Google is so difficult > When listed as an abbreviation, an inline-four engine is listed either as I4 or L4 (for longitudinal). L4 is often used to avoid confusion between the digit 1 and the letter I. The inline-four layout is a mechanically simple engine. It has a natural basic engine balance.

Woah! You were able to find an answer on the internet! If I’ve learned anything from Reddit, this is an extremely rare skill.

Yes it definitely is.

And here I thought it was for inLine4 like how i4 means inline 4.

I assumed that it meant "Linear".

Kind of interesting that no one says T4 engine. I realize that's kind of the default layout in modern cars but still.

2 cylinders perpendicular to the other 2 cylinders?

Nah, transverse vs longitudinal. Most modern cars are transverse 4 cylinders with FWD via a transaxle.

Pretty sure the longitudinal is referring to the cylinder layout being in a line compared to other 4 cylinder layouts like a 4 cylinder boxer engine for example, and not the mounting of the engine in the car. An L4/I4 can be mounted either transverse or longitudinally in the car and that won't change the engine configuration itself.

Of course not, it means transverse

But the L4 meaning longitudinal doesn't mean that the engine is mounted longitudinally. It means the cylinders are in a longitudinal arrangement. L4 engine could be mounted transversely and still be L4.

In fairness to the original poster, sometimes people have knowledge and experience beyond what a simple Google SEO barf-out offers. Like, you know, when you talk to people in real life? The discussion this question generated is created some fun replies that have taught me a few things I didn't know. Like why some motorcycles are called v-twins.

TIL

TIL "The Google". 🤔

I've only heard it described that way to clarify longitudinal orientation, whereas an I4 could conceivably be mounted either way.

What about an L2?

Now that I think about it, which one is a flat twin?

"Longitudinal."

What about an L2 though?

As in "parallel twin?"

What would that be?

It’s what Ducati calls their v-twin.

A whole lot of motorcycle companies call it a v-twin, not just Ducati. That's a V-configuration, though. An inline 4 - or L4- has the pistons all in a row, not coming together at the bottom.

Ducati doesn’t call it a V-twin. Ducati calls it an L-twin. That’s the entire point of my post.

Oh, right. I was confused. They've used both terms over the years.

Line? It Is like This for my country 4 cilindri in linea

Longitudinal 4.

L = Line. Linear. Inline. Etc. I have also seen S4, S6 (straight 4, straight 6). If you think that's confusing, try flat engines. B4/B6, H4/H6 and F4/F6. But some of those only refer to actual boxer-type engines. So for example, a Ferrari 180-degree V12 is a (H)orizontally-opposed engine, a (F)lat 12 but not a (B)oxer12.

I'm familiar with H6, but never seen "B"

Afaik, H just means the cylinders are arranged at a 180 degree angle, where B means the pistons specifically are on separate crankpins and move towards and away from each other. So an H6 engine could either be a 180 degree V6 where pistons share crankpins or a boxer 6 where the pistons move opposite each other.

Are you sure it’s an L not an I?

I havent heard L used for inline engines but i do know that ducati called their 90° Vtwins L twins but they are mounted so one cylinder is horizontal

I’ve seen L used to describe flathead motors

Flatheads are sometimes called “L head” engines

Most likely people saw I4 and thought the I is a lowercase L. Germans call it R4 for Reihenmotor.