Taking a break from the Lincoln/"The Car" project. But I had this idea for what was going to be a table showing how the four engine cycles (Intake / Compression / Combustion / Exhaust) overlap in the GM 2.8 Liter V6.
Exciting, huh? Gearhead stuff ahead!
In one of my old auto mechanic books, there's a simple illustration of the overlap in a V8. I'd been meaning to do something similar to that for years just out of curiosity. I did scribble a table in my notebook last night, but when it came to copying that to a CAD drawing, I decided on a diagram instead. Think of it as a map of how the engine runs.
For the car-guys-in-training:
Each ring is a cylinder, #1 on the outside, #6 on the inside. This follows this engine's 1-2-3-4-5-6 firing order.
Red represents the combustion cycle (or "stroke"), where power is generated.
Gray is exhaust.
Blue is intake.
Orange is compression.
Each cylinder follows these four cycles (hence "four-cycle" or "four-stroke" engine). Technically, the intake cycle should be first, since everything else depends on that: air and fuel are drawn into a cylinder, the mixture is compressed, then it's ignited, and finally the burnt gases are pushed out of the cylinder.
I put the combustion cycle first on cylinder #1 (closest to 0 degrees) because getting all those things to happen properly depends on getting that cylinder set up properly (Top Dead Center) while the engine is being put together.
The wheel represents two full turns of the crankshaft, since it takes that long for a single cylinder to go through all four cycles--intake and compression in one, combustion and exhaust in the next.
Looking at how the circular markers line up, you can see which pairs of cylinders are moving together: 1 and 4, 2 and 5, and 3 and 6.
While Cylinder 1 is burning fuel, #4 is breathing in--and both pistons are moving downward.
As #1 breathes out, #4 is compressing its air-fuel charge--both pistons moving upward.
As #1 breathes in, #4 burns its fuel--both pistons moving down.
As #1 compresses, #4 blows its exhaust--both pistons moving up.
The other pairs perform the same way, but overlap the rest in such a way that there's always one cylinder firing for every third of a rotation, or 120 degrees.