This is a topic that a lot of people tend to avoid. They find it difficult before sitting down and trying it or looking it up; its treated like math in a way. I’d like to give an overview of what engine tuning is in layman terms. I will go over an engines mechanics, fuel, timing, sensors and tuning devices.
Engine Basics
An engine is a block of metal that has holes(cylinders) 95.5mm in diameter in the case of a VQ35. Below the cylinders inside the block there is a separate rotating piece of metal called a crank. Inside a cylinder there is a piston that moves up and down, pressurizing as they go up since the top of the cylinder is blocked off by whats called a head. Air and fuel is sent into the cylinder through the head and a spark plug that is screwed through the head and into the cylinder ignites the mixture.
This explosion pushes the piston down into a rod that’s connected to the rotating crank. The stronger the explosions within the cylinders the more force there is to rotate the crank. The crank is connected to the transmission which then sends the torque to the wheels and moves the car.
Fuel and Timing
The fuel entering the combustion is controlled by the injectors spray. The rate in which the injectors open and close and the duration while open determines the amount of fuel delivered. The injectors are controlled by the cars computer, the ECU(engine control unit or module). When you hear the term “timing” being mentioned, this is referring to when the spark plug fires and ignites the compressed air and fuel mixture.
As the piston travels up the spark plug fires before the piston has reached the top (TDC – top dead center). By the time the piston reaches the top and starts going down thats when the mixture is starting to fully ignite. The goal is to have the combustion event occur right after the piston reached TDC but not too late that the piston is already traveling downward too far. When combustion occurs before the piston has reached TDC thats when you break parts because the combustion’s pressure will be pushing down while the piston is still going up.
Engine Knocking
Something important you have to know if you care about the longevity of your VQ or any engine. Learn what knocking sounds like. Knocking sounds like marbles hitting each other repeatedly. You may have heard this when putting a lower octane fuel than a car asks for. The higher the fuel octane the higher the pressure it can withstand before exploding therefore more timing could be advanced. That means having the combustion closer to TDC once the piston starts to come down. If the fuel octane is too low for the pressure being generated in the cylinder then random combustion events will occur without the spark plug even firing.
On Maxima’s and most cars, engine knock is detected via a knock sensor that is mounted in the middle of the engine between the two heads. This sensor tells the ECU when knock occurs and the ECU makes proper adjustments in timing to reduce the knocking.
In the next article I will talk to you about sensors and tuning devices.
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