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BLWRDR
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Discussion Starter #1
i am installing a second MAF and i dont know how to wire it up, ive read it somewhere before but could not find it now...if anyone out there knows how please let me know


kahlee
 

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kahlee,
You wouldn't happen to be the same Kahlee that bought my old Blitz kit would you? If so, I didn't hear back from you letting me know if you got it ok but I'm assuming you did. I know it must have been a pain in the ass getting it out of that casket I built for it. I sort of overshot the measurements on that one. Anyway, post some pics once you have it installed.

As far as wiring up dual MAF's check out Steve Vache's site at www.vache.org/supra/dual_maf.htm
Hope this helps ya out.
Brian
 

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BLWRDR
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Discussion Starter #3
yup man, i heard its the only one in the US now....let me tell you how much money i spent to get the corners fixed... you never told me how bad of a condition it was in, stress cracks missing corner and etc. its alright though.... no hard feelings... put it this way i could have went to japan and bring a kit back for the price i paid all in all from the kit to redoing the bumper....check it out at autophiles.com


kahlee
 

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Generally people wire it up to an APEXi SAFC. Then average the signals. This will input a signal to the computer very similar to one MAF. In my opinion, it doesn't make much sense, but won't hurt either. I was going to use a second MAF just so I would be dealing with a known volume of air. Exactly 100% more than with only one MAF. Then adjust fuel accordingly. Skip the wiring completely for simplicity and better reliability. Good luck with it.

If you do wire, don't wire the temperature signals together. Just the MAF outputs. If you need any help let me know.
 

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Grant has already pointed out that there is a little more work to do if you want to do it correctly. The MAF voltage is not linear with airflow. You can see this in the factory manual. There is another circuit you will need to create. He can explain it better than me. Basically the combined voltage of two MAF's will not give you the same voltage as one MAF.

Later, Steve
 

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This is a ops scenario that I came up with based on what I read about the MAF's operation.

"A"=Thermistor
"B"=Platinum Hot Wire
The stock MAF can only meter so much air based on its operating principle of trying to maintain a common resistance between "A" and "B" by adjusting the voltage to the platinum hot wire. The more airflow you have = cooler hot wire = less resistance = more voltage to keep the resistance equal to "A". The system can only provide so much voltage to keep "B" at the desired temp./resistance before it maxes out and there is not enough voltage left. This would be the scenario when upgrading to a large single turbo that flows more air than the stockers.
Running a dual MAF set-up would divide the load, so to speak, thus utilizing less voltage to keep the platinum wires hot. The voltage used to maintain the wires temp. is also what's measured by the ECU, which in turns adjusts the fuel accordingly. This can also lead to a false signal. If dual MAF's are requiring less voltage to keep the wires hot, the ECU will read this and assume that the airflow is less than what it actually is.
There was a previous post on here about the idea of fabricating a non-inverting amplifier to boost the voltage signal when using dual MAF's. It's an op amp circuit which you can find the schematic for on the National Semiconductor web page, just use a search engine to find the site. As far as the signal not being linear to airflow, the op amp circuits output is determined by its input. It's only job is to boost the voltage/signal.
Sorry for the long post and if there are any discrepencies please correct me as this is only my analysis of how a dual MAF set-up would be successful.
--B--
 
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kahlee,

come on man your not driving a damn honda, take those stupid ass neons off.
 

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BLWRDR
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Discussion Starter #11
i dont ever use that neon..... only during those dark car shows...yeah its ricey you dont have to remind me....what do you think about the rest of the car...

kahlee
 

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What kind of Silver paint is that? looks real nice, I have been meaning to do my dash trim silver as well, my car is the same color and I dont know of a really good paint to use, I was going to just get it sprayed alpine silver by a body shop but Id like to look into less expensive options if possible..

was that professionally sprayed on, or is it spray paint I can pick up at a store?... looks really clean.
 

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BLWRDR
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Discussion Starter #14
if you go to a auto store you should find all the matching paint for a car just match it w/ the number inside you driver side door... its a do it your self kinda thing.... i suggest a coat of paint at a time.. dont try to paint the thing quickly take your time or else you will start to see tear drops on it.......
 

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ok, i'm bringing back up an old thread because i still have some questions. so should i wire in the second maf when i put it in or not? i will be going with a setup like on steve vache's page, any info would be appreciated.
 

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Tom,

I got your email. Basically, I've decided to scrap this idea. My goal was to match the airflow to my 720cc injectors which flow about 30% more fuel. I was going to use a second maf so I would be dealing with a known volume of additional air (100%). Then I was going to make adjustments with an AFC (-70%). Instead I found a much simpler solution of just creating a bypass around the MAF. Right now I just have the return port of the bov open so additional air is sucked in there on the other side of the MAF. That hole is about the size of a quarter and seemed to work out just about right. In closed loop the O2 is going to have the computer adjust fuel accordingly. If you've really got it out of whack the fuel maps will get adjusted also. I'm getting ready to go single and will do the same with a bypass about the size of a quarter. Even if you get two maf electically working you are still limited by what the computer can work with. The maf signal is only good to 500~550 rwhp range from what I've read. With a simple bypass you're not electrically limited. Hope this makes since. I can't remember their names, but there are a few high hp cars around using the bypass method. That's where I got the idea from.

It just ended up being to much of a pain in the ass, physically fitting 2 mafs, electrically getting them to work and then if my understanding is right, the computer can only deal with a signal in the 500~550 rwhp range. Too low for me since I'm after 600 at the wheels.

Let me know if anything didn't make sense. ATLSUPDAWG#2 made some good points and explained it better than me probably.
 

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Yes the ECU can only read ~550 rwhp. But thats because injector duty cycle is approaching %100 at those levels. Bypass tube or not, you can't get the ECU to recognize that amount of airflow, you need to balance the injector size with the size of the intake leak. Personally I'm going with dual MAFs, because I don't want drivability issues with a bypass tube.

The voltage from one maf is Vout = a + airflow^.5 (There are other variables, but they can be ignored for our purposes, they can be ignored for now. See the NCF for more details.).

'a' is a constant, and hopefully pretty small.

So if each MAF gets 1/2 the airflow, you've got (a + (.5airflow)^.5) from each MAF. Average the signals, and you've got:

.707*airflow^2 + a = Vout

So the new airflow needs to be corrected by 2^.5, adding 41.4% fuel. This is why Clint's setup works, the ratio of his injector size to the stock ones is close enough to 41.4% that the ECU can make up the difference in fuel trims, plus his own tuning.

I have a circuit to multiply the voltage by different amounts by ajusting a pot (a few $$ from Radio Shack). Problem is, your multiplying 'a' with it. So with stock injectors, for getting (1+(2^.5)) * a. I've also added an ajustable voltage subractor to try and subract the extra 'a'. Will it work? I kinda doubt it :) I'll post about it if I get it working correctly. 'a' might not even be big enough to make a difference. If it does work, I should be able to control any size of injector and keep the stock fuel curve.

See here: http://www.vache.org/supra/dual_maf.htm
 

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I understand that the MAF can only send a signal up to 5 volts, but is it true that the ECU can only receive a signal up to 5 volts?

If this is true, the maximum hp will still be limited even if you go with a dual MAF setup and remove the restriction. You wouldn't even be able to use a S-AFC to add more fuel over the 5 volts. I guess using bigger injectors and using a S-AFC to reduce the voltage from dual MAF's before the signal is sent to the ECU is the only way?

Later, Steve
 

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Ken S. is one of the single turbo guys (TPC) running 720 injectors with stock MAF. It was set up by Bryce. He has two 7/8 inch bypass tubes but I know it also has a G-force ECU that took some speical tunning to get right. The setup works well and he was able to pass smog values here in CA.

Bill P 95 6spd sp63
 

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I am runing stock injectors with upgraded fuel pumps and fuel lines, should I start thinking about dual MAF or stock MAF is good enough?
 
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