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In this video we are going to be comparing inline four cylinder engines with boxer four cylinder engines, and talking about the individual advantages and disadvantages of each engine layout. We have a 3D printed EJ20 Subaru boxer engine, as well as a 22RE Toyota inline-four engine. We’ll start fairly basic and work our way through several different topics for each layout, including the four strokes, the firing interval and order, the vibrations of each layout, the packaging differences, the cylinder head differences, and finally a bit about the sound.

Looking at either layout, they’re both based on the same four strokes. Intake, compression, power, and exhaust. Both engines fire one cylinder for every 180 degrees of crankshaft rotation, but they have slightly different firing orders. On each engine, we can see cylinders one, two, three, and four. For the boxer engine, the firing interval is one, three, two, four, while on the straight four it’s one, three, four, two, so the order of the last two cylinders firing is switched.

On the boxer engine, you’ll notice the pairs of pistons move in and out together. This means that the primary forces when the piston reaches the top of the cylinder, as well as when they reach the bottom of the cylinder, are canceled out. On the inline four cylinder engine, it’s the same story, the primary forces cancel out as the pairs of pistons reach the top and bottom at the same time.

When we get into secondary forces, however, the engines begin to differ. Secondary forces are created due to the piston traveling faster at the top half of the piston than at the bottom half, something I’ll include a link to in the description for a video that breaks it down in great detail. What you need to know though, is that when the piston reaches the very top of the cylinder, or the very bottom, the secondary force points up or out from the piston. Now with the boxer engine, since the pistons point opposite each other, these forces are balanced out, resulting in a very smooth running engine. For the inline four, all of the forces point in the same direction, and thus do not cancel each other out, causing the engine to vibrate unless balancing shafts are used.

The boxer engine isn’t perfect, however, because the pistons do not perfectly align with each other, it creates a rocking moment which makes the engine want to rotate back and forth along the vertical axis. What’s fascinating, however, is that if you add two cylinders to either of these designs, whether it’s a boxer six or an inline six, you can perfectly eliminate all first and second order forces and moments. You might think the boxer six would have a rocking motion from the cylinder banks of three, but each bank of three cylinders cancels out the rocking motion of the other, unlike in a V6 configuration.

The other biggest advantage of the boxer engine is the low profile, which keeps the center of gravity low and thus reduces the amount of load transfer you have in the car during braking, cornering, or accelerating, which improves grip. With a lower center of gravity, you can also reduce body roll and choose to use softer springs. Additionally, in the event of a collision, it’s easier to position the engine so that it goes underneath the passenger compartment, rather than into the passenger compartment, for improved safety.

That’s not to say the inline four doesn’t have it’s own size advantages. Generally it’s a bit more compact, with only one cylinder head, and it’s not quite as wide as the boxer engine. This leaves more room for suspension geometry, and can also allow for a better steering angle, since the tires won’t have as much of an interference at full lock.

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    • Engineering Explained
      Engineering Explained

      My S2000 is for sale for anyone interested! No reserve, 20% to charity. Happy bidding!

      about 2 months ago
    • machia0705

      The old German engineers were always thinking out of the box. The opposite opposing layout is quite novel.

      about 22 days ago
    • Sheldon Bourgeois
      Sheldon Bourgeois

      I'll take a crossplane inline 4 all day long.

      about 23 days ago
    • steve walker
      steve walker

      That Toyota must of had its flywheel resurfaced at napa......

      about 26 days ago
    • Janusze Mechaniki garage
      Janusze Mechaniki garage

      Extra engine. Pozdrowienia z Polski!

      about 26 days ago
    • Juan Cano
      Juan Cano

      Whats your opinion of the FA20dit engine

      about 1 month ago
    • Martin Wagner
      Martin Wagner

      I love my subaru I tell you what, bobby.

      about 1 month ago
    • Sebastian Seanz
      Sebastian Seanz

      Yo I’ll take the 3D printed boxer engine for $200

      about 1 month ago
    • cobra king
      cobra king

      nice video

      about 1 month ago
    • Brian Teeter
      Brian Teeter

      What printer or printers do you use?

      about 1 month ago
    • Sparky The skater
      Sparky The skater

      How about inline six and v 6

      about 1 month ago
    • Flavio

      1st time watching your videos, subscribed

      about 1 month ago
    • markus ray
      markus ray

      Very cool video

      about 1 month ago
    • Nancy Roumayah
      Nancy Roumayah

      Yep he never mentioned the boxer head gaskets are bad news.

      about 1 month ago
    • Alexandre Dufour
      Alexandre Dufour

      Inline power boxer got twice the parts for nothing

      about 1 month ago
    • theoutbackbandit

      Actually I THINK the biggest 4cyl was used in racing, over 600 cubic inches.

      about 1 month ago
    • Chris Kelleher
      Chris Kelleher

      I like your 3d engine print outs. No idea how it's done but it brings these explanations alive.

      about 1 month ago
    • Eric Bledsoe
      Eric Bledsoe

      No no 22re 2.4 L my guy

      about 1 month ago
    • Alex Rodriguez
      Alex Rodriguez

      Por que mierdas ponen el titulo en español si el video esta en inglés? Vaya mierda de manera de ganar visitas en la comunidad hispana

      about 1 month ago
    • Mersedes Benz
      Mersedes Benz

      Нихуя не понял....но очень интересно...

      about 1 month ago
    • TMB


      about 1 month ago
    • 3K

      Which is more reliable engine among the two? Which is more easier to fix?

      about 1 month ago
    • Chris Orr
      Chris Orr In reply to 3K

      A boxer engine is generally harder to get access to if you're a mechanic as theres not alot of room at the sides of the engine. I'd say the inline 4 is easier to fix because of that. Unsure about reliability, but there would significantly more inline 4 cylinder engines out there in the world.

      about 1 month ago
    • Benjamin Chang
      Benjamin Chang

      I think:
      Inline 4, V 6, Boxer 8 could be meaningful.

      about 2 months ago
    • Patrick London
      Patrick London

      I've had both Subaru's and Toyota's. The Subaru's have a tendency to blow head gaskets.

      about 2 months ago
    • Dinh Dover
      Dinh Dover

      The visuals are GREAT!!!!

      about 2 months ago
    • Vitalik Sinkin
      Vitalik Sinkin

      Ничего не понял, но было очень интересно 😝

      about 2 months ago
    • keith cunningham
      keith cunningham

      Inline all the way unless you want an oil burner that loves being in the shop.

      about 2 months ago
    • Johny Machette
      Johny Machette

      tell about lubrication systems and problems

      about 2 months ago
    • CallMeSamuel

      I'm watching this like I know what he's saying

      about 2 months ago
    • Phuque2

      Boxer is a CAR name. The ENGINE type is called "horizontal opposed". Basic "engineering" terms, douchebag. Duuhhh.

      about 2 months ago