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Old 04-27-2007, 09:54 AM   #1
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Default S-AFC in "MAP mode"

It seems as though not many people bother with the Apexi S-AFC (I'm talking about the blue screen one and newer versions, the **** version I believe was simply known as an AFC). I can see why, without a TPS sensor the device won't function properly. But there is an alternative. A MAP sensor outputs a 0-5v signal just like a TPS, and one might argue it'd give a better sense of load for the S-AFC to use to switch between fuel maps.

Only reason I bring it up is cost. Blue screen S-AFCs can be had for under a hundred dollars now and they offer a couple things. Firstly, 50% of +/- adjustment. Secondly, they have two tuneable maps and then a virtual one that is an average of the two, it's not true 3D but it's better than one 2D map.

Anyone doing this?
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Old 04-27-2007, 10:17 AM   #2
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or get an auto TB and you'll have yourself a TPS sensor...
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Old 04-27-2007, 10:27 AM   #3
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or get an auto TB and you'll have yourself a TPS sensor...
Didn't know about the auto TB, still too green. Probably for most people it'd come down to whether they can get an auto TB for less than a MAP sensor and pigtail, which I'm guessing is the case. But also I, and others, believe a MAP sensor will work better than the TPS regardless.
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Old 04-27-2007, 10:40 AM   #4
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there's a couple of posts over on m.net about this.

http://forum.miata.net/vb/showthread.php?t=223147
http://forum.miata.net/vb/showthread.php?t=174241

short answer, the SAFC is useful in open-loop cases, but aside from that, there is really no benefit to the SAFC at all in closed-loop situations (at least w/ the 1.6L ECU). The ecu will adjust the injector pulses to maintain a 14.7 AFR no matter what you do with the SAFC. I tried pulling 30% across the rpm range, and it only affected the AFR's in open loop. That said, the MAP mod doesn't really do a whole lot because the SAFC is really only working in the 4000-redline range where you're basically going to be tuning for power (not mileage) anyway. I had it hooked up for a bit, but after realizing it's relative uselessness, I ripped out all the extra wiring for the MAP mod.

Lesson ==> SAFC is <$200....so is the Megasquirt. and it can do a hell of a lot more.
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Old 04-27-2007, 10:55 AM   #5
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Hmmm, so the Miata differs from other applications I am used to (DSM) because it relies so heavily on the o2 sensor in closed loop?

The thing that sucks for me is I've spent eight years on one platform and now, moving to a new one, I find only the basic principles to be the same and none of my trickery and prior ingenuity applies despite the two looking similar on paper.

Now I am starting to realize why there is no easy engine management solution for a Miata. You either have to make <200hp, use fifty different overpriced black box bandaids, or go standalone.
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Old 04-27-2007, 11:36 AM   #6
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welcome to MEGAsquirt....

and what's with all the DSM owners going to Miatas?
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Old 04-27-2007, 12:19 PM   #7
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and what's with all the DSM owners going to Miatas?
I dunno. Bewhare, however. I know a lot of DSM guys all over the country and Canada and I can only think of maybe 3-4 guys that have gone Miata, or always had a Miata. The deal with DSMs is they are now cheap enough that every 18-year-old piece of **** can own one for $2500, then they spend the other $2500 they saved up from their Best Buy job totally destroying the car. Then I guess they must all be selling their basketcase fucked to hell DSMs for $5000 to buy a Miata.

I got a Miata because it's light/spartan, a true 2-seat roadster and one of the only real sports cars the average guy can afford to buy and maintain. It's really everything most car enthusiasts want, even if they don't realize it. That's from a driver's standpoint. People who like to show off and be asses, well it looks like they're buying Miatas now too.
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Old 04-27-2007, 12:47 PM   #8
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i used safc to run 460cc injectors on stock ecu but the lack of map or TPS made tunning difficult for the 1.8's it did allow me abit more hp through leaning out my midrange. moral of the story i paid as much fir my new safc as i did for my MS and have alot more stuff to help me out FWIW the safc and EM blue do the same things ot controll fueling via AFM signal manipulation ubt the EM blue has abit more to fine tune and the ability to autotune.
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Old 04-27-2007, 04:09 PM   #9
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I've had my 92 TSi since 1999 - it's FWD, has a few basic mods (including S-AFC), and runs 13.3s @ 107 on street tires and 93 octane. Now that I've finally gotten around to picking up a pair of slicks, I hope to crank the boost this summer, add some 110, and see what I can manage at Beech Bend in the 1/4. I've had my Miata for about 1 1/2 years now and am still waiting to improve the straight line deficit...

Still, I find myself driving the Miata 80-90% of the time.

Last edited by spoom; 04-27-2007 at 05:26 PM.
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Old 04-27-2007, 06:13 PM   #10
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With a good set of slicks you should have no problem hitting 12s with that MPH. All my DSMs were AWD.
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