IC Engine: Why four valves instead of two?

Car engines are designed to satisfy a wide range of demands.

I am a calm driver (in 46 years of official driving I only received one speeding ticket and that was caused by wild hormones after a visit to a hot girl) and the current designs seems to be much better than the 2 valve, 3 forward gears etc. of the "wonderful" 60's when most of the cars was friends of OPEC.

I am only interested in going from A to B (or C..Z) in as much comfort as possible. If you are interested in performance you will have to pay the price for poor economics.

One thing I miss with the 2 valve system is that you cannot force a backfire to wake a sleeping town when yo pass through it.

I haven't design an engine yet but I imagine more valves will give you better control over flow, pressures, vacuums and noise because one can open and close them at different times.

I am a calm driver (in 46 years of official driving I only received one speeding ticket and that was caused by wild hormones after a visit to a hot girl) and the current designs seems to be much better than the 2 valve, 3 forward gears etc. of the "wonderful" 60's when most of the cars was friends of OPEC.

What was the object lesson?

Eh? Friends of opec? I agree the label of economy had no application in the 60's instead they used luxury class, family, transportation, utility etc.. Normal economy could be expected as example:

1963 Chevy Impala sedan with enough shoulder room to seat three football players abreast. Having a 283 CID factory engine with two 2-speed auto transmission averaging 18 mpg city / 24+ mpg highway.

Or the 1968 Dodge corona with 383 CID factory mill 3-speed auto averaging 18 mpg city / 22 mpg highway.

Interesting lack of electronic gadgetry needed to equal mpg of today's average sedan.

Those types offering could be improved in the comfort department but not greatly. The average commuter travels 45 miles or less, what do you need for a commute? A clean seat, climate adjustment, visibility; considering all other automobile aspects are a given.

production motor transport production is always a juggling feat.

I.E.:

1st cost/ lifetime cost

power/ economy

style/ function Ad Infinitum

DisAdvantages of multi-valve (includes 3 & 5 valve , also) arrangements: total number of parts, seem to be a bit fussy in setup

Advantages: Easier heat management of multiple exhaust valves (2 smallish valves cool better than a single largish unit {read: longer life})

Largest advantages: better flow rates at low-to-intermediate lift heights; utilise by using more conservative cam-timing.

Lower inertia; will allow faster open/closing rates; again an opportunity to utilise shorter cam timing for the level of performance desired.

Both of these previous aspects should offer operating economy, in relation to a 2V equivalent at a similar performance level. If a manufacturer were to offer a 4V version with lorry type timing (camshaft), i'm guessing you'ld love it.

It seems that your real issue is that most mfg'r's are aiming at a maximum output for advert purposes; with today's fuel availability situation, we may be trying to build a generation of 'too frantic' engines!

same reason we use 4 strokes now.makes no sense to me but noone can afford that kind of mileage anymore.

better heat dissipation and temp. control + better control on the fluid dynamics are good reasons i guess.

Basically, efficiency.

I loved the old 4 Cyl. rockerboxes too.

You could actually work on them.

But you can't argue with the MPG. we get out of the new FM (F**king magic), engines.

Production of the 45+ mpg FM engines stopped about 1998...

Snaketails:

Lubrication of the early engines often included oil bath and/or oil pumped up to lubricate the valve train then run down exterior of engine block into a gutter then draining back into the sump (:

A crank shaft looking like a bent stick (no counter weight)

Engine life expectancy? 1500 miles maybe (:

For all of the reasons above, the three-valve-per-cylinder and the four-valve-per-cylinder are quite the norm these days.

It is interesting to note that many of the efficiency improvements made on the four-stroke piston engine had their beginnings on motorbike engines, and not just the racing machines.

This reminds me of my old Harley-Davidson 80 in2 Big Twin Dresser. In stock condition, it only made about fifty-two (52) horsepower set to a very lean fuel:air mixture. Mine develops sixty-four (64) horsepower through very slight engine modification, i.e., an S & S Super E carburetor and slightly advanced timing. I will never take it further, because even this slight modification caused accelerated wear on the drive train. Dressers are heavy machines and really stress their intermediate drive sections.

But, give another motorbike manufacturer that much engine displacement and they will deliver 100% more horsepower. How? By using more valves, improved timing and ignition, etc.. Longevity and reliability? Yes, they will achieve that as well. I realize that many of us yearn for the days of yore when things were more simple. I reminded myself of that this weekend as I installed a timing chain, sprocket, and guide rail set, plus new water pump, thermostat, and radiator on my 1995 Nissan pickup. It was a real chore to finally reach the simple timing chain. But, that is just the way things are now and I accept that.

To me, the rotating camshaft is still the limiting device in the piston engine, and a replacement technology has been in the works for a few years now, i.e. rotary valves with computer-controlled variable timing. But it would add a substancial cost to the manufacture of an engine so it is not easily marketed.

I could say that my old motorbike is designed the way motorbikes should still be designed, but I know from the point of efficiency and reliability that is not true. The newest design of the Harley-Davidson Big Twin makes more horsepower with less fuel than does mine. It is easier to start, and more reliable. Now, if I could just pony up the money for the new 96 inch2 six-speed Dresser......

Best Regards,

Ing. Robert Forbus

the real answer to 4 versus two valves is somewhat simple. the limiting part fro airflow has always been valve lift. four valves gives twice the lift, with smaller stems. allowing a more docile cam profile and less loading on the valve springs, mening less power loss driving the valves ( which on small engines can take well over 30% of you power). Initially they were used only on aircraft engines, largely because with cylinder capacities approaching the gallon you just couldn't make valves big enough, so they used two instead, beides they fit better. 4 valves didn't always work better, some engines need more squish area than is available with four valves in the head.

We bolted a Yamaha 1100 cc/DOHC head with carburetion attached onto a Toyota 18R engine and realized 200 hp on regular gas (:

Less engine, same power. Simple.

To my knowledge, the reason for using multi valve cylinder heads over 2 valves is quite simple: basic geometry. Valves are circular, so is the cylinder. So when you have two valves (inlet and outlet), these have a certain maximum diameter possible. As the opening is defined as the circumference multiplied by the opening height (and not by the surface of the valve opening), it is quite easy math to see that with more, albeit smaller, valves you get a bigger opening for inlet and outlet flow.

Engineers try to have the biggest opening in the cylinder head for performance and efficiency reasons. A smaller opening creates drag and thus filling problems, so that's not what you're after.

So whether you're a calm driver or looking for performance, multi valve engines are benificial. Then everything comes down to reliability.

An example: In F1, teams as Ferrari and Honda have experimented in the early nineties with 5 valves per cylinder, but they went back to 4 valves as this was less complex and more reliable. They still do so today.

dear friend ,

as you must be aware of the fact that in four valve system combustion procedure is completed & no waste of good fuel. In result of the same the pollution is negligible.

Hence practically speaking efficincy of the Four valve system is more than the two valve system. That's why now a days automotive manufacturers prefers 4 valve engines

Surendra

You basically want the biggest intake and exhaust valves you can get. 2 valves limit the size. About the only way to get bigger valves is to double them up. Each pair of valves is larger than the biggest values you could get using only two.

Hi vermin

You want large.............try this valve and its cooling system.

It is from a large slow speed, two stroke, marine engine.

I've seen sodium filled valves before, but nothing on this scale!!!

vermin, don't touch that please.

Your primitive intellect wouldn't understand alloys and compositions...........things with molecular structures and the............oh! I forgot what what I was going to say!!!

Back when I was that wild kid next door, I put a high lift, full race cam, and a big old Holly four barrel - well two- to increase the horse power. Had to grind the pistons to allow the valves to operate with out interference.

Had to change the jets several times to adjust the fuel flow, not too rich on the low end and not too lean on the high end.

The four valves are to do the same thing as the high lift cam, that is to get the most air in and the exhaust out faster. And to do it without four foot of flame out the exhaust pipe.

Greatest advantage as already pointed out........better scavenging.

Hello bgd73:,

I put a Webber on my Mini engine and the sound was gorgeous!

There are better qualified posts than mine which explain some of the advantages/(disadvantages). I would have thought it was more costly to make a four valve per cylinder engine but, I would imagine it produces more power at any given revs?

Just one more point, I have read a car can never use as much power as it takes to makes one. I would think that is a fact. So, as long as we use any type of powered vehicles, and if we take that statement as fact, any 'Earth warming' and the detrimental effect it is supposed to have, will continue...............?

jfmfit

i assume you are reffering to power losses.they are to many to count.efficiency does not go over 40% if im not wrong.heat is lost to environment at different sections,power lost to overcome friction between mechanical parts,etc.list goes on from major to minor losses.
as we design different parts of the engine theres a whole bunch of losses in each of them.even if design is optimum certain losses are unavoidable so yes among others heat will always escape to environment and problems resulting are also unavoidable.

but with better engg. this can be controlled and used even.or at least turned in a direction that wont be as injurious as current effects.

Hello shanky1367,

it is not surprising to see the IC is 40% efficient really, with all that steel to move so quickly?

My other point was that a car will never ever use as much power in use, as it does to build in the first place. That is what I read anyway...........

jfmfit

This too will pass

The Chrysler Lean Burn engines were designed to get to the emission levels that were mandated by the US government. By replacing the distributer with an older unit, or one from a truck that did not meet the same emission standards, you would have had a distributer with a vacuum advance device and a centrifugal advance built in. The Lean burn design had two electronic pick up devices and could switch between as needed. In the early seventies the US made cars were as poor a driving group as ever created. A common ignition timing setting was at top dead center. Some engine combinations even used timing after TDC. Increasing power in these years was as simple as advancing the distributer timing to the settings used in the mid sixties. Typically 6 to 12 degrees before TDC. When this was done the driver loved the way the car drove as the mileage and power increased. BUT they would always fail the emission tests.

Later as the manufactures worked with the emission standards longer they found ways to pass emissions and still give drivability. Look at the current mix of vehicles and the mileage / performance combinations we have now. That is a result of applying computer controls to solve the emission-fuel mileage-power problems.

One additional reason for the 4 valve head design. horsepower increases as RPM increases until friction overcomes power. The increasing speed of the single large valve requires progressively stronger valve springs to keep the valve from floating off the seat. By using smaller valves, but more of them the lighter weight of the valves are easier to control at elevated engine speeds.

One answer to valve design may be solenoid operated valves. International Harvester has been working on this for a few years already. I have not heard anything lately from the IH factory people because I have not been to a trade school lately. The design should be good for smaller low speed engine designs.

"I have yet to understand the disappearance of two valve internal combustion cylinder heads. The vacuum acheivable was extremely stable, predictable, less moving parts, efficient, disciplined, and still running 21 years later, if to use my original as an example.

Four valves on the other hand... sloppy fuel injection.over sized intake for given combustion chamber and stroke, bore. It all boils down to sensors with maps that are so far from nature given thier steppings of the "bog VOID" , there is yet to this day to be enough resolution ..."

I've still got a 21-year-old 4Valve/cylinder engine (VW GTi 16V). The original engine had over 170,000 miles of being driven hard when the bearings needed replacement - the engine had NEVER been opened up (if you don't count having had the spark plugs replaced - ONCE - at that point. It had never required timing or valve adjustments (and still didn't), never needed a gasket or seal replaced, anything decarbonized, and was delivering more than 31 mpg (US gallons) on regular gasoline. I also owned an '89, which I sold with over 175,000 miles showing [engine internally as-built at the factory except spark plugs] and is still being used today. It won't reach 21 years old until 2010, though. Neither had "bog" problems, ever. The '89 gave a bit over 33 mpg, BTW.

My current car should be an even greater anathema to you: five valves per cylinder AND turbo-charged, 150 hp and 164 pound-feet of torque from 109 cubic inches (1.8 liters), stock. It has had the spark plugs changed, just once, in 127,000+ miles, and I'm getting about 32 mpg day-in, day-out, driving it hard. Uses no oil between changes. It has slight turbo lag, but no bog due to FI. Oh - and I've been driving cars with fuel injection as standard equipment - not optional - for more than 38 years, now. That has given the cars better fuel mileage, more horsepower, more torque, better driveability, and lower emissions than any directly comparable carbureted car available at the same time. In hundreds of thousands of miles, my biggest problem has been a flexible fuel hose bursting. Other than the faster flow through the hole, not a lot different than what I'd experienced on carbureted cars in the past. Other than possibly restoring something old, I cannot imagine why I'd ever return to 2-valve engines and carbs.

There is a way to stop the turbo lag, inject some fuel into the exhaust port before the turbo, so keep it spinning ;o)

They have been doing that in the WRC

Are you sure it is fuel being sprayed? Some forms of racing are spraying nitrous oxide to help the turbo spool up faster. Two fold benefits, more power when fuel is enriched, and turbo spools up faster.

Yes, check out Toyota in the WRC, they inject fuel into the exhaust port, the fuel ignights almost instantly and drives the turbo.

Also whats possibly happening is that they turn off the injectors during deceleration, so raw air is being fed thru the engine, heated inside and assisting the combustion in the exhaust, the back pressure also helps to slow the engine?