Desired torque implications on tuning process

Tuning discussion for all first generation Mazda RX-8 (2004-2008)
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zenvirzan
Posts: 15
Joined: May 6th, 2022, 3:52 am

Desired torque implications on tuning process

Post by zenvirzan »

Hi all, I'm currently trying to understand how the Desired Torque table works.

Can anyone confirm if this is how the calculations are applied? Looking at the table axes, this is the only flow I can think of that makes sense.

IRL APP -> Throttle Duty table = "Requested" Throttle Position (degrees)
"Requested" Throttle Position -> Desired Engine Torque table = Virtual "torque" [and this is an abstract value, not calculated using any sort of closed loop calculation etc, simply used as an index in the next lookup?]
Virtual "torque" -> Relative Throttle Plate Position table = Actual Throttle Position

I'm assuming changing the Desired Engine Torque table has no impact on fuelling or ignition on its own, but is just used as an index for other tables?

How does the Calculated Engine Torque table affect things? Is it a cruise-control thing, considering there is no APP or TPS in the axis?

Assuming this is the case, assuming I had the time to spare, to do a full tune to the best of my ability, would it make the most sense to (ignoring ignition timing tuning for the minute):

1. disable closed loop (zero the Closed Loop Max RPM value)
2. modify the Throttle Duty table to ease-in to linear (similar to stock)
3. Flatten the Desired Engine Torque table values to be linear (from 0 to x, x can be whatever)
4. Modify the Relative Throttle Plate position table axis to be from 0 to x as set in the Desired Engine Torque table and set the values to be linear from 0 to 84
5. Set a flat AFR in the AFR table (eg. 13.8 or 12.5) for tuning purposes
6. Tune using the VE table to make the actual AFR match the intended AFR as close as possible

EDIT: as Walle has pointed out, it may be more effective to utilise the trims + the actual AFR, rather than use the possibly erroneous "target AFR" value. There is also no requirement to do step #5, however I would personally just to make the math easy.

EDIT 20230110: actually using trims is probably not a good idea as it targets 14.7-15.2 (based on the Closed Loop offset table) which isn't safe for high load. Honestly I'd suggest setting a flat AFR across the board in the AFR tables, then comparing the actual AFR to whatever you're aiming for. Then use

Code: Select all

ActualAFR/TargetAFR = multiplier
and use that to multiply into your VE table

After that process is over, the AFRs can be tweaked in the AFR table to go for maximum power as usual.

Steps 3 and 4 should effectively disable the Desired Engine Torque table if my understanding is correct to reduce the variables at play, making the TPS correlate to the APP as specified in the Throttle Duty table?
EDIT 20230110: yes as per my thread here it is safe to make the desired torque and throttle plate position tables linear as long as calculated load is updated too. I haven't tried it without updating calculated load.
Last edited by zenvirzan on January 9th, 2023, 4:52 pm, edited 2 times in total.
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wcs
Posts: 61
Joined: May 12th, 2021, 12:46 am

Re: Desired torque implications on tuning process

Post by wcs »

Good questions.
Wish I could add some input.
But I'm interested in your post.

I don't know if there is anything I could do or try here to maybe help validate or test ideas?
Walle
Posts: 51
Joined: August 29th, 2021, 7:27 pm

Re: Desired torque implications on tuning process

Post by Walle »

step 5 and 6 can be done irrelevant. VE table is very rough in OEM config. viewtopic.php?f=25&t=4316&p=16161#p16161 read my post/answer in this topic. :beertoast
zenvirzan
Posts: 15
Joined: May 6th, 2022, 3:52 am

Re: Desired torque implications on tuning process

Post by zenvirzan »

Thanks Walle, I'll keep that in mind. Comforting to know that even stock it wasn't perfect.

Still curious if anyone has tried effectively removing the Desired Torque table as mentioned in the OP--I have starting issues currently and it really didn't like it when I tried it, but I also didn't try very hard (fairly sure it was due to my throttle plate not being open far enough at idle in the relative throttle position table). I'm more worried about if it'll do any weird ignition timing stuff as a byproduct.
Walle
Posts: 51
Joined: August 29th, 2021, 7:27 pm

Re: Desired torque implications on tuning process

Post by Walle »

but why would you mess with torque tables ? imho they are also used when ESC , ESP and TC are engaged. could make for a very unpredictable car.
zenvirzan
Posts: 15
Joined: May 6th, 2022, 3:52 am

Re: Desired torque implications on tuning process

Post by zenvirzan »

After some further experimentation, it looks like it works as expected! I'm super happy with the outcome, I think this may change the way we tune RX8s from now on! I know I'd never go back :bouncinggrins

See my new thread with the example tune for more information!
tophe88
Posts: 29
Joined: May 6th, 2022, 8:31 am

Re: Desired torque implications on tuning process

Post by tophe88 »

VE table is volume efficient ?

EDIT: as Walle has pointed out, it may be more effective to utilise the trims + the actual AFR, rather than use the possibly erroneous "target AFR" value. There is also no requirement to do step #5, however I would personally just to make the math easy.

How you do for use trim ? please
zenvirzan
Posts: 15
Joined: May 6th, 2022, 3:52 am

Re: Desired torque implications on tuning process

Post by zenvirzan »

tophe88 wrote: January 9th, 2023, 10:42 amHow you do for use trim ? please
To use the fuel trims, you will need to leave Closed Loop enabled. Simply hold the engine at the RPM and Load level you're tuning, and let the fuel trims balance themselves out. Once they've stabilised, update the VE table accordingly.

eg. Long term: 2% Short term primary 6% Short term secondary: 1% = Multiply the relevant VE table cell by 1.09

This is only safe for light load though, as by default it will target 14.7-15.0 which isn't safe for high load tuning. I'll update my first post advising away from it.
tophe88
Posts: 29
Joined: May 6th, 2022, 8:31 am

Re: Desired torque implications on tuning process

Post by tophe88 »

zenvirzan wrote: January 9th, 2023, 4:41 pm
tophe88 wrote: January 9th, 2023, 10:42 amHow you do for use trim ? please
To use the fuel trims, you will need to leave Closed Loop enabled. Simply hold the engine at the RPM and Load level you're tuning, and let the fuel trims balance themselves out. Once they've stabilised, update the VE table accordingly.

eg. Long term: 2% Short term primary 6% Short term secondary: 1% = Multiply the relevant VE table cell by 1.09

This is only safe for light load though, as by default it will target 14.7-15.0 which isn't safe for high load tuning. I'll update my first post advising away from it.
Thank you for yout reply. And the VE table is ?
mituc
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Re: Desired torque implications on tuning process

Post by mituc »

tophe88 wrote: January 11th, 2023, 8:33 am Thank you for yout reply. And the VE table is ?
Volumetric Efficiency.
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
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