How big an engine is or how many cylinders it has might sound like a good gauge of how powerful it will be, but things are way more complicated than that. Although everyone dreams of having a massive V8 or similar under the bonnet, a little engine with not many cylinders has serious advantages too. Read on and find out why…
Straight, Flat or Vee?
Although plenty more exist, the three most common engine layouts these days are straight, flat and vee. But what the hell does that actually mean?
Straight, or inline, engines are exactly what they say on the tin, an engine where all the cylinders are in a row and the pistons travel vertically up and down. They can range from sub 1-liltre engines up to four litres in modern petrol engines, and there’s some bloody enormous inline diesel versions too. The main limitation of inline engines is beyond six cylinders, they simply get too long to fit under most car bonnets.
Flat engines are what we see in most Porsches, Subarus and old Beetles, and have two sets of pistons firing horizontally in opposite directions. This means the engine is far shorter and lower than an inline engine, but is much wider. This is good for a low centre of gravity, but not so good if you have a narrow engine bay.
Vee or ‘V’ engines are named because they have the cylinders laid out in two banks positioned at an angle, creating a V-shaped engine. The angle of the V is most commonly 90 degrees, but can be almost anything, and has been as little as 14-degrees. While wider than most engines, they are quite short compared to the amount of their cylinders, so are very common when it comes to big capacity engines; a six litre V8 can fit under most RWD car bonnets, where as a six litre straight engine would either be far too long or far too tall to fit.
Bore and stroke
Bore and stroke is one of the main factors that make manufacturers choose the amount of cylinders an engine has, but what the hell is bore and stroke? It’s quite simple actually. Bore is the diameter of the piston, and stroke is the distance it travels between its lowest and highest point in the cylinder.
While long stroke makes for good torque, good low rpm performance, and an easy way of making a big capacity engine in a small engine block, it’s bad for high rpm reliability. Bigger bore is never really a bad thing in performance terms, but a big bore in a small block means for very thin cylinder walls, and therefore a weak engine.
When it comes to capacity and cylinders things get a bit weird when it comes to Mazda rotary engines, mostly as they don’t have any cylinders at all! While a normal two rotor engine, that you’ll find in RX-7s and RX-8s may only technically be 1308cc, due to the way they work they have the performance and economy similar to an engine twice that size, to the extent most insurers class them at 2.6-litre.
In an ideal world, rotaries seem far better than any piston engine, being very small and light for the power they produce, and their internal design means with very few moving parts, they can rev very high too. Unfortunately they’re a new design compared to piston engines, so they’re still quite temperamental when it comes to reliability…
So the more cylinders a car has, the bigger the engine?
While that’s not a bad general rule, in reality it’s not the case. Good examples of this in road cars are the tiny 1.8 V6 from the Mazda MX-3, and little 3.5-litre Rover V8s, while on the other hand some 1990s Porsche 944s and 968s had 3-litre four cylinder engines.
Current Subarus have 2.5-litre flat four lumps, and Toyota also do a 2.7-litre inline four. In race engines unusual capacity to cylinder combos are even more common, with extreme examples like 16 cylinder 1.5-litre Formula 1 engines, and massive 4.7-litre four cylinder drag race engines.
The most common performance engine layouts
Until recently the only performance inline-three cylinder was the 1-litre turbocharged Charade GTti of the 80s and 90s, but recently Ford and BMW have developed tiny 3cyl turbo lumps which look to have big tuning potential. The main advantages of just three cylinders is they take up very little room, are very light, economical, and can sound pretty cool too. We’re unlikely to see any performance versions bigger than around 1.5ltr though.
By far the most common engine type around, and this is simply because it’s a good all-rounder. Small enough to fit in most engine bays and give good economy, but big enough to have good performance too. Technically inline fours are not the best balanced engine, which is why it’s not common in dedicated race cars, but when tuned well they can rev sky high and we love them, lots.
Although not that common, some of the most badass cars of the past and present pack inline-five engines. The old Focus RS and Audi TT RS, the Volvo T5, and of course the legendary Audi quattro rally cars all pack powerful inline-five cylinder engines. Inline five engines are considered to be a mix of the best four and six cylinder characteristics. The thing most people remember them for is the noise; an unmistakable warble that makes tuned five cylinders one of our favourites.
Inline-sixes are the second most common engine in performance cars in the UK behind the 4cyl, and include legendary engines such as the Nissan Skyline RB lump, the Toyota 1JZ and 2JZ, and of course countless BMW engines. Unlike the other engines mentioned to far, straight sixes are very well balanced and smooth, meaning not only are they popular for luxury cruisers, but they can safely be revved very high and therefore make some serious power once tuned.
Better balanced than an inline four, a much lower centre of gravity, and an exhaust note you either love or hate, flat fours are very common these days thanks to one car, the Subaru Impreza. The engine is very wide though, too wide to fit in most engine bays, hence why it’s very rarely seen in other cars.
Made famous by Porsche in the 911, it was chosen by them as it’s compact enough to fit behind the rear wheels, well balanced, and very important to them at the time, lends itself well to air-cooling. Aside from Porsche and Subaru, who both still use them as they’re known for using ‘flat’ engines, nobody else uses this layout; as to be honest, there’s no need to!
Shorter than a four cylinder and often narrower than a V8, it’s no surprise they’re popular in a lot of modern performance cars as with a V6 you can fit a lot of engine capacity in a small engine bay. One main weakpoint on big power V6s is that they are almost always turbocharged, and due to the turbos being hidden beneath the outside of the V, they’re a pain in the arse to work on!
Without doubt the most famous of all engine layouts, and the one everyone seems to want. While far from small, the V8 layout means you can fit a huge amount of capacity in a fairly short space. Road going V8s are usually big capacity and due to their design rarely rev above 7000rpm. V8s in race and supercars usually run a flat plane crank, which means they are capable of much higher sustained rpm, but sound totally different; listen to a big American V8 and a Ferrari V8 and you will see what I mean.
Not that common on road cars, for no reason apart from the traditional the fact most cars struggle to fit a V8 under the bonnet, and the ones that have no problem with a V8 can also fit a V12! Apart from the Dodge Viper, V10s were almost unheard of until recent years, but thanks to V10 becoming a popular layout for F1 engines in recent years BMW, Audi, Lamborghini, Lexus, and more have all brought out screaming ten cylinder lumps.
Technically, a V12 is one of the perfect layouts, with ideal balance for smoothness and high rpm use, and huge capacity is possible without requiring rpm-limiting long stroke. It has one main problem though; it’s bloody massive! Being as long as a straight six but as wide as a V8 means very little cars can cram one in, and even if you can it’s likely to be heavy and hard to work on. If you have the room though, a V12 can be very special, with countless Ferraris, Lamborghinis, and even the legendary McLaren F1 packing seriously powerful twelve cylinder lumps.
Rare engine layouts
Ignoring single cylinder two stroke setups you might find in your little brother’s moped or your old man’s lawnmower, there’s some seriously weird engines that have actually made it under car bonnets, and here’s a few of ’em…
Yes, two cylinders, half your usual inline four engine, and the current Fiat 500 TwinAir and Tata Nano are both packing them. Small yes, economical yes, fast, err, no. In 1955 a Ferrari F1 engineer built a 2.5-litre inline-two cylinder engine, hoping it would be much torquier than the usual V8s and V12s. It was torquey all right, but it vibrated so bad it even snapped the test bench they ran it on, so just like the broken test bench, the engine was binned.
VAG V5 and VR6
These aren’t true V engines, in fact there’s no true V5 car engine, they are actually a odd mix of V and straight engines. The pistons are slightly staggered from each other, making for a five or six cylinder that isn’t quite as long as an inline engine, and not quite as long as a V engine. Weird, but it works.
The VAG W engines, as seen in things from the VW Passat to the bonkers Bugatti Veyron, is like a double V, with each V having the staggered cylinders like the V5 and VR6 lumps. The main reason for this setup is packaging; you can fit shitloads of cylinders in to what is a fairly small engine. Ferrari actually built one of the smallest W engines ever in the 1960s, a 500cc W3 engine that produced 80bhp@11000rpm!
These were the engines to have in your road car from the ‘20s to ‘40s, but these were also the days of cars with long noses; the blocks were often 4 foot long! Beyond the mid 1950s straight eight engines died away even from race cars, and now are only seen in museums.
While being low, flat 12 engines are long and very wide, meaning they’ve been only used in race cars, albeit some bloody quick ones. The insane 1100bhp Porsche 917/30 was a flat-12, and Subaru actually built one for Formula 1 too; though it was a bit crap to be honest….
BRM are an extinct UK racing team who built some of the nuttiest engines ever. Their V16 was a 1950s 1.5litre 16 cylinder supercharged lump that ran up to 72psi boost and 12,000rpm! The H16 was just as mad, an engine with 16 cylinders arranged like two flat 8s sat on top of each other. It had two cranks and 64 valves, but was only a three litre!
Honda ‘X’ engine
Honda experimented with a 32 cylinder engine for Formula 1 in the 1960s. It was in an X shape, basically two V16s joined at the crank. It was abandoned due to being so complex. 32 cylinders and 128 valves is complex? No shit…