VTCS, VAD, VVT, VLIM/VIS. So much variable, so little time - Mazda3 Forums : The #1 Mazda 3 Forum


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Old 05-25-2004, 02:01 PM   #1
psyton
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Default VTCS, VAD, VVT, VLIM/VIS. So much variable, so little time

http://www.mazda6tech.com/index.php?...&Itemid=33

that's a link that describes all of the induction technologies employed on the 2.3 liter mazda engine in the mazda 6

as far as I know.. I have VVT (variable valve timing), VTCS(variable tumble control system), and VLIM/VIS (variable length intake manifold/Variable Intake System (as mazda calls it)). I do not have VAD (variable intake duct) which basically is a switched, loud second intake that clicks on at a certain RPM.... it seems like those are only on the mazda 6... instead, I have an intake muffler in the wheel well combined with the VLIM that lots of people like to take off in favor of a Cold air intake.

but yea, as far as I can tell, I have a power/time line

as I rev:
at 3750, VTCS (variable tumble control system) clicks off, meaning that the small butterfly valve right before the intake chamber stops restricting airflow to make the air more turbulent and mix with fuel better. Mazda says this is for emissions and not torque.
at 4500 RPM, the VLIM (variable length intake manifold) adjusts a valve to maintain hemholts resonance, and the VVT (variable valve timing) adjusts the positioning of a cog turning the intake camshaft so that the timing and intake manifold length are now optimized for the higher RPM.

My impression: this is a system that involves more parts, but not as effective as honda's VTEC... which instead of using a VVT actuator on the intake cam to increase or decrease the timing... just has a camshaft that can be shifted left or right by a servo to change the cam profile (thus, actually adjusting the valve lifts and timing, not just timing). Toyota's VVT-i also uses a special camshaft but I don't know as much about how it works.

Mazda opted to use the more sane VVT actuator in combination with VTCS to have the same effect that the variable valve lift of VTEC gives.. but the torque band is really only shifted and not as broadened as they are in VTEC engines.

but yea, finally found something describing mazda's systems, squee!

How does the 3 differ from the 6? As far as I can tell... it seems that the 3 doesn't have a VAD, and they somehow combined an intake muffler with the hemholtz resonator in some sort of box in the wheel well.
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Old 05-26-2004, 01:16 PM   #2
digi0123
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Default VTCS, VAD, VVT, VLIM/VIS. So much variable, so little time

They look different too <hides>
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Old 05-26-2004, 01:36 PM   #3
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Default VTCS, VAD, VVT, VLIM/VIS. So much variable, so little time

i-VTEC involves infinitely variable front and back ends, Mazda's front end isn't infinitely variable.
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Old 05-26-2004, 02:33 PM   #4
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Default VTCS, VAD, VVT, VLIM/VIS. So much variable, so little time

does this mean they will come out with a vtcs,vvt,vlim/vis, afc controller. if so they might as well just make a replacement pcu
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Old 06-23-2004, 11:01 AM   #5
bestos
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Default VTCS, VAD, VVT, VLIM/VIS. So much variable, so little time

Not a big fan of Civic's VTec. the torque is much lower than in our 3. i know our engines are bigger displacement, Mazda 3 still wins race over Civic Ex or Si - thats all that matters to me.

thanks for the info however, always nice to know how stuff works.
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Old 06-23-2004, 11:47 AM   #6
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Default VTCS, VAD, VVT, VLIM/VIS. So much variable, so little time

psyton, your analysis is dead on. I really don't think that the VAD does a darn thing... the primary resonances of the intake are taking place in the intake runners and plenum, not anything prior. I think the VAD was primarily designed for NVH.

The dynos for the 6i and 3s look pretty much identical.

Bestos, there's always somebody faster. What makes all these variable technologies interesting is their wonderful volumetric efficiencies- their ability to fill the cylinder with its full swept displacement of air (or more!), allowing the addition of more fuel, and consequently making more power in a smaller physical displacement. FI is another way of adding more (drastically more!) volumetric efficiency. Adding displacement always adds more power, and if you want displacement- look at pushrod engines. Pushrod engines are amazingly compact, allowing huge displacement in small engine bays. But the downside is that their volumetric efficiency tapers off quickly due to their single cam, two-valve-per-cylinder design. You get big cylinders that only flow optimally for a narrow RPM range (usually very low), so they add less fuel to compensate for the poor flow or air. Thus while the specific output of a pushrod is usually poor, I'd hardly say the engine's efficiency is- nothing but FI makes more power in a smallish engine bay.

Gettin off-topic. As far as VVT goes, Mazda is pretty run-of-the-mill. Their VVT system is like "half" of a Nissan or BMW engine (cam-phasing on intake and exhaust), and less than half of a Honda or Toyota (yamaha) engine (same, but with cam profiles too). I'm not sure which manufacturers use variable intake runners, but at least some designs from Toyota, Honda, Nissan, and others certainly do. They're rather common. So while this engine is certainly a class above some, it's hardly as impressive as others.

A stock Mazda 2.3 puts down as much power as Honda's 2.4l engine, but the Honda engine has oodles more torque south of 3000rpm. You can always shift the torque curve higher by using higher lift or differently timed cams, making the car faster but less drivable. But in the Honda, you have two cam profiles- so you need not make that sacrifice. The VTEC "kick" you feel in a Honda engine is a wonderful thing- it shows you how big a difference a second, higher-lift cam profile makes. Since the second profile is independent of the first, you do not loose low-end torque. That kick is entirely added power, not possible with a single-profile cam.

In recent Honda engines, Honda has added continuously variable cam phasing (changes timing) to their variable cam profiles (which change timing AND lift). This has smoothed out their engine response. The former, variable cam phasing, is what Mazda uses. On the intake only. I believe Honda also uses variable intake runners, just like Mazda. The Integra type-R actually had a variable exhaust manifold too.

So anyway, my point in all this is that Honda definately wins big on engine technology. Mazda acheives the same specific output by sacrificing low-end output (kind of like removing the low-rpm cam from a Honda engine). In my opinion, so long as low-end torque is sufficient enough to be drivable, this makes for a fun-to-drive car- one that always need be driven hard

I believe it was Ford who has made a variable diameter intake runner. I think that'll be a HUGE design improvement for Ford engines, and hope Mazda adopts this technology. This one move, I believe, would put Ford/Mazda in a league with Honda or Toyota, in a different-but-equal, but totally seamless way.
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