TFX Engine Technology - Opwer Tuning

Power Tuning - Four Stroke Engines

TFX Engine Technology Inc. pressure analyzers provide a tremendous advantage over and above conventional methods of making power, including vast amounts of tuning experience. Everybody has a theory about why a particular modification did or did not work. The only way to really know is to see what is happening inside the cylinders.

One needs only to read through any of the Engine Masters summaries to realize how important it is to know what is going on inside the cylinders. Some of the best engine builders in North America participate in this contest. More often than not the engine builder finds out that the setup that worked back at their facility just doesn't live up to expectations at the contest facility where the location and atmospheric conditions may be a little different. Even with many years experience most engine builders just cannot get the engine to work correctly after several attempts. Now if the engine builder has a hard time getting things right at a dyno facility, imagine what the chances are of a raceteam tuner being able to optimize the engine at the track where conditions are even less favorable and the tuner has only one attempt to get it right before the next run.

Our pressure analyzers record the pressures generated in the cylinder and the intake and exhaust ports relative to piston position. Based on the pressures and engine specs the HP, torque and volumetric efficiency of each cylinder can be determined for every cycle. In addition, the burn rate of the air/fuel mixture can be plotted relative to piston position indicating whether the burn is fast or slow and how it is located relative to TDC. All data is displayed on a per cylinder basis and data from several cylinders can be plotted simultaneously vs. rpm and time.

TFX Engine Technology Inc. pressure analyzers provide the customer, whether a novice or experienced tuner, with access to critical power tuning information which cannot be had by any other means. A “window” is provided into the engine’s combustion chambers and intake/exhaust ports, allowing the tuner to see exactly what is happening inside each cylinder of the engine under all conditions of load and speed.

Over 20 data plot formats are provided including:

HP, torque, IMEP vs. rpm and time combustion pressure vs. piston position detonation intensity AF mixture burn rates vs. piston position volumetric efficiency vs. rpm and timecombustion efficiency port pressures during valve overlapintake port pressures vs. piston position exhaust port pressures vs. piston positionexhaust stroke back-pressureindividual cycle and overall data summary
Plots of multiple cylinders overlayed

How to make more power using this technology

A brief outline of some of the graphs and a few basic ways to use this technology to further increase engine power are shown in the examples below. Many data displays and analysis techniques are not included on the website, please contact TFX Engine Technology Inc. for more detailed information. View more data...

Combustion Pressure Graph

The combustion pressure graph is only 1 of 20 different ways of displaying the data. The combustion pressure graph allows the tuner to determine in a single engine test the peak combustion pressure, location of peak combustion pressure and the combustion temperatures for every cycle of the entire test load/speed range. The correct ignition timing can be established using the combustion pressure graph, energy release graph and numerical data for the entire range of engine speeds.

Adjustments to the air/fuel mixture may also be required at certain engine speeds. As the dynamics inside the engine change with changing rpm and engine modifications, so to does the air/fuel mixture ratio. Powerband flat spots and detonation zones, related to the air/fuel mixture ratio, show up immediately on the combustion pressure trace.

The numerical data can be used to determine how well the cylinder was filled with the air/fuel mixture (volumetric efficiency). Everytime a modification is made to the engine which affects cylinder filling i.e. camshaft, intake, carb, header, turbo, supercharger etc. the impact on how much air/fuel mixture is retained in the cylinder is indicated under the heading volumetric efficiency. The more air/fuel mixture that is retained in the cylinder the greater the potential for power. Sometimes an increase in cylinder filling does not result in an increase in power due to changes in some other aspect of the engine which causes a reduction in the amount of energy released from the fuel and/or how efficiently the energy was applied to the crankshaft. The pressure analyzer data indicates how well the cylinder was filled and if any other aspects of the engine, related to combustion energy and efficiency, need to be corrected to realize the power gain.

The combustion pressure trace can also be used to prevent engine damage. Detonation spikes will show up on the combustion pressure trace at the first sign of detonation. Sometimes detonation may start out by occurring mildly only every 3 or 4 cycles. Knowing when detonation is just barely begun allows the tuner to avoid making any changes which could lead to more severe detonation on the next test. The pressure analyzer data can also be used to effectively tune a commercial knock sensor so that the racer knows how much knock is OK and how much is too much.

Combustion Pressure

In the example above the scale on the left side shows the pressure (psi) in the cylinder. The scale along the bottom shows crank position in degrees. -90 indicates the piston is at 90 BTDC, 0 indicates the piston is at TDC and 110 indicates that the piston is at 110 ATDC. The blue curve shows the actual compression and combustion pressure in the cylinder. The lower pink curve shows what the pressure in the cylinder would have been if combustion had not occurred. The upper pink curve shows the combustion temperature in degrees Celsius (multiply by approximately 1.8 to convert to Fahrenheit). The software allows the user to scroll back and forth through the data in a manner similar to using a VCR.

Energy Release Graph

Some of the biggest power gains can be made by looking at the energy release graph. This graph indicates when combustion starts, how fast the mixture burns and when combustion finishes relative to piston position. It should be noted that the crankshaft rotates several degrees between the time the spark occurs and the time when any measurable increase in pressure occurs in the cylinder.

Energy Release

The pink curve shows shows how much of the mixture has combusted (left side scale in %) relative to crank position in degrees (bottom scale). In this example combustion starts at 16 BTDC. By the time the piston reaches TDC, 22% of the mixture is combusted. 75% of the mixture is combusted by 20 ATDC and combustion is completed by 85 ATDC. The blue curve shows that combustion is occurring at the quickest rate at about 5 ATDC.

Significant power gains are made by burning the entire air/fuel mixture as quickly as possible and by positioning the combustion process appropriately around TDC. Almost every engine modification has an effect on the burn rate, but without using a pressure analyzer it is impossible to know how the burn rate is affected. Many fast-burn combustion chambers allow the tuner to reduce the ignition timing, suggesting that the burn rate is improved, but in most cases only the first 50% of the mixture burns more quickly, not the entire mixture.

Although the big block engine in the energy release graph above is making 896 HP at 7454 rpm, a 10% increase in power is a realistic goal simply by getting the last 20% of the mixture to burn more quickly. Many tuners strive for a 1% increase in power thinking that there may only ever be 2 or 3% more power available. Our pressure analyzers show the tuner where to look for more power and how much more power is realistically achievable.

Valve Overlap Graph

The conditions that exist in the intake and exhaust ports during valve overlap on a racing engine have a tremendous influence on engine power. Any exhaust gas left in the combustion chamber or pumped back into the intake port, not only reduces HP by reducing the amount of air/fuel mixture that can enter the cylinder, but the exhaust gas also slows down the combustion process. The result is a two fold gain or loss in HP. Exhaust gases also tend to heat up the air/fuel mixture resulting in detonation.

Intake/Exhaust Port Pressures at Valve Overlap

The red curve shows the pressure (left side scale) in the exhaust port and the white curve the pressure (left side scale) in the intake port relative to crank angle in degrees (bottom scale). Intake valve opening is indicated at IVO and exhaust valve closing at EVC. TDC is TDC during valve overlap.

In this example the pressure in the exhaust port is greater than the pressure in the intake port during valve overlap, indicating that the combustion chamber is left full of exhaust gases on this cycle. An easy gain in HP of several % can be made by changing the exhaust header dimensions to provide a vacuum in the exhaust port during valve overlap, over a wide range of engine speeds. Pressure analyzer data has shown time and again that at high rpm, exhaust header design based on selecting certain primary tube lengths and diameters, has no bearing on reality. This often leads to a reduction in peak power and a reduction in the rpm at which peak power is attained.

The pressures during valve overlap are often overlooked on turbocharged engines. Just as with a naturally aspirated engine a good flow of intake mixture into the cylinder and out the exhaust valve is need to flush the exhaust out of the cylinder and cool the exhaust valve. Conventional pressure sensors that are often used on the intake and exhaust systems of turbocharged engines are not fast enough to measure dynamic port pressures. The pressures in the ports during valve overlap can easily be the reverse of what the conventional pressure sensors read, due to the dynamics in the engine. These types of sensors read essentially an average pressure. The sensors used by TFX Engine Technology Inc. to measure intake/exhaust port pressures are made by the same companies as the cylinder pressure sensors and are designed specifically for very high speed response.

Exhaust Pressure Wave Graph

The conditions that exist in the exhaust port during the exhaust stroke and when the intake valve opens can also have a significant effect on engine power. The goal is to minimize the pressure in the port during the exhaust stroke so that less power is spent pushing the exhaust out of the engine and to ensure that the pressure in the cylinder (as dictated by the exhaust port pressure) is low when the intake valve opens.

Exhaust Port Pressure

The blue curve shows shows the pressure in the exhaust port (left side scale) relative to crank position in degrees (bottom scale). Of particular importance is what happens from the time the exhaust valve opens at EVO to the time the intake valve opens at IVO and finally when the piston reaches TDC at the end of the exhaust stroke.

In this example an unconventional exhaust header is used to generate a tremendous vacuum after the exhaust valve opens (EVO) and part way through the exhaust stroke (right quarter of graph). A conventional header would generate a high pressure in this region blocking the flow of exhaust gasess. This vacuum helps the exhaust gases escape and is maintained until a little before the intake valve opens. Unfortunately a high pressure is generated in the exhaust port leading up to when the intake valve opens. It is obvious that by further modifying the exhaust to extend the exhaust port vaccuum to include not only the exhaust stroke but the valve overlap period will result in significant power gains.

The theory of how an exhaust header works can be complex and the actual results are almost always different from the theory. There is no way to accurately predict how an exhaust header will affect the port pressures. The pressures must be measured and with a little experimentation, based on fact not theory, significant power gains can be realized.

Intake Pressure Wave Graph

The conditions that exist in the intake port during the intake stroke and when the intake valve closes can have a significant effect on engine power. The goal is to generate a rapid increase in vacuum in the intake port as the piston descends on the intake stroke, then generate a rapid increase in pressure in the cylinder all the way until the intake valve closes, without pushing very much of the air/fuel mixture back out the intake valve. This is fairly obvious to most tuners but the pressure waves that exist in the intake system can wreak havoc with the intake flow. In some cases the intake pressure waves try to pull the air/fuel mixture out of the cylinder when the piston is trying to pull it in. In some high boost applications the intake valve closing required to provide maximum cylinder filling can be beyond even what is considered to be an extreme cam.

Intake Port Pressure

The blue curve shows shows the pressure in the intake port (left side scale) relative to crank position in degrees (bottom scale). Of particular importance is what happens from the time the piston leaves TDC (extreme left side of graph) until the piston reaches BDC and finally the intake valve closes at IVC. The goal in achieving maximum volumetric efficiency and HP is to generate a very strong suction shortly after TDC then a steep increase in pressure all the way until the intake valve closes.

In this example the intake pressure waves are well behaved. Pressure in the intake port at BDC is about 1 psi, indicating that the cylinder is slightly supercharged at this point. By the time the valve closes the pressure in the intake port has increased to almost 5 psi but the piston is no longer at BDC. Is the cylinder still supercharged when the intake valve closes? The answer is no, the volumetric efficiency value displayed on the right side numerical display indicates a value of 99%. The cylinder is less than full, let alone supercharged. Between BDC and intake valve closing some of the air/fuel mixture was pushed from the cylinder back into the intake port. At this engine speed ( over 7000 rpm) more power could be made by closing the intake valve sooner or using a longer intake runner.

Of secondary interest is the pressure in the intake port when the intake valve opens at IVO (right side of graph). In this example there is a pressure in the intake port at IVO which can act to prevent the flow of exhaust gases from the cylinder back into the intake port and partially counteract the effects of a bad exhaust header design at this engine speed.

Power vs. RPM Graph

As previously indicated engine power and torque can be plotted vs. RPM for each instrumented cylinder. This is not possible with conventional dynamometer outputs. Each cylinder can be tuned to provide equal power as well as equal cylinder pressure.

An often asked question is how many cylinders need to be instrumented? The answer is 1 cylinder. Most customers instrument no more than 2 cylinders. One of the benefits of using a pressure analyzer is that all modifications can be carried out on 1 cylinder since power etc. is determined for each cylinder. Once the cylinder is optimized within time constraints, the modifications can then be transferred to the other cylinders. In some instances physical limitations dictate that each cylinder be tuned differently. For these cases each cylinder can be optimized independently either by transferring the sensor from cylinder to cylinder or instrumenting most or all of the cylinders.

Power vs. RPM (per cylinder)

The purple curve shows the power being generated by one cylinder for each combustion cycle as the engine speed is gradually being increased during the engine test. The pink line shows the average power being generated by the cylinder. All instrumented cylinders can be displayed simultaneously so that the power vs. rpm of each cylinder can be compared. Plots of torque vs. rpm and IMEP vs. rpm are also included in the software.

Maximum Combustion Pressure Graph

Maximum combustion pressure of each engine cycle vs. RPM can be plotted for the entire engine test either as a function of time or cycle number. Fluctuations in maximum combustion pressure and fluctuations in the location of maximum combustion pressure relative to TDC, need to be minimized, allowing each cylinder to put out as much power as possible on every cycle. Significant fluctuations in maximum combustion pressure from cycle to cycle are a sign of poor air/fuel mixing, insufficient ignition energy and sometimes a poor combustion chamber design.

Maximum Combustion Pressure Graph

The purple curve in the upper graph shows the maximum combustion pressure developed on each cycle. The purple curve in the lower graph shows where the maximum combustion pressure occurred relative to TDC for each combustion cycle. A zoom feature is also available which allows the tuner to zoom in on any cycles of particular interest.

Significant fluctuations are evident in both curves indicating that the mixture is not burning consistently from cycle to cycle. Substantial increases in power are available by making modifications to the engine which eliminate the lower pressure cycles. Reducing the higher pressure cycles a little can help the engine stay away from detonation.

As an example, if the ideal cycle for this engine combination has a maximum pressure of 1800 psi which occurs at 7 degrees ATDC then all cycles which generate maximum combustion pressure values which are lower than 1800 psi or positioned earlier or later than 7 ATDC result in a loss in power.

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