- S​orry for the blurry photo. Or maybe I’ve got severe cataracts. Who knows?

Crossplane vs Flatplane

F​latplane crank vs Crossplane crank

5w ago

A​s the era of combustion engines comes to a close, and with more and more manufacturers shunning combustion engines like a Heavy Metaller shuns baths, the sound of V8s will be replaced with the sound of, well, a library. A slight hum, akin to that of a printer or computer in an exceptionally quiet building is all that we’ll have left. Unless you pay more for Porsche’s spaceship sounds. But in the meantime, let’s make hay. So in honour of this sentiment, I’ve decided to divulge some arcane combustion engine knowledge to whoever can be bothered to read this. (Thanks for being here, by the way).

Before we get ahead of ourselves, though, and get to the meat and bones of the article, we should acknowledge the vegetables: we should try and wrap our heads around what a crankshaft is, and what it does for a living. Basically, it‘s a metal rod with lumps sticking out of it at strange, seemingly random angles (see picture below). It’s natural habitat (if you didn’t read that in Sir Attenborough’s voice, then shame on you), is towards the bottom of the engine, connected to the pistons, which have a hole in the bottom of the bit that goes into the cylinder head. As we all know, pistons go up and down. Because of people with big foreheads, the crankshaft converts reciprocal (up and down), motion into rotational motion, which is what the wheels need to go round.

A​ flat plane crank.

A​ flat plane crank.

Now for the real meat ‘n‘ bones of the article. Cross-plane crankshafts have a 90 degree rotation between crank ‘throws‘. In layman’s terms, every time the crankshaft rotates by 90 degrees, one of the cylinders fires. In comparison, a flat plane crankshaft has to go 180 degrees before one of the pistons can be bothered to do anything. This difference means that engines with a cross-plane crank need counterweights to make it run more smoothly, which in turn (pun intended), means that cross-plane cranks aren’t as high revving, literally because they’re heavier to turn. American V8s tend to be cross-plane cranks, which deliver the lazy power typical of muscle cars, whereas European V8s often have flat-plane cranks, which gives you the shriek associated with Ferrari V8s and suchlike. There are exceptions to both, though. For example, the Ford Mustang GT350 has a flat-plane V8, and the Lancia Thema had a Ferrari-derived cross-plane crank V8. I​n terms of which is better though, there’s no real answer to that. Both have their good points, as well as their weaknesses, so it’s as much down to personal preference as anything else.

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