The SCT tune advanced the ignition too much (my opinion) sounder slow acceleration the spark works against the up-going pistons.. this explains the difference I discribed before.
1st, good for you to get all squared away!
Brasil.........this observation you've made really isn't an opinion........it is a fact that all serious racing entities (NASCAR, F1, Indy, etc...) has known for quite some time......the OEM's have also adopted this as well & started to produce IMs, cyl heads\combustion chambers\piston designs in the early 2000's forward (FYI......this includes these Ford 3V's w\ the IM CMCV's......as well as GM's LS\LT series engines & other modern engine designs......) to improve intake port\chamber swirl\tumble to speed up AFR burn rate\shorten burn time to improve engine combustion efficiency........most think\have been led to believe this Ford CMCV component is just an emissions thing, but it really isn't. The main reasons were all TQ related thus improving engine available HP\TQ output across the board (exactly what you're experiencing from the tune cal restored back to stock.....) by speeding up fuel burn rate\reducing burn time which will increase net cyl pressure buildup by reducing the amount of crank rotation necessary to reach the ideal 12*-15* ATDC crank angle for max cyl pressure buildup\application from the ignition point during the power stroke thus can allow reduced ignition timing which will reduce the amount of power robbing pumping loss getting applied to the following piston during compression\after ignition (exp: 90* bank V8 engine firing at 90* intervals at 30* BTDC ignition, the piston is still moving upwards at .320" from TDC @ 45* total crank rotation across fuel burn time......fuel burn time at 1.2-1.4 ms will impart a fair amount of cyl force against this following piston moving upwards until the piston reaches around 5*-10* BTDC crank angle (.010"-.030" from TDC thus is considered "at the deck") checking against the diminishing force on leading piston ahead of this 1 during its power stroke downward travel AND eating up some of the inertial momentum stored in the flywheel\TC (now needed to counter this pumping issue instead of getting used mainly to assist the leading piston during power stroke applying more net force to crankshaft) thus is causing a TQ net output loss to crankshaft........in addition to the net pumping loss gained when the EVO event occurs too late during the power stroke thus the piston has to do more work pushing out spent exhaust gasses from the chamber against atmospheric pressures on its way up towards TDC (start of overlap to intake stroke)........in addition to the amount of heat release lost thru the cyl head (also lost cyl pressure buildup from the extended fuel burn time) resulting in even more net TQ loss to wheels..........but an increased loading to crank\rod journals & bearings, piston skirts\wrist pins & cyl walls......for relatively little to no meaningful overall TQ gains. When an engine reaches true MBT, this really means that the engine has essentially balanced enough counter force against the wanted directional force that the engine will stop making TQ gains w\o fuel exceeding it's AKI index.
Simple application of operational physics\geometry & a place you DON'T want to actually be at.........that is, if you also want your crank\rod bearings to live longer..........
If folks would've just ran the Ford BKT side spark timing against the Ford MBT side spark timing as the ECU OS is programmed to do, you would've seen that the lower overall spark timing was mostly from the MBT side, not the BKT side AND the actual total spark timing would've been between 17*-32* total timing being applied--at WOT this would've been between 17*-22* total timing...........nowhere near the 28*-30* most folks try to push thru these engines. The reason why\how 1 can push 30* ignition timing is due to the CMCV's removal which causes a stratified air\fuel\EGR mix due to the absence of airspeed velocity hyper tumbling which causes the need for more spark timing to try to extract the same amount of cyl pressure generation which causes all of what I just typed above........even when using 93 oct fuels. Cam profiles play a large part in this as well.........but the cam designers knew all this & ground their cams to compensate\offset for this at low engine RPM\part throttle operations from off idle thru mid-range thru the use of VCT.......but due to most tuners leaving the low end TQ Management Driver Demand mapping below 148 A\D counts & the subsequent BKT\MBT spark maps, VCT maps below .50 load essentially stock (some of this is also disabled as well due to the thinking that it doesn't do anything........the reality is that it will take some time to reallocate all this properly around a set of cams that aren't close enough to a stock cam's timing profile (even the stock cam is somewhat neutered from a purely performance perspective from the factory........) to actually get all of the total performance the cam designers ground into them......so most wouldn't learn\do it AND also due to most tuners using inertia dynos instead of load bearing dynos w\ drivability tuning modes programmed in the dyno stack software (think the Mustang chassis dynos here--that most revile the use of.....) .........which aren't very useful to adequately tune these regions of the tune cal....only WOT.......thus would've HAD to tune all this on the street which would've taken even more time to do it properly........costing customers more money than most wanted to spend as all they wanted\concerned over was PEAK HP\TQ outputs......
not available total HP\TQ outputs across the board & drivability as close to stockish levels\feel as can be gained......thus wouldn't pay for tuners time that would've done this............thus is a 2-edged sword in reality..........this 3V engine IMHO got the shaft end out of all this over the last 15-20 yrs..........for being so technically advanced vs its peers at the time of its arrival on US roads.......this is the main advantage of using VCT........not so much for WOT (even though it does provides some advantage...) but the far & away advantage is
the rest of the engine's total power curve from off idle thru to WOT..............
including drivability, MPG & emissions.
The side benefit from all this is improved fuel MPG & yes emissions due to the fuel\air & EGR mix (intentional thru VCT usage to improve fuel MPG & to discourage NOx generation.....) being fully homogenized from the increased hyper tumble since these 3V cyl heads\combustion chambers do not have near adequate squish\quench control\area from the design.......but ARE designed to adequately cause the incoming tumbling induced air\fuel velocity
from the intake port thru the intake valves (think semi-Hemi design......intake valves located at the top of the cyl chamber which allows a high angle intake runner\port which will flow better & FASTER......think line of sight.....the CMCV's job is to further induce airspeed velocity at low engine RPM's (like a long runner IM....the CMCV closed position achieves this.....) AND to induce a hyper tumble motion in said intake airspeed velocity at ALL ENGINE RPM's (the offset section in the CMCV blade design--causes sheer from 1 side of blade accelerating air faster across it than the other side thus the hyper tumbling motion when the air converges downstream of the blades....)--even when they're fully open......in the cyl head intake port....
where all of the calculated fuel amount is sprayed on the back of the intake valves prior valve lift off the seat.....that is, if the tuners properly set the FI EOIT Crank Angle Ref timing in tune cal using the cam's actual .006" adv dur IVO timing event @ VCT 0*---instead of just leaving the stock cam's .006" adv dur IVO CA ref timing of 345* @ 15* BTDC set in the cal when swapping cams---so the ECU can maintain this fuel spray position properly while the ECU is also swinging the cams using VCT........all engine cold start, idle & power output fueling is predicated on this being set to properly reference to the cam's actual IVO timing event.......to be able to achieve adequate evaporation into the IM runner air\fuel puddle maintenance prior valve lift off the seat........fuel puddling affects transient fuel application\performance as well as cold start performance.......kinda hard to do this if the intake valve is opening\open while the fuel injector is still spraying fuel..........) to further roll inside the cylinder due to the dished piston top to maintain homogenous mixing until ignited\burned.......thus needs less ignition timing to reach the same ideal cyl pressures for max TQ generation AND reducing the power robbing pumping losses at the same time--increasing overall net TQ gain AND efficiency by actually BURNING more of the available air\fuel mix INSIDE of the cylinder causing LESS work for the catalysts to clean up.......improving emissions while at the same time, reducing the amount of excess heat the engine cooling system has to get rid of due to the SHORTER burn time\faster burn rate.......which helps air\fuel to retain more net density once it passes the intake valves while inside the cyls from cooler chamber temps thus also increases the amount of heat release thus TQ generation.........not to mention less prone to knock......in NA config as produced from the Ford assembly lines at the time of manufacturing.
Enough for now...................FWIW.
