The firing order of a four-stroke, four cylinder, inline engine is always either 1342 or 1243, so that the power strokes of the cylinders separated furthest from each other, i.e. 1 and 4, do not occur right after each other.
However, in a horizontally opposed four cylinder engine, like a subaru flat four, or a VW beetle engine, the firing order is usually 1324 or 1432.
Can anyone give me a good explanation as to why this is so?
In mostg flat engines each pair of opposing pistons shares a crankpin so one row will be at TDC while the other is at BDC. Most logical firing oder is going to be one from the first pair, one from the second pair, the other from the first pair and the other from the second pair. I assume your numbering systems is kind of like this
1 4
2 3
If that is the case both those firing orders might be valid to design. Reasons might be how exhaust or intake manifolds are designed.
And, of course, a radial would have firing order of 1234. :rolleyes:
Guess again. Radials that I’ve seen have an odd number of cylinders and fire alternate cylinders such as 1357246.
That’s where I got you.
The April 1982 issue of Popular Science features a NASA prototype radial four cylinder two-stroke turbodiesel aircraft engine.
I almost wrote “all radials have an odd number of cylinders” and then changed it to all “I’ve seen.” Four will work with the lineup 1 power; 2 compression; 3 intake; 4 exhaust. Someone else can puzzle out the crankshaft.