atmospheric pressure (generally listed in the local newspaper or on the local weather forecast on TV). Higher barometric pressure readings mean more air is getting into the engine, requiring a richer mixture setting to balance the air/fuel ratio.


Altitude:

Altitude is an important factor that most of us ignore, yet it affects the engine's performance possibly more than any other element. The general formula for power loss with increases in altitude is 3 percent for every 1,000 feet above sea level. If you race in Colorado at 5,000 feet instead of in California at sea level, you can expect to lose about 15 percent of the engine's potential power output, if the engine is tuned properly.

Air is thinner at higher altitudes, which means there's less fuel-burning oxygen than at sea level. You might sense a common theme here: less air (oxygen) means less fuel to maintain the proper air/fuel ratio. So, running at higher altitudes requires a leaner mixture setting than running at sea level.

This chart indicates the direction in which you should adjust the fuel mixture when faced with changing weather and other conditions. It assumes the engine is currently well tuned. You could face any combination of conditions listed in the chart; knowing which way to go with the mixture adjustments is half the battle.

Higher air temperature Lean

Lower air temperature Rich

Higher humidity Lean

Lower humidity Rich

Higher barometric pressure Rich

Lower barometric pressure Lean

Higher altitude Lean

Lower altitude Rich

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Click to expand...

Another link full of Good Info. . .
http://forum.mazda6club.com/engine-...g-performance-how-understand.html#post3227248

Again, I take no credit. The general information is applicable to all engines. . .

The Great NY said:

ENGINE KNOCK/DETONATION/COMBUSTION:

ENGINE KNOCK: (Wikipedia Definition)

Knocking (also called knock, detonation, spark knock or pinging) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.

The Air/Fuel mixture is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle. The peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. This change in combustion creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Just think of a handful of common air gun BB's tossed into a soda can and shake the can. That is typically but not 100% of the time what it sounds like.

Effects of engine knocking range from inconsequential to completely destructive. It should not be confused with pre-ignition (or preignition), as they are two separate events.

PRE-IGNITION:

Pre-ignition (or preignition) in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Hence its term, Pre-Ignition.

Pre-ignition is caused by an ignition source other than the spark produced by your spark plugs, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to beyond its current states flash point by previous engine combustion cycles.

The phenomenon is also referred to as after-run, or run-on when it causes the engine to carry on running after the ignition is shut off, or sometimes dieseling. This effect is more common on carbureted gasoline engines, as the fuel supply to the carburetor is typically regulated by a passive mechanical float valve and fuel delivery can feasibly continue until fuel line pressure has been relieved, provided the fuel can be somehow drawn past the throttle plate. This occurrence is very rare in modern engines with throttle-body or electronic fuel injection, as the injectors will not be permitted to continue delivering fuel after the engine is shut off, and any occurrence may indicate the presence of a leaking (failed) injector.

NORMAL COMBUSTION: (wikipedia explaination)

Under ideal conditions the common internal combustion engine burns the fuel/air mixture in the cylinder in an orderly and controlled fashion. The combustion is startedtop dead center (TDC) by the spark plug some 10 to 40 crankshaft degrees prior to , depending on many factors including engine speed and load. This ignition advance allows time for the combustion process to develop peak pressure at the ideal time for maximum recovery of work from the expanding gases.


The spark across the spark plug's electrodes forms a small kernel of flame approximately the size of the spark plug gap. As it grows in size its heat output increases allowing it to grow at an accelerating rate, expanding rapidly through the combustion chamber. This growth is due to the travel of the flame front through the combustible fuel air mix itself and due to turbulence rapidly stretching the burning zone into a complex of fingers of burning gas that have a much greater surface area than a simple spherical ball of flame would have. In normal combustion, this flame front moves throughout the fuel/air mixture at a rate characteristic for the fuel/air mixture. Pressure rises smoothly to a peak, as nearly all the available fuel is consumed, then pressure falls as the piston descends. Maximum cylinder pressure is achieved a few crankshaft degrees after the piston passes TDC, so that the increasing pressure can give the piston a hard push when its speed and mechanical advantage on the crank shaft gives the best recovery of force from the expanding gases.

ABNORMAL COMBUSTION:

When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat and pressure for a certain duration (beyond the delay period of the fuel used), detonation may occur.

Detonation is characterized by an instantaneous, explosive ignition of at least one pocket of fuel/air mixture outside of the flame front. A shockwave is created around each pocket and the cylinder pressure may rise sharply beyond its design limits.

If detonation is allowed to persist under extreme conditions or over many engine cycles, engine parts can be damaged or destroyed. Severe knocking can lead to catastrophic failure in the form of physical holes punched through the piston or head (i.e., rupture of the combustion chamber), either of which depressurizes the affected cylinder and introduces large metal fragments, fuel, and combustion products into the oil system. Hypereutectic pistons are known to break easily from such shock waves. This is what most newer motors are equipped with and is the main reason why detonation and pre-ignition needs to be under control during a full N/A build or Blown Build.

Detonation can be prevented by any or all of the following techniques:

-the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate

-enriching the fuel/air ratio, which adds extra fuel to the mixture and increases the cooling effect when the fuel vaporizes in the cylinder

-reducing peak cylinder pressure by increasing the engine revolutions (e.g., shifting to a lower gear, there is also evidence that knock occurs easier at low rpm than high regardless of other factors)

-increasing mixture turbulence or swirl by increasing engine revolutions or by increasing "squish" turbulence from the combustion chamber design

-decreasing the manifold pressure by reducing the throttle opening; or reducing the load on the engine.

Because pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures by compression ratio reduction, exhaust gas recirculation, appropriate calibration of the engine's ignition timing schedule, and careful design of the engine's combustion chambers and cooling system as well as controlling the initial air intake temp.

Knock is less common in cold climates. As an aftermarket solution, a water injection system can be employed to reduce combustion chamber peak temperatures and thus suppress detonation.

Engines with good turbulence tend to knock less than engines with poor turbulence. Turbulence occurs not only while the engine is inhaling but also when the mixture is compressed and burned. Also known as the "Swirl Effect"

During compression/expansion "squish" turbulence is used to violently mix the air/fuel together as it is ignited and burned which reduces knock greatly by speeding up burning and cooling the unburnt mixture.

DETONATION CAUSED BY PRE-IGNITION

Due to the way detonation breaks down the boundary layer of protective gas surrounding components in the cylinder such as the spark plug electrode these components can start to get very hot over sustained periods of detonation and glow.

Eventually this can lead to the far more catastrophic Pre-Ignition as described above.
While it is not uncommon for an automobile engine to continue on for thousands of miles with mild detonation, Pre-Ignition can destroy an engine in just a few strokes of the piston.

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From the previous post I found this to be note worthy and may have a little to do with why engines in my grasp live a longer life than some others.

I don't lug them - it wears them quick by inducing extreme loads and these loads wear an engine out quickly as temperatures rise quickly and oil is the only boundary keeping the reciprocating parts alive. . .

-reducing peak cylinder pressure by increasing the engine revolutions (e.g., shifting to a lower gear, there is also evidence that knock occurs easier at low rpm than high regardless of other factors)

-increasing mixture turbulence or swirl by increasing engine revolutions or by increasing "squish" turbulence from the combustion chamber design

-decreasing the manifold pressure by reducing the throttle opening; or reducing the load on the engine.

Marthy, you see anything in hear that is of questionable origin?

I was always taught to get through the gearbox and use all of the gears even at slower 50kph (30mph) speeds.
If I need to increase speed then I use the gearbox to go down a few gears.
I'm not saying that I am right in my riding method. I am happy to be educated. I guess that I have always worked on the theory that higher rpm burns more fuel.
The FZ6 will happily cruise in 6th at low speeds with a barley open throttle.
I appreciate that if your at low speed in 6th and open the throttle the engine will struggle. To me this is where forward planning of traffic and gaps come into play.
As stated if they way I'm riding is damaging the engine I will change riding style to correct this.
On a side note with wet slippery roads riding in a higher gear at lower speeds helps smoother power deliver, especially with the on off throttle.

Neil:thumbup:

PS a great read and very informative.

Nelly said:

I was always taught to get through the gearbox and use all of the gears even at slower 50kph (30mph) speeds.
If I need to increase speed then I use the gearbox to go down a few gears.
I'm not saying that I am right in my riding method. I am happy to be educated. I guess that I have always worked on the theory that higher rpm burns more fuel.
The FZ6 will happily cruise in 6th at low speeds with a barley open throttle.
I appreciate that if your at low speed in 6th and open the throttle the engine will struggle. To me this is where forward planning of traffic and gaps come into play.
As stated if they way I'm riding is damaging the engine I will change riding style to correct this.
On a side note with wet slippery roads riding in a higher gear at lower speeds helps smoother power deliver, especially with the on off throttle.

Neil:thumbup:

PS a great read and very informative.

Click to expand...

Hmm - we came from different places and different styles. I'll opt for what gives the best control typically but from the engines perspective, I'll pull RPM from a cold engine (not allot) before i ever lug it. I don't short shift often and not for the sake of using the all the gears. Its just extra load and most engines will build less deposits from light reving than lugging and get better fuel economy while reducing wear. Just my 2 cents. . .

I would be happy to find out what other riders do.
MPG wise I am getting some of the best economy since I discovered it was possible to ride below 10000 rpm.

Neil:thumbup:

On exhaust build/design. This one is too crazy big to paste and from another Mazda forum. The author says straight up, it applies just the same. Hint think rotary!

If you go far enough - it gets into our favorite topic; Back Pressure!

Here is a little teaser. . . Lets see who bites. . . FP

<<PASTE, I TAKE NO CREDIT FOR THIS WORK>>
OK it’s time to get back to doing what I’m good at and originally known for here. Contrary to popular belief it is not being a tight *** as a moderator although I am good at that too but rather it is writing extremely long tech articles that require you to read them over and over again over the course of several sittings or one really long stay on the toilet just to comprehend them fully. Even then you’ll probably be bored to death and die from a brain cramp. How do you think I feel typing these things! I thought I’d deal with exhaust systems in this one even though I’ve dealt with it in the past. I want to go far more in depth on this one though so this one will probably have to be written in a few parts to fit on the forum. There seems to be some misunderstanding as to how certain exhausts are good for one particular application and not another. Hopefully I’ll clear that up here. I also want to deal with exhaust tuning. I know the RX-8 hasn’t been very forthcoming with gains in this area but it will. Give it time. It’s been 2 years and we are only now seeing good forced induction kits and ecu’s hit the market. I’d still like to deal with it anyways as this generally applies to all 4-stroke engines. You’ll find that some of this when it comes to sizing is also directly related to porting as well.

I’d like to start with what a lot of people try to worry about first. That is flow. People like to say that one exhaust must be better because it can flow better than another one. Air however is funny stuff. Just because it looks like it should act one way through a system doesn’t necessarily mean it will act that way. Unless you have tested it, you don’t absolutely know for certain. Just to get to the point, bigger isn’t always better when it comes to exhaust. Many already know this. The main thing people forget though is that the engine can only flow so much air. There is really no point in going any larger in pipe area when the engine can’t flow that much. Or is there? This all really depends on what your goals are surprisingly enough but for the sake of a street driven naturally aspirated car, there isn’t. I really need to deal with this in 3 main parts. These will be naturally aspirated, turbocharged, and supercharged. A lot of people may be surprised that supercharged and naturally aspirated need different systems since there isn’t anything in the way in the exhaust system such as a turbocharger. There is a need difference though.

Let’s start with naturally aspirated. In a perfect world we would know exactly how much air the exhaust ports of the Renesis can flow for any given pressure drop. Too bad we haven’t seen these numbers yet. If anyone has them from their own flow testing kindly let me know the testing procedures and results. I’d love to know. I do have a flow bench but lack an engine to test. Oh well. In the mean time, let’s get back to theory. I know some people hate theory and say that it isn’t accurate. That’s true to a point but theory needs to be tested and generally gets you very close. It is much more accurate than just pure guessing which is the preferred method of many. Even many so called “experts”. Basically on a streetcar, we want a nice broad power band with a flat torque curve. This gives us a very nice driving engine that is very well behaved that can do a broad range of driving conditions very easily. A racecar needs a narrow peaky power band as it will typically only stay in a narrow rpm range and run a close ratio gear box. This of course depends on the type of racing being done. Obviously they have different exhaust requirements from a street car. Have fun guessing which one will work best for each scenario!

The biggest secret to going fast is to remember one very important thing. It is backwards from common thinking. This applies to intakes, exhausts, porting, etc. That secret is that smaller is usually better! High velocities that don’t incur pumping losses is the rule. The whole point of flow testing, porting, etc is not to make something big so it can flow as much as it can. Take a look at the dyno of a mega horsepower Supra sometime. You might find a car that makes 300 hp at 5000 rpm but at 7000 rpm it makes 1000 hp. (for any Supra guys reading it's just an example so get over it!) That just isn't drivable on the street or a road course. It is possible to be good at a drag strip though. These are called dyno queens. These guys like big fat but very short intake runners, big plenum chambers, big turbos, big throttle bodies, big big big everything. This makes no average power and only top end power. I'm not willing to go tell these guys that it is in fact possible to make almost as much peak power but significantly more average power which would be more streetable and spool a turbo faster. They can figure it out on their own. They do have fast cars though so they probably don't care about what I think. OK off of the Supra tangent. On a rotary making a port larger changes port timing and this is also very critical to power band. Why the rotary community predominantly uses this larger logic for porting baffles me. Bigger is not always better. The key is to only go as large as you will need. That’s it. You don’t need to build in room to grow. It’ll only slow you down. I’ll give you an example. If an exhaust port can only flow 124 cfm (I’m making this number up), what is the point in having a nice large exhaust runner that is capable of 224 cfm? You’ll never use it and the added area will only slow the exhaust gasses down. You are losing free energy this way that you could harness to gain power. Why make a port rally large when the runner behind it can’t flow as much as the port window? Just to confuse you guys I’m going to go back later and show you how even this simple rule doesn’t always apply. You’ll find there are no absolutes here. There are generalizations within a certain application that should be adhered to but they may not necessarily apply in other situations. You can see how guessing which one is best is really difficult to get right. Especially when the people doing the guessing don’t even know about the generalization differences.

Follow the LINK. . . >> Another one of my insanely long exhaust tech articles - RX8Club.com

LOTS MORE TO READ. . .

Nelly said:

I guess that I have always worked on the theory that higher rpm burns more fuel.

Click to expand...

Throttle opening is more critical to fuel consumption figures than engine crank revolutions. Not to say RPM isn't directly correlated, but it's not always (think engine braking). So RPM shouldn't be the only indicator for fuel consumption.