In for A/B/C results. Props in advance.

 

<p>Please explain double switching of VICS.</p>

 

When stock ECU NB2 owners complain about "poor driveability with standalone ECUs", I laugh IRL. The VCTS makes the car undriveable below 3500rpm. I couldn't believe how bad it was in my NB2 - I always kind of thought the car was just broken or had sticky VCTS butterflies or something.

 

Is there even a standalone that has it activated and operational by default? Pretty sure it's disabled by default, and Rev's MS3's have the ability to activate/operate if one so desired. Unless the silly hydra or ems4 actually use it.

If your car is un-driveable below 3500 and when warmed up, you have a problem.

 

Perhaps your car did have a problem?

I have no drivability issues below 3500. If anything, I'm fairly impressed by the low-end torque of the VVT engine, coming from a 1.6 background. I can definitely feel the butterflies open when the engine is cold, but it's a subtle kick, rather than an "OMG, the engine is finally on."

If I had the manifold off, I'd probably remove them. But to call the car "undriveable" with them in place needlessly deprecates the value of your opinion on such matters.

 

The only two 100% stock NB2s we have had in the shop ran the same as Andrews. Hesitation and very weak power unless you floored it before the butterflies opened. You notice it less if you drive it with the throttle just barely cracked open accelerating very very slowly until the engine warms up.

 

It was functional as OEM on my Haltech.

 

I initially ran the VTCS in standard OEM style when I was running my megasquirt. Then I realized that the ridiculous choke feeling I was getting when the car was cold was a bunch of turbo backing up against those butterflies and I set the RPM down to around 1750 so it would never interfere with any meaningful boost (big trubo).

But other than that, I did leave it fully operational, remaining closed below 60C / 1750 RPM mostly for cold idle stability. I found idle to be much harder to tune with it wide open and the car cold (like daily driver in winter cold).

 

The reason why the VTCS can cause a driveability hiccup is because the engine is old and controls torque with a throttle cable and dumb lookup tables.

Now before you sharpen your pitchforks, keep in mind that electronic throttles can use torque based software control to transition the opening and closing of these systems such as VTCS, swirl control valves, cylinder deactivation, etc. It's all similar.

The ecu is smart enough to coordinate throttle opening, spark, gear shifting (for AT) and fuel cut so you don't feel a dip if it's done right. That's why cylinder deactivation is imperceptible on modern engines.

The stock ECUs of those days just weren't smart enough, and since the VTCS only ran when cold it was a bandaid to meet California LEV I regulation (like the tumble valves in subarus were at the time) without Mazda spending more money than necessary.

 

So obviously people much more experienced with this platform than i have shared their experiences, but this is more or less the result i kept coming across. I understand its not strictly apples to apples though, so im approaching this with a healthy dose of skepticism. I'd like to break out a shift point calculator and see where the shift fall back point is and calculate the areas under the curves. Obviously the VICS takes a strong lead at the end, but only in the very last 500 rpm of the power band...

I have two VCTS manifolds, one on the car obviously, then a spare i picked up for free i was going to gut. I suppose it wouldn't be too hard to do my own testing. Just when its not 100* outside haha, im in no particular hurry.

 

My MINI Countryman is DBW and the power delivery when cold is seamless. And it feels like it has about 3 horsepower when I floor it.

 

no. this is dumb. youre stupid. get a new brain.

 

Remember these are two different engines too. For whatever reason, I think VTCS manifold car would maintain it's current power from 0-6500rpm, and just keep climbing (or at least not fall off) with a VICS.

Although that's just speculation.

The VTCS engine was built by Mazda for an '03, and sat in front of an automatic tranny for around 100k before we dyno'd.

The VICS engine was used and abused by none other than Doppelganger for 170k when it developed rod knock. Used stock rods, a rebuilt (and .060 shaved) head, bearings/rings/gaskets, and an Ebay header/VICS mani later, and it's making 140hp again.

Comparing the ignition tables, the higher midrange is most likely because it maintains 24-25* from 2500-7500rpm, while the VICS engine runs 18-28*.

Oregonmon I need to borrow your car!

 

Ahh, thank you for taking the time to clear a little more of that up.

 

Stock pistons in both, so the '03 has a half point higher compression (give or take due to the head shave)?

 

It's very confusing when you don't personally know the engines and the cars they're in.

The auto '03 is stock with VTCS

Doppel's '02 has the shaved head with VICS

What's even more confusing is we're talking about two white NA6s.

 

The MS3PnP doesn't have a pin for VTCS since it is normal open which releases all hamsters.

Switch on at low rpm then switch back off again at higher rpm. OEM just switches on once, at 5500 or thereabouts. This tuning really has to be done on a dyno. Every engine set up will respond differently. Last time I posted a table was about 8 years ago. I finally stopped getting emails asking why that map didn't work in their car like a year ago.

Tend to agree, based on the cars I've tuned and the kpa they pull at different parts of the powerband. Flattest torque curve overall is a VICS, squaretop loses a skosh below torque peak and VTCS falls off right at the natural power peak of the stock cams. All of the BP6D engines we have tuned with VICS or squaretop make peak between 6500-7200. With VTCS that drops to 6300-6500 it seems.

Joe,

To clarify on the undriveable, my two cars didn't have enough power to keep up with traffic without bucking and surging. I'd have to go WOT on a stone cold engine which I don't like to do. So I put up with driving a 2350# 45whp Miata for the first few miles of my commute. :( Our current NB2 is in excellent condition. Brand new rebuilt engine, fresh cat, injectors and everything dialed. We went though that extra prep because the car is being used for the Jackson Racing Rotrex calibration. So it's fair to say that's it's representative.

 

I think you and sav were referring to dead cold engines, but sav's post made it sound like it was always like that, even when warmed up. I'd tend to agree with the car being un-driveable during warm up with vtcs operational. It usually doesn't take any more than about half a mile for it to finally open up though.

 

Does gutting the VTCS throw a code on an otherwise stock car?

 

I find this difficult to reconcile, based on having owned a 2004 for the past year, driven daily in every weather condition ranging from 10°F and a foot of snow on the ground to 85°F and sunny.

My experience parallels Curly's. When the engine is cold and I'm accelerating under part throttle (anywhere from, say, 25-50%), there is a perceptible increase in power that comes on at exactly 3,000 RPM. Where I differ with your experience is that the car is by no means difficult to drive below this point. There's a slight hill coming out of the apartment complex where I live, and the car climbs it easily and with zero drama, regardless of engine temperature, at part throttle.




I'm quite certain that it would throw either P1512 (VTCS malfunction stuck close) or P1518 (VTCS malfunction stuck open). See next post