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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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Just some guy
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It's been a while since I've had a Toyota flapper in my hand, but IIRC, the risistance values produce a sign wave, not a straight line, when opening the flapper.
 

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Dr. Jeff Lange
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Racefiend said:
It's been a while since I've had a Toyota flapper in my hand, but IIRC, the risistance values produce a sign wave, not a straight line, when opening the flapper.
I don't think so, but I can't remember off the top of my head, but I can't think of any that do that aside from non-flapper types. IIRC I think the Toyota flapper ones are reverse 5V...

I'll go look through my stuff to find out more.

EDIT: Found the Toyota PDF I was looking for, they go through the types of AFMs in it, and cover Vane AFMs.

They're not linear output as can be seen in the PDF, but they are voltage output. I don't know if the 7M-GE uses the 1st (rising voltage) design, or 2nd (dropping voltage) design.

http://www.autoshop101.com/forms/h34.pdf
 

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Just some guy
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Hmm...I'm going to have to go dig up my old mk2 afm tomorrow, it's around here somewhere. I thought back when I tested it I had an ascillating resistance as I opened the flapper. :dunno:
 

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1/2 Na-T Project
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Racefiend said:
Hmm...I'm going to have to go dig up my old mk2 afm tomorrow, it's around here somewhere. I thought back when I tested it I had an ascillating resistance as I opened the flapper. :dunno:
My 1/2 Na-t isn't running right now but I believe the voltage increases as the flapper door opens, ask Jong, he will no for sure and was thinking about running dual flappers. Later.
 

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Moo
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Personally I don't see how being a turbo owner puts me out of any luck. I'm lucky to have bought a turbo in the first place. In stock form it's already 1000x's better than any n/a and makes gobs more horsepower and torque with just a few cheap mods. No flames - I've owned and modded enough Supras - n/a and turbo, to know. I just thought your comment was rather funny.
 

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Dr. Jeff Lange
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BFR1992T said:
Personally I don't see how being a turbo owner puts me out of any luck. I'm lucky to have bought a turbo in the first place. In stock form it's already 1000x's better than any n/a and makes gobs more horsepower and torque with just a few cheap mods. No flames - I've owned and modded enough Supras - n/a and turbo, to know. I just thought your comment was rather funny.
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....
 

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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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Destroyer of Turbos
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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?
 

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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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