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Discussion Starter · #1 ·
Here is my theory... According to http://www.miata.net/solo/airflowmtr.html the air flapper is of liner progression... this means at 50% air flow, 50% of 5 volts (or 2.5 volts) is fed to the computer via the signal wire. If two air flow meters were used, and the potentiometers for both ran in series, the 25% of the flow that each of the air flow meters were reading would create the 50% resistance needed to feed a 50% signal to the computer. This will only work on the flapper style AFM's, so turbo guys are ou of luck. Also, according to the above site the "flowmeter bench tested it flowed 165 CFM at 10 inches water ." 10 inches of water is the standard for an NA motor. The flowmeter bench tested, although out of a turbo II RX7 is the exact same as the Supra flapper style, I have personally dissassembled both. The differance is the pinout.

Two AFMs will flow about 330 CFM, and at a redline of 6500 RPM and an estimated volumetric efficiency of 85%, the 7MGE can flow 293 CFM......

Here's more to ponder, and maybe someone has an answer for me... The NA intake manifold has that Y thing above the valve covers for the intake track. Is one of those for before AVIS opens its second set of runners up, and the other after? If it isnt, or even if it is, I think that running dual throttle bodies on those two openings and getting rid of the Y pipe altogether would increase flow nicely. A progressive throttle linkage might be needed to control throttle at low RPMs...

Alot of this theory has been pieced together from reading books and forums. Ive seen multiple threads about people whining about the restriction that the AFM causes with the NA motor. Im posting this to bounce it off an educated mind... This thread wasnt started to ask if this would be good or not. It is to have a fresh mind look it over and point out things I've looked over, or to ask me a question that I might have not asked myself... Thanks in advance for the input!
 

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Discussion Starter · #8 ·
Jeff Lange said:
I think you totally misinterpreted his comment, in pretty much every way possible.

That wasn't what he was saying at all, he was saying as far as twin AFM's go, Turbo owners are out of luck....
*points to jeff* what he said! Pertaining to this post only, turbo guys are outta luck. Pretty much everything else and you have us beat...

And... the Apexi SAFC can take two MAF signals and average them into one signal... I was looking into this, but I dont know if you can take two KV signals and use the SAFC as a translator into one 5v signal...
 

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Discussion Starter · #11 ·
MKIIINA said:
sounds like a very interesting theory. how would this be a benefit though? i mean for the 1/2 na->t guys its a way for more air but what will this do just regular NA guys?
Did you read the original post?

THESCAMP said:
according to the above site the "flowmeter bench tested it flowed 165 CFM at 10 inches water ." 10 inches of water is the standard for an NA motor.
THESCAMP said:
Two AFMs will flow about 330 CFM, and at a redline of 6500 RPM and an estimated volumetric efficiency of 85%, the 7MGE can flow 293 CFM......
This means there won't be a restriction on the NA motor...

As for the NA-T guys the website mentioned states "When I had the flowmeter bench tested it flowed ... 300 CFM at 28 inches water." Lets say you're running 14.7lbs of boost (i know thats too much, but the math is easier this way) that puts your air ratio at 2:1, doubling your engine's airflow rate to 586cfm, at 6500 RPM and a volumetric efficiency of 85%. Now, those two airflow meters can flow 600 cfm on a turbo motor... Still giving you enough room to breathe up top. I think that the dual flapper will be a must for the NA-T guys, myself included, as soon as I perfect the setup. The non linear progression thing is making me worry.... But nonetheless... back to the drawing board!
 

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Discussion Starter · #13 · (Edited)
Robbman said:
Output signal is exponential (or logarithmic depending on how you look at it ;)) not linear.
Do we possibly have a graph or equation to confirm this? If we had that we might be able to make something work... Or at least be one step closer...

I dont think anyone even make a maf translator for the 5-0v system do they?
 

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Discussion Starter · #15 ·
Robbman said:
Hmm..... Looks like if this were the case then the air flow would lean out in mid range, but be pretty close top and bottom... If i could only get one to curve the other way then i think that would even everything out...........
 

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Discussion Starter · #16 ·
The exponential curve must be based on the spring tension... Well off to my mr2 flapper to tear it apart!
 

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Discussion Starter · #18 · (Edited)
Robbman said:
You may want to look at these as well

Air induction system
According to this the "air volume entering the engine is directly proportional to the amount of movement detected from the measuring plate."

EDIT: but clearly the toyota graph shows that the voltage:airflow is definately not directly proportional...
 

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Discussion Starter · #20 ·
Robbman said:
Yes, it is.

The signal graph is still exponential. Take a look at the MAP signal graph for comparison.
Lol... just edited my last post with the same revelation...
 

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Discussion Starter · #24 ·
MKIIINA said:
see there is what i was talking about. how would this benefit just the NA guys, not the NA -> T ones. Obviously for the Turbo swap guys its a plus as you can have all sorts of fun adding air in and what not but standard NA's only have so much room to play with. so easy there killer :hug:
The point was more towords the fact that the Turbo gets a karmen vortex style MAF, not the flapper style. The NA-T guys would definately benefit, even more so then the NA guys! I'm just looking for a solution here...
 

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Discussion Starter · #30 ·
DeanMarcum said:
I tried the "dual flapper AFM" mod on my N/A + T. No benefit. Remember, the majority of the restriction in the AFM is because of the flapper door spring tension, NOT the meter itself. You must cut the tension in half on each AFM to make the system "flow" any more (if you keep the same spring tension then you will more half as much air through each AFM which will give a very lean reading). With that loose of spring tension though (1/2) the car would run VERY rich at anything but idle because the flapper would swing open all the way almost immediately whenever throttle was applied. I unltimately ran a VPC with the GE electronics (yes, it can be done just think about the MR2 turbo with flapper door meter). If you can make it work, good for you but IMHO you would be better off using a MAFT with the proper conversion. Much simpler to do.
Actually, the wind drag is caused by the fact that the AFM's hole is 2" wide, compared to the 3" air tract that the intake has, although yes, the flapper's spring tension does cause some drag. I think that the dual VAF theory has been disproven. So now on to other options... the DIY Maft on the prior page... With this lil unit you can even create your own fuel curve...

Or for the people that arent that DIY... Perfect Power has the SMT6 for about 450 bucks that will allow ignition and fuel tuning, along with replacing the AFM with MAF, hotwire or a MAP sensor, removing it completely. The translator is built in... I've been doing some reading on this unit, and it is definately on my list of future power mods... Can you say 6 throttle body'd MAP sensor NA? hmmm.....
 

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Discussion Starter · #34 ·
So does this mean that one side of the Y feeds the long runners, and the other one feeds the short runners? If so, at 4200rpm you'd effectively double the amount of flow the motor would see, kind of like mashing the throttle from 1/2 throttle to full, it'd be jerky and not fluid at all. And the power differance from below 4200 to above would be huge. It is supposed to give two torque peaks, not one little one then another big one...
 

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Discussion Starter · #37 ·
Robbman said:
No... it means that when the valve is closed, cylinders 1-3 are fed from one side of the y pipe, and 4-6 are fed from the other. The chamber in the upper manifold effectively becomes part of the runner.

When the valve is open, the chamber becomes the starting point of the runners.

*lightbulb* I get it. So two throttle bodies would be beneficial!
 

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Discussion Starter · #40 ·
This is true... So, upon the completion of the twin AFM project, why not build a manifold to feed 1-3 and 4-6 with seperate throttle bodies, and remove the ACIS system completely? Is it really that huge of a differance in power? Personally, I would like one power curve to base my shifts off of...

I think that I'm going to open a thread on a VPC system for the NA motor. No one makes ANYTHING like this, so it'd be original definately. Alls it would take is building a microchip to convert the vacuum readings to an analog output using a table that is adjustable by EPROM programming, to get the right fuel curve. From there, modifying and tuning the fuel curve is as easy as reading a wideband O2.
 
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