V6 vs V8 vs Inline-Six: Which Engine Layout Is Smoothest? (Redlined 101, Ep 16)

V6, V8, or inline-six? Take the same size engine, three liters, and lay it out three ways. One rumbles, one shakes, and one runs glass-smooth. And the smooth one is not the one you'd guess. Last episode was about what an engine makes; this one is about how it's built, and why that changes the way it sounds and feels.

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The three layouts

• V8: two banks of four cylinders, set at an angle to each other in a V, sharing one crankshaft.
• V6: two banks of three, also in a V.
• Inline-six (straight-six): all six cylinders in one straight row.

Same displacement, same cylinder count for two of them. The difference is all in how the pistons and the crank are arranged, and that decides which forces cancel out and which ones shake the car.

The rumble: the V8

The rumble is the V8. With eight cylinders and four-stroke combustion, it fires once every ninety degrees of crank rotation. That part is perfectly even.

The lump comes from how those firings are shared between the two banks. Each bank of four fires unevenly: two pulses land close together, then there's a long gap. Each bank has its own exhaust manifold, so each exhaust hears that uneven rhythm, not the smooth one the whole engine makes.

That lumpy beat out each exhaust is the burble. It's the sound people mean when they say a V8 "sounds like a V8." It's not roughness in the engine; it's rhythm in the pipes.

(How you route those pipes changes the sound too. That's a different episode: muffler delete vs resonator delete vs straight pipe.)

The shake: which one is it?

So the V6 or the inline-six: which one shakes? Both have six cylinders. If you think more cylinders automatically means smoother, you'd expect a tie.

It's the V6

The V6 shakes. It's two banks of three, and here's the problem: a row of three can't cancel itself.

Picture one bank of three pistons on its section of crank. While the piston at one end of the crank is pushing up, the one at the other end is pulling down. That doesn't make the engine bounce up and down; it makes it rock end to end, like a seesaw. The middle piston can't fix it, because it sits right on the pivot. Put two of those rows side by side in a V and you still have a rocking engine.

That's why many V6s add a balance shaft: a spinning weight, driven off the engine, that exists only to fight the shake. It adds parts, weight and a little friction, all to cancel a vibration the layout creates on its own.

The smooth one: the inline-six

The inline-six needs none of that. Its crank is a mirror: the back three pistons copy the front three in reverse.

Number the cylinders one to six, front to back. Cylinders one and six move together. So do two and five, and three and four. Whatever rocking the front half tries to start, the back half does the exact opposite at the exact same moment. The rocking of one half cancels the other. No balance shaft, no tricks. It's smooth because of how it's laid out.

How smooth? Balance a coin on one at idle, and it stays standing. That's the classic party trick for a straight-six.

That's why BMW and Toyota's 2JZ swear by it. Both are famous for their straight-sixes, and the 2JZ shows up again in next episode, with two turbos bolted to it.

The catch: six in a row is long

If the inline-six is so good, why isn't everything an inline-six?

Because six in a row is long. Most front-wheel-drive cars mount the engine sideways across the engine bay, so it lines up with the front axles. A V6 is short enough to fit that way. A straight-six usually isn't. Turn it sideways, and it doesn't fit.

As front-wheel drive took over everyday cars, the V6 took over with it. Shorter engine, fits the bay, and a balance shaft takes care of the shake. The inline-six stayed mostly in longitudinal, rear-wheel-drive layouts, where a long engine pointing front to back is no problem. (More on why the layout of the driveline matters in FWD vs RWD vs AWD.)

Which one suits you?

There's no single best layout. Each one wins at something:

• V8: the sound. Lots of cylinders in a compact block, and that burble from each bank.
• V6: the space. Short enough to mount sideways, which is why it's in so many family cars and front-drive performance cars.
• Inline-six: the silk. Naturally balanced, no balance shaft, smooth from idle to redline.

And the myth that more cylinders always means smoother? The V6 and the inline-six settle that. Same six cylinders, very different feel. Layout beats count.

How to tell which one you've got

Pop the hood and look at the top of the engine:

• One cylinder head, six coil packs or spark plug leads in a straight line, front to back: inline-six. It'll usually sit lengthwise in the car, pointing at the front bumper.
• Two cylinder heads in a V, three plugs on each side: V6. In a front-wheel-drive car it'll usually sit sideways, with one bank toward the radiator and one toward the firewall.
• Two heads, four plugs on each side: V8.

Engine covers can hide all of this, so if in doubt, check the engine code in the owner's manual or on the sticker under the hood.

The verdict

V8 for the sound, V6 for the space, inline-six for the silk.

So next time your buddy says more cylinders means smoother, put a coin on his V6.

Recap: V6 vs V8 vs inline-six

1. V8: fires every 90 degrees, but each bank of four fires unevenly. That lumpy beat is the burble.
2. V6: two banks of three. A row of three rocks end to end, so many V6s add a balance shaft.
3. Inline-six: a mirror-image crank. The back three cancel the front three, smooth enough to balance a coin.
4. The catch: an inline-six is long and doesn't fit sideways for front-wheel drive, so the V6 took over.

Which one's in yours: V6, V8, or inline-six?

Next episode: small turbo vs big turbo vs twin turbo.

Frequently asked questions

Which is smoother, a V6 or an inline-six?

The inline-six. Its crank is mirror-symmetric, so the front three cylinders cancel the rocking of the back three. A V6 is two rows of three, and a row of three rocks end to end, so many V6s need a balance shaft to calm it down.

Why does a V8 sound like that?

A V8 fires every 90 degrees of crank rotation, but each bank of four fires unevenly: two pulses close together, then a long gap. Each exhaust hears that lumpy beat, and that is the burble.

What is a balance shaft?

A spinning weight driven by the engine that exists only to cancel a vibration the engine can't cancel itself. Many V6s use one to fight the end-to-end rocking of each bank of three.

Why don't more cars use an inline-six?

Six cylinders in a row make a long engine. Most front-wheel-drive cars mount the engine sideways, and a straight-six usually doesn't fit across the engine bay, so the shorter V6 took over.

Do more cylinders make an engine smoother?

Not by themselves. A V6 and an inline-six both have six cylinders, but the inline-six is far smoother. The layout and the crank decide how well the forces cancel, not just the cylinder count.