Mechanical tuning - theory.
In consience of average driver the most importanat is maximum power that disposes our car.
There is no more misleading opinion. Maximum power is a mathematical parameter, that describes only maximum speed that our car can reach in good conditions, f.ex.: long straight road and lack of radar control.
What is really importanat is torque and exactly its characteristics in full range of rounds of the engine.
In this moment we should put a question: what we want to achieve?
Should the car be to reach speed records, and then the power is most important, or the car should have good acceleration and then the most importanat is torque.
Increasing of maximum power and rounds by which it appears is quite simple, but may cause that the car would be faster on lower gears and slower on higher ones – slower than before modification. This kind of modification is implemented in racing cars in which we can freely change gears eliminating this discomfort.
On the chart above there are presented characteristics of Fiat engine with serial 115 KM and tuned with the simpliest way which means by replacing cumshaft on so called fast one.
Despite of sagnificant growth of the power from 115 KM up to 140 KM the car after such a tuning is slower on 5th gear than serial one. In this case to advantage rise in power it is necessary to change shifts of the gearbox.
In serial cars mostly we are not in such a comfortable situation and have to adjust modifications to existing gearbox. In practice it consists on such a modifications that improve charscteristics of the engine and its power without sagnificant growth of rounds by which it appears.
Achieving of such predicted effect is much more difficult because typical ways of modifications f.ex implementing of fast cumshaft, planning and modifications of cylinderhead, wide throotle valve, if they are not well syncronised, they do not bring expected effects.
For example using wider throotle valve will impact in sagnificant rise in fuel intake with paralel agravate work of the engine on lower rounds.
I will try to present shortly (all the orthodoxes please forgive me...) the most importanat elements and parameters of the engine:
Pressure level – mathematical parameter defining theoreticaly how many times air-fuel mixture will be pressured in a cylinder. I used word „theoreticaly” because it does not regard that in some period of the pressuring stroke both valves are opened and part of the mixture is thrown away through exhaust valve, especially if we use so called fast cumshaft. In sportive normal aspirated cars we tend to increase in pressuring level - the higher it is, the better, but it is limited by quality of the fuel, durability of materials of the engine's construction. In serail cars engines it vary from 9-10, sportive ones 12-15, turbocharged 7,5-8,5.
Intake system – (s.c. throotle valve, injection system, sucking collectors) in great simplification the more narrow diameters and the longer channels the better engine works on lower rounds, but the worse on higher. In sportive high rounding engines even small changes may bring very good effects.
If you wish to se graphs ilustrating imfluence of intake system on engines characteristics click here.
Precissive adjust of intake system is possible in narrow range of rounds, that is why in many modern constructions there are adapted collectors of variable parameters (length, capacity)
Cylinder head – is an element which influence on engines parameters is impossible to overwhelm and which modifications are one of the most difficult ones. During tuning the bigger problems are material limitations bordering modifications of the shape and diameters of used valves. And here, similarly as by intake system small dimensions of valves anable good work on lower rounds and big dimensions – on higher ones.
Cumshaft – 80% of our customers wish that first our activity by tuning their cars would be replacing the cumshaft on s.c. „fast” one.
Dozen of years of work have taught me very sceptical approach to such a type of modifications because of two reasons.
First of all counting and making good cumshaft which means this kind that would not damage valves and pivotsand do not wear away after fiew thousands kilometers is very taugh. In Europe there are only fiew companies that disposes of specilaistic equipment, knowledge and experience, f.ex. Shrick or Kent Performance Camshafts. In Poland the main producer of cumshafts is the company of Lech Świątek from Bydgoszcz.
Prices of this professional wares vary from 1000 to 4000 PLN and apart from cumshaft you should paralelly replace also valves, valve springs, etc. Home made shafts characterise with low price and the same quality.
Secondary sportive cumshafts increase sagnificantly rounds of maximum power that way, that to be able to advantage such engine changes of the shifts in gearbox are necessary. Replacing of cumshafts should be adapted only in case of lack any other possibilities, f. ex. Precissive adjusting of serial one what gives spectacular effects.
Exhaust system - recently more attention is payed on this element. Of course the case is not chrom endings or emptyfing of last muffler, what causes sagnificant improving of sound effects, which is as much important for many drivers as increased power.
The rules are relatively simple – the nearer of the head, the bigger influence of element on engines parameters. That is why the most importanat element of this system is exhaust collector with its shape and length.
Basicly it is all simple and easy to count, but worse with realisation.
There is even a software enableing to check the effects of done modifications, but its only failure is that not always tell the true.
Steering computer of the injection system (ECU)
Nowadays in times of advanced technic almost every activities concerning managing of engine's work does ECU, so called computer. To the ECU flow among others signals from sensor describing rounds of the engine, loadings, temperature, air pressure, charging pressure, lambda sensor signals. Basing on this constantly changing datas the ECU generates signals steering with injection and ignition system.
In case of doing tuning modifications, implementing of serial programme in ECU may totaly eliminate effects of our work and in extremal situation damage engine.
However some of described above modifications of the intake systems or cylinderhead are possible to do by talented mechanicans and with not much devices' help, doing new programmes of the ECU ourselfs is practically impossible.
In practice we practice two solutions.
In sports cars we use completely new ECU's with simplified software and possibility of its fast programming during road and testbench trials.
In sportive cars we modificate oryginal programmes using specialsitic devices - the same as by CHIP TUNING.
How you can see, the only way is complex adjusting of certain engines' elements.
Achieving of predicted results is possible only by high specialised tuning services, who's workers disposes of specialsitic knowledge and experience.
Basical tool to check out engine's parameters is an engine testbench.
Our testbenches anable very precissive description of every engine's work parameters.
During tests we change many parameters, as length of sucking collectors, we adjust position of the cumshaft, and we observe influences of this changes on external characteristics (torque, power, etc.)
The biggest problem causes mutual dependence of every changable parameters. In practice it means that by change of the cumshaft we have to change pressuring level, size of sucking and exhaust collectors, of course ECU's programme.
Despite of great ardousness of theese analyzes, they are the fastest way to get from the engine what's possible.
Testbench measurments anable to count out the Power of the engine and describing its external characteristics, what has sagnificant impact on acknowledge of traction possibilities of tuned car.