Do to recent events I am making this data public and not specific to my Facebook page. This is our findings on our ‘18 Mazda3 2.5 Skyactiv. We have substantial data and multiple dyno runs to support this conclusion along with data from two separate tuners.
So here is data on our cars ECU. This seems to be a very miss understood concept. In this reading you will see a few traits.
First our cars absolutely adjust for fuel grade. It’s not just a little adjusting either.
Secondly bolt ons do add power without a tune. Our ECU actually self tunes fairly well to having bolt ons.
Purchased our car and told them explicitly to not put fuel in it. Car had less then a gallon of regular when I picked it up. Car had 12 miles on it and generally takes 50 or so miles to set fuel and timing trims.
Once I picked it up I put 91 octane premium in it. Car has never seen anything less since.
Broke in the motor and swapped oil at 4k miles. We then loaded the car onto a dyno. We laid down 176 WHP. Car was stock as far as the motor and ECU is concerned.
See picture above. This shows that we are roughly 20-25 WHP higher then most stock tune Mazda3’s. Stock 2.5 on regular generally run around 150-155 WHP.
Bolt On Gains:
The next step was to do a few bolt ons to see how it adjusted. We put on Corksport’s short ram intake, crank pulley, and 60mm cat back. Most members here will claim they don’t add any power but again we show they did. This raised is to 180 WHP. Again no tuning on 91 octane.
See picture above. This picture compares our baseline run and our full bolt on. Blue line is stock car, and orange is bolt ons only.
Now we started tuning. This is where most people change fuel octane. We stayed with 91 octane ourselves though.
Most 91 octane tuned guys are around 185 WHP tuned.
We tuned via DRTUNED this time around. Our finalized tune we made 183 WHP which is slightly below average. We are slightly below average power at this point.
I actually flashed back to stock after the pulls to verify stock flashing. We did 9 pulls that day. Stock was still settling in towards the end of the six pulls at high 170’s.
See picture three. In this you see our finalized tune run and our worst stock tune run. Light green is DRTUNED, and dark green is lowest stock flash of the day.
At this point we had a few issues and decided we should seek out a different tuner. We were making arrangements to tune via OVT when Corksport offered to let us beta test their header.
Their header on their Mazda6 2.5 put down 191 WHP with only a header and tuned via DRTUNED. As far as I know nothing else was done to the car.
See picture above. This is Corksport’s beta race header tuned via DRTUNED. Green line is stock with tune, and red is header with tune.
Now we retuned with the beta header on OVT. When completed we again loaded the car onto the dyno. This is where we pulled our current numbers. We laid down 194 WHP still on 91 octane.
We again flashed back to stock ECU and pulled those numbers as well. That produced a staggering 190 WHP with 91 octane and no tuning.
See picture five. Our stock tune vs OVT header tune. Green is OVT tune with CorkSport beta race header, and orange is stock tune with header.
So the trait here is that our car baseline was high. By the time we finalized the tune the first time we were actually slightly under par for average with our modifications, tuning, and fuel. We gained more from the bolt on parts then we did from the actual tuning in both cases. Meanwhile with us and bolted on the header you’ll notice that the ECU actually self tuned within relatively close to where it was with a custom tune. Obviously they aren’t 100% the same and a tune will still help squeeze out a little extra in the mid range. However the ECU does account for changes fairly well, this includes fuel octane levels.
*As a side note. On each of these we had a fresh fuel and timing trim. When you flash a car it resets all its self learning from previous flashes. When the car was brand new it was still fresh and learning.