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Discussion Starter · #1 ·
I'm trying to understand why the modders are removing their VTCS [variable tumble control system] flaps, or keeping them open all the time.  From what I read in the Service Highlights, that surge in torque in 3.5k is actually the VTCS flap closing, creating making the air move faster creating a stronger "tumble".  It doesn't say it opens again, but it looks like it stays closed since the A/F ratio on the dynos are consistent until another valve engages at 4.7k.

So from reading the posts saying they feel the difference-- how?  I feel the VTCS engage in the first 4 gears (i only use 5th on cruise) even without mashing the gas.  So if the VTCS valve never closes (makes the opening narrow), how do you feel the power in the low end when it's open until 3.5k anyway?  Shouldn't it be modded to stay closed instead?
 

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I think it helps tumble before 3.5k. If I remember correctly it helps with fuel atomization (bascially mixing the air and fuel together) to get a a better burn in terms of emissions. However it does restric the amount of air that can go through. They remove it or keep it opne to allow teh maximum amount of air to get in the cylinder at all times.
 

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[quote author=siefert link=topic=31990.msg448888#msg448888 date=1129939677]
I think it helps tumble before 3.5k. If I remember correctly it helps with fuel atomization (bascially mixing the air and fuel together) to get a a better burn in terms of emissions. However it does restric the amount of air that can go through. They remove it or keep it opne to allow teh maximum amount of air to get in the cylinder at all times.
[/quote]
so if an air intake is getting more air its' bettr right?
so shoudl i remove this?
 

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Discussion Starter · #5 ·
what i have read in the service manual, when the engine's cold, it closes to increase combustion efficiency, emissions, etc.  Then it opens up again when the engine's warmed and below 3750 RPM.  After it reaches that RPM and the coolant is 63c (61.9 for the 2.0L) it closes again increasing power because of the intake air speed creating that tumble.  The book does not say that it opens up again.

from the service highlights book:
Engine speed approx. 3750 rpm or more and engine coolant temp approx 63c (145f) and more (variable tumble shutter valve is closed)
- intake manifold vaccuum is applied to the varriable tumble shutter valve actuator by the operation of the variable tumble solenoid valve, closing the variable tumble shutter valve.  At this time, the intake passage is narrower than normal, increasing intake airflow speed and also creating a powerful air tumble in the combustion chamber.

what i don't understand is this part at another section of the book:
inhibition conditions:
When a DTC for the engine coolant temperature sensor or throttle position sensor has been stored, the variable tumble control is inhibited and the variable tumble shutter valve is constantly open.

doesn't say how or why or when it's stored for the flaps to open.

mazda6tech.com has this:
The variable tumble control system (VTCS) was created to help emissions at low RPMs. The valve closes part of the intake path, increasing the velocity of the intake charge. The faster intake charge then has the inertia to swirl around the combustion chamber and more thoroughly mix with the fuel for combustion. Intake charge speed is less of an issue on valves that do not open very much, but recall that Mazda's VVT does not vary valve lift. At low RPMs, VTCS is needed to compensate for this. The valve does not completely disengage until 3750rpm. Mazda claims this technology is used to improve emissions, not torque.

which contradicts the "closing" of the flaps at 3750 from the service highlights.

back to my initial question-- how could the owners with deleted VCTSs feel any low end power when the flaps are open after the engine's warmed up anyway?

yea robbiec, I searched.  i read the vtcs posts-- many of which are butt dynos and some cels- no real hard evidence on a 3.  when i see a dyno for this mod done on a mz3, then yea-  i'd delete it.  Yes, i know more air = more power.  I have a CAI for that, and i'm waiting for a stock TB to arrive to study and enlarge.  I guess I have to wait till I get an answer from mazda regarding this then.
 

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The flaps are open 99% of the time. As soon as the temp gauge gets to halfway, those flaps stay open. There is no possible way they could close at 3,500 RPM during hard acceleration. It would be like hitting a brick wall. The motor would be choked and you'd get no power. Look at the pics of the removal process. See how large the flaps are. You'll see how much of the runner they obstruct.

Even when the flaps are open, they cause a great deal of turbulence. You want nice smooth laminar flow through the runners and intake ports. Nice straight unobstructed path into the cylinder. That is how you pack the most possible air into the cylinder. Take those flaps and the actuator shaft out. You'll feel a nice midrange boost and it doesn't cost anything. I did it 2 months ago and have driven the car every day since without incident.
 

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Actaully a straight lamilar flow would not be good, the fuel atomization would suck. this is why carbs are actually such a hot thing. The atomization on a normal carb is equivelent to what you would get if you had a fuel injector placed about a foot from the intake port.

At anyrate, yes the flaps even when open provide a fair amount of restriction. A throttle body when fully open provides a fair amount of restriction. That valve still has some cross section when it is open reducing air flow. Think of the VTCS as 4 throttle valves (one in each runner) with a large notch out of the top of each one. There are no mad 30lb-ft gains to be had anywhere in the rev range, but I can easily see 3-4lb-ft gains through out the rpm band with them removed.

Also it is incorrect that it is closed after 3750, it is open after 3750 when cold or open full time when the engine hits the temps listed (actually about 1/4 on the temp gauge).
-matt
 

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Hi all,

I did the VTCS removal and I can NOT get this car to run right. I get from stop to acceleration lag, poor power etc.

I reconnected the actuator to the intake and connected the vacuum back to it for the computer to read.

Can anyone help me with this?

Thanks in advance

2005 Mazda 3 2.3 Auto
new O2 sensors, MAF sensor, timing chain, valve job, rings


The flaps are open 99% of the time. As soon as the temp gauge gets to halfway, those flaps stay open. There is no possible way they could close at 3,500 RPM during hard acceleration. It would be like hitting a brick wall. The motor would be choked and you'd get no power. Look at the pics of the removal process. See how large the flaps are. You'll see how much of the runner they obstruct.

Even when the flaps are open, they cause a great deal of turbulence. You want nice smooth laminar flow through the runners and intake ports. Nice straight unobstructed path into the cylinder. That is how you pack the most possible air into the cylinder. Take those flaps and the actuator shaft out. You'll feel a nice midrange boost and it doesn't cost anything. I did it 2 months ago and have driven the car every day since without incident.
 

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When performing this mod you have to also update your tune for it, otherwise it will give you all kinds of problems. I removed my VTCS when installing a big turbo, it’s a requirement (in my opinion) for anyone building big power.
 
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