Could anyone explain this to me?

fjon

I know little about car engines, and this was something I have googled for the last hour without finding an answer.

What exactly do different valves to to a car performance? What I mean is, when we see 16v or 32v etc, what does it actually mean?

Very basic question I know, but I can't seem to find any answer for it!

mike65

Valves are part of the fuel-air delivery, I'll let someone else do the techy speak (!) but basicly an engine needs 2 valves per cylinder, one for the air going in and the other for the air going out (to the exhaust), so a 4 cylinder engine will have at least 8 valves, these days 4 valves per cylinder is pretty common hence 16v (ooh I'm all excited) badges. There are a few 12v engines around these have two valves in and one valve out or is it the other way round!?

The valves are connected to the camshaft so the vlaves open and close at the speed of the engine turning.

Mike.

seamus

mike65 wrote:

The valves are connected to the camshaft so the vlaves open and close at the speed of the engine turning.

It's so painfully simple when you see a diagram of it, but it's something you'd never come up with in a million years.

Not sure what exactly a doubling of the valves does for performance, but one would assume it allows for higher performance, particularly at higher revs.

ds20prefecture

seamus wrote:

It's so painfully simple when you see a diagram of it, but it's something you'd never come up with in a million years.
Not sure what exactly a doubling of the valves does for performance, but one would assume it allows for higher performance, particularly at higher revs.

There's a good description of how engines work here:
http://en.wikipedia.org/wiki/Internal_combustion_engine

Doubling the number of valves per cylinder allows for a freer breathing engine - more air/fuel in and more exhaust out - without resorting to the much greater inertia of large valves. A freer breathing engine means higher revs are available, which means more power.

There are some 5 valve per cylinder designs (Like Volkswagen/Audi/Seat/Skoda 1.8 turbo 20v) and some 3 valve per cylinder engines (like some Mercedes Diesels, and small Daihatsus) but most modern cars use 4 valve per cylinder engines as the best complexity/efficiency compromise. Older designs use two valves per cylinder.

Most cars (in Ireland anyway) have 4 cylinder engines. The combined capacity of the cylinders is the "size" of the engine - i.e. 1.6L, 2.0L, 4.2 litres, etc. For similar reasons to having lots of smaller valves, it is better to have lots of smaller cylinders. For example, it is rare that you'll see a 4 cylinder engine greater than 2.3 litres. The reason isn't just about inertia, but balance. Some engine configurations are basically better balanced than others. The inline 4 of 90% of cars today is fine in small capacities (<2.0L) but needs balancer shafts to be smooth if the capacity is above that. Porsche once made a 3.0l 4, but only in very small quantities.

By contrast, the inline 6 cylinder (e.g. BMW, Jag, TVR). engine can happily sized at greater than 4 litres. Most manufacturers prefer a V configuration for the 6, with two banks of 3 cylinders. If you drive a very smooth 4 cylinder car and then a very smooth 6, you'll notice a marked improvement in the level of noise, vibration and harshness. The BMW and Lexus 2.0L inline sixes are very sweet small sixes and the Mazda 1.8 V6 in the MX3 is also a nice small capacity 6.

Most engines you see > 3.5L have 8 cylinders, almost always in a V configuration. In this case, the engine is arranged as two banks of 4 cylinders both usually acting on one crankshaft. There are also V10, V12, W12 and even W16 engines but it's fairly rare to be in the market for one of these.

Hope this helps.
PS: I only have 8 valves in my car, and I certainly don't miss any!

Banjo013

It's all about efficiency really ...

All other things being equal, a 2.0 litre engine with 16v will typically produce more power than a 2.0 litre engine with 8v.

Imagine a bucket with a 1 inch hole in the bottom. It might take 3 minutes for all the water in the bucket to drain out. Now imagine the same bucket with a 2 inch hole in it. The water might drain out in half the time.

Keeping the above concept in mind, the quicker you can ger the air/fuel mixture into the cylinder, and (after combustion) the quicker you can get the exhaust gases out of the cylinder ready for the next intake, the more efficient the process is and the more power is likely to be produced. Keep in mind also that with two intake and two exhaust valves, the process is far more efficient because while you're still dealing with the same volumes of intake (fuel/air) and exhaust (gases), there is double the room for them to get in and out.

A bit like people rushing out of church after mass on Sunday morning ... the bigger the door the quicker they can all get out to the pub.

That's about it really.

lomb

never buy an 8v motor they sound like tractors and dont rev, 16v motors rev like sewing machines, and have more power.

ds20prefecture

lomb wrote:

never buy an 8v motor they sound like tractors and dont rev, 16v motors rev like sewing machines, and have more power.

You should really listen to an Alfasud, Lomb. I wouldn't say it sounds like a tractor. But is generally true that 16v engines rev higher. The Honda S2000, for example can hit 9000rpm!

greglo23

the only problem with multivalve engines is when the cambelt goes you get multi dent in your wallet. timing chain engines are much more reliable if a little noisier. nissan changed from belts to chains in the late eighties and i`ve seen some with over 300,000 miles on them with no problems. i`ve seen belts go and cause major damage after 20,000 miles.

lomb

ds20prefecture wrote:

You should really listen to an Alfasud, Lomb. I wouldn't say it sounds like a tractor. But is generally true that 16v engines rev higher. The Honda S2000, for example can hit 9000rpm!

of course there are exceptions u are correct but in general, 16v engines are way smoother, and rev easier. for example my mum had the old shell 1998 vw golf 1.4 with the 8 v engine and then bought a 99 new shape one with a 16v 1.4 engine, and whereas the old engine was a joke, the newer one although lacking power revs freely, whereas the old one didnt like revving at all. light years difference.

bazz26

Just to confuse you a bit more there is also variable valve timing which is used by alot of manufacturers these days. This is were one or more of the valves opens and closes when necessary allowing the engine to be more fuel efficent while still delivering optimal performance. Toyota have their VVTi system while Honda uses their VTEC system, both use different methods of this concept.

fjon

Thank you everyone - it really does make sense now!

AMurphy

greglo23 wrote:

the only problem with multivalve engines is when the cambelt goes you get multi dent in your wallet. timing chain engines are much more reliable if a little noisier. .....

Thanks for the reminder.

btw, when (year) do ye think 4V per cyl was first deployed?.

mukki

your making the usual mistake, people always think that by adding more valves or a turbo charger makes a car stronger,

thats totally wrong!!!!,
the valves/turbo just let in more air so you can burn more fuel

having more fuel above the cylinder before its ignited is what makes it stonger ( as long as it burns in enough air)

so adding more valves just means you can pump in more fuel and hence stronger
adding a turbo means you can pump in more fuel and hance stronge

and with the fooken price of fuel these days your all bloody mad

AMurphy

I think you just contradicted yourself.
If by "stronger" you mean produce mower power per Liter or engine capacity, they you are correct. If you stuff more "fuel" into the cylinders, whether it be by turbo, tuned intake, more valves, variable valve timing or overlap, etc./, then you should get more power, ie "stronger". In your average petrol/gas car the Air includes the "fuel", unless of course you were thinking about a diesel, or DI petrol, where the fuel and air are delivered via a seperate mechanism, in which case you might be depending on the "excess air" for some of the performance.. in which case valves and turbos are all important again.

So what was your point again...?.

ds20prefecture

AMurphy wrote:

btw, when (year) do ye think 4V per cyl was first deployed?.

I know there was a 16 valve Triumph Dolomite Sprint in 1973. I believe it is the first mass-market 4 valve per cylinder engine.

I am fairly sure that it was used before then, definitely in Honda racing bikes of the late 50s.

ds20prefecture

mukki wrote:

thats totally wrong!!!!, the valves/turbo just let in more air so you can burn more fuel

This is wrong, but not "totally". They dont "just" let more air/fuel mixture in, they also let more exhaust out, which is every bit as important for boosting the efficiency of an engine.

Seth Brundle

16 valves? jeez I have 24

ds20prefecture

kbannon wrote:

16 valves? jeez I have 24

There's always someone with more valves....
http://www.modernracer.com/features/newkidsontheblock6.html

I reckon it is only a matter of time before VW use their 5V technology on the W16 to make an 80 valve engine. There were rumours of a W18 too.....

The_Bullman

Maybe I should start a new thread on this but anyway

What's the effect of a twincam on an engine? How does it work?

Seth Brundle

the cam rotates along with the speed of the engine and whilst rotating there are lobes on it which allow the valves to open and close at therir respective times.
Having a 2nd cam (twin cam/ or dual overhead cam [DOHC]) per cylinder head allows the head to have more room for valves.
I presume it is covered in http://auto.howstuffworks.com/camshaft.htm

ds20prefecture

The_Bullman wrote:

What's the effect of a twincam on an engine? How does it work?

Twincam refers to a method whereby inlet and exhaust valves are operated by seperate camshafts. It is very common for 4 or 5 valve per cylinder engines to use two camshafts per cylinder bank, but it was also used on 2 valve per cylinder designs and there are 4 valve per cylinder engines with a single camshaft per cylinder bank (e.g. VW VR6)

There's pros and cons to each, I believe the principal advantage of a twin cam engine is more independant control over the timing of exhaust and inlet operations. The trade off is more mechanical complexity, more weight and a greater dependence on timing accuracy, where timing is the position of the valves relative to the combustion cycle.

fletch

lomb wrote:

never buy an 8v motor they sound like tractors and dont rev, 16v motors rev like sewing machines, and have more power.

Agreed I drive a car with an 8V engine...never again I tell ya! The thing is SO slow

jayo99

>the only problem with multivalve engines is when the cambelt goes you get >multi dent in your wallet. timing chain engines are much more reliable if a little >noisier.

Not necessarily.. If your engine is a non-interferace engine you can break as many timing belts as you like :-))

ds20prefecture

I'd love to know how the valves work on a rotary engine. Anybody care to explain?

Thumper Long

how would you find out if an engine is non-interference is there a list or something as i hope to buy a new car in the next while and it would be a nice feature as the expence of replacing the valves and cylinder heads is not an experience i want to experience again.

De Hipster

ds20prefecture wrote:

I'd love to know how the valves work on a rotary engine. Anybody care to explain?

http://auto.howstuffworks.com/rotary-engine.htm - 11 pages of rotary engine explanation.

CrowdedHouse

AMurphy wrote:

Thanks for the reminder.

btw, when (year) do ye think 4V per cyl was first deployed?.

I think the old Bentley 'Blower' and Mercedes racing cars of the 1930's had 4 valves per cylinder

ds20prefecture

De Hipster wrote:

http://auto.howstuffworks.com/rotary-engine.htm - 11 pages of rotary engine explanation.

Thanks - so the answer is "there are no valves in a rotary engine"!!

Capt'n Midnight

CrowdedHouse wrote:

I think the old Bentley 'Blower' and Mercedes racing cars of the 1930's had 4 valves per cylinder

was it the bentleys that first used superchargers, getting loads more power from a tiny little 5.5L than many of the macho cars with their 12L engines (is F1 still only 1.5L ?)

slightly off topic - anyone know where I could get info on WWI rotary aeroplane engines , where the entire engine rotated before they got radials ?

ds20prefecture

CrowdedHouse wrote:

I think the old Bentley 'Blower' and Mercedes racing cars of the 1930's had 4 valves per cylinder

The Bentley had 2 valves per cylinder, and the 1950s Mercedes 300SL and SLR (it's racing variant) used a 2 valve 6 cylinder engine This engine was regarded as "advanced" in that it used fuel injection, but it still only used 2 valves per cylinder. I'd be surprised if 1930 mercs used 4 valves per cylinder.

By the way, the Bentley "Blower" was not an "proper" bentley at all, WO Bentley described it as a perversion of his design and rejected it. It used a Rootes supercharger, but was far from the first to do so.

It seems the first 4 valve per cylinder engine was a Bugatti Type 23 race car
of 1920 http://www.ultimatecarpage.com/frame.php?file=car.php&carnum=1497.

I still think the Dolomite was the first 4vpc mass-market car.

mike65

It was this or a propellerhead!

Mike.