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post #1 of 9 (permalink) Old 01-14-2005, 04:21 PM Thread Starter
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Valvetrain Technology Explained

I wanted to put together a thread about the new valvetrain technologies that are improving power, efficiency and emissions on cars these days. I also included older technologies so you can see how things have moved forward.

Honda VTEC

The original VTEC was a big step. Back in the dark ages, you had to sacrifice low RPM torque and drivability for high RPM power. Bigger cams mean more valve lift, and more valve overlap, but automakers couldn’t do this, because the car would run really rough at low RPMS, and gas mileage would be horrible.

Honda came up with the idea to add more lobes to the camshaft. The idea was to have the regular cam lobes for lower RPMS, but once you reached a certain RPM, the engine would switch to the other set of lobes on the cam, which were bigger and provided more lift, which keeps the valves open longer and open deeper into the cylinder. This allows for more air & fuel into the combustion chamber, thus making more power. Honda has 2 and even 3 stage VTEC systems. One thing to note, is that the original VTEC system, is not a variable valve timing system. It is a variable LIFT system.

SOHC vs. DOHC VTEC

SOHC VTEC = Applies the lobe changes to just the intake valves.

DOHC VTEC = Applies the lobe changes to both the intake and the exhaust valves. The S2000 is a DOHC VTEC engine. I believe it is only a 2 stage and makes an impressive 120 HP per liter. (The original S2000 had a 2.0 liter engine and still made 240HP)

i-VTEC

i-VTEC was introduced to improve on the original VTEC system. It adds variable valve timing to the VTEC system. Now Honda not only has variable lift control, but also can adjust the timing of when the valves are opened. The addition of the VVT system to i-VTEC also smoothes the transition between lobes. It is also intelligent and can change valve timing depending on load, RPM and other environmental variables.

Toyota VVT-i

Toyotas VVT-I system is a much simpler technology than VTEC. There is no lift control with VVT-i. All VVT-i does is change the timing on when the intake valves are opened. The “i” in VVT-i stands for “Intelligent.” The system is intelligent because it varies the valves timing depending on load, engine temp, rpm, etc. By varying the valve timing, low end torque and high RPM horsepower are achieved. The intake valves are continuously variable throughout the RPM range. Meaning the VVT-i system can retard or advance intake valve openings throughout the whole RPM range. Even though VVT-i doesn’t have quite the same performance benefits as VTEC or i-VTEC, it is a cheaper system and has a much smoother power band than VTEC.

Dual VVT-i

Dual VVT-i applies this technology to both the intake and exhaust valves. This allows for more valve overlap in the higher RPMS, which improves power and emissions. The illustration below shows the amount of valve overlap with just intake VVT-i.



With the addition of this technology on the exhaust valves, this allows for more valve overlap. Here is an example with BMW’s Double-VANOS system. You can see there is more valve overlap when compared with just the intake only VVT-i system.



The 2.0 liter engine in the Altezza code named BEAMS is a dual VVT-i engine that makes an impressive 110 HP per liter.

VVTL-i

VVTL-i adds the lift control to the VVT-i system. The “L” stands for “Lift.” Basically, i-VTEC and VVTL-i are very similar, since they both can adjust lift and valve timing.


BMW VANOS

The BMW VANOS system is a variable valve timing system just like VVT-i. This technology can be found on most of the current models from BMW. This VVT system only functions on the intake valve. One thing to note is on most BMW engines that use single VANOS, the timing of the intake cam is only changed at two distinct rpm points, while on the double-VANOS system, the timing of the intake and exhaust cams are continuously variable throughout the majority of the rpm range.

Double-VANOS

Double VANOS adds this technology to the exhaust valves. Double-VANOS improves low rpm power, flattens the torque curve, and widens the powerband for a given set of camshafts. The double-VANOS engine has a 450 rpm lower torque peak and a 200 rpm higher horsepower peak than single-VANOS, and the torque curve is improved between 1500 - 3800 rpm. At the same time, the torque does not fall off as fast past the horsepower peak. This technology can be found in the current M3 and will be integrated in to the new Inline 6 motors for the 2006 3 series.

Vavletronic

This is a new technology from BMW. Valvetronic engines use a combination of hardware and software to eliminate the need for a conventional throttle mechanism. BMW has one upped Honda with an infinite variable lift system. The Valvetronic engine replaces the function of the throttle butterfly by using an infinitely variable intake valve lift.

“Fuel injection systems monitor the volume of air passing through the throttle butterfly and determine the corresponding amount of fuel required by the engine. The larger the throttle butterfly opening, the more air enters the combustion chamber.”

“At light throttle, the throttle butterfly partially or even nearly closes. The pistons are still running, taking air from the partially closed intake manifold. The intake manifold between the throttle and the combustion chamber has a partial vacuum, resisting the sucking and pumping action of the pistons, wasting energy. Automotive engineers refer to this phenomenon as "pumping loss". The slower the engine runs, the more the throttle butterfly closes, and the more energy is lost.”

“Valvetronic minimizes pumping loss by reducing valve lift and the amount of air entering the combustion chambers.”

“Compared with conventional twin-cam engines with finger followers, Valvetronic employs an additional eccentric shaft, an electric motor and several intermediate rocker arms, which in turn activates the opening and closing of valves. If the rocker arms push deeper, the intake valves will have a higher lift, and vice-versa. Thus, Valvetronic has the ability to get deep, long ventilation (large valve lift) and flat, short ventilation (short valve lift), depending on the demands placed on the engine.”

“Valvetronic reduces maintenance costs, improves cold start behavior, lowers exhaust emissions, and provides a smoother running engine. Valvetronic does not need specific fuel grades or fuel qualities because of its fine atomization of fuel.”

“The entire Valvetronic system is pre-assembled and inserted as a module into its position in the cylinder head. Valvetronic engines are built at BMW's brand new engine plant at Hams Hall near Coventry, England.”

“Because Valvetronic allows the engine to breathe more freely, fuel consumption is reduced by 10%. The fuel savings are greatest at lower engine revs. Valvetronic is an important element in BMW's aim of meeting the 2008 carbon dioxide fleet requirements of 140 gm/km.”

http://www.bmwworld.com/technology/valvetronic.htm

Yup

Last edited by Norcal IS300; 01-14-2005 at 05:36 PM.
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post #2 of 9 (permalink) Old 01-16-2005, 02:53 AM
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Great job on the write up.

Quick question though, do you know why vvtl-i's system kicks in so much later in the rev band than the i-vtec?

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post #3 of 9 (permalink) Old 01-16-2005, 03:00 AM
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only car that has vvtl-i in US is the 2ZZ-GE Celica GT-S and i believe they open up at 6000 rpm. maybe its just set there?

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post #4 of 9 (permalink) Old 01-16-2005, 11:59 AM Thread Starter
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When variable cams are used, the higher RPM cam is usually set to switch at the RPM when the smaller cam starts to drop power on the dyno graph. Toyota/Yamaha must have used a more agressive low RPM cam that can produce a linear power curve all the way up to 6000 RPM.



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Originally Posted by Paki_Sleepa
Great job on the write up.

Quick question though, do you know why vvtl-i's system kicks in so much later in the rev band than the i-vtec?

Yup
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post #5 of 9 (permalink) Old 01-16-2005, 04:15 PM
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wow. Thanks

Earlier when you told me that dual vvti times both exhaust and intake, while I was cool with the fact that you're were right, I still couldn't make any sense of it. The idea of timing your intake timing directly against your exhaust timing (regular vvt) had me thinking that being able to control your exhaust timing wouldn't do anything. Thanks for graphs, they do explain a lot more.

And thanks for clarification of vtec. After much discussion, I was under the assumption that vtec was able to retard or advance intake valve openings in chunks (ie 1-3 chunks over rpm range) and then hit a critical rpm speed in which the lobes switched over to something larger.

It didn't occur to me at the time that all vtec does is move the cam shaft laterally the whole way through to provide timing. If this is the case, I can see why you think that vvti is better, it definitely has less parts to go wrong, and better scaling.
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post #6 of 9 (permalink) Old 03-12-2005, 03:20 AM
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Quote:
Originally Posted by youngji
wow. Thanks

Earlier when you told me that dual vvti times both exhaust and intake, while I was cool with the fact that you're were right, I still couldn't make any sense of it. The idea of timing your intake timing directly against your exhaust timing (regular vvt) had me thinking that being able to control your exhaust timing wouldn't do anything. Thanks for graphs, they do explain a lot more.
.
When you get to a point where you're playing with the way the engine flows(i.e. bolt-ons,etc) being able to control exhaust cam timing is as important as the VVT-i working on the intake. If you look in the Go Faster forum you'll see that those of us playing with the exhaust cam timing are getting 5-8whp and torque gains across the entire rpm band(by mearly adjusting cam timing). DasGalloway did a very good write-up on the process and results.

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post #7 of 9 (permalink) Old 09-20-2005, 02:18 PM
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good write up norcal - some corrections however.
vtec DOES do vary the timing and lift HOWEVER it is staged in 2 or 3 finite stages and NOT infinitely variable.
i-vtec adds the infinitely variable HOWEVER the lift still remains staged.

i-vtec does lift in the traditional honda method using the wild cams, vvtL-i (yamaha/toyota design) uses a spacer to create that lift instead. not as good for the reason that toyota can't define the final profile like the vtec wild cam instead just lift the currently available profile by the amount afforded by the spacer.

hope this cleared it up. let me know if you have any questions.
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post #8 of 9 (permalink) Old 09-30-2005, 09:51 AM Thread Starter
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Quote:
Originally Posted by papercliprebel
good write up norcal - some corrections however.
vtec DOES do vary the timing and lift HOWEVER it is staged in 2 or 3 finite stages and NOT infinitely variable.
i-vtec adds the infinitely variable HOWEVER the lift still remains staged.

i-vtec does lift in the traditional honda method using the wild cams, vvtL-i (yamaha/toyota design) uses a spacer to create that lift instead. not as good for the reason that toyota can't define the final profile like the vtec wild cam instead just lift the currently available profile by the amount afforded by the spacer.

hope this cleared it up. let me know if you have any questions.

Good info thanks. How does Honda vary the valve timing? Is it just the cam profile or do they use a system like VVT-i/Vanos?

Yup
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post #9 of 9 (permalink) Old 09-30-2005, 03:37 PM
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for the original vtec it was just a different cam profile. the i-vtec operates the valve timing in the more traditional vvt-i/vanos method.

Last edited by papercliprebel; 09-30-2005 at 03:44 PM.
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