Inline-Six vs V6 vs V8: Luxury Car Engine LayoutsExplained, and Which to Buy in India

An inline-six puts six cylinders in one straight row, a V6 splits them into two angled banks of three, and a V8 uses two banks of four. The inline-six is the smoothest of the three by design, and it’s the reason BMW, Mercedes-Benz and Land Rover all use one in their big SUVs and saloons. A V6 is more compact, so it suits cars that don’t have room for a long engine. A V8 gives you more power, more torque and a sound the others can’t match, at a much higher price. For most Indian luxury car buyers, a 3.0-litre inline-six is the one to buy. Pay for a V8 only if you want it for its own sake.

The three layouts at a glance

Price bands are our reading of Autocar India’s October 2026 price listings and its V8 list, ex-showroom. They’re a rough guide.

Why an inline-six is so smooth

A piston going up and down shakes an engine. The trick is to get another piston to cancel that shake. In an inline-six, the cylinders work in matching pairs, and they are arranged symmetrically along the crankshaft, so the forces from the front half mirror those from the back half. The cylinders also fire evenly, one every 120 degrees of crank rotation, so the power delivery has no lumps. As Hagerty puts it, the layout is “naturally balanced”.

That’s why Mercedes-Benz went back to it. In January 2018, the company’s then research head, Ola Källenius, said it would replace its V6s with inline-sixes. He called them very smooth, but smoothness wasn’t the only reason, and the others explain why the layout has returned so strongly.

They’re cheaper to build. A six is effectively a four-cylinder with two more cylinders. Mercedes said its four and six share essentially the same combustion chambers and 90mm cylinder spacing, so they can run on the same production line. BMW’s three-, four- and six-cylinder engines also share bore spacing, according to WhichCar.

Turbos are easier to fit. In a V engine, the hot exhaust side and the cool intake side are hard to separate, and there’s only so much room in the valley between the banks. A straight six has one side free for the turbos and the other for intake, as Hagerty explains.

Length stopped being a problem. Long engines used to eat into crash structures. Moving belt-driven accessories to electric drive has shortened the package.

In India, this is the engine in the BMW X5 and X7, the Mercedes GLS 450, the Range Rover and Range Rover Sport 3.0, and the Defender 3.0.

Where a V6 still makes sense

A V6 is shorter than an inline-six, which helps fit it in a tighter engine bay. Inline-sixes are hard to package across the car, so any transverse-engined model that needs six cylinders generally uses a V6. A V6 derived from a V8 can come with a cost: WhichCar says Mercedes’ old V6 was a V8 with two cylinders cut off, and its 90-degree angle compromised refinement against a 60-degree design.

Don’t read too much into that. Modern V6s are well developed, and the engine’s designers usually have an answer for the shake. Audi and Porsche both use 3.0-litre turbo V6s in India, and the Maserati Grecale Trofeo’s V6, developed for a supercar, makes 530hp. In a Q7 or Cayenne, the layout won’t be what you notice. The tune, the gearbox and the sound matter much more.

V8: what you’re really paying for

A V8 fires every 90 degrees of crank rotation. Most road-car V8s use a cross-plane crankshaft, which runs smoothly and produces the familiar deep burble. Flat-plane V8s, used in many expensive European sports cars, rev faster and sound higher and harder, but vibrate more, as Jalopnik explains.

Whichever you buy, a V8 is mainly a power and character upgrade. The numbers below, from the Porsche Cayenne, tell the story.

Source: Autocar India, 31 October 2026.

The V8 costs Rs 70 lakh more on the road for 147hp and 160Nm extra. The GTS brings other equipment, so this isn’t a pure engine price, but it shows the scale.

The Defender makes the case even more sharply. Its 3.0-litre inline-six makes 400hp and, since the car went local in October 2026, costs Rs 1.18 crore. The 5.0-litre V8 made 425hp when Autocar India listed it in September 2025, at a price starting from Rs 1.52 crore. That’s a lot of money for 25hp. You’d buy it for the noise, and that’s a perfectly good reason.

Which luxury cars in India use which engine

Sources: Autocar India model pages (October 2026) and Motozite’s earlier reviews. Equipment and tune differ by variant.

Look at the X5 against the Q7: same 3.0 litres, and the BMW has about 40hp more. That gap comes from the tune, not from the layout. So choose the car first, and treat the layout as a tie-breaker.

Notice too where V8s are going. Two of the cars on this list use one as part of a plug-in hybrid. As Autocar India’s list shows, the V8 is increasingly reserved for cars above Rs 2 crore.

Is a V8 expensive to run in India?

Yes, though the fuel bill isn’t the biggest issue. On a used car, a V8 means more oil, more complex turbo plumbing in a hot engine bay and a higher repair risk if anything serious goes wrong. Team-BHP owners of older Range Rovers warned of a possible Rs 15 lakh to Rs 20 lakh for a major drivetrain failure. If you’re buying used, keep the warranty running or budget accordingly. Our guide to the pre-owned luxury cars with the lowest running costs puts real owner numbers on this.

A big six is usually the better compromise. It has the smoothness and the torque, and a Mercedes E 350 CDI owner on Team-BHP reported about Rs 1.25 lakh a year in running costs on a used V6 car past 1.5 lakh km. Note that this is a V6 Mercedes, which leads to the next point.

Check the engine, not the badge, on a used car

Badges have stopped telling you what’s under the bonnet.

• BMW: an X5 xDrive40i is a 3.0-litre six, but BMW’s numbers don’t always match engine size, so check each car.
• Mercedes: a 450 today is a 3.0-litre inline-six. Older cars with similar names may be V6s, because the switch took years. The E 350 CDI above is one.
• Audi: a badge number isn’t an engine size. A Team-BHP case we cited in our pre-owned Audi guide involved a Q5 described as a 3.0 V6 whose RC showed a 1,964cc four-cylinder.

So check the cubic capacity on the RC. Anything around 2,995cc to 2,999cc is one of today’s 3.0-litre sixes. About 3,982cc to 4,395cc is a modern V8. A seller’s listing title isn’t proof.

Our verdict: which engine should you buy?

• Most buyers: the 3.0-litre inline-six. It’s smooth and strong, and you get most of what a V8 offers at a much lower price. A BMW X5 or Mercedes GLS is the obvious place to start.
• If you like a car that uses a V6: don’t let the layout stop you. A Q7 or Cayenne is a great car, and few owners would feel the difference in balance.
• If you want a V8: buy it now, buy it new if you can, and enjoy it. Do it for the sound and the character, because the sums won’t justify it. You’ll want the warranty too.

You can compare new luxury cars and browse pre-owned luxury cars listed by sellers on Motozite. For a closer comparison of the big six-cylinder rivals, see BMW X5 vs Mercedes GLE vs Audi Q7.

FAQ: inline-six vs V6 vs V8

Is an inline-six better than a V6?

For smoothness, yes. An inline-six is naturally balanced and fires every 120 degrees, and it leaves more room for turbos. A V6 is shorter and can fit where a straight six can’t. In a modern luxury car, the tune, gearbox and sound usually matter more than the layout.

Why is an inline-six smoother than a V6?

Its cylinders work in mirrored pairs along one crankshaft, so the forces from the front half cancel those from the back half. A V6 has two banks of three, which don’t cancel as neatly on their own, so its designers need more work to reach the same smoothness.

Why did Mercedes go back to inline-six engines?

Mercedes announced in January 2018 that it would replace its V6s with inline-sixes. It said they’re very smooth, and that they share cylinder spacing and combustion chambers with its four-cylinder engines, so they can be built on the same line. That saves money and suits turbocharging and hybrid systems.

Is a V8 better than an inline-six?

A V8 makes more power and torque and has a richer sound, but it costs far more and is thirstier and more complex. In India, the Cayenne GTS V8 costs Rs 70 lakh more on the road than the V6 Cayenne, for 147hp more. Most buyers will be happier with a strong six.

Which luxury SUVs in India have an inline-six engine?

The BMW X5 and X7, the Mercedes GLS 450, the Range Rover and Range Rover Sport 3.0, and the Defender 3.0 all use one. The Audi Q7 and Porsche Cayenne use a V6 instead.

What is the difference between cross-plane and flat-plane V8s?

A cross-plane V8 has crank pins set at 90 degrees, which gives a smooth engine and the deep burble most people associate with V8s. A flat-plane V8 has its pins in one plane, so it revs faster and sounds higher-pitched but vibrates more. Many European sports cars use flat-plane cranks.