How to Read What Kind of Motorcycle it is from the Specification List? | Engine Edition

You are very interested in the specifications of a vehicle that you like, aren't you? It's a lot of fun to look at the numbers on the specification sheet and try to work out what's going on. The power is 0 horsepower, what does it feel like? How does it handle? How does it feel other than the maximum power?

If it's a new motorcycle, you can check it out on a test ride, but if it's a used or out-of-print motorcycle, you can only guess from the specs list.

You can read the characteristics of a motorcycle quite accurately by looking at the spec sheet. Even more so if you're a seasoned veteran who's ridden a variety of motorcycles!

WebiQ is here to bring you a little happiness and motorcycle knowledge. I'm talking about the trick of deciphering what kind of motorcycle it is from the spec sheet. This time it's the engine version!

I'm talking about on-road vehicles!

Even if you imagine a motorcycle from a specification list, you can't read much into moped 1 (~50cc) scooters or off-road vehicles. Basically, there is no big difference between each motorcycle, and there are very few things that are unique to that motorcycle. It doesn't mean there's no difference at all, though.

Scooters also have a little more personality when they become mopeds 2 (50-125cc) and can be read and understood. 

On the other hand, for scooters and off-road vehicles, images of the vehicle body are more helpful in deciphering "what kind of motorcycle it is" than spec sheets. The reason is that the body structure, which is not shown in the specification list, is much more unique.

Exhaust is a different way of thinking.

I know this is a bit off-topic from reading characteristics from a spec sheet, but displacement is super important This is because, in the case of motorcycles, it is safe to say that small displacement and large displacement are completely different vehicles.

Of course, this is not to say that small displacement is bad or anything. I'm not talking about the common story of where it's impossible to go full throttle to rev limit on a large displacement, but it's fun to go full throttle on a small displacement. A good example of this is the 85cc motocrosser, which is definitely a small-displacement machine, and even the most skilled rider would not be able to casually ride it around.

Displacement represents 'room'. It is generally correct if you think that there are some super fast motorcycles out there with small displacements, but those types of motorcycles are usually only fast if you drive them at full throttle all the time, etc. In other words, we can't afford it.

It's not that there's anything wrong with that, it's just that sometimes the aim is to enjoy the lack of room (this is usually the case with small displacement sports motorcycles). So, what you want to do, what you think is fun, and how far you want to pursue it, the displacement you want is determined by this area.

If you want to enjoy long-distance touring with plenty of room to spare, then a small displacement motorcycle is not the right choice for you, and if you want to enjoy sharp behavior with the right controls at the right time, then a large displacement motorcycle is not the right choice for you.

However, it can be fun to go on a long tour with a small displacement motorcycle and get into a lot of trouble, so it is very important to choose the right displacement for your purpose.

Maximum output, maximum horsepower, output characteristics

Now that you've decided on the displacement, the next thing to consider is the maximum power output. It's easy to go for the most powerful motorcycle, and it can be a bit daunting to buy a motorcycle with a lower maximum power than its rivals.

However, there is a serious pitfall here. This is because the maximum horsepower stated in the catalogue specifications is only 'horsepower at full throttle'. The power curve is just a graph showing the power output when the throttle is fully open. The graph of chassis dynamo is also the same. The graph of the chassis dynamo is the same.

Furthermore, if you look closely at the graph, there is no line in the low RPM range, right? That's because the engine will stop if you open the throttle fully from below that RPM. I don't care about such low RPM! This is not the reason. All the numbers in the catalog specs are when the throttle is fully open. This is super important.

Of course, the maximum power comes out when the throttle is fully open, but you wouldn't normally go from a very low speed where the motorcycle is about to stall to suddenly opening the throttle fully and waiting for the maximum power to come out, would you? The throttle is not an on-off switch.

So, while the maximum power output is what the spec sheets and graphs say it is, the truth is that the catalog specs are virtually useless when it comes to mid-range power output. It's not a case of, well, it'll go up to 15,000 but there's a trough at 6,000rpm, if the engine is capable of 15,000 rpm, there is no reason to wait for the throttle to open up below 6,000 rpm.

The maximum power is necessary to achieve the maximum speed, but that is only possible with the throttle fully open. How many situations like that are out there? If you think about it, you will come to the conclusion that 'almost none.

As you can see, it is not the maximum power output at full throttle that is important for the motorcycle, but the power characteristics in the middle range that are important.
What can be read from the output characteristic graph is, Is it a high-rpm, high-output type? or Is it a low-speed torque type? or something like that.

So, to be honest, I don't recommend being overly concerned with maximum power or torque figures or power curves.

Cylinder number and engine characteristics

I wrote that you can't read the real engine characteristics from the maximum output, maximum torque or power curve graph. To review, the reason you can't read is that those are all at full throttle. Then, the engine characteristic in the mid-range is not readable at all, but it is not so.

The most influential engine characteristic in the mid-range is not maximum power or maximum torque, but the number of cylinders in the engine.

If you're thinking, "What?" you might have a four-cylinder motorcycle all your life. Even four-cylinder engines have different output characteristics, but these are minor compared to the differences in the number of cylinders.

To make the story easier to understand, imagine that you are accelerating from a fully closed state where the engine speed has dropped to about half at a certain corner and you are standing up.

First of all, the parallel four-cylinder engine is a favorite of the Japanese, but it was originally designed for high revs and high output. It's been aged so much that it produces plenty of torque from very low speeds (in fact, it's the easiest to make a U-turn with), but you can't erase the traces that it was designed to rev high. This is most noticeable in the mid RPM range.

The four-cylinder is more sensitive to throttle action (call it good pickup), but the engine just reacts and doesn't actually produce much torque or power. The power and torque values are high to begin with, so even if you say "not much", it's still quite a bit, but despite the numbers, it feels gentle.

As a result, it starts accelerating smoothly, and when it continues to open up as it is, such a characteristic that demonstrates the intense power that seems to be a four-cylinder. It's a bit like opening the throttle and waiting for a while for the power to come through.

On the other hand, the engine speed of the single-cylinder is not as high as that of the four-cylinder, so the engine does not react as quickly when the throttle is opened. However, compared to a four-cylinder engine, the single-cylinder engine does not respond as quickly as a four-cylinder engine. But once it starts to react, the torque and power come out at once as you open the throttle. It's quite a violent, kicking acceleration, quite different to the gentle acceleration of a four-cylinder. It's like a four-cylinder with the power and torque you want the moment you open the throttle.

Two-cylinder and three-cylinder are the middles of each.

This is the basic characteristic depending on the number of cylinders, to varying degrees.
Whether it's a high-revving, extreme single-cylinder or a low- to mid-range-focused four-cylinder, the basic characteristics remain the same no matter where you go, to varying degrees. The four-cylinder is like having a hand gently placed on your back from behind and then continuing to be pushed hard. A single-cylinder is like being kicked from behind suddenly, but gradually the kicking leg becomes unreachable.

When I say "gentle power characteristics", people with power-supremacist 4 cylinders get angry, but it's true, so I can't help it. This is the reason why single-cylinder and two-cylinder motorcycles, which obviously have a lower maximum power output than four-cylinder motorcycles, can be very fast in situations where there is a lot of mid-range speed (this is usually the case on public roads, including mountain passes).

Relationship between Bore and Stroke

Even with the same displacement and the same number of cylinders, the piston diameter (= cylinder bore diameter) and the piston stroke volume differ from engine to engine.
It's the item that says "inside diameter x process" or something like that. And the combination of the two can read the characteristics of the engine to some extent.

First, if you have the same displacement and the same number of cylinders, the relationship between bore and stroke is inversely proportional. A larger bore will reduce stroke and a smaller bore will increase stroke. Displacement is, in essence, the volume of the cylindrical shape that the piston moves through, so if you imagine how to find the volume of a cylinder, it's pretty obvious.

I'm not going to go into all the details as it would be full of numbers, but it can be concluded that the lower the throttle volume (the larger the bore diameter), the higher the power output at higher revs.

There is a physical reason for this, as there is a limit to how fast the piston can move through the cylinder. The longer the stroke, the lower the engine speed, the more the piston speed reaches its limit.

It is a bad habit of the Japanese who love the catalog figures to think that the bigger bore and less stroke is better. Of course, it is easier to get the maximum output from a high revving, high power type engine with a large bore, but such an engine tends to be an uninteresting engine that is merely spinning in the low to mid-speed range that is frequently used in city driving.

Is it better to have fun with the torque even at normal rpm, or is it better to ignore normal use and have the extraordinary feeling of bursting with power when you use high rpm regularly? If you compare the bore to stroke ratio, you can see the characteristics to a greater or lesser extent.

As a side note, if you call the bore x stroke ratio "bore stroke", it sounds like you're an expert, so try it.

Compression ratio and engine characteristics

After displacement, the number of cylinders, and bore to bore ratio, the next step is the compression ratio. Honestly, I think very few people care about the compression ratio. The compression ratio has a considerable effect on the character of the engine.

High compression ratios are a sign of a high performance engine, and as a result require high octane petrol, which is a subject for another article.

Between this combustion and the combustion, we are doing things that eat up power: exhaust, mixture intake, and compression, so there are big waves of power output.

The size of the wave (height of the wave) is proportional to the engine output, so the higher the engine output, the larger the wave. But that's a story that also happens with displacement differences, so it's not a characteristic based on compression ratio.

Rather, the higher the compression ratio, the more the corners of the waves become more like right angles. On the other hand, at lower compression ratios, the corners of the waves become rounder, and at very low compression ratios, they have a very mellow, "wave-like" feel.

For example, if you have a small-displacement engine with low power but high compression and a gruff engine, or if you have a large-displacement engine with high power but low compression and a mild engine, you'll feel a significant difference in experience that goes beyond mere power differences.

So at what compression ratio does it start to have a rumbling and extreme feeling? You may be thinking, but there is no clear delimitation. The reason for this is that the compression ratio and the valve timing are very much related to the "actual compression ratio which is not written on the spec sheet" and it is difficult to say in general. However, an engine that exceeds 12:1 will undoubtedly have higher compression and therefore tend to have a more aggressive feel than a normal engine.

In addition, if the displacement is the same, the more cylinders are used, the more the number of waves increases and the less the height of the waves decreases, so it is less affected by the waves.

So, even with the same 'high compression ratio engine', a four-cylinder engine doesn't feel so radical, whereas a single-cylinder engine tends to feel like 'amateurs go home! But a single-cylinder engine tends to have a more extreme feeling.

It may have less than half the power of a 200-horsepower-over a high-performance four-cylinder, but it's so extreme that it's unrideable for most people. In many cases, veterans of various motorcycles end up tuning the Yamaha SR because it is the most extreme motorcycle, not because of nostalgia or a sense of nostalgia.

Off-road competition vehicles are usually single-cylinder vehicles with high compression and extremely high-revving bore ratios, so they have the most extreme engine feel.

There's more, but it's more difficult.

As mentioned above, there are many other factors that affect the engine characteristics such as cam timing, number of valves, cooling system and so on. There are many other factors that affect the engine characteristics such as cam timing, number of valves, cooling system, etc. These factors are often written in the specification table, so you can make a rough estimation by combining various conditions.

However, it is very difficult to imagine the factors other than "displacement", "maximum power and torque", "number of cylinders", "bore to cylinder ratio" and "compression ratio" which are described in the specification list. Unfortunately, it's a world where experience counts.

The lubrication system is irrelevant

I don't know who started it, but there is a long-standing belief that dry sump engines produce more power because the crankshaft does not scrape up the oil, reducing the resistance to oil stirring.

But, at least on modern motorcycles, this is false. This is not true, at least on modern motorcycles, as the crankshaft is not immersed in oil, even on a normal wet sump. It was a long, long time ago when wet sump crankshafts were actually soaking in oil and scraping up oil.

Therefore, there is no difference in engine feeling between different lubrication systems.
You don't have to worry about the lubrication system.