ENGINE BALANCE: Inline 6 vs. V6 vs. VR6 vs. Flat / Boxer 6
1,296,394
Published 2021-03-14
Today we're hitting on all sixes as we explore the engine balance as well as the strengths and weaknesses of the four most popular six cylinder engine configurations, the inline six, the v6, the vr6 and the flat six.
Let's start with the inline six cylinder engine. We already covered it twice in our videos and many of you by now know that the inline six is a beautifully simple and beautifully balanced engine configuration.
It's beautifully simple because it needs only 1 cylinder head and only 1 or two cams. It also needs only 1 exhaust manifold. It's only real downside is that it's long so fitting it transversely is extremely difficult and it needs a relatively long engine bay to fit in longitudinally. But other than the length it's very hard to fault the inline six.
When it comes engine balance the inline six is essentially two inline three engine's mirroring each other. You may remember that the inline three cylinder engine has a primary imbalance in relation to it's center of gravity due to it's odd number of pistons. This imbalance is especially apparent every time the first or last cylinder fires. When cylinder one fires the force pushing the piston down in this direction creates a reaction at the other end of the engine and tries to yank the engine upward, in the opposite direction. The third piston can't cancel this force out because when 1 is at TDC, 3 isn't at bottom dead center, it isn't doing the „opposite thing“ in order to be able to cancel out what cylinder 1 is doing – the final result is that the inline three rocks in relation to it's center of gravity.
But the inline six doesn't. It doesn't because the inline six is two inline three engine's mirroring each other so the primary imbalances of each individual inline three cancel each other out.
When it comes to secondary imbalance the inline three doesn't have problems there because different pistons are at different parts of their stroke which means the there are no significant secondary imbalances in the inline three. The inline six of course inherits this characteristic as it consists of two inline three engines.
Now the V6 engine. Last time we learned that separating an inline engine into two banks of cylinders meant that we had to select an appropriate angle between the two banks. The correct bank angle for a V engine that wants to use shared crank pins always equals the firing interval. Because we have six cylinders that's 120 degrees. Unfortunately a 120 degree V6 is impractical for packaging. It's almost as wide a flat six while also being a lot taller. This is why we have to settle for a narrower bank angle which is usually 90 or 60 degrees for most V6 engines. But when we do this we can't have both shared crank pins and an even firing interval. To have an even firing interval a 90 or 60 degree V6 must employ split crank pins. Opposing piston rods are offset by what's called a splay angle. The splay angle makes up for whatever is missing from the bank angle and ensures an even firing interval just like in an inline six.
Now the VR6. The best way to explain the VR6 is to imagine it as the child of an inline six father and a V6 mother. A child whose goal was to inherit the good and drop the bad genes of each parent.
VW developed the VR6 with the goal of making it compact, like a v6, but without the double cylinder heads, cams, exhaust manifolds and other components all while preserving the inherent balanced nature of the inline six. So how did they do it? Well they did it by creating what's a essentially V6 but with an extremely narrow angle between the banks. Instead of 60 or 90 degrees, a vr6 ENGINE HAS only 10.6 or 15 degrees between the banks, bringing them so close to each other that you can cover all the cylinders with a single, slightly wider, cylinder head. Yes you need slanted pistons to make it happen, but it works.
Our final configuration is the flat 6, or more accurately a boxer six. Not every flat engine is a boxer engine but all relevant modern mass produced flat six engines, like those made by Porsche or Subaru, are boxer sixes. In order to be a boxer, a flat engine must have the pistons moving in and out in unison. In order for the boxer thing to happen each piston has its own crank pin and the crankshaft looks like this. A flat engine can't be a boxer engine if the pistons share a crank pin. An example of a flat engine that isn't a boxer is the Flat 12 in the Ferrari Testarossa.
Anyhow, you're often going to hear how the boxer six engine is perfectly balanced, and it is, although there is a bit of a catch.
A special thank you to my patrons:
Daniel
Peter Della Flora
Daniel Morgan
William
Richard Caldwell
Pepe
Brian Durning
Andrew Ruud
Brian Alvarez
Holset90
D4A merch: teespring.com/en-GB/d4a-merch
Patreon: www.patreon.com/d4a
#d4a #enginebalance #enginebootcamp
All Comments (21)
-
Let's hang out: superpeer.com/driving4answers Support d4a: driving-4-answers-shop.fourthwall.com/ Build the flat: amzn.to/2OpcIfa Wear the VR: amzn.to/3qOHDhM Read the V: amzn.to/37wLhX4 GTV6: amzn.to/2ZvB9JF Such a bore: bit.ly/36jYWQI
-
4 in the morning, gotta be up at 7, i think now's the time to learn about engine balance.
-
Bro love all your videos. You brake shit down so simple man, I'm actually using your videos to help teach my 15 year old daughter. She turns 16 in September and I bought her an older car we have to fix up to get running and I think it important someone knows how cars work and your videos do that better than than all else. You speak clearly, slowly and show great animations, it leaves nothing to guess at. Perfect bro thank you
-
The inline 6 is really something special, let me tell ya. I was driving an old AMC with the 232 inline 6, I couldn't even tell the thing was revving out because it was so smooth. I can always tell when almost any other engine is revving out because they sound more rough and like they are about to rattle themselves to death.
-
Straight 6 engines feel the best to me. Smooth and sound right to my ears. Love em!
-
Primary and secondary balance videos? Yeah seen those. Skip the recap? No sireee, wouldn’t want to miss a moment of any of it 😁
-
My friends think I am an internal combustion engine engineering genius because of you. Keep making me smarter, D4A!
-
The straight six has always been my favorite configuration. I think it's the best trade off of characteristics: simplest, requiring the least number of engineering fixes to get it to run smoothly (which allows it to be lighter and simpler), most economical to manufacture, simplest to work on once installed because there's usually plenty of clearance in the engine bay around it, etc. Here in the US V8s were always preferred for power because you can stuff a bigger, higher displacement engine (and thus get more power) in the same engine bay, and as a result, all the straight six engines here have really been smaller-displacement "base model" engines for cars, where the emphasis was on economy. Apart from maybe the Hudson Hornet in the 1950s, there really hasn't been a performance-oriented I6 made in the US -- and even there, I think it was a more a matter of the small Hudson company getting the most performance out of an engine that had originally been meant for economy, and if they'd had the kind of money the Big Three had to play with, they'd have designed and built a V8 as well. I've always admired the I6 performance engines that European car makers made, like Jaguar, Aston-Martin, Ferrari, etc. -- lightweight, aluminum block, DOHC straight sixes designed for performance, but smooth-running and high-revving, and because they're not great, massive lumps of iron, the cars are lighter overall and have better weight distribution, so the car handles better.
-
As an owner of a vr6, an in line 6 and a v6 I got very excited about this video. Nice work...
-
My first two cars were bmws. The e46 325i to be exact. That m54 was such a smooth engine and the power and was delivered beautifully as well. I long to have either another zhp or an M3 one day. Prices have gotten crazy in just a few years.
-
In terms of smoothness, Inline 6 cannot be beat. When I was a teenager on my stepfather's farm, his brother had a 1984 Chevy pickup, Inline 6 & 3 on the tree . Loved driving it around the farm land. Dispite the truck suffering from the harsh Michigan winters and holes rusted in the body, that engine and transmission was bulletproof, to say the least. Unfortunately it was parted out around 2008. R.I.P. Chevy half ton 1984-2008.
-
He literally didn't pause one sec nor look up information. Did he really do this whole video from his memory? That alone is incredible. Content was amazing as well. I learned a lot. Subcribing!
-
This was so educational I feel like I should have gotten some kind of credits just for watching it.
-
Great explanation! The most balanced engine I ever owned, was a 3 liter inline 6 in a Lexus GS300. I could easily balance a coin on top of the running engine. Its exhaust runner was a masterpiece. Great to see the Alfa Romeo V6 at 4:45, that I also owned long ago. The difference between V and inline is so striking.
-
Straight-six for the win.
-
That was THE best comparison on the different engine configurations I've ever seen on youtube - you did a great job AND it was fun to learn !!
-
Inline Six has always been my favourite, it's always been the smoothest, and most reliable. I don't care that it's hard to fit transversely in an engine bay, because I don't like front wheel drive, rear wheel drive please. The amazing B58 fits fine under the bonnet of my M140i hatchback :-))
-
Boxer 6 is awesome... Until you want to service it... Then it stops being awesome and starts being a pain.
-
I am a car mechanic for 12 years now most stuff you tell i am formulier with. But still I really love you’re videos! And the way you tell it makes it real nice to watch! Greetings from the Netherlands! 🇳🇱
-
My first, and still current, inline 6 was the 4.2-liter Atlas I-6 in my 2005 trailblazer. It's one of the best engines I've ever had and worked on. It still runs like brand new and I'll keep it till it's completely dead. It's got crazy amounts of power and can still haul ass being in a huge heavy chassis.
