In Summary
  • The “cc” of a car is called the engine displacement, which in layman’s terms means the engine size.

Dear Baraza,

Please enlighten me on the 1500cc and 1800cc capacity of a car. I want to choose between a Toyota Wish, a Fielder, a Premio and an Allion. My question is, what does the cc of a car translate to?

I have been told an 1800cc car consumes more fuel than a 1500cc. But is there a benefit I would derive from the 1800cc? Does the car “perform” better? Is it “stronger/more powerful”?

I live in Kikuyu and currently drive a 1500cc NZE. On a rainy day, a 200m stretch of a dirt road takes a lot of prayers as I skid through the mud. A 4 x 4 is not within my budget at the moment.

Caro

The “cc” of a car is called the engine displacement, which in layman’s terms means the engine size. In a nutshell, an engine works like this: air goes into the engine, this air is mixed with fuel in a particular ratio then this air-fuel mixture (called the intake charge) is fed into the engine cylinders where it is set on fire by spark plugs through electrical arcing.

Petrol is explosive, so when mixed with air and set on fire, it explodes.

This is the basic set-up of a cylinder: at the top are two sets of valves, one set called the inlet valves which allow the intake charge to enter the cylinder, and another set called the exhaust valves that allow the burnt gases (exhaust) to leave the cylinder. The cylinder is basically a tube with a tight-fitting but movable piston within it.

When the intake charge enters the cylinder, it is set on fire and explodes. This explosion forces the piston downwards, in what we call the power stroke.

The effect of this explosion pushing the piston downwards is equivalent to that of your leg pushing downwards when pedalling a bicycle. It provides the torque that gives rotating motion and movement.

This is where we pause for a moment. The piston goes down, but how does it come back up? Just like a bicycle, when the pedal goes down, it is brought back up by the downward push of the opposite pedal.

The main sprocket (the big-toothed wheel to which the chain and pedals are attached on a bicycle) has its equivalent as the crankshaft in a vehicle engine. It translates reciprocating motion (up and down or back and forth movement) into rotating motion (circular movement).

Therefore, the piston in an engine is brought upwards by the downward motion of other pistons (a typical engine has several pistons: 3, 4, 5, 6, 8, 10, 12 or even 16, but the commonest number is four).

For single-cylinder engines like motorcycles and chainsaws, the momentum gained by the downward push is what brings the piston up.

So, back to the cylinder: Primary school mathematics taught us that cylinders have volume, got by the base area (pi multiplied by the square of the radius) multiplied by the length/height of the cylinder.

The length of the cylinder is determined by the limits of piston travel, that is, from the topmost limit that the piston reaches before starting to head back downwards, to the lowest limit it reaches before going back up.

This cylinder volume, multiplied by the number of cylinders, is what gives us the engine capacity, commonly expressed in cc (actually cubic centimeters) such as 1500cc or 1800cc; and in litres as 3,0-litre engine or 4.7-litre engine.

More cc means more swept volume by the cylinders, right? More swept volume means more intake charge going into the engine, right? More intake charge means more air and more petrol, and therefore, bigger explosions which create more downward force on the piston crowns.

So yes: a bigger engine develops more power. An 1800cc car is “stronger/more powerful” than a 1500cc one and it performs better.

I also live in Kikuyu, but I will not specify where exactly for obvious reasons. It can get quite unbecoming in the rainy season, I know, and now that you cannot buy an SUV, your options are a little limited.

You could buy a 4WD version of the listed vehicles (they do come with 4WD as an option, these cars) which will offer increased directional stability and better traction, and/or (especially and) buy deeply treaded tyres which have better grip in the mud.

You will be surprised at how well they hold the muddy ground. The payoff is that they are not very good on tarmac, but then again, they are not disastrous either.

I don’t think you spend your time cornering at the limit or hunting STI Subarus, so the reduced tarmac-gripping ability will go unnoticed. Just buy the treaded tyres.

Hi Baraza,

Good work you’re doing.

I bought a non-turbo Imprezza in February last year. Towards the end of the year, it developed a clunky noise at the front right wheel, which I suspect to be a worn out bush.

As I organise my finances, please tell me what risk(s) I run if I delay replacement of the same.

Lastly, which exhaust configuration would you recommend for a non-turbo to gain slightly more pick up speed?

Ndung’u Ngaruiya

Hello,

A late replacement of the bush means you first have to put up with the clunky noise a bit longer.

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