VTCS - Stock operation and implications

[RABID_MP5]

I know we have a thread for removal of this, due to its impeding airflow. And that it's mainly a "tumble" deal to clean up emissions. But I'm trying to understand how it works.

I think the butterflys are normally open? Under what conditions does the ECU tell them to close? When closed, how does anything get though - are they not fully "closed"? Does it flutter the butterflys, or what? Has anyone looked at mileage effects, or just the performance gains of pulling this?

 

[CheeseHelmet]

I know we have a thread for removal of this, due to its impeding airflow. And that it's mainly a "tumble" deal to clean up emissions. But I'm trying to understand how it works.

I think the butterflys are normally open? Under what conditions does the ECU tell them to close? When closed, how does anything get though - are they not fully "closed"? Does it flutter the butterflys, or what? Has anyone looked at mileage effects, or just the performance gains of pulling this?

Under normal conditions the VTCS butterflies are open, that way the car will still run well if there's a problem with the VTCS solenoid or actuator. The butterflies are closed if two conditions are met: the coolant temperature is less than 65C and the engine RPM is less than 3000 (see page 01-03B-57 of the service manual). If either of those two conditions are not met they won't close.

The butterflies close all the way, air can still get through because there's a smaller passage cut out on each butterfly. The smaller passage greatly increases the air's velocity which promotes swirl and the positioning of the hole promotes tumble. This makes the air/fuel mixture heading into the cylinders much more homogeneous and (because of the tumble) less likely to hit the cylinder walls. This should help increase fuel economy because on a cold engine when fuel hits the cylinder wall it condenses and doesn't end up getting burnt, some of it gets scraped in the crankcase and some gets pulled through with the exhaust gases. The "tumble" helps keep the incoming air/fuel charge in the middle of the cylinder away from the walls. This results in better combustion on cold starts and less wasted fuel.

I'd also be interested to hear from people who've removed their VTCS. Clearly it's not super important (they left it out on the MP3) and it doesn't stay on for very long except for very cold days (a cold but idling engine will have a coolant temp of >65C in less than 5 minutes on an average day). I'd like to know if they saw a noticeable increase in mileage (I suspect that won't be the case) and if they live in colder climates I'd like to know if they noticed that their car idled shittier after a cold start in the winter.

I found a pic of the butterflies if you're curious (see this thread for more):

 

[tweety2300]

Not much to contribute but I have an mp3 and it idles perfectly fine in the winter whether its 5 or 80 outside. although I think with the mp3s they actually left the butterflies in intake but not positive I've just seen a few threads stating that but havnt pulled it off for myself

 

[RABID_MP5]

Thanks for the explanation - I hadn't heard it all before. And that pic is worth 1000 words, since I've yet to pull the mani.

Also - I have had an odd "shreek" sound - once and only once - as the car warms up. Now I'm thinking it may be just these turning. Guess I can pull the solenoid lead to verify.

 

[RABID_MP5]

This was a good thread on VTCS. Question: Which color solenoid is for VTCS vs. VICS, white or green?

 

[CheeseHelmet]

This was a good thread on VTCS. Question: Which color solenoid is for VTCS vs. VICS, white or green?

I don't remember off hand, but you can always follow the vacuum hoses back from the actuators to the solenoids. The actuator that operates the valves closest to the head is for VTCS, and the one that operates the valves furthest from the head is for VICS.

If you want to be extra sure, this information is available in the service manual.

 

[Installshield 2]

on the passenger side of the intake manifold you can see a dual solenoid thing with two actuator arms coming from it, the arm heading just under and behind the fuel rail is for the VTCS (the butterflies are right at the very end of the intake runners...the electrical control and connections is mounted on top of the runners, but i forget which is VTCS and which is VICS...

VTCS is 100% not even for improving anything driver related...it doesn't make the car run 'better' when cold...its entirely emissions related, but the ecu in equipped cars is designed to use the system...VTCS drops the 'normal' BJ proteges into U-LEV compliance...where as the MP3 does not have this, and is only LEV compliant...

The posts above are great...the only thing i'd add is to think of the VTCS system as a simple 'choke' for cold starts...When an engine is not up to operating temp, it behaves very differently than when it is. Fuel condenses on cylinder walls and piston heads, and doesn't burn properly. The traditional way to fix this issue during warm up is simply to pour more fuel into the engine...making it very rich will slow warm up (good for the life of the engine), and guarantee enough aerosolized gasoline is in there to burn....as after the cylinder walls are coated with liquid gas, the rest will remain air born...But obviously, the government hates this...

The VTCS attacks this problem from the other direction...it restricts air flow, and by doing that, will automatically richen the mixture...No more fuel is used for a cold start than normal idling, and with very little air making it in there is little threat of it leaning out...resulting in too fast warm up, detonation, etc...the tumbling effect also does what was mentioned in earlier posts, by keeping the mixture swirling and not 'sticking' to cold surfaces.

but..the important part is a key difference with how the system is controlled...All proteges use an open loop cold start up map. The Mp3 ecu has a cold start protocol for starting WITHOUT the VTCS...the p5s and sedans do not...So when you remove or disable the system on regular proteges...you get a code (unless you just leave the actuator hanging there), but will definitely not have a proper warm up mixture...its not a huge deal, but your engine will run like shat until its warmed up properly...and its advisable to not even move the car for at least a minute or 2 after starting...

luckily though...spicyorangemsp offers a $150 service to flash any ecu to MP3 settings...so if you want to completely remove the system, do it while having your ecu flashed...you can then completely remove all parts of the system, never get a code, and have a start up procedure that feels the exact same...

 

[CheeseHelmet]

^Thanks for the information, it's stuff like that which makes these forums so great

 

[T-Rash]

I removed mine due to the screws coming loose and making a really bad situation. Luckily the 3 times it happened, the spark plug tip was crushed and the screw must have been sucked out the exhaust. I feel I lost a bit in gas mileage, getting about 300 miles per tank, but feels like a bit more torque in the higher RPM (4k range). Although the MPG loss could be due to my s*** ass tires, which will be replaced this week. Also on cold starts, been in low 30's mid 40's in the morning, no prob starting, but did feel a bit of a hiccup shifting into 2nd gear, but runs great once warmed up.

Also, upon removal of the manifold, some of the butterfly valves were not even attached, just sitting there all loose and chilling. Its was this forum that help me pinpoit the random misfires, crushed sparkplugs and headaches cause by this problem. Which was actually a factory recall for my year P5, but my VIN # was too early to fall in the covered recall. Thanks!!

 

[BRIAN_MP5T]

Fantastic news.

I would like to add to that post and say that Mazda is one of the only car companies to get this Hot and Heavy into the idea of variable length intake runners on a passenger (Economy) car.

Removing the flaps will pose no major reduction in driveability

 

[Installshield 2]

^^yeah, mazda was the only one i know of to do that stuff on 'cheaper' cars...

its a dying design though...at least for something like VTCS (variable runners will remain around, especially as factory ITBs become more and more common)...as there is no use for VTCS at all on something with direct injection and electronic throttle control...that setup already uses ridiculously high fuel pressure compared to our own, which allows much faster and accurate changes to AFR, and because the TB is not connected by a physical cable...the computer will simply limit the TB butterfly during warm-up...to have much the same effect that VTCS has...with out any restrictive mess in the system when not in use...

its sad though that most pollution that a particular car makes comes during the minute or two after its started...When U-LEV cars first started coming around back at the turn of the century...I read a Road and Track article stating that these cars being used in LA...had cleaner stuff coming out of the exhaust pipe than what was going in the intake...if that is true, thats bat s*** crazy...

 

[sleepwalker]

Fantastic news.

I would like to add to that post and say that Mazda is one of the only car companies to get this Hot and Heavy into the idea of variable length intake runners on a passenger (Economy) car.

Old thread, but hey.

I just wanted to add that, while I'm not sure about any other cars or makes out there, I do know that 2001+ Dodge Neons with the 2.0L Magnum engine (R/T and ACR models, I think) had active intake manifolds with dual-length runners. It was intended as a performance add-on, as opposed to a cold-start improvement - if I recall correctly it simply opened up a second set of runners at WOT. I'm not entirely certain whether there was much of an appreciable benefit from them and I don't know if they carried the design along with the Caliber/"World Engine" platform they switched to.

But a neat little fact, at least.

 

[BRIAN_MP5T]

^^ You are talking about only one set of flaps.

The Protege has Two sets. They do different things.

VCTS and VICS

Here this is a Copy Paste from Edwins Effing Website.

He said not to copy paste and that it is a copyright infringement, but to him I say.

1. Whatever man, you take yourself too seriously...
2. Its the Internet, you publish something, expect to have it stolen.

What is VICS?
VICS is "Variable Inertia Charging System" and is also refered to as "Variable Intake
Control System". In conventional intake manifolds, they are designed to have an air flow
compromise between low end and top end power. Because of this compromise, power
delivery from the engine is not optimum nor ideal. What some manufacturers (such as
Nissan and Mazda for example) have done is designed the intake manifold to have an
isolated runner system (there are many types of intake manifolds) to offer the best flow
characteristics. They didn't stop there. To squeeze as much power out of the engine, yet
allowing the vehicle to be streetable and mass producable, they added a secondary set
of intake runners into the manifold. With this dual runner system, there is the long runner
system for low to mid level RPM operation, and the short runner system for high RPMs.
On Mazda's dual runner intake systems (hereafter refered to as "VICS"), they designed
the long runners to be narrow and oval in shape to help promote air velocity at the lower
RPM ranges. As for the short runners, they are much larger and circular in shape to allow
for maximum flow capability at high RPM. There are butterfly shutter valves fitted over
the short runner and they are normally closed off. When engine speed is reached to a
predetermined rate by the ECU, a solenoid valve is opened and vacuum opens the
butterflies to allow for additional air flow into the engine. Hence the reason why the
system is "variable". It allows for optimum drivabilty and performance at most RPM
ranges. Note when this system is used with high boost forced induction systems, they
hinder performance rather than aid it because of the runner sizes. For high boost
applications, it is recommended that a large single (stage) isolated runner intake manifold
be used.


What is VTCS?
VTCS is "Variable Tumble Control System" or commonly refered to as swirl control
valves. This system only exists on the 3rd generation ULEV certified cars and is used
only on engine cold starts (under the following criteria: coolant temperature is less than
65C/149F). When active, the butterflies located at the end of the intake runners are
closed leaving a small notch aproximately 1/4 the size of the runners to allow for
turbulent air flow to reach the head and combustion chamber. The swirl caused by the
turbulent air aids the combustion process when the engine is still in its cold state "rich
fuel mixture" condition, therefore reducing cold start emissions. Hydrocarbon emissions
are significantly reduced due to this system. This system is also the cause of the infamous
cold start engine rattle that seem to happen between 2500-2800rpm on some 2.0l
engines. There is no known legal fix to this issue yet and Mazda is aware of the problem.
What is happening on the few 2.0l engines is normal and there is no need to worry. The
inclusion of this system also causes some performance restriction to the engine even when
the system is inactive.

 

[sleepwalker]

Oh yes, I know. The system that Dodge played with in their Magnum Neons seems to have been their take on VICS. I'm pretty sure they didn't have anything like a VTCS going on.

I'm totally not disagreeing with anyone; I just happened to be digging around in the forum and saw your remark about very very few manufacturers using a variable length intake runer system on econobox cars, and thought to myself, "Hey, I know of another econobox car with that!"