The quest for enhanced performance from an engine has led many an engineer and owner alike to find out various ways and means to extract the maximum from the engine of the car. Sometimes from the entire vehicle and not just the engine. Tuners like Abarth and Alpina made "hotter" versions of the road cars from FIAT and BMW respectively and thus began a long journey to be knows as an established brand that they are today. Even today the Alpina Logo carries the crankshaft and Weber carburetors insignia to signify the beginnings of their attempts to extract more power. Before there were ECU's and Electronic Fuel Injection systems, there were carburetors and mechanical fuel injection systems (for both petrol and diesel). To get more power from them the mods were simple and would be like : a "hotter" cam, better exhaust system, a bigger carburettor and the like. There was no computer to tinker with. In diesel engines with mechanical injection, you had to tamper with the fuel pumps and if you had a turbo engine you played with the turbo wastegate and tried to compensate with the mechanical boost actuator to let the fueling be correct. The importance of reading the spark plugs was paramount in those times, in case of petrol engine. Though it still is today, but in those days there wasn't any indication of what the air-fuel ratio was doing apart from chopping up spark plugs and seeing the color on them. This is what gave birth to the term "plug-chops". Moving on to the present scenario of a normal car carrying way too much computer wizardry, the way to extract more power presents it's own unique challenges as well as opportunities. Challenges as to making sure you have the complexities of the computer figured out and opportunities as to how a simple laptop can enable you to yield more power. The fundamentals of engine operation have remained pretty much the same - put in air+fuel in an enclosed cylinder, ignite it and let the expanding gases move the piston downwards which in effect turns the crankshaft and consequently the gearbox and the wheels. What modern technology has done is to control these events to a very fine level - leading to greater power and efficiency. Now, what all happens in a remap? Let's take the simplest scenario - you put in more air and more fuel and you make more power. That's your remap accomplished. Now, let's see what a remap in a turbocharged engine is all about and what factors need to be addressed ideally. I stress the word ideally. 1. More air : You take the help of your little friend, the turbocharger. The turbocharger is set to produce max boost of X psi by the factory. After X psi the wastegate opens and the excess boost is routed out to the exhaust than to the intake. Now, either with the mechanical boost controller OR an electrical one, you cause that wastegate to open later and let the turbo exceed the target set by the factory. So, now you have the turbo working harder to enable more air into the cylinders. Right. But, here is the caveat : The turbos are meant to work in a band where they perform the most efficient. You push them harder than they are designed to and they will just end up heating up themselves and the air that they send into the engine. Push them too hard and they can say goodbye pretty soon. We must be knowledgeable about these limits. In the middle of all this the tuner should be familiar with how much the cylinder head can flow efficiently before it creates a blockade which serves no other puropse other than to increase restriction and temperatures. 2. More fuel : In a modern Electronic Fuel Injection system, highly precise amounts of fuel are sent in by the injector which recieves its operating signal straight from the ECU. This precise amount enables a complete combustion leading to better efficiency and power. Now, the remapper will alter the quantity of fuel going inside to compensate for the additional air that he is sending in - otherwise the engine can pretty much self destruct if inadequate amount of fuel is going in. How? more air + less fuel = Lean combustion i.e. temperatures rise, detonation occurs and you can put a nice hole in the piston - destroying the engine. This is the scenario in the case of a petrol engine. Diesels are harmed more by excessive boost and excessive fuel going in which raises the temperature, sometimes alarmingly. Running them leaner, contrary to petrols, actually makes them run somewhat cooler. The caveat : An injector can only flow so much. It is rated for X amount of flow. If you exceed that, the injector is just not going to keep up with the demand and a lean situation can be presented where an inadequate amount of fuel is going on w.r.t demand. Also, the fuel pressure will be altered when you play around with injectors. So a keen eye needs to be kept on that as well. In a normal remap, the injector aspect is somewhat not that important. Most are capable of handling additional flow requirements. Now, at this stage, we know we can hook up a laptop, alter the ECU to put in extra air and fuel and make more power. But - how do we know what is actually going on inside the engine? What are the feedback mechanisms to let us know what effect our alterations are doing on the engine. Is the engine running within limits or is it close to exploding. OK, not exploding but that scenario is never too far away with a bad remap. Feedback Mechanisms: * The Air-Fuel ratio (AFR): When it comes to petrols, this is by far one of the most important ratios. Basically, it tells us what amount of fuel/air is being burnt inside the engine. The readings are taken from the exhaust gases via a sensor known as the "Lambda / O2" sensor. It is also called "the sniffer" because it sniffs the exhaust gases and lets the ECU know what exactly is going on. The ECU takes this reading and adjusts fuel and ignition timing accordingly. We shall discuss the ignition timing aspect of the petrol engine in the next para. Now, when it comes to air fuel ratios, there is something known as the "stoichometric ratio" which is 1 part of fuel for every 14.7 parts of air. More air/less fuel than this is known as "running lean" and less air/more fuel is what is known as "running rich". Now, max power is not really made at stoich but somewhere slightly apart from it. This is what the tuner needs to be aware of for every engine he is remapping. He should not let the AFR go anywhere near dangerously lean which can potentially cause disaster (Lean mixtures run VERY hot or overly rich which can cause black smoke/low power and other issues. So, the AFR's play a critical role in letting the tuner know what exactly the changes in fuel delivery are resulting in. Now, a lean AFR can give rise to what is possibly a nightmare situation for petrol engines= detonation or pre-ignition or engine knocking/pinging. Basically, detonation happens when the gases inside the cylinder have become so heated up (due to the engine running way too lean AFR / wrong timing ) that they self ignite without the need of a spark plug. As we can very well imagine, when things start to happen on their own - it is not an idea scenario. This pre-ignition event happens before the piston has had it's opportunity to reach the top of the cylinder. Hence, it has to fight it's way amidst the already ignited gases to reach the top. Naturally, the piston is just a piece of metal and it can only tolerate abuse for a while till it becomes something like this : In diesels, I am not really sure the use of an AFR meter apart from some Emissions stuff. Please let me know more. *Ignition timing/Knock sensors: The second most critical aspect when tinkering with petrol engines is knowing what effect the ignition timing changes are having on the engine. Basically ignition timing in a petrol is the moment when a spark plug is fired. It is fired some degrees of crankshaft rotation before the piston reaches it's top dead centre. Why so - Let's leave that aspect. Now, if we fire this spark plug wayy too early then the combustion gases can ignite much before than the piston has been able to reach the top i.e. effectively countering the upward movement of the piston. Not an ideal scenario by any means. You do NOT want the piston to fight it's way upwards. This situation can give birth to the phenomena of detonation as we discussed above. If the ignition event occurs too late, that leads to gross inefficiency and loss of power apart from heating up the exhaust/turbo to dangerous levels. Now, the feedback mechanism of a knock happening in the engine is the knock sensor. It's a sensor attached to the engine which let's the ECU know if the engine has witnessed any knock events. If it has, the ECU is programmed to "pull" i.e. alter the ignition timing to a state where knock no longer occurs. This results in a lower power output from the engine. Normally, ECU's are self adapting and if the knock was caused by, say poor quality petrol, over the next couple of batches of good quality fuel the ECU will try to bring everything back to an optimal level. Same is the liability of the remapper. He must keep a keen eye on the knock sensors and see what they are telling him. Under no circumstances should he allow any knock to remain in the remap. *Exhaust Gas Temperature (EGT) Gauge - This is a gauge which has become critical when it comes to remapping diesel engines. As I said earlier, the temperatures in a diesel engine rise proportionately as we pump in more fuel in an effort to make more power. This leads to a rise in the EGT's. It is this EGT that we must monitor closely before it leads to a total meltdown. Usually, the placement of an EGT probe is done either before the turbo i.e. in the exhaust manifold itself or the post turbo exhaust path. Some guys place 2 probes at both the places. Normally, the reading pre-turbo is more critical and important. That is the temperature your pistons,valves and the turbo is immediately seeing. This is the temperature you must keep within safe limits. This EGT is logged at varying engine speeds and under varying conditions of load. Only when the EGT's have been logged across the rpm range and under varying loads can the remap be called a safe remap. Many drivers have a EGT gauge in their remapped diesel cars and keep a keen eye on it on and off. By the above arguments, what I have attempted to give is a broad outline of what all factors need to be kept in mind while thinking about the concept of a remap. A holistic view, if there is one. As always the same disclaimer holds true that the above are the musings of a person with no background in Mechanical/Automotive Engg. Just a hobby and a passion. Feel free to discuss and add more constructive points to the discussion. Cheers.