Tuning the Cylinder Head and the ECU
The cylinder head is as important as the cylinder block, so maximizing the performance of a racing engine requires the same attention and expertise in tuning both. The cylinder head consists of several segments that can be tuned. These are: valves and their accompanying elements (seats, valve guides, valve springs, valve spring retainers and locks), the camshaft, the combustion chamber and the intake and exhaust valves. All these together greatly affect the performance of a newly built engine.
In this segment of tuning, the aim is to add as much air as possible - something that is strictly limited in serially produced engines. Adding air is limited not only by the height, the time and the angle at which the camshaft opens the valves, but also by the width of the channels and the valves. As we know the fuel and air ratio to be 1:12 or 1:13 (depending on your tuner’s choice), we begin to understand how hard and how demanding it is to make it possible for an engine to take in as much air as we want it to. Our story of tuning the cylinder head begins with calculating what the maximum diameter of the valve is.
Valves and Accompanying Elements
The dimensions of the combustion chamber dictate the maximum width of the intake and exhaust valves, be it for two valves (one next to another) or for 4 valves (one pair opposite to the other pair). Having said that, your tuner will also leave a small gap between the two, just enough to make sure they don’t touch. However, in order to be able to install bigger valves in the first place, we must expand the valve seats. This means that the cylinder head will be machine-processed in a specialized workshop, where a professional will take out the existing seats, expand their nests up to the biggest diameter possible and then install new seats.
The aforementioned seats also require the valves to be positioned at certain angles so as to enable uninterrupted “breathing” of the engine. Tuners have a few options for this, but most often, they opt for 45 degrees and 30 degrees. You tuner can also add two smaller angles to soften the edges created by processing the valve seats, again, to facilitate air circulation. The exact same procedure must be applied to the exhaust valves.
A serial valve is made in a standard (quality) that requires the valve head and neck to be massive, whereas the valve pole should be made in the dimensions and quality that fits the valve guides. Unlike the serial valve, high-quality racing valves are evidently lighter, which is especially important for easier and quicker acceleration of the engine. Because of that, the head of the racing valve is thin and elegant, the neck is discrete enough to connect the head to the pole, and the pole is refined to meet the valve guide.
Once we have defined the valves and the valve seats, next we deal with valve springs. The purpose of a spring is to retrieve the valve in its initial position once the camshaft peak is finished pressing the valve and opening the channel. We know that tuned engines rev at higher rpm, so now serial valves which are made in certain hardness designed for lower rpm can no longer retrieve the valve fast enough, causing a constant hammering on the valve. Your tuner’s task is to determine a new, desired hardness of the valve springs that will retrieve the valves seamlessly at certain rpm as close to the camshaft as possible.
Manufacturers that produce racing camshafts usually produce the above mentioned accompanying elements as well, and these can be found in specialized tuning shops.
Cylinder Head Channels
Try pressing one of your nostrils to inhale deeply. And now, release it and inhale again. We hope now you understand the importance of the cylinder head channels through which air and fuel circulate. A tuned engine needs to have much wider channels than a serial one, whose channels are dimensioned to maintain fuel efficiency. Of course, this is not what you’d expect from a racing engine, so you are allowed to install channels as wide as the calculation allows. But how and how wide?
The width of a channel is calculated according to the size of the valves that we opted for instead of the serial ones. Once your tuner has defined the valve angle, he will determine the size of the channel by deducting the angle and the valve pole surface from the valve diameter.
Many years of building and testing racing engines have lead tuners to conclude that top-notch engines used in circular races require that the fluid dynamics be cca 120 m/s. When it comes to rallying and hill climbing, it can be somewhat slower, depending on the design of the engine.
A tuner will calculate what the necessary speed of the fluid should be based on the crankshaft’s circular path. When it comes to the exhaust valves, the diameter should be as big as possible in order for the exhaust gases (that have expanded manifold) to leave the cylinder head, making way for a new cycle of taking in fresh air and fuel.
The speed of the gases leaving the combustion chamber is so great (greater than the speed of a sound) that it breaks the sound barrier in the exhaust system. In order to silence it, manufacturers install sound silencers, because otherwise the noise would ne unbearable to the human ear.
If we have prepared the cylinder block in all required tolerances and the cylinder head in the sense that we gave it more air, we can introduce the a higher quality durable camshaft as the key element that will boost engine power.
Depending on the number of cylinders, a camshaft has several “hills” in the shape of an egg cut in half. Unlike racing camshafts, standard ones have a much lower rise, which represents the difference between the base and the peak (the pointy part). Breathing of such an engine is conditioned by a small economic lift (for example 8 or 9 mm).
Racing camshafts have a much higher rise (11.5 to 13 mm), almost 40-50% over the standard one. Why is this important? The reason lies in the fact that the pointy part dictates how long the valve is open, that is, the length of the path from the moment the camshaft begins opening the valve until the moment it is closed again. The longer the path, the longer the time the valve’s closed, and more air and fuel mixture gets sucked in.
We will give you one example. If we have a four-cylinder atmospheric engine the volume of which is 1,600 ccm, and a camshaft that holds the valve open long enough to suck in a volume close to the cylinder capacity, that kind of engine will be very fast, much faster than an engine that will be able to take in, say, 350 ccm. The camshaft enables the engine, whose head and block have been tuned, to breathe fully and produce strength.
The situation is a bit different when it comes to turbo-charged engines in the sense that taking in air is aided by a turbine that employs extra pressure. So, if your tuner programs the turbine to a pressure of say 1 bar, the performance of such engine will be much better than that of an atmospheric engine of the same volume. However, turbo-charged engines require additional cooling due to higher working temperatures and the extra heating of the piston head and the exhaust valve. In some cases, more fuel than necessary is added due to the fact that cold fuel cools the elements it touches.
Compression ratio is a very important segment in tuned cars. It represents the ratio between the total volume and the compression volume of the cylinders. The total volume of the cylinders is a sum of the volume of all cylinders, the volume of the seals beneath the cylinder head, and the volume of the combustion chamber whose shape is most often irregular and requires special instruments for measuring. This method of calculation may vary depending on the position in relation to the engine block.
For example, if our math shows that the total volume of the cylinders is 500 ccm and the compression volume of the cylinders is 50 ccm, the compression ratio will be 10:1. For the sake of building a race engine, your tuner will strive to increase the compression ratio from 11.5:1 up to 13:1, depending on the purpose of the engine. Increasing the compression ratio can be achieved in many ways. The most frequently used one is replacing existing pistons with high compression pistons that have raised heads, thus reducing the compression space dramatically. Most piston manufacturers state the compression ratio for which the piston was designed.
One important thing to note is that higher compression ratios (from 11.5:1 and up) require using higher quality fuel with the octane rating being no less than 100. The reason behind this is preventing detonation inside the engine; although contemporary electronic systems can override this issue by using different engine maps.
If you strive for high-end racing performance, you can opt for reducing and balancing the rotating masses like the crankshaft, the flywheel, the clutch basket, the pistons and the piston rods.
As we already mentioned in the previous article when we talked about the crankshaft, turning linear motion into circular motion gives us a higher power engine that rotates raster. Building high-end racing engines requires a substantial reduction of weight which is conditioned by the weight of the elements inside the engine, these being the pistons, the piston rods and the piston bolts. The total weight of these elements dictates the minimal weight of the crankshaft. As a counterweight to all these rotating elements, a tuner will opt for a lighter flywheel necessary to run the system. One can only go below this in case of an extremely powerful engine on which the rotating masses no longer have an effect. In case the engine power is so great that it makes it impossible to transfer the power to the driving wheels, one solution is to install a double clutch.
Remapping the ECU
Having tuned the cylinder head, the cylinder block and all the accompanying elements, your tuner will remap the ECU so that it can manage supplying the new engine with fuel and the moment of combustion. Normally, tuners begin with a basic map at low rpm (2-3,000 rpm) which is being displayed on the dynamometer. The number of revolutions is then gradually raised and adjusted until the parameters are nearly ideal. Remapping an ECU is a very sophisticated process and one not to be entrusted with beginners, but only with professionals who either sell ready-to-use products or have the knowledge and the skill to make completely new maps on the spot.
Important notice: everything that was stated above falls under general tuning principles. In some specific cases, one must act in accordance with the chosen elements and electronics that they plan to install.
With this segment, we have rounded up the story of tuning the engine. In our next article we will talk about tuning the transmission tuning, so stay with us and feel free to write for any questions and unknowns.