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Can you change the FD from a speed density-based system to a MAF-based system???

Can you change the FD from a speed density-based system to a MAF-based system???

 
 
 
 
Old 07-04-04, 12:21 AM
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Question Can you change the FD from a speed density-based system to a MAF-based system???

We got in a little but VERY interesting discussion about this in a different thread, and I definitely wanted to further explore the possibility of doing this on our FDs, yet I didn't want to sideline the purpose of the other thread...so I started this one.

Here's the highlights from the other thread.

Originally posted by SPOautos
HaHa, I see.....yea wrong Stephen.

I'm throwing around the idea of pulling the trailing and testing out a good piston engine standalone that does auto tuning and mass air flow to see if I can convert to mass air flow.

Mostly just for the hell of it.....I thought it would be interesting to see how it works. I've got a few ideas up my sleeve.

STEPHEN
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Old 07-04-04, 12:22 AM
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Originally posted by t-von
You know Stephen that sounds like a really good idea. You may very well be on to something if these plugs prove themselves.
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Old 07-04-04, 12:22 AM
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Originally posted by SPOautos
Yea, maybe....I want to consult a couple choice people that have a lot of experience tuning mass air flow piston engines as well as speed density rotary engines and get thier take and info on it. Just kina pick thier brain a little before I start spending money.

I'd like for anyone to throw up some comments if you have any.

STEPHEN
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Old 07-04-04, 12:23 AM
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Originally posted by FDNewbie
Stephen,

My comment: I dunno what the hell you're talkin about lol. Break it down for a newbie, will ya?

~Ramy
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Old 07-04-04, 12:23 AM
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Originally posted by t-von
Anyone know why Mazda never decided to use an air flow meter? This could have helped save a few engines that were improperly moddified.
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Old 07-04-04, 12:24 AM
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Originally posted by Fatman0203
Like a MAF sensor? It probably would have been expensive since they may have needed 2 for each turbo. Just my guess.
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Old 07-04-04, 12:25 AM
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Originally posted by jimlab
You're right that it would have been more expensive, but not because of the number of turbos. The MKIV Supra uses a single MAF for twin turbos.

A MAF-based engine management system measures the volume of air being ingested by the engine and provides appropriate amounts of fuel. A Speed density-based system "guesses" how much air is actually being ingested and cannot compensate for significant changes without being reprogrammed.
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Old 07-04-04, 12:27 AM
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Originally posted by FDNewbie
Jimlab, thanks for the explanation. I heard what you're talking about before...about how the MKIV Supra automatically senses increased airflow, and adjusts the A/F ratio accordingly...no programming necessary.

Just curious...I may be way off (newbie), but this MAF differs from our speed density-based system in what? It's a different sensor, correct?

So is it possible to switch out our speed density-based sensor, and replace it w/ an MAF, which would practically make tuning an FD correctly incredibly simpler??

I'd even venture to say that the MAF, being so much more sensitive, since it measures actual volume, would practically eliminate ppl blowing engines from boost leak or spike, because it would sense the increased air, and increase the fuel accordingly??

I'd imagine since the speed density-based sensor on our cars is run off our stock ECU, that you prob. couldn't use an MAF sensor on the stocker, since the ECU is static. But maybe w/ a PFC or another programmable ECU, you can run a MAF sensor off it?

I'm probably oversimplifying this considerably, given I don't understand exactly what and how much goes into this, but I think the concept seems fairly simple enough...and worth a thought??
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Old 07-04-04, 12:27 AM
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Originally posted by jimlab
Well it adds an additional sensor, at any rate.

A MAF sensor has a heated element which cools as air passes it, obviously. The ECU measures how much voltage is required to keep the element at a given temperature, and can estimate how much air is passing through the sensor based on that reading.

The MAF sensor is placed in the intake tract in front of the turbos and immediately after the air filter, as shown below. The blow-off valve on the Supra feeds back in behind the MAF sensor, in front of the turbos, because that air has already been metered. The RX-7 dumps the BOV output back into the air box.



No, because there is no "speed density sensor", per se. A speed density system uses a number of sensors to determine how much fuel needs to be injected. Boost/vacuum (MAP or manifold absolute pressure sensor) level, intake air temperature, and engine rpm (and other sensors, in some systems) are used to "look up" a pre-set value in a table or matrix, and fuel is delivered accordingly.

As long as it was tuned properly and the fuel system and injectors were up to the task, sure.

The PFC is designed to work with the stock sensors. It would have no idea what to do with the input from a MAF sensor, and neither would the stock ECU, obviously.

Stephen is talking about using a system not originally intended to work with a rotary engine, but after converting the system enough (single plug per "cylinder", MAF sensor, etc.) that it no longer matters.

I've said for years that the FD should have been designed more along the lines of the MKIV Supra, with MAF-based engine management and a vastly simplified sequential turbo control system. Those two changes would probably have totally altered the perception of the reliability of the rotary engine.

Here's a pretty good article on the subject of Mass Air Flow vs. Speed Density.
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Old 07-04-04, 12:29 AM
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Originally posted by Fatman0203
Hey Jim, wouldnt it be even better to have both MAP and MAF sensors (which I think some cars have) because the more sensors (yes more chances of something f*cking up) but at the same time less chances of detonation and let the computer take charge.
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Old 07-04-04, 12:29 AM
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Originally posted by FDNewbie
[B]Jim,

I haven't read the article yet...I definitely will in the next few minutes. Again, thanks for breaking it down. Stuff like this is invaluable to me. Seriously.

[B]
In regard to the BOV, on the RX7, we can change where the BOV is placed, so it doesn't feed back into the airbox, correct? Many people put the BOV (aftermarket one obviously) on the IC piping...so wouldn't that solve one problem?

[B][B]
So for the MAF to work, you simply have to add a sensor in a given spot (as you've shown, after the intake). Now getting an ECU to understand that imput would obviously be a challenge...given that no ECUs for the RX7 are designed for that.

[B]
Piggybacking on Stephen's idea, aren't there EMS' that are used on both rotaries and non-rotaries? PFC (MR2s), AEM, I believe Haltech as well on other cars?

So you could take one of those ECUs for non-rotaries, say, one for the Supra (so it already has a program and map/table to utilize input from an MAF sensor), change the ignition timing and what not so it would work on a rotary, and boom...you're good to go? Also, the supra has sequential twins (more or less), so you wouldn't be dealing w/ trying to program an ECU for a single turbo into a sequential system...(or at least the work involved would be greatly reduced)??


I haven't been saying it for years, but I definitely agree with you. I thought the same from the first time I heard the Supra dynamically sensed changes in airflow, and thus automatically adjusted the AFRs. That pretty much eliminated the "three mods' rule for them I'd think...and they can up the boost, go freeflow intake & exhaust on a stock ecu, and not worry about blowing the engine! (provided they have adequate fuel supply)
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Old 07-04-04, 12:30 AM
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Originally posted by jimlab
MAF-based engine management systems do have a MAP sensor, even for naturally aspirated engines.
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Old 07-04-04, 12:31 AM
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Originally posted by Fatman0203
Ahh i see, thanks for the heads up.
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Old 07-04-04, 12:33 AM
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Hopefully we can continue from here...
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Old 07-04-04, 12:39 AM
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This seems like an awesome thread but have they gotten anywhere about what type of ECU that you could possibly use. I mean, hell, if we could get rid of some of the known villians of rotary deaths, all the owners would be that much happier (and wealthier). Is it possible to find something out there for this and possibly to simplify the trubos (the true killers)?
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Old 07-04-04, 12:46 AM
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Stephen's known to always have a trick or two up his sleeve...so I hope he's got some ideas.

I dunno if it'll work, but my guess is an aftermarket ECU for a supra running twins would be perfect, as I said in my other post. It's already setup to run twins, it's already setup w/ the programmed values to interpret and execute changes utilizing a MAF sensor, so the main thing would be getting the ignition timing and what not to run from a 6 banger to a rotary...but that's where Stephen comes in haha. He was talking about somehow doing that...

As for simplifying the turbos, I'm doing my best to find out as much info about the 99 rat's next black box replacement that no one seems to know about...it's got me goin nuts!
https://www.rx7club.com//showthread....postid=3139751

Last edited by FDNewbie; 07-04-04 at 12:50 AM.
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Old 07-04-04, 01:05 AM
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dude, you have me drooling. If we can find a way to meld this together, I might be able to offer up mine as a test bed. All thats done to her is a DP. ---with of course a discount and help rebuilding it if it blows LOL
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Old 07-04-04, 01:12 AM
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That's if I don't beat you to it haha. I'm telling you, I REALLY hope some ppl jump on this bandwagon and chime in w/ serious thoughts, ideas, criticism, experience, etc, because I think this could lead to a very much needed and overdue improvement to the FDs we love so dearly...
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Old 07-04-04, 01:12 AM
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Does the 3 rotor from the Cosmo use a MAF sensor by chance?
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Old 07-04-04, 01:15 AM
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Originally posted by Fatman0203
Does the 3 rotor from the Cosmo use a MAF sensor by chance?
Very VERY good question. But that would mean that most of the problem is solved, since ppl running 3 rotor conversions would have to be using an aftermarket ECU for a rotary that has maps and calculations for a MAF sensor. Unless Jim and Stephen overlooked that, I'd say probably not...
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Old 07-04-04, 01:27 AM
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Originally posted by Fatman0203
Does the 3 rotor from the Cosmo use a MAF sensor by chance?
Not to my knowledge, but earlier 13Bs did. The Turbo II used a MAF sensor for at least some years.

It's possible that a Wolf 3D system might work, but unfortunately I don't know much more about the Wolf than that I've seen one running in a local club member's 1st gen. with a Turbo II 13B swap...

Last edited by jimlab; 07-04-04 at 01:30 AM.
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Old 07-04-04, 01:30 AM
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Originally posted by jimlab
Not to my knowledge, but earlier 13Bs did. The Turbo II used a MAF sensor for at least some years.

It's possible that a Wolf 3D system might work, but unfortunately I don't know any more about the Wolf than that I've seen one running in a local club member's 1st gen. with a Turbo II 13B swap...
I was going to mention that, the Turbo 2 does run a MAF sensor *( a giant one may I add)*. The only problem I see to running a MAF sensor is how to get the ECU to read it and input it into the cars diagnostics. I mean APEXI would have to make maybe an add on or something to their PFC , and a software update. Thats the only way I see it happening.
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Old 07-04-04, 01:30 AM
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one thing not to overlook is the tunability of the ecu we are dropping in. How much could we actually get out of it without running into a roadblock again?
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Old 07-04-04, 01:36 AM
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Originally posted by Fatman0203
I was going to mention that, the Turbo 2 does run a MAF sensor *( a giant one may I add)*. The only problem I see to running a MAF sensor is how to get the ECU to read it and input it into the cars diagnostics.
I just mentioned that the Wolf 3D works with a MAF-based system. The Wolf also supports larger injectors (Carlos Iglesias used one to get to 39x RWHP on stock twins, IIRC), so the only question is whether or not it can be used without trailing plugs, if that's still something people are interested in.

I also think you'd have a lot better luck getting Wolf to work with you than you would getting A'pexi to make changes to the PFC.
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Old 07-04-04, 01:40 AM
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Originally posted by jimlab
I just mentioned that the Wolf 3D works with a MAF-based system. The Wolf also supports larger injectors (Carlos Iglesias used one to get to 39x RWHP on stock twins, IIRC), so the only question is whether or not it can be used without trailing plugs, if that's still something people are interested in.

I also think you'd have a lot better luck getting Wolf to work with you than you would getting A'pexi to make changes to the PFC.

Sorry, I didnt know you could adapt the Wolf System to work with an FD and then a MAF etc etc. I agree with making Wolf work with you than Apexi, it was just an example that this isnt something that can be done by the enthusiast (at least I think) unless some really profesional guy is able. Jim please explain to me what the f*ck is the deal with the trailing, cause I read through 4 posts and like over 20 threads of BS, and flaming and bashing and I think my IQ just hit below 90 =?. I mean the only bad thing (so far) Ive heard about the trailing is that a bit of the exhaust gases from the combustion leaking into the incoming charge when the seal passes over thats it.
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