Your engine is just a giant vacuum pump: An Animated depiction of a four stroke engine
Engine timing never really changes much unless there is a mechanical failure or in some of the more sophisticated cars of today with computerized variable valve timing, you could experience a computer or related issue. Most times if this happens you will get a "check" engine code to let you know something is wrong. So for the most part, the mechanical timing was taken care of at the factory or by your engine rebuilder. Ignition timing is taken care of with your tune-up, so all we have left is INDUCTION.
Your engine is nothing more than a large vacuum pump. The proper air/fuel mixture is drawn in, compressed as the engine tries to expel it, ignited and burned at the proper time, which expands and pushes the piston back down and on the next stroke up is expelled through the open exhaust valve, which opened at the correct time and will close as the intake opens so a new volume of air and fuel can be drawn into the engine to start all over again - simple -
Over the years all sorts of things have been used to produce the perfect fuel to air mixture delivered at just the precise moment, at just the correct volume, to give you either the best fuel mileage possible or the most horsepower available or as in most street cars some sort of happy meeting ground of both. Extreme power comes by giving up mileage, extreme fuel mileage comes at the price of giving up maximum power potential - there is no perfect world.
Some of the ways that have been used to achieve this are various types of carburetors, up-draft, down-draft, side-draft, single barrel, multiple barrels and multiple carburetors. Super charging and Turbo charging and fuel injection both mechanical and now electric computer controlled. All are trying to achieve either pure power, pure fuel economy or the best blend of both.
The perfect air fuel mixture for most of us is 14.7 parts of air for every part of fuel and they call this, stoichiometric. Now this is only the perfect mixture after the vehicle is fully warmed up, the air temperature coming in to the induction system is correct, the humidity is at a certain point and you are no more than a thousand feet above sea level.
Yes, you see the problem - how do we do this - we have a cooling system in the car, actually a system to maintain the proper internal temperatures of the engine. Sometimes we are trying to remove heat from the engine and other times we are trying to hold it in. Remember heat is energy and the more I can keep in your cylinder, the more I can eventually send to your wheels as power. We also have used all sorts of methods to both heat the air and then cool the air as it enters the induction system. If the air is to cold the fuel will actually go from an atomized mist to little droplets. Unfortunately liquid fuel in your combustion chamber, as opposed to an atomized gas, does not burn very well and causes all sorts of issues. On the other hand if the incoming air charge gets to hot we can actually vaporize the fuel so completely that there is nothing left to "burn" plus the warmer the air, the less dense, meaning less oxygen per given volume so less fuel can be mixed in to obtain the proper fuel mix so our power begins to drop dramatically so we begin to press on the accelerator pedal harder trying to get more fuel in and our mileage can actually go down because we are now too lean and have gone to far in trying to get the best mileage possible.
In today's cars we can achieve so much because of the computers used in the management of your engine. Today your computer system looks at the ambient air temperature, the incoming charge air temperature, the temperature of your engine, the density of the air coming in and for many it evens knows the altitude you are at. The computer looks at the exhaust as a way to know how completely the fuel is being burned and it measures the need for power, your foot on the accelerator combined with monitoring the speed you are travelling at. It does this constantly and then adjusts the operation of the cooling system to maintain the proper engine temperatures, will adjust the amount of fuel delivered and adjust exactly when to deliver it and when exactly to turn on the ignition to fire it. Pretty amazing isn't it. All of that takes proper care and maintenance. It is more critical today to follow the factory guide lines and schedules right down to the exact oil they want you to use because the whole system working is predicated on the computer carrying out a set of commands based on information programmed into it when new based on the systems working the way they were designed using the fuels, oils coolants, etc. the factory and the original engineers decided on.
Yes you can change those settings and we have the experience to help you do it correctly but in today's world it takes even more thought than it did in the day of carburetors.