Boost Based vs Load Based - ECU Tuning - Episode 1 - Mazdaspeed 3

[@mituc]

Keeping everything in ambient equal, load and boost tuning are very similar or equal. If you have the load reference in your MAP, then 1.0 load is essentially 1BAR MAP (0 boost). Load 2.0 would be 2BAR MAP or 1BAR of boost (BOOST = MAP - BARO). But temperature is a very important parameter to account for, especially when talking summer versus winter, FMIC versus TMIC, DI versus PI+DI, and so on. The only true reason why you'd have to boost tune is when you have a parallel fueling system (PI in our case) and at that point you're basically only relying on the O2 sensor readings to make sure you've got the fueling right. And even in that situation up to the point where you cap the factory DI (by altering the MAF curve to trick the ECU into not spraying more fuel, since you rely on the PI at that point) you're more or less load tuning (and 100% load tuning in closed loop). With load based tunes you basically target a specific mass (NOT FLOW) of air. This will correlate with the amount/mass of fuel you need for that mass of air based on the AFRs you target. With boost based tunes you are targeting air flow or volume and then rely on MAF (and wideband O2) for the fueling, while with load tuning you are targeting air mass (as measured by the MAF and confirmed by the wideband O2 - pretty similar, eh?). The OEM ECU logic provides more means/tables/strategies to properly control load than boost, including per gear, while for the boost you only have to rely on tables that contain strictly limits as values: throttle close and fuel cut overall limits, limits per RPM and per throttle input which is also a general table, not a per gear table, is not correlated with IAT/ECT, and so on. What this means is also that when properly tuning a car to also grip in every gear, the by-gear control of torque is gone (to my knowledge I'm the only one tuning on this platform who properly implemented true boost/load-by-gear tuning, so all other tuners do not seem care, nor do their customers since most of them do straight line pulls anyway). Even on aftermarket ECUs you're basically tuning the fueling based on the estimated/calculated mass of air, not boost. Yes, you are tuning on MAP, but the injector pulse width will have corrections applied based on the IAT/BAT. The mass of air is a function of MAP, temperature and reference density, and depending on the engine RPM you can also calculate the mass of air entering the engine at a specific RPM based on the VE, and then you adjust the fueling based on exactly that, not only on the manifold pressure. The AFR is a proportion of masses, not volumes. Mass means load, boost alone means nothing. So the boost-based tuning on these cars is possible only because we have a MAF sensor ;) Even with PI systems you pretty much load tune even though you're kind of guessing (or enforcing) the boost based on the AFR readings (which is more or less another MAF), so it load-based tuning done backwards :) These are a few counter-arguments of load based tuning against boost-based tuning, at least for mid/big turbo cars which can hit the fueling limits of the factory DI, meaning they have the ability to produce enough torque to spin the wheels in 3rd and even 4th gear. For factory K04 cars... I tune them to 90 or more WGDC anyway... and let them make whatever they can make when they can make it (at least in terms of power, not also torque). Yet regardless of the tuning strategy used, in my opinion is a lot more important to get your fueling, timing and comp/limits tables right so that you can still have what to tune after each spirited drive or track day :)

[@WannabeTuners]

@mituc This is a great explanation. As I continue with this series of videos, I'll try and give my take on things. There's so much I don't know, so I really appreciate your knowledge :)

[@jasonc2948]

Your explanation of 'hybrid tuning' is how I've been managing things for the last few years. Works very smoothly with the multitude of throttle reduction strategies in the background. If I change turbo's or do any other airflow mods, I usually force open-loop during WOT to set the base MAF scaling and hit target AFR's, then reintroduce the WOT closed-loop functionality. Great video as always man

[@WannabeTuners]

@jasonc2948 That's exactly what I do as well when initially dialing in my Air Fuel Ratio. Since my 6th port AUX fuel setup isn't regulated, boost pressure within the boost piping affects the amount of fuel coming out of the AUX injectors. So having the Open Loop fueling enabled allows me to get my AFR as close as I can to where I want it during a 4th gear WOT pull without the ECU correcting. Once I'm 'happy' with the AFR curve in my datalogs, I'll re-enable Closed Loop fueling corrections to allow the ECU to correct for any variances. I haven't been using any load caps for a while now (ever since I went BNR S5) because boost control is so much better now with the EWG. The other thing I did with AUX fuel is I started the ramp in of additional fuel at a slightly higher MAF voltage. That way boost pressure is already higher when AUX fueling initially kicks in, and I won't have as much of a rich dump of fuel in 1st and 2nd gear which naturally achieve lower boost.

[@jasonc2948]

@@WannabeTuners very interesting. I had a similar experience tuning Methanol. Using a single 1000cc nozzle spraying 100% meth from 12psi would see afrs dip down into the 10's, then rapidly recover to the target 11.7. To be honest it didn't really feel like it was bogging the car down, but raising the start point to 15psi really helped. Now I'm just tuning the car to the limit of timing and IDC on 98RON, then adding 325cc of meth for cooling only and letting closed loop self correct for that. I feel I've pushing my luck with loads of meth and high boost for long enough haha

[@WannabeTuners]

@jasonc2948 That's awesome, I remember reading somewhere (I think it was on the old forum) that the ECU can only correct the AFR so much at WOT, and that the GEN 2 Speed 3 can correct more precisely than the GEN 1. I can't remember the exact percentage of maximum correction though. What you're describing with Meth Injection is what I was doing on the K04. My issue was, that at the time I wasn't aware of the ability to tune a true AFR/MAF calibration by enabling true open loop fueling via reducing the load values in the 'Closed Loop Load Limits A, B, and C' tables. So whenever I would do a MAF calibration, I wasn't truly dialing it in, as the ECU was already correcting the AFR.

[@jasonc2948]

@@WannabeTuners I think this is the trap everyone falls into, as none of the online guides (cobb/versa) explain to do this. I own a 6 now, but when I used to tune my gen 2 3, the WOT afrs would show typical closed loop feedback instability if the base calibration was too far off the target. I notice my 6 doesn't try as hard to correct if it's too far off, which aligns with what you said.

[@rynoPelser-e7p]

Thanks for the good learning video.every bit of information helps😊

[@WannabeTuners]

@@rynoPelser-e7p Glad you liked it :)

[@ArmaturaRecords]

Thanks, enjoyed this type of video. Good thing my tuning with Justin came over the fall-winter phase. ^_^

[@WannabeTuners]

@ArmaturaRecords Happy to hear :)

[@31Ramble]

Nice!