8 valves vs 16 valves

Hi,

I was going thru the specification of Figo diesel and Swift diesel. Figo diesel Engine -Valves are 8 whereas for swift , it is 16...

I was told that less number of valves will increase Maintenance of the car ... that means Figo will have more maintance than Swift. is that true?

ur suggestions.......

Well 8 valves (8v) basically means a 4-cyl engine with 2 valves/cyl (one for intake and one for exhaust). 16 valves (16v) means 4 valves/cyl (two each for intake and exhaust). The 16v engine is better in terms of performance as it has an easier time taking in air and pushing out exhaust (i.e, breathing).

Now, from a maintenance point of view, 16v is somewhat more prone to problems than 8v in that there is double the no. of valves to take care of than an 8v engine. However all said and done, the difference is not that much except for a bit more effort/complexity involved in 16v engine repair. State of the art is such that 16v engine will, in most circumstances, give no more problems than an equivalent 8v engine. So no worries on that front. 16v engine for the same capacity will be a bit more expensive than its 8v equivalent - but it will have better performance.

MODS: I guess this thread belongs to the Automotive Terminologies category. Please move it there. Thanks!

8 valves vs 16 valves

I would think its better that 8 valves would be better for petrol engines, 16 valves would be better for diesel engines, as you know petrol cars makes lesser noise than diesel

8 valves petrol cars would be cheaper to afford than 16 valves,

but in diesel cars that works the same but 8 valves are much noisier than 16 valves, power is also compresed in 8 valve engine

Dan, 16v is better in terms of performance for both petrol & diesel. You see its just an advancement of technology - adding an extra valve to the intake and (optionally) the exhaust ports. The only tipping point between the two is cost v/s performance. Low cost will tend to favour 8v and better performance will tend to favour 16v - and there is a compromise here: the 12v 4-cyl engine with 2 intake ports and one exhaust port per cylinder. Noise is not an issue here.

Consider the intake port on a cylinder. One intake port/cyl will mean that there is a max size limit to the port diameter - this has two implications:

1. The port must be as large as possible to enable maximum air intake. This diameter cannot exceed the radius of the port and probably has to be much smaller than the radius otherwise the cylinder head will physically not be strong enough to take the physical, mechanical & thermal stresses that occur in the engine.
2. Since the port is as large as possible, the valve is bigger and heavier (relative to multiport cylinders, read on).

1 leads to a situation where there is a limit to the amount of air the engine can draw in and 2 leads to a situation where there are greater mechanical/inertial losses in the valve. With 2 ports/cyl and hence 2 valves/cyl the following happens:

1. We can have two ports each of smaller dimension than a corresp. single port engine but at the same time, the combined diameters of the two ports will be equal or even more than the single port.
2. Smaller ports means smaller valves which are lighter.

1 leads to a situation where the same amount of or more air can be drawn in. 2 leads to a situation where there are lesser mechanical/inertial losses in the valve. In combination, 1 & 2 give the engine greater capacity to take in air and at the same time have less losses. The result is an engine that can perform better both in terms of RPM and power output.

It has nothing to do with noise nor it is a question of choice. Petrol or Diesel these sort of modifications are made to  meet strict pollution  norms.

If somebody is interested Ill eloborate.

I'm not sure I'd call either of them higher tech or more advanced than the other at this point.  Both single overhead cam (SOHC) and dual overhead cam (DOHC) engines have been around since the 1920s or so.  For a long time overhead cam designs were just too complicated and expensive to use in regular cars.  Mostly they went into things like aircraft and military vehicles.  Up into the 1940s/maybe 1950s cars often had simple side valve engines.  Then overhead valve (OHV) designs displaced them as the side valve design had a poorly shaped combustion chamber.  The last couple decades or so SOHC and DOHC have taken over, and at this point DOHC seems to be in the majority.

4 valves/cylinder is popular because it makes for a good cylinder head design.  The valves are simply arranged in a square at the top of the cylinder.  This comes pretty close to maximizing airflow without being too complicated.  There are engines around with more than 4 valves/cyl, but they're fairly rare.  VW-Audi was building 5v/cyl engines for a while, but I'm not sure they're still doing that.

There really isn't any maintenance difference between 8v and 16v engines unless your engine breaks as Rohit mentioned.  Hopefully that will never happen, and I wouldn't worry about it.  Just don't buy a car with a reputation for catastrophic engine failures.

There's no real differene in FE just from the number of valves.  A lot of 4v/cyl engines close off half their intake valves at lower rpms to improve FE and torque.  Restricting the intake increases turbulence and helps fuel mix better.  At higher rpm they open to allow more air in.  With more air coming in a 4v/cyl engine can burn fuel faster than a 2v/cyl engine.  If you drive the car hard you can get lower FE out of a 4v/cyl engine than a 2v/cyl one, at least in theory.  The key word here though is can.  It just gives you the option of going faster at the expense of less FE.

From maintainance point of view, 16v will have to be given more attention, but the performance will be comparatively higher.

@Mike and Rohit- Very elaborate explanation..and very useful too.

Thanks a lot.

Excellent explainations.. We need more of such valued discussions..