Why every automaker is quietly bringing back the inline-six engine

Question about that, wouldn't packaging be an issue unless you really shrunk the engine size? I thought that's what makes LS swaps into planes so interesting because you get a fair amount of power in a small package.

Correct

750iL, but I do appreciate the E31

>Six cylinders are the smoothest engines out there.

I dunno man, have you ever driven a rotary? The design has a lot of problems, but smoothness isn't one of them...

My older brother had a mighty CBX. Smooth as silk, and very fast. Carburetor synchronization was troubling!

Yup I imagine the vast majority of car "enthusiasts" out there wouldn't be able to beat the Golf R Nurburgring lap record of 7:47 [1] in any car of their choosing. And more power would probably only serve to increase their odds of crashing.

[1] https://www.youtube.com/watch?v=gt9l4NwHB8s

I've owned a handful of BMWs (no S54 though) but I'm partial so the sound of the S62 V8. The turbo 6 generations were truly a remarkable change for BMW in terms of power, though.

At the moment, I have a Boxster, and the flat 6 somehow feels smoother than any I6 I've owned. I've done some research and sure enough, the inline 6 is (mathematically) smoother than an inline 6. The only way I can explain the fact that the boxer feels smoother is because it's mounted low and behind me, away from steering components? Whereas in my I6 cars, with the engine in front, you feel it through the front subframe and steering a bit.

It's been done many times before, quite successfully. The Napier Deltic (3 crankshafts!) and Junkers Jumo are two examples. The Commer Knocker is another (which had only one crankshaft I believe). Two crankshafts makes the engine slightly taller, but not egregiously so.

I'd be curious to know more about the heat problem you've mentioned. Naively, there should be much less waste heat to dispose of due to the fact that the same cylinder volume is doing twice the work.

That sounds fantastic but it means nothing in practice. It's like something you'd hear in a "Engineering Explained" video, but with no real-world application. There's so much more that goes into an engine that it doesn't matter.

Again, it's a myth.

Similarly, there was always the debate over rod length (in the same displacement engines). You use the same crankshaft but the piston has the wrist pin located higher. The longer rod was always supposed to make "more torque" because of the angle but that ended up not being the case.

You can verify this buy putting engines together with different bores and strokes that are roughly equal displacements, and with the same heads/cam on them, they will make identical power. Picture something like a 3.50" bore and 4.00" stroke, and vice versa. Look up someone like Richard Holdener on YouTube for actual data. Displacement is displacement, it doesn't really matter how you make it.

Bore is what would make you more power after a certain point, anyway. You get more surface area to fit larger valves, etc. But again, using the same heads (that aren't shrouding the smaller bores), either combination of bore/stroke will make the same power throughout the rev range.

Then you get into things like piston speed and all that but none of that matters unless you're talking about a race engine. And when you are, they'll just rebuild it more often so they don't care how long it lasts.

Here's another read:

https://rehermorrison.com/tech-talk-53-big-bore-or-long-stro...

Nope. As I said, you can build two engines with different bore and stroke, but the same displacement, and they will make mirror images in the power curve.

If it was such and advantage, wouldn't all performance engines have much longer stroke?

The newest Corvette ZR1 makes 1064hp from a 4.1 inch bore and 3.1 stroke. How much power are they leaving on the table by not making it a larger stroke than bore like many inline 6's? (Hint: inline sixes don't have larger stroke than bore for "torque")

Any change in power from a larger stroke is due to the larger displacement. It goes up with a percentage of the increase. Nothing to do with the leverage of the longer stroke.

By the way if you work the math out on that, it's not significant. And there are many other things that go into the losses of and engine turning. It's such a useless micro optimization, like speeding up a function that takes two seconds to run by shortening it by only a couple instructions.

I think we simply call them "Sechszylinder" - six cylinders. Non-inline engines are a small percentage of engines in Germany, so we don't usually call inlines anything. The term for an inline engine is Reihenmotor (I had to look that up!), "line" or "row" engine.

Like electric vehicles?

In my country its based on emissions, 1.6l 4 cyl 140g/km co2 is ~150e, 3 litre V6 300g/km ~500e.

I'm not sure if displacement taxes still exist, but direct car taxes are fairly low in any case (like 200€ per year or so for an average car in Germany?). Most of the tax is paid through the fuel. The actual reason for downsizing (small turbo engines) is that they consume less fuel under light load, which is where car engines spend most of their time. It's not great for longevity though. Car engines had become more and more reliable over time apart from a few teething troubles of occasional new technologies, now some people say it's trending down due to downsizing.

I have a Mazda CX-9 with an I4 and, my anecdote, it sucks on gas. About 14 mpg in non-highway short hop driving. That might be fine as part of larger group but it always feels embarrassingly low.

One of my old cars was a 1996 XJ (Cherokee), 4.0, and I sold it with 319,000 miles.

I still see it around town from time to time, must have 360 on it now. Original engine and as far as I know, transmission as well.

I ran it out of oil once without damaging it.

Since then, I bought two inline-6 Ford F150s from the mid-90s. I plan on running them forever. I bought two so I can learn to work on them, and have a backup to drive. Both manual, as well.

Jeep XJs from the 90s are still great cars to buy, so are the fords from that era (all the engines are reliable, but the I6 is starting to have a cult following online). I was working on that Jeep before I had any mechanical experience at all. It never failed to start.

I had an AMC with the 232 inline 6. Wonderful engine.