Why Isn’t There A 7-Cylinder Engine? 

Thoughts on the sound of the inline-seven? 🤔Thanks to Bespoke Post for sponsoring today's video - New Bespoke Post subscribers get 20% off their first box of awesome - go to bespokepost.com/drivetribe20 and enter code DRIVETRIBE20 at checkout.

More educational content please, Mike has a great way of explaining it while posing a genuinely interesting question.

In radial engines odd numbers are generally preferred because then on the opposite side of a cylinder (a weakspot in the block) will be a particularly strong spot where the walls of two cylinders come together. And radials with even cylinder numbers, like 14 or 28 cylinders, often tend to be built like multiple odd-numbered radial "discs" behind each other

When you're talking about Sisu Diesel engines you're incorrect. The engines they build are 3, 4, 6 and 7 cylinder engines with displacements of 3,3L for 3 cylinder engines, 4,4L/4,9L for 4 cylinder engines, 6,6L/7,4L/8,4L for 6 cylinder engines and 9,8L for 7 cylinder engines respectively. And every single one of those is turbo charged. They are indeed modular in the sense that they only use 3 and 4 cylinder heads which they then combine to make 6 or 7 cylinder engines. The new engine family they just launched is quite different though and they have a V12 engine that's no longer manufactured.

The inline 7 cylinder that he was talking about at the end was the 98AWF by Agco. It's used in grain combines.

One thing you forgot to mention with those massive ship engines is that they have a number of markings on the power setting lever. Some of those are more critical than others, but they all have one thing in common: you can run the engine(s) at that setting for only a very short time, as the vibrations will tear the engine apart and generally speaking it's better not to run the engine at those settings at all. You can actually feel it when a ferry ship is docking and at times during the docking procedure the engine(s) run(s) momentarily on one of those power settings, as the whole ferry starts to vibrate. You can imagine the severity of the vibrations needed to vibrate an entire ship.

8:37 I would only like to correct on one thing, super chargers and turbo chargers have been around just as long as adding more cylinders. 1905 for turbo chargers, and 1848 for super chargers forced induction has been around just as long as the internal combustion engine.

I love the educational type of content, would like to see more of it. I'm not really into the insane physics calculations and don't expect to see a 45 minute lecture calculating forces, but showing a quick final formula that is used like the one to calculate engine overlap is very nice.

There were also straight 8's. Buick and Packard were known for their straight8's.

I was expecting this to be a long intro to why you are making a 7 cylinder car.

Been wondering this for years now, always trust drive tribe to answer my dumb questions 😂

Also note that even though the straight 6 has its cylinders _moving_ as pairs, they are not _firing_ as pairs. A cylinder fires every 720 degrees of crankshaft rotation. Each member of a pair is 360 degrees out of phase with the other, which means you get six individual firings instead of three pairs. It's not just a doubled inline 3.

I wonder if a VR7 would work any better? Still fairly pointless but it would sort the long crankshaft issue

Don't forget that the radial engines almost require an odd number of cylinders per bank in order for the firing order to work out in a simple way that's relatively easy to drive mechanically. They fire every other cylinder, and going around the whole engine twice will wind up firing every cylinder as long as it's an odd number.

I built and ran a FrankenBriggs 7 cylinder gasoline engine about 5 years ago (vids on my channel) It is made of individual single cylinder engine blocks with the cranks fastened together, and using a common ignition distributor and 2 carburators. It does indeed have its own unique sound, and ran very well. Cheers.

Really like how this was explained clearly. Love the sound of my 5cyl, even if it is a diesel

This is a really well made video explaining this topic. Tbh I think a lot of people that have nerded out on exotic engine designs have thought about the idea of a 7 cylinder.

Having owned cars with both straight 5 and 6 engines, I found this fascinating. The straight six that I had was in a 2ltr Triumph Vitesse. That was a great car for a 21 year old to own! Sad to see it go, especially now, after so many years.

There are plenty of straight seven and straight nine Diesel engines out there. French manufacturers like Duvant and Japy made a lot of them for example. Deutz also makes inline 7 and V14 engines.

2 of the best/reliable engines I've owned were both inline 6's

This is a clear and concise means of explaining engine balancing. Thank you for helping an old car guy learn something about the very heart of his machine!

One of your best videos in ages DriveTribe. Thanks for the thought provoking subject. Peace

And then there was Volkswagen in 1991 and developed the VR6. The idea was having a V6 but with a much smaller footprint. 15° cylinder angle and one head. BUT: the crazy part is that Lancia originally came up with that idea - in 1915. 😎🤟

I've though about this for many many years and eventually came to the conclusion that the main reasons probably are impracticality and diminishing returns. Seems like that was pretty spot on. Awesome video!

Absolutely fascinating content this time around Mike. By far one of my favourite Drive Tribe videos! 👌

I once had a 7 cylinder engine in my Rover but a new sparkplug turned it back into an 8..😉

Sisu makes an inline 7 cylinder diesel engine for agricultural equipment.

Wow, great explanation, loved this vid! You should do a series on this sort of thing…

Lots of ship engines are 7 cylinder 😊. Many ship engines now can be isolated. One cylinder can be shut off for repairs while the others still run. Radial aircraft engines may have odd numbers partly to avoid harmonics.

I liked that Mike! Well presented and visually very pleasing and easy to follow! Thank you.

Brilliant, really enjoy the engineering videos. Keep them coming.

So many variables! You shared some things I never thought about. Thanks for the incite into the complexities of cylinder layouts.

One of your best videos in years. Informative, interesting, and down to earth.

Thank you mate, great work done in explaining to the point. Easy to understand and no unnecessary talking.

Love this style of video and would love to see more technical/engineering oriented content. You touched on radial engines, which makes me wonder: has there ever been an attempt to put a radial engine in a car or truck?

Now I need someone to build a VR7 engine. The VR5 engine exists and works beautifully. Its just a VR6 with one cilinder less. If you take have Veyron engine and cut one cilinder of you have i. Although a VR8 would also be epic. 😊

Love this engineering content. Really, really interesting. More of this please.

I've had several 7 cylinder engines in my cars. Although to be fair, they started out as 8 cylinder engines 🤕

Quick correction on the AGCO engine as someone who uses a tractor with it. Each cylinder does not have its own head, and it appears that they use an inline 3 head and an inline 4 head. Also, your comment at 12:40 about them being naturally aspirated is incorrect as basically no modern diesels in the 10 liter range are, and the AGCO has a compound turbo setup making about 40 psi on the monitor. The in-line 7 9.8 liter is governed to 2300 rpm, and makes 431 hp @ 1700, and 1,417 lb-ft @ 1500.

8:00 It maybe a synthesized engine note, but I want a car that makes that sound

Thank you. I found this very interesting. Something you might want to look up is when a yamaha team in the UK built what was called the pig engine. Basicly what the wanted to do was to compete with the V twinn Ducati's of the day in the sense that they had better grip due to far less firing/power pulses throug the drive train and rear wheel resulting in better grip. They did this by simultaneously firering cylinders 1&4 and 2&3. I suspect that firering 1&3 and 2&4 wold result in fat less tortional flex of the crank shaft, but would have ment the had to completely replace the crank. To the best of my knowledge this would have been against the rules. Thus valve, injection and ignition timing was all they had to work with. Another very cool engine was the 2T 115deg V5 that Honda used in the GP500. Those were the days. Keep it coming. Love the content.

I knew 7 cylinder radial engines existed but I was completely unaware that an Inline 7 was a thing! I’ve always wondered why we didn’t have them in cars, but didn’t know they did exist in other applications.

In-line 9 cylinder engine is like butter though! Worked on many different engines with different cylinder configurations including inline 7 which has a slightly odd sound, 9 is the best in line though, even over a 6.

I've seen one of those AGCO straight-seven engines set up as a stationary power source. It fills a niche where a straight six wouldn't be enough and a V engine wouldn't fit. Besides its interesting exhaust note, the AGCO engine can shut off fuel to individual cylinders when there's only a partial load.

This may be one of the best videos you've done, mate. My first car, a 1965 Ford Galaxie, had a 240 ci (3.9 l) straight six in it. That engine was one of the best ever, I just didn't appreciate it at the time. It was the fourth generation inline six that Ford made, and stayed in production until 1996.

I did see a inline 7 diesel once.. I was in new hampshire and there was this snow plow machine, one of those tracked machines you use to smooth the snow at ski resorts, with the plow in the front and the rakes at the rear and it had in inline 7 turbodiesel. It was some strange scandanavian design. And there are slow speed inline 7 diesels used in ships.

7 being my favorite number, I’ve always wondered this as well! I will eventually get a car with a 7 speed manual (Porsche, C7 Corvette)

I hope I am not in the minority but I really find these educational videos highly informative and most enjoyable and if they get you the appropriate views I hope you keep can keep rolling them out.

Amazing. I just learned something useful on the internet. Way to go DriveTribe!

There are plenty of 7-cylinder engines, they just happen to be for airplanes, in the form of radial engines. All radial engines have an odd number of cylinders, 3-5-7-9, with 7 and 9 being the most common.

I love this type of vid. It's what got me into Drivetribe in the first place (have loved all the content since, don't get me wrong!) It does make me wish I'd studied automotive engineering though!!!

Thank you for presenting this in a way that someone like me can follow. I'm not a petrolhead, but I'm interested in the topic.

Oh darnit! I thought I had you when I read the title, knowing there's 7 cylinder radials used in some light aircraft but, you had them covered too. I am a little confused by the fact all radials are odd numbers of cylinders though, that's something I'll probably never comprehend. Incidentally, my car is a Nissan Pathfinder and it's got their 3.5 litre V6 and that engine is literally one you could balance a coin on it's edge on. I have had many old carburetored straight sixes but none have ever run near as smooth as this thing. Admittedly fuel injection probably helps but I'm guessing there's a lot of counterweighting and balance shafts doing all sorts of magic trickery but, it really is surprisingly smooth at idle.

6:15 my dad had an Audi 4000 with an inline 5, it was the smoothest car engine I have ever heard, smoother than any inline 6

Imagine if Audi and BMW revamped their lineups so that the model designation indicated the number of cylinders (3 series = 3 cyl, A7 = 7 cyl)

Dang, here I was going to remind you about the Warner Scarab aircraft radial engines, which were among the smaller radials produced during the interwar period.

In fact, all radial engines are odd-numbered, and the ones that aren't are composed of multiple odd-numbered banks stacked in a row behind each other (e.g. "18-cylinder two-row radial engine".

No doubt Allen Millyard could make one in his shed from old Kawasaki engine blocks and it would run beautifully!

Outstanding explanation ... more of this please folks

Loving the educational content, so interesting!

Very intersting topic and nicely done Video. Thx

I had a Subaru Justy(3 cylinder) as soon as I added power(intake, exhaust, tune) and it drastically shortened the life of my crank shaft. Boom

Look up simulations of how an i7 would sound, they’re the creepiest coolest sounding thing I’ve ever heard, like a v8 and i5 made a baby. They’re wicked.

Very informative. Often po dered this exact question. You should follow it up with a story on the best Straight 6 from around the globe.

11:13 an inline 8 is not two inline 4s joined together, since an inline 4 usually has pistons 1 & 4 and 2 & 3 moving together. The animation shows it with opposite cylinders moving together.

Very cool sound that seems worth doing

I've been wondering about this. Thanks!

One of the best videos I've seen on this channel; I gained knowledge.

Loved the genius of the Opposed piston engine the US Navy uses. Always wondered why cars/ trucks don't use opposed piston engines.

you can totally do a 7-cylinder engine. My brother built a functioning one out of legos. It's an inline-3 spaced out with a v2 between the inline cylinders. 1, 2, 1, 2, 1. A straight 7 may be a bad idea, but the staggered 7 is easily achievable with current technology.

always nice to learn a thing or 2! nice vid!

Packaging and balancing. Edit: glad you covered it immediately.

So, if you can fit it under the bonnet/hood, the best balance for the fewest cylinders is a straight 6. No wonder most trucks use them. Conceptually, put a mirror after the third cylinder and you will "see" the other three in the mirror.

Many years ago there was a car dealer in East London who 'specialised' in yank barges. The oldest one he had was a 1925 Studebaker President that had a straight 12 engine. Never heard it run but he was trying to offload it for £250!

Seven cylinders is one of the most common setups for radial engines. In fact, all radial engines have odd numbers of cylinders.

Interesting and informative video thanks Mike

the agco power 98hd is a 7 cil diesel used in some big agricultrel machines

Y'all should really give Angethegreat some credit fir their engine simulator and its sounds if you're gonna use it.

Hey Mike. Love your work 👍

Definitely more videos like this please.

all makes perfect sense, the flywheels purpose being to carry the engine through the idle strokes, I wondered for many years about Rolls Royce Merlin / Meteor, no flywheel, enough compression strokes, so close to each other that it carries itself

What makes the old 6 cycl in-line Cat engines so smooth?

I do enjoy my Volvo’s odd 5 cylinder diesel noise quite satisfying

Could you imagine what a F1 7cyl would sound like😮 suit you sir 😂👍

I love how cyberpunk/hyper futuristic a 7 cylinder engine sounds.

I always wondered about a straight 7. I also wondered about a V4 and VR4 engine, a VR5 and VR7 engine and also W14 engine instead of a W16

Mikes finally finding his platform 👌.. for sometime there seemed to be a sense the big three looked on him as a less than an equal presenter.. but not now. Great video 🫡

To make a complex answer simple, derivatives of 360 are the reason why. When you degree a crank or cam shaft, it helps to work in the 360' notions that we use. Here are some common fraction uses of 360 1/360 or 360' 2/360 or 180' 3/360 or 120' 4/360 or 90' 5/360 or 72' 6/360 or 60' 7/360 has the first decimal degree of 51.428571 repeating. 8/360 or 45' 9/360 or 40', however, 9 can also be broken into 3, kinda like how you see inline 6 cylinder engines only having 3 camshaft degree positions, essentially making it 2x 3 cylinder engines or in the 9 cylinder, 3x 3cylinder engines. this describes a lot about the problem with certain engine combinations. While you could make a 7 cylinder engine, it would be out of balance or to make it in balance would be next to impossible.

That racing XJ looks so cool 👌

Panhard, before its final demise under Citroën, was working on a radial car engine. But it's very difficult to find info on it. Maybe a video on Panhard would ve nice? Definitely one of the weirdest - and at the same time most revered - car manufacturers.

I've wondered this point, but I'd still want one! Especially now someone simulated the sound! 😢

Uhhh, there IS an inline 7. They're giant diesel engines generally used in marine applications.

The "counterweight" mentioned at 14:23 is actually the flywheel, which is not a counterweight at all.

The Audi 5000S had a 5 cylinder engine, a V-4 with an inline 1

I'm always up for 15 mins of engineering geek-out.

There were even I8s made by Olds, Buick, Pontiac and Packard and the last three stuck with those way into the early 50s. While those were indeed torquey for its day they clearly showed their disadvantages in car use : a long crank that doesn't like high revs + packaging. A 7cyl is simply not sensible for car use since an I6/V6 can be built to do the same job at same displacement or as a V8 which is a much sturdier and rev-friendly more compact package. Since both inline and radial 7cyl can be ruled out of car use due to packaging, we're left with either VR7 or multibank alternatives and those come with their own limitations and unnecessary complexity compared to I6, V6 or V8 alternatives that make a lot more sense. I'm pretty sure some exotic car company could possibly develop a 7cyl for car use just to prove to their limited audience that they CAN, however it would be unnecessarily complex, expensive and impractical for use in regular high-volume car production

The applications mentioned for inline 7 and 8 cylinders engine also operate at much lower RPM's. Back when strait 8's were used in cars they would often only revv to 4,000rpm or something. That was the case for most at the time i guess. But once you start increasing the RPM the downsides start to show them selves more. Like pushrods.. Which for some reason are still being used!

Here in the US straight eight cylinder engines were extremely common before the mid 1950’s. Never thought about a seven cylinder! Cool! 👍🏼

The timing of the inline-8 shown at 11:17 makes sense... but note that it is certainly not the same as two inline-4's connected end-to-end.

Now because of that simulation, i would love to have one 7Cylinder :(