Does the RX-8 employ just a MAF sensor, or does it have a MAP sensor as well? Which one helps the ECM adjust fuel, timing etc. better?

Okay. After checking my trusty service manual, the RX-8 doesn't employ a MAP sensor. There is a barometric pressure sensor, though. Are the two analagous?

Okay. After checking my trusty service manual, the RX-8 doesn't employ a MAP sensor. There is a barometric pressure sensor, though. Are the two analagous?

Indeed, no MAP. As the air measurement strategy is MAFS based, it doesn't need one.
Both most probably use the same sensor technology. And that's it for the analogy.

Well, since mass air flow is temperature and pressure dependent, it shouldn't need a MAP. I think the barometric pressure sensor helps determine what the mass air flow is. Thank you for your help IKnowNot'ing.

Well, since mass air flow is temperature and pressure dependent, it shouldn't need a MAP. I think the barometric pressure sensor helps determine what the mass air flow is. Thank you for your help IKnowNot'ing.

According to my Ford EEC5 training book, BP is used in the different strategy modules for :
- crank fuel
- desired mass air flow through the idle air by-pass valve
- switching to altitude tables for EGR and spark advance
- torque converter lock-up
- shift chedules
- calculation of theoretical air charge at WOT
- self test
and I believe it also affect electronic throttle body progression.

Real-time analysis give me a headache :(.

MAP is for forced induction.

Okay, so why is a MAP for forced induction?

MAF is and Air Flow sensor....MAP is a pressure sensor

I don't think anyone is going to clarify this :confused: :(.

Just two different ways of determining the same thing: how much gas to mix in with the air going into the engine (at the most basic)

MAF measures the airflow passing through the MAF (Mass Air Flow) sensor and the baro pressure to calculate the amount of air being ingested by the engine, MAP uses the pressure inside the intake manifold (Manifold Absolute Pressure) and some assumptions/rules about the volumetric efficiency of the engine along with the RPM to calculate the same.

One advantage of MAP is that there's no (potentially) restrictive sensor that the air must travel through since all you need to do is measure the pressure in the intake. MAF is good in that if you make an adjustment to the engine which changes the VE of the engine, then it will compensate.

MAP is not solely relegated to FI cars - the 2nd gen turbo'd rx7's used a MAF system, the 3rd gens used MAP - both were forced induction.

This is somewhat a simplified description, however I believe it touches the main points.

Simon.

Manifold Absoulte Pressure.
Well you can use a MAF for FI but I think MAP is better for a few reasons. A MAP system does not have the MAF flapper restriction (FI hates restriction) and is better for FI systems that have the blow off valve venting to atmosphere. If you vent to atmosphere with a MAF system you would get un-metered air into the intake charge, or when the BOV operates you would have air that was metered by the MAF escaping and not entering the combustion chamber thereby wreaking havoc with the ECU's fuel tables.
Understand? I don't know how well I explained it?

For example, if I get a turbocharger, would I have to replace my MAF with a MAP? Can I keep both? I am aware of how both work, I was just curious if the stock RX-8 had one (a MAP). Obviously, I didn't consult my service manual before I wrote this.

Until you exceeded the flow capability of the MAF sensor you would not neccessarily need to change it if you got a turbocharger. You would likely need to put a manifold pressure sensor in the system to assist the ECU for things like advance/redard under boost and so forth, however it would play a lesser role in the engine control than a manifold pressure sensor in a MAP based system. Additionally the ECU would need fuel maps for a higher flow rate and so forth that putting a turbo on would produce.

I would be surprised if there wasn't a manifold pressure sensor on the car already - the 2nd gen rx7 (even the non-turbo version) had one in addition to the MAF sensor - it's used to help calculate engine load and stuff like that. The question would be: is it capable of measuring boost? On an NA car, having a manifold pressure sensor that could read boost and vacuum would be a bit of a waste since you'd never see much/any positive pressure in the intake manifold.

Simon.

Thank you sferrett. You are right; the RX-8 doesn't have a MAP sensor. The closest is the BARO sensor. So I would have to get a MAP sensor if I decided to go with forced induction? Electronics are a mixed blessing :confused:. Thank you everyone for answering my question :).

For example, if I get a turbocharger, would I have to replace my MAF with a MAP? Can I keep both? I am aware of how both work, I was just curious if the stock RX-8 had one (a MAP). Obviously, I didn't consult my service manual before I wrote this.

You'd need a MAP sensor input if you wanted to vent to atmosphere and hear that groovy cool PSSSSSSTTT when you shift :cool: or if you wanted to run boost over 6 psi reliably.
I switched to a MAP sensor and fully programmable ECU when I boosted my Miata - works like a charm. And yes my Miata will spank my 8 :eek:

MAP is for forced induction.

Not true. There are numerous NA engines running a T-MAP sensor (Manifold Air Temp and Pressure sensor) for air charge calculation. My previous Audi V6 2.6L was one of them. I know of a lot small European cars who do too. A T-MAP is cheaper than a MAFS.

...MAF flapper restriction ...

There haven't been flappers on MAFS any more for ages. They're all hot wire or hot film now with very little restriction.

Your comment about the blow-off valve vented to atmosphere and unmetered air by MAFS is very pertinent.

shelleys_man_06, another point to keep in mind when going to FI, is to prevent the triggering of diagnostic faults. For example, if I refer to the manual, re MAFS, you must not get beyond 17.2 lb/min under 2000 rpm and the MAFS signal cannot go beyong 5V. Also the difference between IAT and ECT cannot exceed 104°F (that's IAT > ECT of course).
Even if you meet these requirements to avoid a CEL, you still might enter into limp mode if the PCM strategy has authority, for example, to check actual MAFS readings versus expected, theoretical MAFS values.

This must be a good reason why the aftermarket is having such a hard time with high-boost applications for the RX-8, perhaps the 350Z, too. MAP and MAF are two different things, but they share a similar function: helping the PCM figure out fuel delivery, timing, etc. I would suppose a MAF would suffice under low-boost applications, but when the knob is turned up, the MAF can create a restriction in the intake tube, which can confuse the PCM, no? Suppose I run FI on 17+ psi (no metric units :mad: ). Is it recommended that I replace my existing MAF with a MAP, in order to help the PCM? The change-over seems quite a challenge, but I think it can be done. It will be a while before we see anything close to what the FD guys are doing, in terms of power.

This must be a good reason why the aftermarket is having such a hard time with high-boost applications for the RX-8, perhaps the 350Z, too. MAP and MAF are two different things, but they share a similar function: helping the PCM figure out fuel delivery, timing, etc. I would suppose a MAF would suffice under low-boost applications, but when the knob is turned up, the MAF can create a restriction in the intake tube, which can confuse the PCM, no? Suppose I run FI on 17+ psi (no metric units :mad: ). Is it recommended that I replace my existing MAF with a MAP, in order to help the PCM? The change-over seems quite a challenge, but I think it can be done. It will be a while before we see anything close to what the FD guys are doing, in terms of power.

Yeah, taking the MAFS out is really going to help the PCM!! It's going to help it trigger a massive 'limp' mode. Well you'll still be able to drive at 50 km/h :D to the dealer.

Stick to the MAFS, make sure signal output is within the range the PCM is expecting (see manual / diagnostic), and add a MAP and an auxiliary ECU (Canzoomer II?) to control fuelling under boost.

Yeah. Limp mode is a bad thing :o.

In short, are MAP and MAF similar to ammeters, ohm-meters, and voltmeters in circuits? They, ideally, are supposed to only take readings without restriction, no? We shall see what happens to this car in the future :).

Kind of I suppose..

A MAF could be equivalenced to an ammeter measuring the current through the circuit (airflow) directly

A MAP system could be equivalenced to using a voltmeter to measure the voltage drop across a circuit (air pressure) and therefore inferring the amperage (airflow) by having a known circuit restistance (the volumetric efficiency) and doing the math.

Simon.

Thank you sferrett for the clarification :).

Both my turbo Miata and turbo MX-3 used the stock MAF (no MAP) and open BOVs with no problems, sags, limps, idle issues or the like.

It is all in the tuning and how you handle the fuel delivery on throttle closing.

The real issue is what to do when the MAF reaches its limits. I clamp mine since the added fuel for the added air is controlled by a piggy-back system so there is no need to alarm the ECU.

On the Miata, I draw through the MAF. On the MX-3, I blew through it. It is all about logging, adjusting and loging some more.:p

To the computer!

What about getting a bigger MAF, like the Lightning boys do? What effect does that have?

What about getting a bigger MAF, like the Lightning boys do? What effect does that have?
The difficulty is the weird, non-linear response of Mazda's MAFs. You would have to match it exactly to get the smooth throttle response that the OEM MAF affords the car.
The precision of the tuning with a MAF is the main reason Mazda uses them.

What about getting a bigger MAF, like the Lightning boys do? What effect does that have?

You would have to know its MAF response characteristic, measured on a flow bench with the Mazda RX8 airbox and intake spout. And include this information into the PCM calibration :eek: .

OR : use an auxiliary ECU that would convert the new MAFS signal into a signal corresponding to the original MAFS fed to the OEM PCM. When the MAF gets above what was the upper limit of the original MAFS, the auxiliary ECU would limit it at just below 5 volts (corresponding at max MAF with the original MAFS) for max usage of the existing injectors, and the auxiliary ECU would drive additional injectors under boost, based on the new MAFS signal and also on a new MAP signal (for better boost control).
You still need to now the characteristics of the new and original MAFS with airbox and intake spout (OEM or your own design).

You would have to know its MAF response characteristic, measured on a flow bench with the Mazda RX8 airbox and intake spout. And include this information into the PCM calibration.

I think using the stock MAF is just fine :). I don't think there is any reason to mess around with the current MAF, unless it starts messing around. In addition, I hear that rotary engines are worthless on flowbenches. Is there any truth to this?

I think using the stock MAF is just fine :). I don't think there is any reason to mess around with the current MAF, unless it starts messing around. In addition, I hear that rotary engines are worthless on flowbenches. Is there any truth to this?

It's just the MAFS and intake that needs to be flow tested, not the engine!!

BTW - the RX-8 MAF puts out just under 4vdc at 9000 RPM and WOT.
The FSM indicates that it is a 5vdc MAF, so it would appear that, based on the linearity of its response as indicated in the data logs I have collected in my endeavors with the E-Manage, we still have up to 20% of the MAF's capability left for "future use" (i.e. - FI).

I hear that rotary engines are worthless on flowbenches. Is there any truth to this?

uh, how on earth would that be true??

I think using the stock MAF is just fine :). I don't think there is any reason to mess around with the current MAF, unless it starts messing around. In addition, I hear that rotary engines are worthless on flowbenches. Is there any truth to this?


that depends on the MAFs you have. some appear to be below par. nothing more to say now. but look for a full write up on the MAFs in the next month or so. i am still gathering info.

Thank you guys for the info :). I look forward to the write up Zoom44.

well YOU might find it uninteresting- i am pretty much a layman so there wont be many equations in it :p but it will be as comprehensive as i can make it within time constraints.

LOL. I'm done with engineering BS for the summer. I prefer to read anything but equations for once. In fact, I'm currently reading Corky Bell's Maximum Boost: Designing, Testing and Installing Turbocharger Systems. It's a good read for those who want to get into the business of turbocharging. I'm still trying to get Kenichi Yamamoto's book Rotary Engine. No luck though :(.

What is the DBW system?

Drive By Wire is too generic as some day steering and braking might be 'by-wire' too.

ETC (Electronic Throttle Control), EGas (mainly German though), E-Throttle....

Charles, was that the ETC supply voltage that was limited to 2.2V or signal voltage to the PCM?

LOL. I'm done with engineering BS for the summer. I prefer to read anything but equations for once. In fact, I'm currently reading Corky Bell's Maximum Boost: Designing, Testing and Installing Turbocharger Systems. It's a good read for those who want to get into the business of turbocharging. I'm still trying to get Kenichi Yamamoto's book Rotary Engine. No luck though :(.

For sure, with Corky Bell your brain should be at rest (I have the his supercharger book).

Yamamoto's book : I know where there is one for sale at a very expensive price. Maybe we could all buy it together (some other poeple are looking for it), and then not copy it and not distribute the copies...

I'm going to borrow Corky Bell's supercharger book on July 31, when I have to return my book to the library. Libraries are awesome :D.

Well, since we're on the subject of MAF and MAP, I wanted to add that most of the turbo kits that are coming out (I hear there are more than three :D ), run off of the MAF. No use for a MAP, just like MazdaManiac said :). Okay, this is great and all, but will the MAF suffice under high boost, say 14+ psi?

I don't think adding a MAP sensor along with a FI system would be a problem...more of an issue may be having to keep the MAF around to keep the stock ECU happy, assuming piggy-back a/f control. Given how the stock MAF seems to react poorly to aftermarket intakes, I shudder to think what it might do with pressurized air flying by.

jds

Well, since we're on the subject of MAF and MAP, I wanted to add that most of the turbo kits that are coming out (I hear there are more than three :D ), run off of the MAF. No use for a MAP, just like MazdaManiac said :). Okay, this is great and all, but will the MAF suffice under high boost, say 14+ psi?

MAP is absolutely needed for close loop boost control, and can be useful for fuel compensation. No MAP means no close loop boost control :eek: = dodgy kit!

Wouldn't the MAF be placed before the compressor, so that it would never see boost?

Wouldn't the MAF be placed before the compressor, so that it would never see boost?
In many systems (like my Miata), it is.
However, this poses new problems stemming from the measurement of air going into the turbo but not necessarily going into the motor.
The ECU will see a volume of air (at ambient temperature) go by, but most if not all of that air gets heated and then expended through the BOV. This causes a huge over-rich situation between gears.
The Miata seems to live with that OK. I don't know that the RX-8 will do as well since its programming is much tighter.

Good point Jeff :). Will the RX-8 ever see high boost :(?

Good point Jeff :). Will the RX-8 ever see high boost :(?
Not in its stock form.

As it is built, there will be no forced induction systems that will safely and reliably introduce more than 7 PSI into the Renesis.
Once someone completely replaces the OEM ECU, you may see systems go as high as 11 PSI, but they will yield very short engine lives as I don't think the side seals will survive the pressure.

That said, I don't think the Renesis really needs "high boost".

To stay in line with its currently high level of refinement, I don't think the RX-8 would be a fun car with more than 300 HP at the wheels as produced by a quirky aftermarket forced induction solution.
100 HP over stock (which is what you would get wit a well developed FI system running 6 PSI) puts you right there.
I'd be overwhelmingly happy at 6 PSI. That would be the third zoom.:D

Then again, I turned down the boost on my Miata to make it more responsive and refined. I keep it around 9 to 11 PSI, even though I tuned it for 14 PSI.
At 14, it was just out of control at WOT, so what is the point?

Indeed. It's too early to tell how the car's characteristics change with power adders. Personally, I'm insane, which is why I am interested in a 360+ rwhp RX-8. Of course, I might lose normal driveability with a such power. However, I believe there is a way for power and comfort to coexist. It's all in the tuning. The only problem I am faced with is getting all the sensors to get the right data. But before I can even do that, the PCM needs to be cracked, badly. Thank you for your insight guys :).

Wouldnt the overrich condition in your miata caused by air venting while switching gears be cured by plumping the bov back into the intake?

Wouldnt the overrich condition in your miata caused by air venting while switching gears be cured by plumping the bov back into the intake?
It is plumbed back into the intake - on the first stage.
But that is only good up to 2 or 3 PSI. After you pass that, you need to vent it to the atmosphere or you will stall the compressor.