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

t-von

iTrader: (8)

You know Stephen that sounds like a really good idea. You may very well be on to something if these plugs prove themselves.

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

FDNewbie

iTrader: (10)

Stephen,

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

~Ramy

t-von

iTrader: (8)

Anyone know why Mazda never decided to use an air flow meter? This could have helped save a few engines that were improperly moddified.

Fatman0203

Like a MAF sensor? It probably would have been expensive since they may have needed 2 for each turbo. Just my guess.

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.

jimlab

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.

FDNewbie

iTrader: (10)

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??

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.

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.

FDNewbie

iTrader: (10)

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.

Quote:

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.

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?

Quote:

Well it adds an additional sensor, at any rate.

Quote:

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.

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.

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.

Quote:

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.

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)??

Quote:

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.

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)

jimlab

MAF-based engine management systems do have a MAP sensor, even for naturally aspirated engines.

FD3SR1

not to be an *** just wondering, mazda put two spark plugs per rotor for a reason why would getting rid of half your spark help you? im sure mazda put lots of research into it when they made the car and if they thought it would give them any benefit im sure they would have done that from the factory. keep us informed on how well it works!

Fatman0203

Ahh i see, thanks for the heads up.

FDNewbie

iTrader: (10)

Jimlab, any take on what I said/was proposing/hypothesizing??

Not to be ****, but this is like the 4th thread about this device, and the answer to your question has been covered in pretty much each one...in detail. Give 'em a quick look-see, and you'll find the answer.

Michael Filippello

"Has anybody done any testing regarding running colder TRAILING plugs than normally thought neccessary. It would also help to increase split under higher rpms and boost. Sure maybe less split might mean a couple HP difference but this is better than eliminating the plugs all together. As I said earlier, you have to give up a little to be safe. It also may mean the neccesity of an ignition amp on the trailing plugs in order to light the spark due to the cold heat range but this is a pure mechanical/electrical problem that can be solved."

As long as we are theorizing and hypothosizing, anybody have any ideas regarding my theory above. It seems like a far simpler solution than some others. I'm not saying that MAF is not a good idea. This is a different topic all together. It would definately make tuning easier and safer once set up. I'm just reffering to the preignition problem stemming from the trailing plugs.

Mike

FDNewbie

iTrader: (10)

Mike,

I feel what you're saying...and I think that's definitely more in line w/ the purpose of this thread.

I'm thinking of starting a thread about the MAF, and getting some concrete ideas and points regarding it...because, who knows...maybe it might really lead somewhere.

What do you think?

FDNewbie

iTrader: (10)

Stephen, Jim, Fatman0203, t-von, and anyone else who's interested, I started another thread specifically about switching from speed density-based system to an MAF sensor based system. I really hope we can continue this and get something out of it, because I believe it's very promising...

https://www.rx7club.com//showthread....hreadid=324071

~Ramy

teamstealth

*Sigh* still no dyno jason?

ZeroBanger

Im Running 12:1 a/f on my car. about 3 weeks ago I ran 89 octain with my water injection kit to see what would happen, no problems
I would never have attempted that without water injection, but it was fun. I would love to run 13.0 afr..but I dont want to risk a clogged nozzel, blown fuse or running out of water.

Michael Filippello

Zerobanger, there is no advantage to running 13.0 afr's. It is well documented that max power is achieved between 12-0 and 12.5 afr, depending on engine type. I have been reading all these posts and nobody brings this up. They keep talking about running all these super lean afr's for no reason. All this does is raise egt's and make less optimal power.

That being said. I think water injection and a colder heat range on the trailing plug is more than enough to stop detonation and achieve the highest HP available with ones mods. This assumes propper tuning in regards to timing.

As you said, you can either run same boost/less octane gas. Higher boost/ same octane gas. Just depends on your goals. You also get those advantages with water injection such as cool egts and clean internals.

Mike

FDNewbie

iTrader: (10)

Mike,

From what I understand, the leaner you run, the more power you make, but also the more dangerous it is to cause detonation.

I guess you're saying there's an upper limit to just how lean you can run and make max power, and after that you actually lose power?

It makes sense to have upper and lower limits...but could you explain how/why this is the case? (Eg why after a certain point, running any more lean would make less power)?

Thanks
~Ramy

Fatman0203

One more thing Mike, doesnt leaner AFRs give you more torque or is this some myth?

Michael Filippello

Here is some useful reading that is put together well. This should explain a lot. I am going to reread it again myself.


http://www.waterinjection.info/docum...epaper/why.htm


Mike