6 or 4 cylinders… which is better?

[Haroundb]

I know that economically it is better to have 4 cylinders car, but still I want to know in the matter of driving and owning a car, which is a better choice? What do you think?

[NiGhTFaCe]

For owning a car is always depends on what purpose you want the car. The 6 cylinders car is better as performace except for some sporty cars holding medium engines with 4 cylinders.

If you are looking for a car to use it around the city, so then 4 cylinders is fair enough, for long trips you either go for 4 cylinders medium engines, or 6 cylinders.

[Ocean]

:3mani:

Go for 4 cylinders with turbo
It’ powerful and economically at the same time

[NiGhTFaCe]

:3mani:

Go for 4 cylinders with turbo
It’ powerful and economically at the same time
Its powerful when you use the turbo only!! I believe you wont be using it all the time ;)

[Ocean]

Its powerful when you use the turbo only!! I believe you wont be using it all the time ;)



U never knew when u need it, therefore u better be prepare ;) :6:

[mimosa]

OK, this is the second thread relating to what a "cylinder" is, and the respective advantages. If anyone can be bothered to read this, I will try to explain as simply as I can, but it might take quite a few words!

Power:

The "power" of an engine, normally shown as "bhp" ("brake horsepower") or "hp" or "PS" (just different units of measurement, with bhp the most common, and PS quite common in Europe), means how much "work" an engine can deliver in a specified period of time. For instance, you could convert a "bhp" figure, to show that the engine could move an object weighing 1kg one metre every second. That "power" figure, in terms of the power of your car, reflects how much energy the engine can transfer through the crank, and then the driveshaft, to the wheels, every second. The more power the engine can make per second, the more energy is arriving to turn the wheels round and push the car. So, the more "bhp", the better your car's performance.

Torque:

This is the other important figure when working out how powerful your car is. The "bhp" figure isn't everything. The difference is that torque is not a measure of how much work can be done by the engine every second, it's a measure of how much force it can apply at any one time. Even if the power seems lower in horsepower terms when you look at the numbers, if the vehicle produces more torque, it is simply pushing harder to turn the crank etc, and therefore the wheels of your car at any one time. You will notice a car with a lot of torque accelerates quickly from a standing start, for instance, or can climb steep slopes without revving the engine hard (more on "revs" in a minute), even though if it does not have a high power figure (bhp etc), it might not go as fast as a car with less torque, but more power, when at full speed. Torque is normally shown in units of NM ("Newton Metres"), or ft/lbs ("foot pounds" - or more correctly, pound-feet).

The Four Stroke Engine and the Two Stroke Engine:

All car engines, and most modern motorcycle engines, are four-stroke. Two stroke engines are mechanically more efficient, but it is hard to keep their emissions of burnt oil, unburnts fuel and poisonous gases to acceptable levels, so they tend only to be used in very small-engined machines, like scooters and lawnmowers, or model aeroplanes, where a very high power to weight ratio is required. Two stroke engines can be lighter than four stroke, and make more power relative to their capacity (more on engine capacity in a minute). But let's leave two strokes for now. The four stroke engine works like this: In each cylinder of the engine, there are valves to let air and other gases in and out, either carburretors or nowadays fuel injectors to squirt fuel in, spark plugs to light the mixture of fuel and air, and a piston which goes up and down to push the crank, which turns the driveshaft, which turns the wheels. In a four stroke engine, there are four movements of the piston. The first is when the fuel and air mixture is lit or ignited. The explosion forces the piston out of the cylinder and drives the crank. The second movement is when the piston bounces back down the cylinder, and pushes all the gases made by the burnt fuel out through one of the valves. The momentum, or continued movement of the crank (sometimes assisted by a "flywheel"), then pulls the piston back out of the cylinder and sucks air in through the other valve or valves, ready for the fuel to be burnt in it. The fourth movement is of the piston back into the cylinder, now full of air and fuel, ready to be exploded out and start the process again. 1-2-3-4. Four strokes - two up, two down. See?!

Revolutions Per Minute (rpm):

In order to increase "power" i.e. the speed at work is done by the engine and energy is delivered to the wheels, this four-stroke cycle must be completed as often as possible. The whole cycle is called a "revolution", or "revs". The more "revs" per minute (shown on your car dash display as "rpm"), generally the more power (bhp) the engine will produce. So, to make power and go fast, the engine must burn fuel, clean out the gases, suck in air and put the piston back ready for firing again, as often as possible. Press the accelerator, put more fuel in more frequently, and the number of "rpm" increases, and you go faster.

Engine capacity - size of the cylinders:

The bigger the cylinder, quite simply, the bigger the bang each time. In the other thread "what do all these numbers mean", people talked about "bigger" and "smaller" engines. E.g. the BMW 740 has a "four litre" engine. Four litres is the total combined space of all the cylinders, regardless of how many i.e how much that space is divided, in the engine (in this case, that's eight cylinders, each with room for 0.5 litres of vapourised petrol and air mixture). As there are four litres of space in there, there is more room for the fuel and air mixture at the "bang" stage of the four-stroke cycle, therefore more fuel can be exploded at any one time, and more torque is created i.e. force on the piston. This is why a four litre engine makes more torque than a two litre engine - it burns more fuel, and makes a bigger bang. But it doesn't always make more power...see below!

Bigger cylinders, more torque; more cylinders, more power:

In order to make as much power as possible and make the car go faster, the four-stroke cycle needs to happen faster. In the BMW 740, the engine capacity is divided into eight small cylinders. In my old Jeep Cherokee, the same four litre engine capacity was divided into only six larger ones. Because of that, my old Jeep made a lot of torque, because the "bang" in each cylinder was bigger. But it wasn't as fast because it didn't make as much power as the BMW's eight cylinder engine. This is because, in order for the four-stroke cycle to happen more quickly and make more power, the division of the BMW's four litres into more cylinders meant that the piston had less distance to travel. The pistons in the smaller cylinders could go up, down, up, and down again in less time. That means that the "rpm" could be higher, and with it the "bhp" increased. So, generally speaking, the more cylinders, the more power for the same engine capacity, but usually less torque. For another example, a six cylinder 3.5 litre four by four makes not much power, but enough torque to push its heavy weight up a steep hill, reaching a peak of only about 6,000 rpm, but with each of its six cylinders making a big bang. A 3.5 litre Formula 1 car, however, has twelve cylinders, and can reach 20,000+ rpm, and makes much more power, so can go very fast indeed, and doesnt need the torque because it's light.

Shape of the cylinder:

In a sporty engine that wants lots of power, the cylinders will be flatter and shorter, to reduce the distance further for the piston to travel, while keeping the same volume or capacity for fuel to be burnt.

So which do you want?

If you car has fewer cylinders, it will not "rev" as fast, and make as much power. But it will also use less fuel. For a more powerful car, more cylinders are better, but fuel economy is worse especially if you drive fast.

Turbos and stuff

A turbocharger forces more air into the engine, allowing it to perform the cycle faster and rev higher. When it does this, it also burns more fuel. It is a good compromise, because when you are not accelerating hard, the turbo is not used, and the engine is economical. When you do hit it hard, the turbo does it's work, and makes the enigne rev higher, and burn more fuel like a bigger engine. It does wear the engine out more quickly though.


Did that make sense to anyone?! I hope so...man, I should get a medal for this shit.... :hmm:

[Haroundb]

mimosa, God bless you, I never know lots of things which you have mentioned here, but still I love the explaination, you dit put it wonderfully...great job and keep us informed man... Thanks alot.

Just two question ...

1-What is the difference between Horse Power and Torque in the matter of speed?

2-Which gives more speed in take off?

3-Which climbs hills faster?

4-Which is more powerful in dragging heavy objects, like a stuck car.

[mimosa]

Well...if you want a fast car, you need peak power...simple bhp.

For the other things, power or torque will do the job...but if you have torque from a nice big engine, you won't have to rev it like crazy to do the job. The downside of it is that if you have that big-cylindered torquey engine, you won't be able to rev it up high anyway, and you won't get the speed.

So of you want a performace car for anything, go for power. But if you're not so worried about top speed, go for the torque...it will last longer too, generally speaking, because all those extra "cycles" your sporty, powerful, high-revving engine go through are extra wear and tear.

Ah what the hell....you need both!

[Haroundb]

Thanks man, that was lots of information.

[NiGhTFaCe]

Good information you put there mimosa :)