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I'm getting into surface-level map editing and one thing I haven't been able to understand is the effect of the Calculated and Desired torque maps on fuel calculations and other values.
This stems from the fact that I have a map where the AFRs I'm getting are much, much lower than the desired AFRs. This map has very altered torque map values, ranging from 0-60. In a stock/barely edited tune the AFRs are always at the desired AFRs, +/- .02 when stable, LTFT 0% and STFT mostly -5% to +5%. I believe this discrepancy to be caused by the torque map as everything else is pretty similar to maps with accurate AFRs.
I have some intuition on how it might affect it but I'd rather get answers before I jump to conclusions.
I have also verified my MAF scaling.
This is not a torque-based ECU. What tables you have in there with "torque" in their name... or tied to the throttle body... don't have anything to do as target values. They are used (solely, I believe but no proof) for traction control limiting and for back-up cases where the MAF is deemed faulty and thus TPS is used to compute an airflow/load figure. This rather antique ECU doesn't work like modern 2010-2015 ones where the driver requests a torque then the ECU works its magic and deems how much throttle opening is needed and how much boost... if it even had any to play with.
So to answer your queston(s) which you never asked:
1) don't touch those maps and revert them to stock for no one knows EXACTLY what they do and when - people are doing twice the stock power while leaving those stock.
2) bad afrs stem from the VE table, bad MAF circuit, poor MAF setup, poor MAF scaling, faulty injectors, even faulty front O2 sensor though that manifests clearly, weird targets, weird everything
There is also closed loop fueling where you'll run nearly stoich targets, and then there's open loop where all hell breaks loose and whatever it is you tuned with act out as such. NO limiters either way.
Thanks for the information! I've been struggling to understand that and the lack of info online didn't help. I still think it's strange that my AFRs are really off target in that tune because in the stock tune it hits target AFRs just fine. This might be because I was in closed loop though as I wasn't revving high or putting it under heavy load since it was basically stoich. I'll "disable" closed loop and do some more logging and see what I can figure out.
Just got back from doing some logging, very different data now that I'm in open loop 90% of the time. Under load it's rich by ~.2 under lambda and while cruising it's pretty lean comparatively. Which should I change first, MAF or VE? It's my understanding that each engine (theoretically) should have the same VE, so should I tune the MAF table first? If the VE table is wrong how would I tune the MAF and vice versa?
I assume you're using one of those "dyno proven" off the shelf maps that versatune provides. There is no such thing as premade tune, because tuning is all about getting YOUR individual car to do what those target tables want it to do. OEMs do it by leaving a tiny bit of power to be had in exchange for getting millions of cars going at 90-95% of their maximum. In the case of the RX8 I'd say mazda got 98% out of the stock tune.
You want to tune, you start with your stock tune and go from there. But keep in mind you're chasing the last 2%. Can't think of any other car that responds so poorly to a tune on a stock car.
Last edited by ciprianrx8; 09-13-2023 at 01:43 AM.
Stock intake system, and you've already cleaned your MAF? Then probably VE. Realistically, you could use VE either way, just be aware that it won't be applicable to other RX8s as you'll be effectively building in whatever your current MAF scaling is into the VE map. That said, apparently the stock VE map is a bit **** and the closed-loop stock functionality bandaids over it a bit, so from my understanding it will naturally run poorly when forced into open loop at idle anyway.
Also have a look in my sig if you wanna try deleting all of that abstraction regarding the desired torque stuff.
I assume you're using one of those "dyno proven" off the shelf maps that versatune provides. There is no such thing as premade tune, because tuning is all about getting YOUR individual car to do what those target tables want it to do. OEMs do it by leaving a tiny bit of power to be had in exchange for getting millions of cars going at 90-95% of their maximum. In the case of the RX8 I'd say mazda got 98% out of the stock tune.
You want to tune, you start with your stock tune and go from there. But keep in mind you're chasing the last 2%. Can't think of any other car that responds so poorly to a tune on a stock car.
I'm aware of this, which is why I'm getting into this in the first place. I want the tune to fit my car better so as to run better, I'm not really trying to squeeze out any extra power because honestly I don't need it. Another reason is I'm just trying to learn for the future and this kind of stuff interests me a lot.
Stock intake system, and you've already cleaned your MAF? Then probably VE. Realistically, you could use VE either way, just be aware that it won't be applicable to other RX8s as you'll be effectively building in whatever your current MAF scaling is into the VE map. That said, apparently the stock VE map is a bit **** and the closed-loop stock functionality bandaids over it a bit, so from my understanding it will naturally run poorly when forced into open loop at idle anyway.
Also have a look in my sig if you wanna try deleting all of that abstraction regarding the desired torque stuff.
It hasn't been too long since I cleaned my MAF but I could try cleaning it. I've already written a spreadsheet to automatically calculate a corrected VE table deviated from the stock table based on deviations from desired and actual AFR, I just need to get more logs for higher accuracy before I implement it into a tune.
If anyone cares, I've created a spreadsheet that (in theory) should make a corrected VE map. Dunno if this works but it looks cool so I'm gonna run with it. Don't have enough logs to put it into practice yet.
Tell me you don't get how this ecu works without telling me you don't know how this ecu works. It won't blow up if you touch the VE table. Hell some even make the target AFRs table look horrible instead of touching VE.
In a few words... the ecu comes up with an amount of fuel it thinks it needs to inject in order to do a certain AFR. Surprise surprise that number may not match up, so you multiply that value with whatever is in the VE table. For series 2 they get 2 ve tables but I don't know why or when is either used. Messing with injector scaling, maf scaling, target AFRs, adjusting VE are all methods of getting to the same result: a certain AFR at a certain load and rpm. It's just that some would scratch their left ear with their right hand snaked around the back of their head.
09-12-2023, 12:07 PM
Understanding Calculated and Desired Torque
