shelleys_man_06

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

MazdaManiac

iTrader: (3)

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.

IKnowNot'ing

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 .

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).

shelleys_man_06

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?

IKnowNot'ing

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

MazdaManiac

iTrader: (3)

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).

wakeech

uh, how on earth would that be true??

zoom44

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.

shelleys_man_06

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

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.

shelleys_man_06

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 .

MazdaManiac

iTrader: (3)

What is the DBW system?

IKnowNot'ing

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?

IKnowNot'ing

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...

shelleys_man_06

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.

shelleys_man_06

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?

bureau13

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

IKnowNot'ing

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

shelleys_man_06

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

MazdaManiac

iTrader: (3)

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.

shelleys_man_06

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

MazdaManiac

iTrader: (3)

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?

shelleys_man_06

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 .

shawnio

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

MazdaManiac

iTrader: (3)

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.