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Old 16th October 2007, 13:49   #1
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Default Variable Valve Timing discussion thread

Browsing through Wikipedia, came across this impressive list of different VVT implementations and their names. Never knew there were sooo many.

What I am trying to understand, leaving aside the passions, is - which of these are superior implementations.

Why is it that VTec seems to have a cult following?
Is it a technically superior implementation of the VVT concept?
Or is it a well marketed product?
Or is it that the cult following is perceived more in India, due to the larger presence of the technology?

I mentioned the last point, since in T-BHP, I've seen the Mivec commands a lot of respect too. However, VVTi, VTVT etc do not seem to evoke any passions.

Quote:
VVT Implementations

Aftermarket Modifications - Conventional hydraulic tappet can be engineered to rapidly bleed-down for variable reduction of valve opening and duration.
  • Alfa Romeo Twin Spark- TS stands for "Twinspark" engine, it is equipped with Variable Valve Timing technology.
  • BMW Valvetronic - Provides continuously variable lift for the intake valves; used in conjunction with Double VANOS.
  • BMW VANOS - Varies intake timing by rotating the camshaft in relation to the gear.
  • BMW Double VANOS - Continuously varies the timing of the intake and exhaust valves.
  • Ford Variable Cam Timing - Varies valve timing by rotating the camshaft.
  • DaimlerChrysler - Varies valve timing thought the use of concentric camshafts developed by Mechadyne enabling dual-independent inlet/exhaust valve adjustment on the 2008 Dodge Viper.
  • GM VVT - Varies valve timing continuously throughout the RPM range for both intake and exhaust for improved performance in both overhead valve and overhead cam engine applications.(See also Northstar System).
  • GM DCVCP (Double Continuous Variable Cam Phasing) - Varies timing with hydraulic vane type phaser (see also Ecotec LE5).
  • Holden Alloytec - Continuously variable camshaft phasing for inlet cams. Continuously variable camshaft phasing for inlet cams and exhaust cams (High Output Alloytec).
  • Honda VTEC - Varies duration, timing and lift by switching between two different sets of cam lobes.
  • Honda i-VTEC - In high-output DOHC 4 cylinder engines the i-VTEC system adds continuous intake cam phasing (timing) to traditional VTEC. In economy oriented SOHC and DOHC 4 cylinder engines the i-VTEC system increases engine efficiency by delaying the closure of the intake valves under certain conditions and by using an electronically controlled throttle valve to reduce pumping loss. In SOHC V6 engines the i-VTEC system is used to provide Variable Cylinder Management which deactivates one bank of 3 cylinders during low demand operation.
  • Honda VTEC-E - Unlike most VTEC systems VTEC-E is not a cam switching system, instead it uses the VTEC mechanism to allow for a lean intake charge to be used by closing one intake valve under certain conditions.
  • Hyundai MPI CVVT - Varies power, torque, exhaust system, and engine response.
  • Kawasaki - Varies position of cam by changing oil pressure thereby advancing and retarding the valve timing, 2008 Concours 14.
  • Lexus VVT-iE - Continuously varies the intake camshaft timing using an electric actuator.
  • Mazda S-VT - Varies timing by rotating the camshaft.
  • Mitsubishi MIVEC - Varies valve timing, duration and lift by switching between two different sets of cam lobes. The 4B1 engine series uses a different variant of MIVEC which varies timing (phase) of both intake and exhaust camshafts continuously.
  • Nissan N-VCT - Varies the rotation of the cam(s) only, does not alter lift or duration of the valves.
  • Nissan VVL - Varies timing, duration, and lift of the intake and exhaust valves by using two different sets of cam lobes.
  • Nissan VVT introduced with the HR15DE HR16DE MR18DE MR20DE new engines in September 2004 on the Nissan Tiida and north american version named Nissan Versa (in 2007); and finally the Nissan Sentra (in 2007).
  • Nissan VVEL introduced with the VQ37VHR Nissan VQ engine engine in 2007 on the Infiniti G37.
  • Porsche VarioCam - Varies intake timing by adjusting tension of a cam chain.
  • Porsche VarioCam Plus - Varies intake valve timing by rotating the cam in relation to the cam sprocket as well as duration, timing and lift of the intake and exhaust valves by switching between two different sets of cam lobes.
  • Proton Campro CPS - Still under development, said to be based on Lotus technology which developed Porsche's VarioCam.
  • PSA Peugeot CitroŽn CVVT - Continuous variable valve timing.
  • Renault Clio 182, Clio Cup and Clio V6 Mk2 VVT - variable valve timing.
  • Rover VVC - Varies timing with an eccentric disc.
  • Suzuki - VVT - Suzuki M engine
  • Subaru AVCS - Varies timing (phase) with hydraulic pressure, used on turbocharged and six-cylinder Subaru engines.
  • Subaru AVLS - Varies duration, timing and lift by switching between two different sets of cam lobes (similar to Honda VTEC). Used by non-turbocharged Subaru engines.
  • Toyota VVT - Toyota 4A-GE 20-Valve engine introduced VVT in the 1992 Corolla GT-versions.
  • Toyota VVT-i - Continuously varies the timing of the intake camshaft, or both the intake and exhaust camshafts (depending on application).
  • Toyota VVTL-i - Continuously varies the timing of the intake valves. Varies duration, timing and lift of the intake and exhaust valves by switching between two different sets of cam lobes.
  • Volkswagen - VVT introduced with the 1.8T engine. The intake timing intentionally runs advanced and a retard point is calculated by the ECU. A hydraulic tensioner retards the intake timing.
  • Volvo - VVT
  • Yamaha - VCT (Variable Cam Timing) Varies position of cam thereby advancing and retarding the valve timing.
  • Proton - VVT introduced in the Waja 1.8's F4P renault engine (toyota supplies the VVT to renault)
Source : Variable valve timing - Wikipedia, the free encyclopedia
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Old 16th October 2007, 14:06   #2
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Here's something u can read about Honda VTEC
http://www.team-bhp.com/forum/techni...tec-works.html (How Honda's Vtec works)

There are diff types of Vtec engines :
1. DOHC Vtec
2. SOHC Vtec
3. 3 stage Vtec
4. Vtec - E (E for fuel efficiency)
5. i - Vtec seen in the Accord and CR-V sold here.

For more details read this
Different VTEC engines
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Old 16th October 2007, 14:20   #3
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I am posting this from the IEA/OECD report on `Making Cars More Fuel Efficient' published in 2005.

Variable valve control has the potential to significantly reduce light load pumping losses. The simpler technology of variable valve timing (VVT) by cam phasing has been widely adopted in luxury cars in Europe and North America, and in a large fraction of all cars in Japan; in fact, almost all Toyota models in 2004 had VVT. Variable valve lift and timing (VVLT) is less common; Honda is the only manufacturer to have a two step (or three-step) valve lift control in many of its models. A continuously variable lift system was recently introduced by BMW in its luxury 7-series cars. More exotic technologies actuate the valves without camshafts, using hydraulic or electric solenoids, but it is not clear if the additional cost is worth the marginal benefit in fuel economy relative to mechanical VVLT systems. Such systems will reduce shortfall in inner-city driving, but will increase shortfall in high speed or aggressive driving.
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Old 16th October 2007, 14:35   #4
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vvti gives economy which v tec dosent . corolla 1.8l 125 hp 0-100 less than 10 sec . and can give you 10-11kpl .mind you it was launched 5 yrs back
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Old 16th October 2007, 14:39   #5
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Quote:
Originally Posted by paras211 View Post
vvti gives economy which v tec dosent . corolla 1.8l 125 hp 0-100 less than 10 sec . and can give you 10-11kpl .mind you it was launched 5 yrs back
VVT-i seems to continuously vary the timing. Is this different from say Vtec, where it kicks in above a certain RPM?

And is VVT-i similar to i-Vtec?
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Old 16th October 2007, 14:48   #6
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I do not know which is better in tech terms: VVT, VTEC, or blah blah. Since these are supposed to enhance FE, the proof is in those numbers. According to recent revised FE figures issued by EPA, both 4-speed Corolla AT and 5 speed Civic AT give equal FE of 29 mpg. Corolla is marginally better in city (26 mpg vs 25 mpg for Civic), but Civic is better on highway (36 mpg vs 35 mpg for Corolla).

However, manual Corolla still gives a higher (31 mpg) FE than manual Civic (29 mpg). In city, Corolla manual gives 28 mpg vs 26 for Civic. On highway, Corolla manual gives 37 mpg vs Civic 34 mpg.

Comparing Camry and Accord (both 2.4 litres), manual versions of both give same FE of 25 mpg: Camry (21/31), Accord (22/31). Another praiseworthy car here is Sonata which also gives 25 mpg (21/31).
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Old 16th October 2007, 15:05   #7
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I think Honda introduced the VTEC in passenger cars very early and hence the following.
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Old 16th October 2007, 16:05   #8
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The Basics

Before we can appreciate how important valve timing is, we 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 engine's 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 air filter.

Since an engine's 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 and quite a number of other manufacturer's have done in recent years. By using advanced systems to alter the opening and closing of engine valves, they have created more powerful and clean burning engines that require less fuel and are relatively small in displacement.


The Concept behind valves


DOHC...................................Pushrods

Until recently, manufacturers used one or more camshafts (plus some pushrods, lifters and rocker arms) to open and close an engine's valves.

The camshaft/ camshafts was turned by a timing chain that connected to the crankshaft. As engine rpm's 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 manufacturer's 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 from parked positions but also allow for strong acceleration and highway cruising.

They were successful but 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 rpm's, many manufacturer's can now tune valve operation for optimum performance and efficiency throughout the entire rev range.

So when it comes to performance timing is everything.


How it evolved/variants

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 on the 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 one 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 drivability at lower rpm levels.

Honda is already out with/working on a newer VTEC systems 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.

Toyota uses a hydraulic rather than mechanical system to alter the intake cam's 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.


Ferrari has a really neat way of doing this.

The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive.

The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. The shaft still spins just like a regular camshaft, but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized.


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 3 Series. Double VANOS manipulates both the intake and exhaust camshafts to provide efficient operation at all rpm's. This helps the 328i, equipped with a 2.8-liter inline six, develop 193 peak horsepower and 206 pound-feet of torque.


BMW Vanos head

More impressive than the peak numbers, however, is the broad range of useable power that goes along with this system.

Several other manufacturers, including Ford, Lamborghini and Porsche have jumped onto this bandwagon because it is a relatively cheap method of increasing horsepower, torque and efficiency.

Source/s: Wiki/Internet
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Old 16th October 2007, 16:15   #9
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Why is variable valve timing important only for gasoline engines?

If the engine is burning diesel, valve timing does not matter at all?
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Old 16th October 2007, 16:47   #10
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Quote:
Originally Posted by anandpadhye View Post
Why is variable valve timing important only for gasoline engines?

If the engine is burning diesel, valve timing does not matter at all?
Actually VVT is applicable to diesel engines also - but still now it is in R&D stage (mostly to marine engines etc).

One advantage of VVT in petrol engines is that it helps betting higher torque in relatively low RPM and better fuel economy. In diesel engines, torque is already higher and fuel economy is better.
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Old 16th October 2007, 17:05   #11
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Very rightly said, there is still a long way to go for implementing VVT for diesel and as I am aware it needs a different approach for diesel engines, also increasing their costs.

Quote:
Originally Posted by sbasak View Post
Actually VVT is applicable to diesel engines also - but still now it is in R&D stage (mostly to marine engines etc).

One advantage of VVT in petrol engines is that it helps betting higher torque in relatively low RPM and better fuel economy. In diesel engines, torque is already higher and fuel economy is better.
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Old 16th October 2007, 20:39   #12
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Quote:
Originally Posted by shuvc View Post
Browsing through Wikipedia, came across this impressive list of different VVT implementations and their names. Never knew there were sooo many.

What I am trying to understand, leaving aside the passions, is - which of these are superior implementations.

Why is it that VTec seems to have a cult following?
Is it a technically superior implementation of the VVT concept?
Or is it a well marketed product?
Or is it that the cult following is perceived more in India, due to the larger presence of the technology?

I mentioned the last point, since in T-BHP, I've seen the Mivec commands a lot of respect too. However, VVTi, VTVT etc do not seem to evoke any passions.
First of all things, I would really appreciate if atleast we team-bhpians respect technology by addressing it correctly. VTEC is not VTec and MIVEC is not mivec. (not pin-pointing someone specific just a general observation which I have seen on the forum elsewhere but didn't want to post just to point it out)

Why VTEC has a cult following?

1. Is it a technically superior implementation of the VVT concept?

Honda's VTEC is the first cam-switching system and one of the few ones still in porduction. Although many other efforts were made to implement VVT by other manufacturers pioneered by Fiat and some were quite successful. VTEC in 1989 was the first time cam profiles were switched on the fly depending on several parameters like engine speed, throttle load etc.

2.
Or is it a well marketed product?

A unit that has seen over 2 million being produced and not even a single failure/recall, does a lot of marketing for itself. So if you have noticed, Honda has never emphasised on the VTEC in its ad-campaigns. The product speaks a lot for itself.

3.
Or is it that the cult following is perceived more in India, due to the larger presence of the technology?

Well to be honest, Toyota has VVT-i implementation in the Corolla, but it is never perceived as a performance car, partly due to the facts that its a very well built but a staidly designed car which does not lend itself well to performance mods. (I am referring to the current generation Corolla or shall I say the past decade. The legendary AE86 does not figure in the list)

Similarly, Hyundai has VTVT (rebadged CVVT in the international markets) on the new Verna, but the performance of the car as a whole, especially the handling is nothing to write home about.

Mitsubishi does not have MIVEC implementation on any of its offerings in India. The reason why MIVEC commands respect on the forum is because of the Engine Swaps into Indian Lancers which are based on the 1.6 4G92 NA Engine. It produces close to 175 bhp, akin to the Honda B16 series powerplants.

Suzuki also does not offer VVT on any Indian offerings.

So these are a few reasons that I could think of why VTEC commands more respect than other VVT implementation in India.

Coming to the best VVT implementation, what an ideal VVT seeks is fully variable valve timing, lift and duration, i.e. the valves should always open at exactly the right point, lift high enough and stay open for just the right amount of time, with respect to the engine speed in use. Until this is achieved, the VVT systems will keep on evolving. However, Honda's a-VTEC (to be introduced in passenger cars by 2009-10) will come one step closer to achieving fully variable valve timing, lift and duration. So lets keep our fingers crossed.

If we consider the current implementations of VVT, any implementation which varies timing (although between a certain range) Using variable camshaft positioning PLUS varying the valve duration and lift by usage of switching cam lobes can be regarded as the best implementation of VVT.

Last edited by doomsday : 16th October 2007 at 20:42.
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Old 16th October 2007, 20:53   #13
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Very nice discussion guys, keep it coming. I'm getting to learn quite a bit here
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Old 16th October 2007, 21:12   #14
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And if i'm not wrong VTEC/i-VTEC is the only VVT engine in India that offers "Valve Lift".

VVTi surely doesn't have lift coz they use the VVTLi engines to do that (which aren't found on their Indian cars). It's the same case with Hyundais VTVT engine.

PS : Do the BMW's sold here come with Valvetronic engines? Coz they also have lift control.

Shan2nu

Last edited by Shan2nu : 16th October 2007 at 21:15.
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Old 16th October 2007, 21:53   #15
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Quote:
Originally Posted by Shan2nu View Post
And if i'm not wrong VTEC/i-VTEC is the only VVT engine in India that offers "Valve Lift".

VVTi surely doesn't have lift coz they use the VVTLi engines to do that (which aren't found on their Indian cars). It's the same case with Hyundais VTVT engine.

PS : Do the BMW's sold here come with Valvetronic engines? Coz they also have lift control.

Shan2nu
Yeah the BMW has the Valvetronic on all the BMW passenger car engines and yes it varies the lift. However, the M-series engines are equipped with the VANOS/Double VANOS.
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