Tuning theory, Part 4
Mapping – the final touch With a new exhaust system and race catalyst, and a more efficient inter-cooler, we have established that there are margins for more boost in the Passat. But a mapping is essential, so we have invited Claus Aichberger from Turbo Center to extract the horses, under the supervision of Rototest Research Institute (RRI).
Bilsport March/April 2006 (In English July 2008) • www.rri.se
Tuning theory, Part 4
Tuning theory, Part 4/5 2006
Imprint:
Tuning theory, Part 4/5 March/April 2006 •
This article is prior published in the Swedish car magazine BILSPORT nr 7, 2006 Text and photo by Gunnar Ljungstedt Publisher: Förlags AB Albinsson & Sjöberg Box 529 371 23 Karlskrona www.bilsport.se
•
Vehicle tests, technical facts and graphs by Rototest Research Institute, www.rri.se Originally published in Swedish
•
Stainless steel, sport exhaust system and new catalyser from Ferrita Sweden AB, www.ferrita.com
•
New intercooler from Setrab AB, www.setrab.com Engine tuning calibration, Turbo Center Stockholm AB, Claus Aichberger, www.turbocenter.se
•
Reader Questions and comments: Please write to tuning‐
[email protected], open to December 2009.
Free non-commercial downloads Except otherwise indicated elsewhere on this web server, any person is hereby authorised to view, copy, download, store, print or distribute anything on this site or obtained through it, but subject to the following conditions: The document may be used for informational purposes only. The document may only be used for non commercial, non profit purposes. The document may not be altered in any way, and must be complete. The document may not be copied to, or made available through, a web site. All other use is strictly prohibited. Rototest Research Institute 2008, www.rri, translation of Bilsport article from 2006 © Copyrights Bilsport 2006 & Rototest Research Institute 2008
2/2
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
CHERISHED CURVE. What we are looking at is the desired volumetric efficiency. The green curve shows the original state.
We have now in three articles looked at the preconditions for extracting more power out of a 150 HP Volkswagen Passat 1.8T, all with the help of the engineers and analysts at RRI. Firstly, we looked at the status of the original car. Then, we exchanged the exhaust system and thereafter, the inter-cooler. By tests with the chassis dynamometer we established that the steps taken gave some more power and torque, but the lower back pressure and the improved cooling capacity shows that the original map is far from optimal. So we borrowed Claus Aichberger from Turbo Center to the RRI laboratory, with the computer under his arm and expertise in his head. What could he do then? The parameters we have to play with are fuelling, ignition timing, desired air volume (boost pressure) and adjustments of program limitations.
3/3
Tough adjustment All modern engines have the capacity to safeguard against knocking by retarding the ignition and/or enrich the fuel. That is also the case with the Passat, but the adjustment is very complicated and Claus has to work hard to stay under the knocking limit. But, at the same time, as close to it as possible. We noticed that the ability of the program to pull back the ignition at knocking was limited to 10 degrees, then it said stop. Unless the knocking stops, the exhaust temperature will rush off (when the mass of the manifold heated up) and the pistons are damaged. One of the first undesired results will be deformed ring areas. A question that does strike you when you see Claus work is whether it would not be worth while to exchange control system for an aftermarket system.
TUNER’S HUMOR. If the curve looks like this, we are likely to have a problem. We must see this as an expression of a poor sense of humor. Maybe a gesture to the Volkswagens programmers?
Original system preferred
does not like more than 1.21.3 bar of boost pressure. We – Not on a street car, says have to compensate with Claus. Some poor soul has ignition and fuel, so we don’t spent 50 million to make it gain more. work. It works in all climates, starts at all times, Difficult torque curve consumes little fuel, and you can make a diagnosis at the The limitation of the original turbo tolerates these charging garage workshop. – To work with the original pressures, but only in a system is ideal, best value, he limited area. So the torque continues. A race car or a car curve will be rather boring, to play with in the summer without real top power. time only is, however, a When the torque goes down different matter. The after the early peak the advantage with an engine will feel lifeless, in aftermarket ECU is the user spite of the fact that it still friendliness. But in the gives more than the original. standard system everything Therefore we even out the for the best is clear. It only needs to be torque adapted to its new purpose. drivability. Claus is well On the other hand, you will aware of the objective. need experience for that. It is – It is interesting to achieve a change and also useful to know the character capacity of the turbo and to adaptation, and to use the understand the physical turbo to make the car more fun to drive, he says. To prerequisites. – Here, we have a make the system tolerate a compression that is quite larger air volume, with safety high, Claus says. If you add and exhaust cleaning as air, the temperature parameters to consider. increases. Eventually, it The first step for Claus is to results in an unreasonably find the necessary control high pressure in the cylinder. matrices in the software. – It seems that the engine There is an important bunch
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
of them, like the limiting matrix for the air volume. Also the ignition position was tested, but there was not much to do there, since it adjusts itself in real time. The fuel also keeps up as far as the air flow meter suffices.
based upon the coefficient of volumetric efficiency, which is translatable to load. This value can be represented by a certain amount of fuel. If you change the distributor, it’s enough to change one parameter, in principle … Claus thinks it is important to avoid knocking tendencies Retain the margins as far as possible. The built The control system of the in diagnosis of the Passat Passat calculates everything will tell when it knocks,
which makes the mapping easier. For normal fuel, two to three degrees ignition retarding at knocking is acceptable. Then there is still a margin. If you go up to ten degrees, the whole safety reserve is used up and the system has no margins left. And if you have no knocking at all, you are not aware of the margins either.
– Breakdowns occur often when the ride is hard and sluggish for a long period of time, Claus points out. You shouldn’t get overexcited because there is no knocking in the second gear. You have to verify in the worst possible environment!
Today it’s the control system that decides, based on approximately 120 parameters. With the gas pedal, you only wish, it’s not you who decides how it turns out eventually.
EMULATOR. With an emulator plugged in instead of the original chip, Claus can control and manage the program during driving, instead of having to burn new chips all the time.
4/4
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Who drives? – Previously it was the engine and the gas pedal that decided the coefficient of volumetric efficiency, Claus says. Today, it’s the control system that decides, based on approximately 120 parameters. With the gas pedal, you only wish, it’s not you who decides how it turns out eventually. We leave the purely philosophical aspects of the modern engines and establish that Claus has persuaded the control system to allow
technically more room for air. As long as everything runs as it should, the system controls itself. The safety in modern systems is generally high, but on the other hand a simple transmitter error can cause serious trouble. – If the potentiometer in the gas pedal goes wacko, the driving characteristics can become quite funny, as Claus expresses it. The error potential is high when it’s a question of ”reversed engineering”.
A warning! We have talked about knocking, or pinging, earlier in the context of changing the exhaust system. There is no harm in mentioning that the risk for high speed knockin is there for all engines, not only for our Passat. With the standard exhaust system, the high back pressure caused residue exhaust gasses to stay behind in the combustion compartment, something called internal EGR. This causes the combustion to slow down and the risk for knocking decreases. Therefore the ignition can take place relatively early. With a new exhaust system (less back pressure) and a bigger inter‐cooler (cooler air into the engine), the engine should be able to take still earlier ignition. At least in theory. Here a word of caution is appropriate. If you increase the ignition by the same number of degrees over the whole map, it can result in too much at high revs. It may not cause trouble during short accelerations, but a day’s flat out on the autobahn may be both expensive and embarrassing.
Trusts the engineers
Conclusions
The advantage with mapping when having the car in the chassis dynamometer, instead of doing it on the road, is obvious. Mapping on the road is always hazardous, and repeatable measurements are of course impossible to achieve. With repeatable values, Claus can do even small adjustments and directly see if the results go in the right direction. – There are thousands of matrices, and I don’t know what 99 percent of them do, Claus confesses. And neither do I want to know. I trust that the VW engineers have done a good job. The same engineers probably knew that a big pipe and a more effective inter-cooler would do a lot of good to the car. But they were not allowed to act because in the carmakers’ world every penny counts. In the next feature article we will tie up the ends by taking a final look at the car’s performance characteristics and explain how we take advantage of the traction force. []
As we already have figured out: by mapping we can profit from the possibilities we have acquired by changing the exhaust system and inter‐ cooler. In spite of the modifications, we could not achieve more than 190 HP at the drive wheels. We have simply exploited the injectors and the turbo to the maximum. We want to point out that the mapping should be left to those who have both the skills and the equipment. ‐ Many consider themselves competent because it requires just a little programming, Jonny warns. Wrongly done, it can lead to expensive experiences!
German words German car, German control system and nice German industrial language. Below, a few German words to brush up on for future visits to the Bosch development department. Load limiter at knocking LDRXNZK, {Maximalfuellung LDR bei Dauerklopfen} Basic/max opening time for waste gate: KFLDIMX, {Kennfeld LDR I‐Reglerbegrenzung}
5/5
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Measurements and results Amazing what a little tinkering with the computer can lead to. However, remember that the mapping scarcely would have rendered so much without changing the hardware, i. e. exhaust system and inter‐ cooler first. Compared with the standard curve, the torque has gone up by 39 percent and the efficiency by 23 (as per Fig.1), in spite of that there still is some tuning left to do. If we check the sweep that was run at 500 rpm/s acceleration, shown in Fig. 2, we see the curve disappearing from the diagram. This is due to Claus putting the revs limit at 7200 rpm. However, exactly as we expected, it didn’t make any difference, since the turbo had already hit the wall. From 4000 rpm, the torque decreased successively, which we pointed out already in the first part. The efficiency is being limited by several expensive components, such as the turbo, the distributors, and the air volume meter that is also approaching its limit.
From now on, it’s becoming expensive On the other hand, it should be possible to raise the torque a bit more. But then you have to know where the limit is. The standard engine has a maximum cylinder pressure at around 80‐85 bar, and with the current 300 Nm, we have increased it to110‐115 bar. You could say that the life of the engine is now more dependent on the behaviour of your right foot than earlier,
6/6
and it could easily be cut to less than half. To increase the torque even further and still be able to sleep at night, you will have to replace components in the engine to tougher ones. We have reached the situation, which we talked about in the first part of this feature article series. If you choose to go on and hunt for more efficiency and torque, it becomes so expensive that the wisest solution is to choose another car. In Fig. 3 you can see a diagram of the injector time. The figures are a bit over what is considered as safe. However, in practice this is not very likely to cause any problems, as the maximum revs are only reached for short moments before gearing up.
Volumetric efficiency The boost pressure has been increased over the whole range, but the greatest difference is found around 4000 rpm. This is also seen in Fig. 2, where the torque curve follows the boost pressure more or less exactly. Maximum boost at steady state is now 0.95 bar (1.03 during a sweep). If we look closer at the diagram in Fig. 4, the deviation between the different ways of calculating the volumetric efficiency, which we discussed in the second part, becomes more pronounced. The relative volumetric efficiency is approximately the same as when the engine was in its original state, which is reasonable considering the fact that we have not changed any hardware in the engine. On the other hand, the total volumetric efficiency has jumped up in a nice way. The exhaust temperature, seen
in Fig. 5, still maintains approximately 800 degrees Celsius as a maximum. Thus, nothing to worry about there. The pressure loss in the exhaust system is about 30 percent of the pressure loss in the standard pipe, in spite of having increased the flow quite considerably. Lovely!
On the limits In the diagram (Fig. 6) on the efficiency of the inter‐cooler we see that some of the gain achieved by the change is eaten up by the mapping. But that was the reason for the change, to prepare for the mapping. Since we now charge more, the temperature increases out of the compressor, but the efficiency has still gone down by only around 5 percent. In spite of higher temperature and higher flow, the air out of the inter‐ cooler is cleaner than in the original concept. But couldn't we increase the charging pressure just a bit to get more HP without changing the intercooler? Unfortunately, the answer is no. Have a look at the temperature out of the compressor in Fig. 7 and you will realise how much more heat will be generated due to the pressure increase. Thus, only a mapping, without a change of the inter‐cooler, is bound to create problems. A not so unusual scenario is to install a magic chip that increases the charging pressure. Then the car will pull like blazes in the first and second gears, only to pass out a bit into the third gear. This may well be due to the charging air temperature having rushed away because of the insufficient capacity of the
cooler. The compressor map (Fig. 8) shows that we have slipped closer to the pump limit or the surge line. It’s unwise to get closer than that. And in the other end we have already passed the margins and a bit more. If we imagine an extension of the grey revs line for maximum revs, we are dangerously close to that one as well. The explanation here is simple. There is no more power to get out of the turbo! A trip up the Alps, where the air is thinner, would be enough to overrev the turbo. []
“Amazin g what a little tinkering with the comput er can lead to.”
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Fig. 1
7/7
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Fig. 2
8/8
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Fig. 3
9/9
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Fig. 4
10/10
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Fig. 5
11/11
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Fig. 6
12/12
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Fig. 7
13/13
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Fig. 8
14/14
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Knocking We already know that a higher boost pressure also results in higher temperature. This is not a problem as long as the increase is moderate. The limit depends on the fuel, how much it can take without knocking. Why does knocking happen? To answer that question we must look closer at the combustion. Three basic prerequisites have to be met for the combustion. There must be enough fuel, oxygen and heat. If not all three elements are there, there will be no combustion. None!
The three elements of combustion
3) Now the combustion spreads in the combustion compartment with increasing speed. When the shaft has turned another 15 degrees, 50 percent of the fuel mix has been consumed. The cylinder pressure increases and reaches usually its maximum value at approximately 15 crankshaft degrees after the upper dead point, when it is of the most “use” at the crankshaft.
Now it knocks The part of the fuel mix that has not yet been burnt up, increases in temperature due to the higher cylinder pressure. Further increase can also take place on local hot surfaces such as exhaust valve, and there is a risk that the temperature increases to such a high level, that the fuel mix self‐ignites. If that happens at an early combustion stage, there is a risk of engine damage. Bingo – we have uncovered the secret of knocking! If it is that bad, how can we avoid the misfortune? First of all by replacing the fuel. By using as high octane number as possible, we raise
The combustion of the Otto engine can be divided into three elements. 1) Start of combustion with the help of the spark in the sparking plug gap. The spark increases the temperature locally so the combustion can start. 2) The combustion spreads around the sparking plug at a relatively low speed. This is influenced by the plug’s electrode. A plug with four electrodes obstructs the combustion more than one with one fat electrode. The electrode cools the flame front; therefore development is towards thinner electrodes. Here we can mention that the coolest guys index their sparking plugs. It can be managed using shims to make the electrodes point in the same direction in all combustion compartments. Which direction that is the right one is of course different in different cases. While burning five percent of the fuel mix, the crankshaft may turn 15 percent.
the threshold for self‐ignition. The next alternative is to see that the fuel mix is as cold as possible when it enters the combustion compartment. Then there is more room for temperature increases. That’s where the inter‐cooler comes into the picture.
Gasoline takes heat A third way is to lower the ignition i. e. to postpone the ignition point of time. Then we move the combustion and the pressure increase to a stage where the piston has moved further on its trip, so the maximum pressure will be lower. As the last resource, we can slosh in more fuel, i. e. use a richer mix. The gasoline absorbs heat when it vaporizes, and if more energy is being used to increase the temperature of the gasoline, less energy is left to increase the temperature of the air, and therefore the total temperature is decreased. Another option is water injection, since water also absorbs heat when vaporizing. The last tip is to put in methanol. Then so much heat
is being used for vaporization that an inter‐cooler is no longer needed, in practice. But … all suggestions above are different ways of solving the knocking problem. If you haven’t got a problem, there is no need to apply any of the above solutions, as they in fact in most cases lower the power![]
“Bingo – we have uncovere d the secret of knocking! ”
15/15
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
Tuning theory, Part 4
Lambda
– it’s all Greek to me
There is a lot of talk about the Lambda value. But what is it? The word Lambda is really a letter in the Greek alphabet (λ). Why this particular character was chosen to symbolize an exhaust value, we do not know. – Maybe all the other characters were already taken, Jonny muses. Epsilon stands for example for compression. So then, we talk about an exhaust value. The Lambda probe is an oxygen sensor that checks the volume of oxygen residues in the exhaust fumes. A lambda value of 1 corresponds to the ideal case of optimal combustion. That’s when the catalyst best takes care of the residues. In theory, that is. When tuning, a richer mix is used (numerical lower Lambda value), which renders a higher combustion speed. At approximately 0.90‐0.93 in Lambda, the combustion is the fastest.
same volume of air (different A/F relationship) to render the same Lambda value as 95 octane gasoline. The first probes were of the type on/off. Nowadays, the development is more towards broadband probes. Previously, the tuner found the Lambda value useful when mapping, but that has become of less and less importance. – The value is useful, but with the engines of today it has lost the cooling function it had before, Claus from Turbo Center says. Now the temperature is fixed by electronically adjusting the throttle and other cooling measures without taking Lambda 1 in consideration.
fixed driving cycle only, to meet the emission requirements. In principle, the engine control totally ignored what the Lambda probe said when you pressed the gas pedal down to the floor. Now, times have changed. The Germans were the first to see that their products kept Lambda 1 even at Autobahn speed, and the rest of the world is on its way to follow. If you abandon Lambda 1, the catalyst quickly loses its function, since there isn’t the right amount of oxygen to burn any more. When Claus maps, he lets the original Lambda probe give a signal to the control box and attaches as well a separate broadband Lambda for his own 200 with environmental checking as well. conscience – I want to be at Lambda 1, Previously the car makers even tighter if cruising at 50 spent all their efforts km/h, and richer on engine making the cars to stick to brake.[] Lambda 1 within a narrowly
“If you abandon Lambda 1, the catalyst loses quickly its function”
Different A/F, the same Lambda If we mix in the A/F relationship (A=air), F=fuel), it becomes a little confusing. It would be simple to assume that it was tied to the Lambda value, but if we change the fuel, the A/F‐relationship changes since the molecule content differ. For example E85 that requires more fuel for the
16/16
AIR/FUEL (LAMBDA). The broadband air/fuel (lambda) is in the operator’s field of vision. 1.0 is the ideal value, that is for low exhaust emissions, not for maximum load, and the Passat kept it at lambda 1 actually right up to190 km/h before it was enrichened.
Bilsport March/April 2006 (Translated July 2008) • www.rri.se
