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Discussion Starter #1
Howdy- Mazda6 2.3l owner here.

On the Mazda6, the VTCS (variable tumble control system) is supposed to stay closed to 3000rpm on warm-up, and stay open all the time thereafter.

I've read on this site that yours closes again at idle even once warmed up.

Regardless, I'm curious what gains ya'll found by totally gutting the valves out of the intake path. I haven't really found much on the subject here. Only one Mazda6 owner has done this so far, and that person seems to have seen a dramatic boost in- surprisingly- the low end. It's the only dyno of the 2.3l engine in the '6 that doesn't lose 10-15ft-lbs of torque below 3000rpm!

Since we've verified that the valves are indeed OPEN once warmed up at this RPM, I don't understand the gain. Nonetheless, I thought I'd see what your experiences were with the Focus. The only drawback the Mazda6 owner reports is an idle that bounces briefly on startup.

Secondly, I've seen Walter Marcy say that removing the VIS (variable intake system, also know as VLIM- variable length intake manifold) removed a "dip" at 4500rpm on the Focus. On the '6, this is exactly where our torque peak is.

I find it hard to believe that keeping the intake stuck on the short runner length produces any meaningful gains. I'd expect to lose low end and gain nothing on the high end. Anyone care to elaborate here?

Do you guys have any dyno graphs documenting the results of these modifications? I've seen lots of dynos, but nothing really comparing A to B.

Here are some Mazda6 dynos- one with the VTCS removed, one with it still there. Note the difference in the low end! (The second dyno is higher despite having VTCS because it's a manual transmission.)

Without VTCS (smooth curve):


With VTCS (look at the huge loss below 3500rpm, but the top-end remains pretty similar):



Any feedback would be helpful. I'd even appreciate a good picture of the tumble valves, if anyone has one. I had some bookmarked, but they disappeared.

Thanks guys!

(I'm up to 147.3whp on my Mazda6, dyno'd on a Mustang dyno. Based on what it's put down on a DynoJet, I'd say that's roughly 165whp DynoJet horsepower. Headers and midpipe picked up 17hp!)
 

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I yanked the tumble flaps only. I have not done anything with the variable length runners yet. All the 03 and 04 2.3's in the focus are partial zero emissions vehicles. Our flaps are set up to be closed all the time at idle. This creates lower emissions and burns less fuel while the car is sitting. The second you blip the throttle the flaps open. When crusing and off idle the valves close, but the second you blip the throttle they once again open. Ther is probably a .3 of a second delay in the time between whne you hit the throttle nad when they open. So #1 removing them gets us a slight improvement in instantanious throttle response, and #2 by not having them in the way it improves overall air flow. If anything i experienced gains at the top end of the power band. But the one thing that has to be taken into concioderation with this mod is that (at least for the focus) you will need tuning so that the vehicle does not run lean when cruising off idle. But another big plus to the tumble flap delete is that the rough idle caused by the motor mount inserts and removal of the balance shafts went away because of this mod.
 

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Re: Deleting and disabling parts of the intake manifold- what wo

Interesting, your motivation for doing this modification is totally different, as the VTCS itself engages at very different times than the Mazda6. I wonder why that is?

But the one thing that has to be taken into concioderation with this mod is that (at least for the focus) you will need tuning so that the vehicle does not run lean when cruising off idle.
Doesn't the computer learn new fuel trims to compensate?
 

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Re: Deleting and disabling parts of the intake manifold- what wo

Our cumputer closes the tumble flaps at idle and off throttle and instantly sends less fuel. It's the way it's programmed for emissions purposes. So you need to adjust for this.

Our setups are "partial zero emissions vehicle" So the computer has a hidden agenda. It wants to run as clean as possible. Lots of pzev owners including myself complain that sometimes the car feels like it has more power than other times. I'm blaming the emissions calibrations in the pcm. But I don't know?
 

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Re: Deleting and disabling parts of the intake manifold- what wo

Whoa, thanks for the pictures- very helpful.

The housing for the flaps in Mazda vehicles is bright orange, but otherwise the manifold looks to work identically- except yours is programmed to be used at different times.

Well, thanks for the help guys- I guess your before & after experiences with the tumble valves are going to be different than mine.
 

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Can you add VTCS dyno graphs? They are not visible
Hey buddy....this is a 15 year old thread..I'm thinking you might not get a response from them....
 
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