Why 270-Degree Parallel Twins Have Become So Popular (2025)

We've seen parallel-twin engines in motorcycles for a long time. But until recently, they were limited to 360 degrees or 180 degrees. Now, times favor the middle point of these: a 270-degree layout. Wait, what do these degrees even mean?

In simple words, a 360-degree twin engine has two crank pins on the same side — the two pistons move together but fire alternatively. On the other hand, a 180-degree parallel twin features two opposing crank pins — when one piston rises, the other falls. In a 270-degree parallel-twin engine, the crank pins are offset by 270 degrees — when a piston is at TDC (top dead center), the other one is midway through its rising stroke.

With that out of the way, let’s come to the meat of the matter: why are motorcycle manufacturers adopting 270-degree parallel twin engines over anything else? There are a few reasons, the biggest being the new emissions norms. But there’s more to this story than just regulations. Let’s dive into what makes cross-plane parallel-twin engines so good for modern motorcycles. And no, Yamaha isn’t the only one to produce crossplane engines, kiddos!

Emission Norms Are Killing Inline-Four Screamers

The biggest reason parallel-twin engines are replacing inline-fours is down to the latest emission norms. Ryan F9 gives a terrific example in his video. Essentially, Euro 5 emission norms cut down carbon monoxide emissions by 12 percent, nitrous oxides by 33 percent, and unburned hydrocarbons by 41 percent. The latter is the biggest culprit here, which is making engines illegal today.

Sure, most of the hydrocarbons get burned during combustion, but a tiny bit of them get left behind in the cylinder’s crevices and remain unburnt. Take the Honda CBR1000RR and the 2018 Honda Africa Twin — both are 998cc, but the Fireblade has almost twice as much space for unburned hydrocarbons as the ADV. This is the 40 percent reduction Euro 5 is asking for, and the reason parallel-twin engines are replacing our favorite inline-fours.

But wait, why can’t manufacturers use V-twins or thumpers? Simple: thumpers are crude and V-twins are notoriously tricky to fit in a frame unless you have a long, raked-out cruiser frame. Just look at how much work went into fitting the L-twin engine in the 916 frame while maintaining a perfect 50/50 weight distribution. Tamburini was truly a genius.

The 270-Degree Firing Order Is Smoother Than 180-Degree And 360-Degree

Parallel-twin engines are much smoother than singles, but only when they are small. Increase the displacement, and you suddenly have two massive pistons moving up and down, next to each other. That produces a lot of primary and secondary imbalances in the engine. The primary imbalance (aka vibrations) is easier to offset with the pistons moving in a separate direction and canceling each other out, which is why a 270-degree crank is smoother than a 180-degree crank. The roughest is the 360-degree crank.

The problem comes with the secondary imbalance, which is the upward force that exists when every conrod has to straighten itself. This imbalance exists at both the top dead center (TDC) and the bottom dead center (BDC). No matter what you do, the balance at TDC will double at BCD, and this matters when the pistons are large and fast-moving.

270-degree cranks fix this issue to an extent. Because in such a configuration, the first cylinder fires, the engine rotates 270 degrees, and then the second cylinder fires. So, when the first cylinder drops, the second one follows three-quarters of a rotation behind. The result is an uneven firing order of 270-450-270 degrees. Essentially, the second piston is at TDC when the first one is halfway down to BDC, resulting in excellent secondary balance.

Excellent Throttle Response, Sound, And Character

360-degree parallel twins have been around for a long time for a reason — they are easier to produce and can get away with using a single carb. It’s easier than syncing two imprecise carbs (a headache on its own). Since the pistons move together, you need to double the counterbalancers, which makes the crank heavy. This results in a meatier power delivery that’s not sharp. It’s a good way to make a small engine feel like a big one.

Since this idea did not convince Japanese manufacturers, they started producing 180-degree parallel twins, where pistons move in balance with each other. There’s no need for substantial counterweights, so the crankshaft feels lighter and can rev faster. Plus, no energy is lost to squeezing air in the constantly changing crankcase volume.

But the 270-degree parallel twin performs even better here for a couple of reasons. First, this firing order eliminates inertial torque since both the pistons do not reach TDC and BDC at the same time. So the engine has a more free-revving character and sharper throttle response. Second, the engine is a lot smoother and the vibes feel more like character and less like an annoyance.

Finally, a 270-degree firing order is the same as a V-twin engine, and we all know how amazing V-twins sound, don’t we? So, these parallel twin engines sound way better than they have any right to; the exhaust note is throaty and pulsing. As a bonus, the uneven firing order produces recovery gaps in the power delivery, which improves traction in the corners.

Yamaha CP2 Engine And Performance Specifications

(Specs sourced from Yamaha, Motorcycle News, and Fastest Laps)

It's Cheaper To Forge Crossplane Crankshafts Now

It’s not like we didn’t know about the benefits of a 270-degree cross-plane in the past. The idea was first introduced by Phil Irving, drafter of the Vincent Rapide, around six decades ago. He realized that a V-twin firing order could be replicated to a twin, but his idea was rejected by Triumph in 1962. Why? Because it’s just cheaper to forge metal crankshafts in a single direction.

Dirk Cookson even produced a functional cross-plane parallel twin three decades ago by hacksawing a flat plane crank in two and using a central phasing to make it cross-plane. It was built in a shed. In the last decade, forging a cross-plane has finally become affordable, courtesy of technological advancements. Honda kicked off the trend with the Africa Twin, and other manufacturers followed suit.

Excellent 270-degree Parallel-Twin Motorcycles

• Yamaha’s CP2-powered bikes like the Tenere 700, YZF-R7, and MT-07
• Suzuki GSX-8R and GSX-8S
• Aprilia RS 660 and Tuono 660
• Royal Enfield Continental GT 650, Meteor 650, and Interceptor 650

But wait, there’s more. If you take a look at it, Irving proposed a 285-degree crankshaft, not a 270-degree one. Essentially, the piston moves the fastest when it's at 75 degrees, not 90 degrees, so a piston's true half-stroke is at 285. A 285-degree parallel twin has the perfect secondary balance. Again, this requires a twisting stage during forging, which is expensive, so most manufacturers stick to a 270-degree crankshaft. The only exception is KTM, a brand that’s known for spending money and charging money. Thank you, KTM.