Any of you guys have an extra VAF?

[cyborgzero]

I need to know if someone has a VAF from a PGT/MX-6 so I can take a look at the innards..

A broken one is fine, and preffed...

I just came across this in my fluids book, and they have the spring rates for various flows... According to that, you *should* be able to properly calculate the spring rate that would allow the VAF to work with boost THEN you would increase your fuel pressure to make up the difference..

This idea is used on 944s ALL THE TIME, which is one of the reasons ppl easily get 400hp daily drivers out of that car. Just slap on the bigger injectors, more boost, then go to the Porsche dealership and have them reset the preload on your MAF with a little round knob that has a wound spring attached to a flap door..

Very simple idea, and it works well...

[Jeff L]

Rob--

I cut one apart a few months ago. I snapped hi-res photos on Josh's camera, but I don't know if he's downloaded them. (if you have Josh, just email them to me--I'll host them)

I got sick of mine sticking, so I cut it apart to find the source of stickiness, fixed it and glued it back up. A few weeks later though, the lube lost its effectiveness and it acted up again.

It's basically a circuit board with metal sensors that look like they output a specific voltage at certain travel points for the plunger. So as the plunger slides back, a rod with a metal indicator slides back and forth on this circuit board, and the board picks up the signal of where it's at, thereby "knowing" the flow of air. But it's not a progressive scale. It has about 10-15 sectors on it, so it looks like it might be choppy if you graphed it. In other words, it looks like it has about 10-15 preset values throughout the entire range, not progressive like how a rheostat works.

I posted it on the Performance & Tech forums a while back but nobody was interested because my name's not famous enough or I don't have 10,000 posts. So it got lost quick. (I figured somebody would be interested, b/c to my knowledge, I've only seen one other pic of a VAF cut open.)

[cyborgzero]

WEll gimme the damn thing!

I just need to figure out what flow equals what *zone* on the rheostat, then preload the spring on the plunger an appropriate amount to keep the plunger from maxing out so soon, then run an FPR with a bit higher fuel pressure to compensate.


Even if you got the bits and pieces it would be helpful.

[Jeff L]

Well, the bits & pieces are all glued up and functioning on my car. That's why I'm saying I took pics, but they're on Josh's camera. I can show you where to cut it open without hitting the circuit board though. Otherwise, they're a bit tricky to borrow from a junkyard.

[imtokay]

Just out of curiosity.
Why do you need to modify the vaf voltage to accept boost? Your still going to have to manually up the fuel flow. I'm just trying to understand your motive.

[cyborgzero]

Originally posted by imtokay
Just out of curiosity.
Why do you need to modify the vaf voltage to accept boost? Your still going to have to manually up the fuel flow. I'm just trying to understand your motive.

Well, here is the logic:

1) run bigger injectors/increase FPR, which increases flow.. Car runs overly rich.

2) THEN, increase the preload on the plunger spring and/or otherwise modify the VAF so that for a given amount of air, the VAF reads lower than before, which then cuts back the fuel for a given amount of air.

So, basically, you are using the VAF to compensate for the increase in injector flow, because now the VAF doesn't want to open as much for a given volume of air, BUT, since you increased the injector output, you won't run lean. This will also help to keep the ECU out of open-loop mode at higher RPMs.

When I do it, I will try to capture a waveform of injector duration vs. rpms.

The good thing is that in my fluid dynamics book, there is a problem that has the spring rate, tube and plunger size, and air volume, so, for a given percentage increase in fuel I can now calculate the percent DECREASE in VAF movement/spring rate needed to compensate properly.

Sort of a poor mans SAFC.. This is why you won't see crap like the SAFC on Porsches.. They don't need it.. You just pop the lid off of the VAF, grab the spring preload knob and give it a turn or two and boom, you have just compensated for increased boost.

The dealerships even have a wideband o2 sensor to dial in your VAF after you crank up the boost. There is NO reason we also cannot do this, none at all, esp. since Mazda is just a japanese porsche anyway.

Rob

[imtokay]

Ok, I thought thats where you were going. I was going to suggest a SAFC for those controllers but I definately have no problem with cheap boost mods