Yes sir, engine layout plays a crucial role

Hi,

Thanks for your informative material. Anyway, just curious about the designs of various engines such as horizontally opposed (boxers), the Vs, straight inline and straight incline. Do these designs impact on performance or are they just for aesthetics? How about a review of the Skoda Octavia with regard to performance, fuel consumption and suitability for our roads.

By the way, I hope Subie guys will appreciate the Evos even in the just concluded safari rally. Evos, thumbs up! Look at the top 10 cars; your guess is as good as mine.

Douglas

Yes sir, these engine configurations do have their purposes:

Straight (inline) 4 engines: Very compact, making them easy to package. They are also very reliable, relatively simple to make and, therefore, cheap. They have only one cylinder head, one exhaust manifold and fewer parts, so they are light, suffer fewer energy losses and are less prone to malfunctioning. The are also easy to repair.

The four pistons provide excellent balance, with two pistons moving up while two move downwards. There is a limit to engine size, however. Also, with large capacity engines, the initial balance is lost, necessitating the use of Lancaster (balance) shafts, which tend to sap quite some power. Given that they are almost always upright, they have a high centre of gravity and lack the inherent rigidity of V engines.

Horizontally opposed (flat) engines: Their biggest advantage is their low centre of gravity, which creates a very stable and balanced car.

There is less weight on the crankshaft too, and the fact that the crankshaft, clutch and gearbox are in a straight line means there is no driveline shunt at all.

However, these engines are wider than usual and can present packaging problems. Flat engines also require two exhaust manifolds, two valve trains, two cylinder heads... making for a costly build and higher odds of mechanical malfunction.

Six cylinder engines 1 (straight 6): 6-cylinders are good for high power outputs. The straight 6 has the added benefit of having a nice, rorty, lubricated exhaust bark in the mid-range (around 5000 rpm).

There is an inherent balance to a straight-6 engine that can’t be found anywhere else, and from an engineer’s standpoint, a very interesting factoid is this: with all the technological advancement in both the computer and automotive industries, we still cannot design a six-throw crank by calculation.

AN ACTUAL MODEL

It has to start with an actual model, which is then honed and fettled into something useful. Some of the greatest engines ever built were straight-6s, starting with the unstoppable M series used in the Mercedes line-up, to the RB26DETT engines used by Nissan in the Skyline GTR, and Toyota’s 2JZ. The issues with straight-6s are length (packaging problems; look at the size of the bonnets on the Nissan Skyline GTR and the Mk. IV Toyota Supra), being long and narrow also compromises their rigidity; they cannot really work in an FF platform (front engine, front wheel drive) and they have a high centre of gravity.

Six cylinder engines 2 (V6): The most common six-cylinder configuration out there, it has the added honour of being the current layout in use in Formula 1. It allows for larger capacities than a 4-cylinder, it gives 6-cylinder power with 4-cylinder compactness, making packaging easy, it is very versatile and can be used in almost any platform: front engine, mid engine, front wheel drive, rear wheel drive etc., and the V design is very rigid. This rigidity has allowed it to be used as a stress member of the vehicle chassis, hence its current application in Formula 1. The two-cylinder banks increase the cost and complexity of the engine, though. The commonest bank angle in a V6 engine is 60 degrees.

Eight cylinder engines 1 (straight 8): This configuration is no longer in use, but it was once common in racecars and aircraft (in the 1930s here). Eight-cylinder engines are good for one thing above all else: torque. One example of a straight-8 engine car that I never get tired of reading about is the Mercedes Benz W125 racer from the pre-war era. That was an epic machine.

Eight cylinder engines 2 (V8): While straight-8s are basically no longer in existence, almost every single 8-cylinder engine currently in functional and operational existence is a V8. You get the insane torque that V8s are famous for, you get 8 whole cylinders, and the advantage is the package is relatively tight. The engine is well balanced, the V formation provides rigidity and you can have almost any engine capacity: the Ariel Atom V8 is of 3,000cc capacity while leviathan American “trucks” boast of anything up to 7200cc.

These engines can get heavy, and though compact, they are still huge. Most V8s come with a 90-degree separation angle between cylinder banks.

Eight cylinder engines 3 (W8): A rare configuration, this one. The only car I know that boasts this engine is the VW Passat W8, and even then, it was not exactly common or popular. The W8 is basically two V4s juxtaposed, and the question is: why? V4s are very prone to vibrations, which is why they are rarely used in automotive applications. This might explain why there are few V4s/W8s.

12 cylinder engines 1 (V12): Two V6s, operating in tandem. These engines are “screamers” and extremely complex, which is why they have mostly been limited to the most high-end models of the most high-end cars (Ferrari, Lamborghini, Mercedes...). Given that they are basically two V6s one ahead of the other, the power outputs can be stratospheric, and that is before the introduction of forced induction...

12 cylinder engines 2 (W12): Another take on conjoined V6s, this time being side by side rather than in a queue. Sporting massive torque levels and being more compact than the V12, the W12 is also extremely complex and can present packaging difficulties, which might result in cooling problems due to lack of space in the engine bay.

FIRST STEP

I have ridden in a Skoda Octavia just once, and that was before I started seriously reviewing cars, so I cannot remember anything about the details of its characteristics. I have dreams of owning an Audi RS6 Avant and The Paji tells me that buying a Skoda Octavia estate is the first step in that direction. I seriously doubt it.

The Evo vs Subaru battle will keep raging. I don’t follow the local rally so in the small, rarefied motorsports atmosphere in which I live, right now Subaru has the upper hand, courtesy of the said Paji and his orange car. Revenge will be served really cold next year, Subie fans, just wait and see...

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Hello, Mr Baraza,

I am a college student with a lot of passion for cars. I have always wondered why at a bend, most Toyotas will raise the wheel of that side while in the case of Nissans, the wheel remains on the ground.

What makes that happen? Someone told me it’s about differential, but I don’t know what that is. Kindly inform.

Peter

At a bend, most Toyotas will raise the wheel on that side? Which “most Toyotas” are these? What kind of bend is that? I have seen that happen very few times, and the few times I witnessed it, the kind of driving involved could be described as “with intentions tending towards suicide”.

Anyway, what you describe is called wheel articulation and is a combination of the stiffness of the body shell and the suspension set-up, travel and stiffness. A car with a stiff body shell, such as a high-performance vehicle or a racecar, is more likely to raise one wheel under hard cornering. This is because of the relative absence of chassis flex. Chassis flex is the bending/warping/twisting of the chassis in response to the turning/inertial moments that are the result of hard cornering.

Too much physics? Let me simplify it. One of Newton’s Laws of Motion says that a body has a tendency to maintain its current state of motion unless otherwise compelled. When cornering hard, several things happen: the car wants to keep going straight but is being forced to turn. The car also tends to lean over on one side, but it prefers being upright as it was originally. All these opposing instructions result in a lot of energy being exerted on the frame in different directions, causing it to deform slightly.

Sporty cars have stiff frames to reduce this deformation. With less time spent deforming, the car reacts quicker, that is, the handling is sharper and response is almost instantaneous. With less sporty vehicles, there is the slight deformation plus bush compression and spring compression, so reactions are much slower, hence things like understeer might occur.

Anyway, with a stiff frame, when the body leans over without twisting, it tends to lift a rear inside tyre. With “softer” body shells, the body leans and twists, leaving the tyre in contact with the ground and only in extreme cornering — on the brink of rolling over, actually — will a tyre leave terra firma. This chassis flex, however, is a very small contributor and might not always come into play.

PRONE TO CHASIS FLEX

Wheelbase length also affects chassis flex. A vehicle with a long wheelbase is more prone to, and experiences, a greater degree of chassis flex than one with a short wheelbase.

Let me clarify one thing here: the deformation is not visible to the naked eye, and this is why: the relatively pliable body shell still requires a tremendous amount of energy to twist. However, lacking in stiffness, it tends to absorb a lot of that energy in the course of twisting, most of which is distributed all over the frame and thus be seen to dissipate.

With a stiffer body shell more resistant to twist, none of that torque (twisting force) is “absorbed” and that energy is thus converted into kinetic energy, which is then transformed into potential energy, which comes about from lifting an object. Think of it as hitting a piece of wood. It makes a sharp crack like a gunshot because none of the energy has been absorbed by the wood and is thus dissipated as sound energy. I hope you get the analogy.

A bigger factor is suspension set-up. Softer suspension with a bigger stroke room (more travel) reduces the odds of a tyre getting off the ground. This is actually the basis of wheel articulation: suspension travel. When the body is lifted on one side, such as when cornering hard, the springs on that side decompress, now that the body weight on them is reduced.

This decompression pushes the tyre away from the body.... towards the ground. A longer suspension travel means the spring can extend further, so the car can lean harder, with the tyre still in contact with the ground. With sporty, short-travel suspension, once the car’s degree of lean (which quite easily) exceeds the suspension stroke room, the tyre goes up and the car “wiggles one leg in the air”.

So most of the Toyotas I see around are unlikely to lift a tyre while turning. The only likely candidate for this kind of manoeuvre would be, maybe a Starlet GT. And it would have to be modified past Stage 1 status, and be driven by a maniac for it to start throwing legs in the air.

QUESTION OF THE WEEK

Kenya and Uganda recently released home-made vehicles. Kenya’s Mobius 2 was a launch-ready, rugged, simplistic jeep-rickshaw hybrid powered by internal combustion while Uganda’s Kiira EV Smak was more of a flashy concept saloon car (with polarising looks) packing a forward-looking petro-electric powerplant under the bonnet.

As their respective road tests are being sought, of the two, who has hit the nail on the head? Are Ugandans aiming too high and reaching for that which is the preserve of industrial giants or has Kenya been outclassed, outmanoeuvred and shown up as having no crystal ball of its own, thus being stuck in the present with only an eye for the past? Patriotism aside, which would you invest in and why?

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