Turbo on RX-8

[Herblenny]

it got me thinking during my work morning...

I guess some of the down fall of maf system would be similar to what i had by using KN filter?? If your turbo's bad and oil in your intake, could cause MAF to be cleaned?? Or is their by pass to this??

Also, I'm also guessing there is some sort of limitation to maf?? ie volume of air (high boost/cfm) and turbo choices?? How would this maf would work for FD, low compression engine that you want to run 20lbs?? sequential?? Would sequential turbos cause problem as it transition from primary to both?? Just few things I was thinking..

I do however like the MAF idea (not thought about in years) and if it works, it will eliminate some tuners out there..

[Herblenny]

One more thing.. I remember.. I remember back when reading about BOV needing to recir. back to post MAF sensor?? Is this necessary if 8 would use MAF system??

[mazdamaniac]

There are several ways to figure out how much air is going into your motor. A MAF is the only method that actually measures it directly.
MAP-based systems need to compute the air mass by comparing pressure to temperature.

The OE PCM is very powerful. It has a different fuel map for each pair of gears and compensation tables for every possible operating condition.
It compensates for intake temp, coolant temp, throttle position, barometric pressure and vehicle speed. It even has compensation for time at a particular load!
It has different latency tables for each bank of injectors (to answer an earlier question, the Renesis has 3 injectors per rotor, instead of the old 2 injector setup; many of us are running the equivalent of a 500/1200 setup by splitting the secondaries into two staged groups for very fine fuel control in boost) and a progressive ignition dwell table that resolves down to .001ms.
There are separate throttle control tables for each gear to adjust throttle sensitivity independent of pedal position and "acceleration" tables that not only compensate for throttle opening rate, but can adjust for engine RPM delta.
There are tables to adjust when to be in open or closed loop for each gear and load level and trim for closed loop at different load levels.

Ignition control is equally dense with completely independent tables for the leading and trailing ignition, idle control matrices with inputs for temp, RPM, gear, vehicle speed, throttle position and delta and engine load.

The best part is that the PCM takes all of the operating condition data and compiles it into a single value - calculated load - that is then applied to the engine RPM to compute the target injector duration based on commanded target lambda.
You don't need to know how much duty cycle you need at a given RPM and boost level, you just tell it you want 11.5:1 at 6500 RPM and it does the rest.

If a Power FC is a knife and a Haltech or Motec is a scalpel, the OE PCM is a laser.

The MAF on the RX-8 is sitting in a 3.375" i.d. tube and driven on a 5v circuit. It has enough resolution to see .001 g/sec variations at idle (~6 g/sec) and still measure out to ~360 g/sec at full load.
For those doing their due diligence, that is about 47 pounds of air or 450 HP.
Realistically, I'd say the OE MAF is pegged at 420 crank HP.
Of course, you could just put it in a slightly bigger housing and rescale it.
Or, you could replace it with the MAF from a Cobra.

On a draw-through application, a boosted motor is going to vent after the MAF, so metered air is allowed out of the system and an over-rich condition may happen between shifts, etc.
In practice, this is negligible with proper tuning, but it can be completely negated by recirculating the BOV.

[Phoenix7]

Originally Posted by mazdamaniac

There are several ways to figure out how much air is going into your motor. A MAF is the only method that actually measures it directly.
MAP-based systems need to compute the air mass by comparing pressure to temperature.

The OE PCM is very powerful. It has a different fuel map for each pair of gears and compensation tables for every possible operating condition.
It compensates for intake temp, coolant temp, throttle position, barometric pressure and vehicle speed. It even has compensation for time at a particular load!
It has different latency tables for each bank of injectors (to answer an earlier question, the Renesis has 3 injectors per rotor, instead of the old 2 injector setup; many of us are running the equivalent of a 500/1200 setup by splitting the secondaries into two staged groups for very fine fuel control in boost) and a progressive ignition dwell table that resolves down to .001ms.
There are separate throttle control tables for each gear to adjust throttle sensitivity independent of pedal position and "acceleration" tables that not only compensate for throttle opening rate, but can adjust for engine RPM delta.
There are tables to adjust when to be in open or closed loop for each gear and load level and trim for closed loop at different load levels.

Ignition control is equally dense with completely independent tables for the leading and trailing ignition, idle control matrices with inputs for temp, RPM, gear, vehicle speed, throttle position and delta and engine load.

The best part is that the PCM takes all of the operating condition data and compiles it into a single value - calculated load - that is then applied to the engine RPM to compute the target injector duration based on commanded target lambda.
You don't need to know how much duty cycle you need at a given RPM and boost level, you just tell it you want 11.5:1 at 6500 RPM and it does the rest.

If a Power FC is a knife and a Haltech or Motec is a scalpel, the OE PCM is a laser.

The MAF on the RX-8 is sitting in a 3.375" i.d. tube and driven on a 5v circuit. It has enough resolution to see .001 g/sec variations at idle (~6 g/sec) and still measure out to ~360 g/sec at full load.
For those doing their due diligence, that is about 47 pounds of air or 450 HP.
Realistically, I'd say the OE MAF is pegged at 420 crank HP.
Of course, you could just put it in a slightly bigger housing and rescale it.
Or, you could replace it with the MAF from a Cobra.

On a draw-through application, a boosted motor is going to vent after the MAF, so metered air is allowed out of the system and an over-rich condition may happen between shifts, etc.
In practice, this is negligible with proper tuning, but it can be completely negated by recirculating the BOV.

so, the electronics are capable of reaching high HP goals. How about the motor itself? Why are the turbo applications yielding such little hp?

[mazdamaniac]

Originally Posted by phoenix7

so, the electronics are capable of reaching high HP goals. How about the motor itself? Why are the turbo applications yielding such little hp?

What do you mean? My "public" dyno at 9 PSI on my nice, extremely streetable turbo is over 315 RWHP.
With meth and a bit more boost, I made 20% more over that.
If someone wanted a 400 HP RX-8 and wanted to deal with the street performance liabilites of that (just like the 400+ HP club of RX- owners do), they could go to a GT3571 or similar and be there all day.

The problem is, most people don't want a high-HP car - they just want to brag about owning one.
A 400+ HP turbo rotary is annoying at best in stop and go traffic. Add summer to the mix and the sacrifices you make in vehicle comfort to make use of that power and you have a car that no one wants to drive anywhere but straight down the 1/4 mile.
RX-8 owners like their DSC/TCS, A/C and power seats. Did I mention the cup holders and the Bose 9-speaker stereo?

On a road course, I destroy cars that are supposed to outclass me by a considerable margin.
Watch as this "500 HP", single-turbo 300 ZX desparately tries to catch me on the 1/2 mile straight at Firebird Raceway as I hit nearly 150 MPH.
Then watch as I out-brake him!
VIDEO
The Cobra and the Saleen did the same thing, only I watched them spin behind me in the second corner after that straight.
Very sad. I almost spilled my latte.

[Whizbang]

i would have to say i am impressed with what the stock computer can do!

[mazdamaniac]

Originally Posted by Low Impedance

i would have to say i am impressed with what the stock computer can do!

I've only touched on a fraction of it.

I've tuned Microtech, Motech, Haltech, Electromotive, Apexi, GReddy, HKS and a few others - many of those on rotary motors and nothing comes close to the PCM in the RX-8.

Now, it would be nice to have some more AUX channels (you can use the VFAD, for instance, to trigger water injection), but that isn't really a legit complaint.
If I needed to control more aux channels, I'd throw a $60 used GReddy e-Manage blue on there just for that.

[85rx-7gsl-se]

Great info maniac. I enjoy this MAF info.

[Whizbang]

how adaptable could the computer be, with the proper tunning abilities? Could you use it on an earlier 13B engine with proper controls and related adapted and adjust everything accordingly?

[mazdamaniac]

Originally Posted by Low Impedance

how adaptable could the computer be, with the proper tunning abilities? Could you use it on an earlier 13B engine with proper controls and related adapted and adjust everything accordingly?

I don't see why not.
You would have to address the wiring harness in a serious way and have to adapt a few important sub-systems from the 8 (the anti-theft system is particularly invasive).
It should work, though.

I'd enjoy that challenge, actually.

I've contemplated putting an REW in the RX-8.

[Whizbang]

You might be able to mimic the signals that the anti theft produces to fool the computer.

But generally speaking, with some knowledge of systems, it might be cheaper than buying a standalone, albeit not easy.

Originally Posted by mazdamaniac

I don't see why not.
You would have to address the wiring harness in a serious way and have to adapt a few important sub-systems from the 8 (the anti-theft system is particularly invasive).
It should work, though.

I'd enjoy that challenge, actually.

I've contemplated putting an REW in the RX-8.

[Herblenny]

Thanks Mazdamania!

Now its making my head turn

Hmm.. I tought about MAF based few years back and never thought about doing it as I didn't see any aftermarket computer I saw.

So, what you are saying is its possible to run REW with RX8 harness and EMS, with larger MAF to run higher boost (or push more air)?? I'm already thinking about getting 4 secondary LIM and using this system.. What do you think?? How about 3 rotor?? Any MAF EMS that might be able to run that??

Sorry about all these questions.. Obviously I know too little to get myself in trouble... And far as tuning, Is it that easy, just putting in n value?

[mazdamaniac]

Originally Posted by Herblenny

Hmm.. I tought about MAF based few years back and never thought about doing it as I didn't see any aftermarket computer I saw.

So, what you are saying is its possible to run REW with RX8 harness and EMS, with larger MAF to run higher boost (or push more air)?? I'm already thinking about getting 4 secondary LIM and using this system.. What do you think?? How about 3 rotor?? Any MAF EMS that might be able to run that??

Sorry about all these questions.. Obviously I know too little to get myself in trouble... And far as tuning, Is it that easy, just putting in n value?

You could do that.
The tuning is ALWAYS as simple as putting in a value.
The trick is knowing that value.
You do have to get the calibration for the MAF and other sensors right, also.

[Herblenny]

Originally Posted by mazdamaniac

You could do that.
The tuning is ALWAYS as simple as putting in a value.
The trick is knowing that value.
You do have to get the calibration for the MAF and other sensors right, also.

how about sequential system?? Do you see any problem running it?? or solution to it??

I feel like now I'm just picking your brain... SO, I apologize if its wasting your time..

[mazdamaniac]

Originally Posted by Herblenny

how about sequential system?? Do you see any problem running it?? or solution to it?

You mean sequential turbo?
First, why?
Second, air is air. The motor doesn't care how it got there.

These days, the water-cooled, ball-bearing turbos are so fast and so powerful, there is no good reason for multiple turbos on a tiny motor like the rotary.
Now, a 7 liter V8 is a different story, but they do fine with a big BB turbo as well.