does the power of any car depends upon the number of valves per cylinder?

Question

i would like to ask that the power of any car does depend on the number of valves per cylinder. as earlier the valves is to be around 2 per cylinder but nowdays there are 4 valves per cylinder. does it makes any diffrence in power, mileage and performance of a car. why the no of valves have been increased require details.

Answer 1

The combustion efficiency of an engine (which would be directly related to power) depends primarily on the ability of the engine to burn the fuel completely with a 'smooth' explosion, as well as deliver the power smoothly.

Most cars come with one intake and one exhaust valve driven by either a pushrod (where the camshaft is on the engine block and not cylinder head - this is old tech and has its limitations though an exception is the scorpio), or an overhead camshaft (OHC). Having just one valve for each function limits the options for aspiration and exhaust 'flow' and turbulence within the cylinder which affect combustion efficiency.

newer cars come with 4~5 valves and two Camshafts (DOHC), where 2~3 valves are driven by each shaft. This allows the engineers to create a 'pressure' and 'flow' pattern within the cylinder to burn the fuel more efficiently. typically this also results in lower fuel consumption for a slightly higher power. This is one of the major reasons why DOHC/4-valves are introduced.

It does not stop with this though. Since the valves are operated mechanically (as against injection timing, which is electronically and software controlled), the engine would experience different efficiencies at different RPMs. So the new cars come with Camshafts that can themselves be 'advance' electromechanically for a new cam set to drive the shafts. The changeover happens typically from city to HighSpeed Driving. This is called as 'Variable Valve Timing' or VVT. You would see 'DOHC' written expensive cars a few years ago. Today you will see 'VVTi' (Toyota petrols, eg) and the like on expensive car brands.

Even higher tech cars have drive by wire, which means cams and cam shafts are eliminated and the valves are controlled by high-tech solenoids which have continuous and non-binary operations. In these cars you would be able to choose your drive mode as 'lean-burn', 'sporty', etc and the engine management tech does the rest for you.

Answer 2

the sheep, lemmings and luddites would have you believe that 4 valves are better than 2. and theyd be somewhat right.

valves are only part of the story. 2 extra valves means you can get more air into the engine, and if you have more air, you can add more petrol (gas) and generally get more power as a result.

but it also depends on the compression ratios, shape of the combustion chamber, strength of the spark, width of the combustion chamber, flame propogation and flame front and a whole bunch of other things that we really cant delve into right now.

if you have an engine, optimally designed for 2 valves, and you add 2 more, without changing the inlet manifolds, spark, shape of the chamber and everything else, then yes, you will get a SLIGHT increase in power.

but, if you redesign the cylinder head and all ancillaries, and optimise it for 4 valves instead of two, you will get SIGNIFICANTLY more power.

the easiest way to think of it is this way; suppose you want to play basketball to get some exercise. you could go buy the most expensive jordans out there at $200 each or whatever, but they are not going to make you jump any higher. or make you run any harder.
but, if you take that same $200 and get some training sessions with a personal trainer, and some cheaper $80 sneakers, you will be a better athlete, and better ball player as a result.

so yes, generally speaking the valves can add some power. but they add the most power when the engine is designed from the get go for four valves.

Answer 3

An engine makes more power if you have more valves per cylinder because it moves more volume of air/fuel through the engine. The power an engine makes depends on many things, but yes the more valves it has, the More power the engine will make. Four valves per cylinder makes a lot of power, but if one uses larger valves on a two valve engine, and adds more duration to how long the valves stay open, the same result can be accomplished. The more valves you have, the more friction the engine makes, and as we all know friction is heat, and heat takes away from the performance of the engine. Go to www.howstuffworks.com and type in internal combustion engine. This should explain what I mean.
Glad I could help. Good Luck!!!

Answer 4

As goobersmooch says, your guess regarding 4 valves is wrong. On a 4-valve engine (i.e. that means 4 valves per cyclinder) there are two exhaust and two inlet valves. I can't remember offhand if there are bikes with 3 valves, but there are definitely cars with 3 valves. They are usually one inlet, two exhaust, because the exhaust valves get hotter (having to deal with hot burned gases) and two valves give a better surface-to-volume ratio, thus aiding with keeping them cool. I'm fairly sure there are bikes with 5 valves per cylinder, but I'm danmed if I can remember what they are. Why? Same principle applies - more valves in a given space means a better area for the gases/vapours to flow over = more efficiency. But eventually the ol' cost/benefit ratio catches up. It's harder to make a valve train to open 5 valves than it is to make one to open 4,3, or 2. All engines have their intakes on the carburettor side, whether 2-stroke or 4. Or, more acurately, their carbs are on the intake side. 2-stroke valves, if they have any, are completely different to 4-stroke, and they are on the intake side only. A 2-stroke engine doesn't necessarily need to have valves.

Answer 5

Yes, it does.
Having four valves per cylinder gives an engine several advantages.


By having four valves in a cylinder instead of two, a larger portion of the area can be used to let air in and exhaust out. The engine can make more power if more air enters the cylinder, and it wastes less power if it is easier to pump the exhaust out of the cylinder.
At higher engine speeds, the engine pumps a lot of air though the cylinders. Having four valves per cylinder allows the engine to pump enough air to run and make useful power at these higher speeds.

Answer 6

no. some of the best only have 2 per cyl. Chev small block. hemi.

Answer 7

Nope.

Answer 8

donno the mechanism!!