I had a thought recently...it came to me in a dream . Its about fooling the AFC into reading boost. Right now, the AFC reads throttle position and RPM and adjusts the MAP sensor output accordingly. The AFC doesn't care what the pressure is in the manifold...you still have to use a boost dependent FPR to bump up the fuel pressure. What if you could make the AFC read manifold pressure and RPM and adjust MAP sensor output accordingly. Then you could use a static fuel pressure and let the AFC do all the work. Now, the AFC looks for a linearly varying 0-5 volt signal from the throttle position sensor right? What if you got a supplemental 2 bar MAP sensor from a turbo chrysler with a 0-5 volt output. Tap the supplemental 2 bar MAP into the manifold some how. Then hook up the 2 bar MAP to the throttle sensor connection on the AFC. At full vacuum, the AFC would see a low throttle position. At full boost, the AFC would see a high throttle position. You could set the high throttle point setting on the AFC to your expected full boost. Then you could set the low throttle setting on the AFC to your expected full vacuum. Then you could set the AFC to trim the stock MAP sensor output to provide the proper fuel at full vacuum and full boost. At any pressure in between those points, the AFC would linearly interpolate how much fuel was needed. I think this could work...I would also trust it better than my flaky adjustable FPR. Let me know what you guys think.
#2635, "RE: Fool the AFC" In response to Reply # 3
Opps, come to think of it, since the AFC is basically outputing the new MAP signal, we can just replace our stock MAP sensor with a MAP sensor that can read boost!
Now where do we get a MAP sensor that will fit right in there...
This is really a good idea, Corbin!
I believe this would make the AFC work even better in our case, since this would reduce the many variables introduced from turbo'ing! (ie FPR, fuel pressure, etc)
#2638, "RE: OK I feel really stupid now, cause I am lost! :)" In response to Reply # 6
LAST EDITED ON 12-Mar-01 AT 05:22 PM (PST)
Just what I was thinking when I first read the post. I wouldn't be suprised if a new Super AFC-B came out after stealing the idea. Especially since hondas run the same type speed density system (and we know how they get catered to. Hell we might luck out and they come out with a SuperAFC-VTEC-B).
10psi of boost needs approx. 590cc injectors. If we install the S-AFC, a 1:1 regulator, and the 440's we can run a max of 10psi !! (440's @ 58psi = 590cc considering a 48psi idle) Or you can even run on the stock FPR and not even install an FMU, but you would further limit yourself to the amount of boost you can run.
**Keep in mind that the stock ECU with the help of the S-AFC can run a max of 440cc injectors!
By my calculations, 9 psi boost <270 hp> would only require 440 cc/min injectors. RC Eng told me we could run a minimum BSFC of 0.525 and recommended a max duty cycle of 0.85. Put those numbers into the injector calculator and you get a recommendation for a 441 cc/min injector. Numbers for 10 psi boost shouldn't be too much higher. Back to the AFC...I'm going to check out the junk yards tomorrow to find MAP sensors from late 80's-early 90's turbo chryslers. There should be plenty of wrecked New Yorkers, Lebarons, Daytonas, and Lasers lying around. If I can get some, I'll start testing them out.
This has crossed my mind a long time ago. The theory is sound, but there is something wrong here I can not put my finger on right now or just do not remember because I can not think right now :-/ I will have to post again after lunch when Ican think about it. Something with the ecu and preprogrammed fuel tables and flow rates. Maybe I am just imagining things. Hrmm..
Oh, I agree, you just want a standalone setup and not the cost lol.
Basically this 'solution' should act as a replacement to the mechanical FMU. With the AFC + secondary MAP sensor combined we would have an electronic FMU more or less.
The only problem that might be is that the ECU won't obey what the AFC tells it to do. One question: Are our injectors primarily controlled by the 1 bar MAP signal output?
One thing you should keep in mind though is that it would be better for you to run at least a stock GST regulator (1:1) than just the stock GS regulator and the AFC. Most GST/X guys run at least 20psi over stock fuel pressure. So i wouldnt throw out that FMU just yet but instead get a lower spring like a 2:1, or 3:1....
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