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172 VVT





I know that with Honda V-techs there is a seperate intake cam that comes in at high revs but can anyone explain how Renaults version works?
 
  Scirocco GT TSi DSG


I think this was looked at in some depth a few months ago on this forum by Ben R and the late Captain Slarty.
 


Yeah Ive just looked at that thread but doesnt really make that much sense. Just seems like a competition between Ben R and Captain Arseface to see who can come out with the most technical terms in one sentence! I need a simple explanation.
 


BMWs double Vanos design is in essence an advanced for of VVT, as it alows advance and r****d of inlet and exhaust indepandantly.

however, on teh 172, our VVT is useless basically.

it turns on when 12V is applied to the plunger adn teh cam phaser shifts (advances) the cam by a set amount of degrees.....its basically on the whole time except at idle and up to 1500rpm....

it doesnt do much and is basically there so Renault can say it has VVT.

nothing special.

unlike VTEC which has , now, the 3 stage VTEC with 3 different inlet profiles which chance according to rpm and oil pressure......
 


Really? thats a bit pants aint it.... if they would have spent a little more on it maybe it would be a clio 190 or something
 


possibly, but the cam profile in it is already what some would call a rally cam....its pretty damn lumpy as it......and anything more would need a far more advanced VVT system.

im not sure but it might be tactics as this way it leaves tehm teh option to scoop more power from the old lump....as in teh porsche boxter, its heavily underpowered and old now, but it still sells, casue new models with mroe and more power keep comming out......if only the cup had 190.......

but the F4R aint the best and is pretty heavily worked as is...for rd use.

but in Zhu Hai we got 215bhp with a sime change to TBs and magneti marelli management......but that was on a cup racer we have.
 


well, not wihtout some mods to other areas which area mainly induction......

the cam is fine really, but the TB and inlet manifold are not the best.....soem 2ltr pug coaches (405,406, 607 etc) have bigger TBs.

anyway, tehre is always some thing you can do.
 


Here you go guys - never say I never contribute anything:

Popet values are used in gasoline and diesel engines to control the inlet and exhaust of air passing through the engine. When the intake values open, air is drawn into the engine cylinder. After the fuel has been burnt, the exhaust valves then open to let it leave.




Honda S2000: Delivering 240bhp Using VVT

In conventional engines, the popet valves open and close at a constant speed. Their timings do not depend on how fast the engine is running. At high engine speeds [e.g. when overtaking a slower vehicle], this starts to become a problem. Large amounts of air are required by the engine at higher speeds. However, the intake valves may close before all the air has been given a chance to flow in.

On the other hand, if the valves were calibrated to remain open for longer periods of time, problems start to occur at the lower engine speeds. In these situations, unburnt fuel may exit from the engine since the valves are still open. This leads to lower engine performance and increased emissions.

Around the early 1990s, Variable Valve Timing [VVT] started to become popular on gasoline passanger cars. Using this technique, engine manufacturers are able to control the extent and duration for which the popet valves are open. In addition, the opening and closing of the valves can also be varied depending on the crank angle.

With VVT, a sensor is used to detect the engines speed. An electronic system then uses this information to adjust the valve opening and closing timings accordingly. This avoid the problems mentioned earlier and allows for maximum torque at all engine speeds.



This should sort out any queries you all may have!
 


And some more-

Variable valve timing, the long time "Holy Grail" of engine designers, has now been reduced to its quintessential form- a single replacement part simply known as the Smart Valve (Patent pending). AATAP is proud to bring motorcycle and car enthusiasts, this new, innovative, and cost effective performance upgrade. Stick around, and learn more about the benefits of the Smart Valve.








So, what is the Smart Valve, exactly?




The Smart Valve is a custom designed replacement valve that provides seamless, variable timing throughout an engines powerband. Installation can be done by you (if you have the skill and equipment), or at a machine shop of your choice. Because it replaces the stock valve in the cylinder head without further modification, the Smart Valve provides a unique solution for enthusiasts that want the benefits of variable valve timing, without the complexity and high cost.







Whats so special about the Smart Valve?





To understand whats so special about the Smart valve and valve timing, one has to understand the some of the things leading up to this point in time.

In the mid to late 70s both GM and Toyota attempted to develop a practical, variable valve timing system.

These systems incorporated an entire auxiliary valve element that employed an on-demand constantly variable actuation. Both Toyota and GM had the right idea, but they simply approached it the wrong way.

By incorporating an entire auxiliary valve required to traverse the full lift range, their designs ended up leading to unavoidable complications and compromises. These systems would actually reduce peak output, for example.



To this day, car manufacturers and aftermarket companies continue to attempt creating truer variable valve timing systems; because the creation of such would have incredible impact on automotive performance technology for years, possibly decades to come. Yet, few if any have been able to produce a system that offers truly continuous variable timing that works independently, per cylinder, per cycle.

The search for practical, variable valve timing systems has been a long and difficult one. The quest for a real solution has been so elusive, that most manufacturers have given up. Those that still try, resort to costly, and extremely complex systems with limited effectiveness, rather than manufacture than a truly practical one.



VTEC for example, is simply a cam changing system that utilizes multiple cam lobes on either one or two camshafts. VTEC shifts between a low cam profile and an high cam profile setting based on rpm. This system does improve peak power, and can raise red line (up to 9,000 rpm in S2000), just like an engine with racing camshafts, and increase power from 10-25%. However, to exploit such power gain, the VTEC engine must rev at or above its threshold rpm. Frequent gear change is required. Because VTEC is biased towards top end power, low-speed drivability can be considered unimpressive. There is no infinite variable timing there.





VANOS and VVT are similar in that they utilize a constantly variable cam phasing gear. Basically, these types of systems allow earlier or later valve opening. The gear changes the phase (or position) of the camshaft based on engine load, and is controlled by engine management system according to need, and actuated by hydraulic valve gears. At high speed for example, the inlet camshaft will be rotated in advance by 30? so to enable earlier intake. Earlier opening results in earlier closing, of course, which means less fuel to fill the cylinders for optimum power. True, VANOS or VVT can vary cam timing, but are not able to provide a more seamless and efficient variable valve timing.



Smart Valve approach to variable valve timing is a bit different. Unlike VTEC, VANOS, VVT, etc., Smart Valves vary timing directly at the source, which is the intake valve. They effectively vary the opening and closing of the intake valve to create truer variable valve timing, which is constantly self tuned on a cycle to cycle and cylinder to cylinder basis. With the variable valve timing capability of Smart Valves, there are no compromises, as fuel economy, emissions, throttle response, starting performance, exhaust temperatures, and mechanical stress all improve simultaneously. In contrast, a high performance cam by itself, will typically degrade all of these areas simultaneously. Therefore the Smart Valve is designed to appeal to those who care as much about the quality of their HP as the quantity.
 


And some more-



There was a time when engines had to be big to be powerful. There was a time when engines could either be tuned for low-rpm torque or high-rpm power, but not both. There was a time was a time when a specific output of 100 hp per liter was the stuff of racecar fantasies. Today these limitations are all but gone. Getting 100 hp for each liter of displacement is now possible on cars that have to get good gas mileage, emit clean air, act civilized enough for your grandmother to drive them and sell for under $20,000. So what happened? Variable valve timing.

Camshaft profile is probably the single most important engine design parameter determining the personality of an engine. One cam profile can make an engine a trucky torque-monster, another can make it a peaky race engine, but no single profile can give you both. For decades engine designers have wrestled with the compromises that are inherent in cam design. A cam that idles well and offers clean emmisions typically wont make much power, while a serious high-horsepower cam can make the engine belch smoke at idle and be balky at low rpm. Some method of changing cam profile on the fly has always been the ideal solution; if an engine needs a different personality for different parts of the powerband, why not give it a split personality? For most of the history of the internal combustion engine this has been an impossible solution - the VTEC arrived.

Teb years ago variable valve timing was exotic technology; today its so commonplace that some automakers have even forgotten to brag when they use it. Like all wheel drive, supercharging, and virtually every other automotive technology, variable valve timing can be achieved through a surprising variety of methods. and for several different purposes.

There are two basic types of variable valve timing systems. variable timing and lift systems can typically switch between completely different cam profiles. most systems, however, vary only timing by advancing and retarding a standard set of cams.



Variable Timing and Lift

Honda broke the ice when the NSX debuted in 1991 as the first production car with a variable valve timing system. Hondas VTEC (which sort of stands for Variable valve Timing and lift Electronic Control) system, which has basically remained unchanged since then, is still one of the most effective systems for making ultra high specific output.

The concept is incredibly simple. So simple, in fact, that you have to wonder why nobody thought of it earlier. Basically each pair of valves has three cam lobes, two that operate the valves at low-rpm, and a third that takes. over at high rom. During low-rpm operation, the two rocker arms riding the low-rpm lobes push directly on the top of the valves. In most cases, the cam profiles of the two intake valves will be slightly different, promoting swirl in the combustion chamber for better driveability. At high rpm (usually 4500 rpm to 6500 rpm range, depending on the engine) the ECU sends a signal to an oil control valve that allows oil pressure to flow into the low-rpm rocker arms. A third, high rpm rocker arm sits between the two low-rpm arms and follows a much more aggressive lobe. When oil pressure arrives, two hardened steel pins pop out of the sides of the low-rpm rocker arms and slide into sockets in the high-rpm arm, and the valves start folowing the larger cam profile. Just when you thought the engine was going to run out of power, output starts climing againas the engine "comes up on the cam" for the second time.

The fact that the pins in the rocker arms have to line up perfectly has caused problems in the past when people tried to make even hotter cams. When a performance cam is reground from an existing stock camshaft, the base circle - the round backside of the cam where the valve is closed - is ground down to a smaller diameter, while the peak of the cam lobe is left at the same height. (Ideally, the base circle would be left alone and the peak raised, but try adding metal with a grinder some time). If the three cam lobes are not ground to exactly the same base circle, the high-rpm cam will not be able to engage. The only time the pins and the holes will line up is when the valves are closed, but if the base circles dont match, the holes will never be aligned. Inexperienced cam grinders making this mistake are probably responsible for the popular rumour that its impossible to make aftermarket cams that work for a VTEC engine. It is possible, you just have to make them carefully.

Until recently, VTEC was a unique system in the automotive world. The came VVL, Nissans new variable valve lift system that, to the untrained eye, looks identical to Hondas VTEC system. In fact, even to the trained eye, it looks the same. This system is currently available exclusively on Japan only versions of the SR engine series (of which the SR20DE in the Sentra SE and G20 is the only US version), so information is hard to come by, but it appearsthat the only significant difference between the VTEC and VVL is the fact that the VVL switches the intake and exhaust at slightly different engine speeds in an effort to smooth the transition between cam profiles. There is no question that the system is incredibly effective, no matter who is making it. The 1.8 liter non-VTEC Integra makes 140 hp, while the VTEC-equipped version makes either 170 or 195 hp (depending on whether you look at the GS-R or Type R). On the Nissan side, a US model SR20DE also makes 140 hp, while the VVL equipped SR20VE makes 190 hp. Stretch the Nissan engines development to the Type R level and you have the hyperactive 1.6 liter SR16VE that was in the Nissan Pulsar N-1, power output: 200 hp.



Variable Timing

Systems that change only timing are far simpler then either the VTEC or VVL systems. It is generally well known that adjusting cam timing with adjustable cam sprockets can yield significant gains at certain points in the powerband, but always at the expense of power somewhere else. If you are designing engines that have to meet LEV (Low Emissions Vehicle), ULEV (Ultra-Low Emissions Vehicle), or even SULEV (Super Ultra-Low Emissions Vehicle) standards, you have other concerns that can be affected by cam timing as well. Emissions, drivability, cold startability - the effects of cam timing are far reaching. A sophisticated cam sprocketthat can advance and r****d intake and/or exhaust cams on the fly eliminates most of the compromises inherent in cam timing.



The number of engines equipped with some sort of adjust-on-the-fly cam sprocket is huge, and growing rapidly. nissan has used a system called VTC (Valve Timing Control) on the Infiniti Q45 and the turbocharged Nissan Silvia, among others. Toyota has begun using VVT-i (Variable Valve Timing with intelligence) extensively on their high end US models (most of which are under the Lexus badge), but as they refine the system and reduce the costs associated with it, VVT-i is bound to find its way down to the four cylinder models very soon. Ford has already brought their variable valve timing down to the 2.0 liter Zetec engine, but unfortunately only on the exhaust cam where it improves emissions but does almost nothing for horsepower.

The actual mechanismsused to advance and r****d the cams vary enormously, but two systems in particular deserve a closer look for how incredibally simple they are.



Porsches VarioCam, used first on the 968 and know used without the fanfare on all (both) of their engines is as simple as it gets. With VarioCam, the exhaust cam is driven by the crank, and the intake cam is driven, via a short chain, by the exhaust cam. In order to advance and r****d the intake cam, the chain tensioner on that short chain simply shifts up and down, moving the extra length in the chain from the tight side to the slack side. When the tight side has no extra chain (ie. the chain is straight), the intake cam is fully advanced, as more chain is shifted to the tight side, the cam is retarded.



Toyotas newest version of VVT-i is also quite simple, though it may look otherwise on initial inspection. Again, the exhaust cam is driven from the crank, while the intake cam is driven off the exhaust cam. This time, the drive is via gears, and a mysterious cylinder behind the drive gear on intake cam controls cam timing. Inside this mysterious cylinder is a simple three fluted rotor that actually drives the cam. By pumping oil into the chambers on either side of the three flutes, the hydraulic pressure can force the cam to advance or r****d. This replaces the previous VVT-i system which was basically an incomprehensible little box of gears, springs and splines. (for a description of the older VVT-i go to http://members.aol.com/juanaday/gs400/vvti.htm http://members.aol.com/juanaday/gs400/vvti.htm)

The VVT-i system can change the intake cam timing over a 60 degree range, changing valve overlap from absolutely zero (for smooth idle, easy starting and better cold start performance), to severely overlapped for a natural EGR effect at medium load (eliminating the need for an Exhaust Gas Recirculation valve), to whatever is ideal for maximum power at any point on the powerband.

The Future

If all this exotic variable valve timing technology is commonplace now, what does the future hold? Currently we are limited to either adjusting overlap by moving a standard camshaft, or switching between two fixed cam profiles. There is no reason (other then cost) why both systems could not be used in parallel on one engine, but the benifits may be limited. The true future of variable valve timing is infinite adjustability of both lift and timing.



The idea of opening and closing the valves with large electrical solenoids has been bounced around for several years. Many different manufacturers from Cummins to BMW have proposed such systems, and even made running prototypes. There are a few problems with electronically operated valves, but lets look at the advantages first.

Current gasoline engines control part throttle airflow via a throttle plate, essentially lowering the air pressure in the intake manifold by choking it off with a partially closed throttle plate. This causes significant pumping losses as the engine fights to suck air in from the manifold, and ultimately reduces the efficiency of the engine. If you limit airflow by reducing the time that the intake valve is open, though, pumping losses could be significantly reduced.

At wide open throttle (or full down pedal in the case of a throttleless engine) the valve timing could be constantly adjusted for maximum power - with no worries about one valve timing profile having to work from idle and redline like they do know.

Now the downside. Eliminating all of the valvetrain reduces the cost and complexity engine and reduces the internal drag, but not as much as you might think. Opening and closing the valves takes a certain amount of power, whether that power comes through a timing belt or a wire, it has to come from somewhere. In this case, the power would have to come from a huge alternator. This is not really a problem, but it is an extra cost that isnt initially obvious. More serious is the question of how to close the valves quickly but still have it land on the valve seat gently. With a cam, you just shape the lobe so it drops shut quickly and then slows down just before the seat. With a solenoid operating the valves, it takes sophisticated electronic controls

Finally, there is the matter of rpm limitations. Ideally, with strong enough solenoids, the engine would be able to spin even faster then a conventional engine, but the current solenoids have a hard time working that fast. On the flip side, though, because the valve opening speed is not engine related, mid rpm performance could be greatly improved by having the valves slam to full open much faster than a conventional valvetrain, improving volumetric efficiency and making more power.



Finally, BMW has actually designed a mechanical system that still uses conventionalcam lobes, but is still able to vary lift and timing by moving the fulcrum point of the rocker arm. The system is incrediblydifficult to visualize (I still dont get it.) but it could offer most of the advantages of electrically actuated valves without delving so far into unexplored technologies.

With the current variable timing technologies, the 100 hp per liter hurdle has been cleared. Honda, in particular, has knocked the hurdle over and stomped it into the ground. With the technologies on their way, 150 hp per liter is on the horizon. I, for one, cant wait.
 


If youve been paying attention to the acronyms used by Honda, Toyota and BMW over the last few years, youve probably noticed that the letter "V" has become quite popular lately. Youve got "VTEC" appearing in all the Acura and Honda brochures and "VVTi" showing up in the majority of Lexus and Toyota literature. Finally, beginning this year with select BMW 3 Series engines, a new Double VANOS system will be advertised.

What do all these Vs have in common? Well, in case you dont already know (or havent yet guessed despite the monster hint in this columns title), the V stands for valves or, more specifically, variable valve timing.

Before you can appreciate how important valve timing is, you have to understand how it relates to engine operation. Remember that an engine is basically a glorified air pump and, as such, the most effective way to increase horsepower and/or efficiency is to increase an engines ability to process air. There are a number of ways to do this that range from altering the exhaust system to upgrading the fuel system to installing a less-restrictive K&N air filter. Since an engines valves play a major role in how air gets in and out of the combustion chamber, it makes sense to focus on them when looking to increase horsepower and efficiency.

This is exactly what Honda, Toyota and BMW have done in recent years. By using advanced systems to alter the opening and closing of engine valves, they have created more powerful and cleaning burning engines that require less fuel and are relatively small in displacement.

Before we take a look at each of these variable valve-timing systems, lets rehash how valve timing normally works. Until recently, a manufacturer used one or more camshafts (plus some pushrods, lifters and rocker arms) to open and close an engines valves. The camshaft(s) was turned by a timing chain that connected to the crankshaft. As engine rpms rose and fell, the crankshaft and camshaft would turn faster or slower to keep valve timing relatively close to what was needed for engine operation.

Unfortunately, the dynamics of airflow through a combustion chamber change radically between 2,000 rpm and 6,000 rpm. Despite the manufacturers best efforts, there was just no way to maximize valve timing for high and low rpm with a simple crankshaft-driven valve train. Instead, engineers had to develop a "compromise" system that would allow an engine to start and run when pulling out of the driveway but also allow for strong acceleration and highway cruising at 70+ mph. Obviously, they were successful. However, because of the "compromise" nature of standard valve train systems, few engines were ever in their "sweet zone," which resulted in wasted fuel and reduced performance.

Variable valve timing has changed all that. By coming up with a way to alter valve timing between high and low rpms, Honda, Toyota and BMW can now tune valve operation for optimum performance and efficiency throughout the entire rev range.

Honda was the first to offer what it called VTEC in its Acura-badged performance models like the Integra GS-R and NSX (it has since worked its way into the Prelude and even the lowly Civic). VTEC stands for Variable Valve Timing and Lift Electronic Control. It basically uses two sets of camshaft profiles-one for low and mid-range rpm and one for high rpm operation. An electronic switch shifts between the two profiles at a specific rpm to increase peak horsepower and improve torque. As a VTEC driver, you can both hear and feel the change when the VTEC "kicks in" at higher rpm levels to improve performance. While this system does not offer continuously variable valve timing, it can make the most of high rpm operation while still providing solid driveability at lower rpm levels. Honda is already working on a three-step VTEC system that will further improve performance and efficiency across the engine rpm range.

Toyota saw the success Honda was having with VTEC (from both a functional and marketing standpoint) but decided to go a different route. Instead of the on/off system that VTEC employs, Toyota decided it wanted a continuously variable system that would maximize valve timing throughout the rpm range. Dubbed VVTi for Variable Valve Timing with intelligence (Is this a dig at Honda, suggesting their system isnt intelligent?), Toyota uses a hydraulic rather than mechanical system to alter the intake cams phasing. The main difference from VTEC is that VVTi maintains the same cam profile and alters only when the valves open and close in relation to engine speed. Also, this system works only on the intake valve while VTEC has two settings for the intake and the exhaust valves, which makes for a more dramatic gain in peak power than VVTi can claim.

Several other manufacturers, including Ford, Lamborghini and Porsche have jumped on the cam phasing bandwagon because it is a relatively cheap method of increasing horsepower, torque and efficiency. BMW has also used a cam phasing system, called VANOS (Variable Onckenwellen Steuerung) for several years. Like the other manufacturers, this system only affected the intake cams. But, as of 1999, BMW is offering its Double VANOS system on the new 3 Series. As you might have guessed, Double VANOS manipulates both the intake and exhaust camshafts to provide efficient operation at all rpms. This helps the new 328i, equipped with a 2.8-liter inline six, develop 193 peak horsepower and 206 pound-feet of torque. More impressive than the peak numbers, however, is the broad range of useable power that goes along with this system. Take it from someone whos driven the new 3 Series and who loves torquey engines-it works!

As the benefits of variable valve timing become more apparent to both consumers and manufacturers, you can expect to see it on just about every vehicle sold in America. I suspect that in five years, variable valve timing will be like ABS or side-impact beams: only really cheap cars wont have it.
 


Very well done, You win todays internet quest for the truth!!!

One thing though, you mentioned poppet valves earlier on, you could actually get sued for that terminology,as Cosworth Engineering hold the patent for that name as it defines there Air Operated Spring Return valves on RV10 F1 engines and the like. It uses air to open the valves and is infinitely more varible than any gear or cam types. Rudolf Diesel had similar technology on his prototype engine, you can see this at the Science and industry museum in Manchester currently. And it is well wicked.
 


Dont worry mate, it took me less time to cut and paste all that guff than it did for you to decide to post a stupid worthless post (attempt at sarcasm) that didnt add anything to this thread...............just trying to put a stop to pointless arguments between those who dont really know (a bit like yourself I imagine) - so read and actually learn something.......) ;)
 


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