99% of intakes WILL LEAN THE CAR OUT
and most will affect the timing a bit
Some of you guys are QUITE mislead about ahow the ECU "adjusts"
ill go into a bit about it:
Short Term Fuel Trim Description
The short term fuel trim is a ECU erasable memory register. The neutral value for the short term fuel trim is 0%. Any deviation from 0% indicates the short term fuel trim is changing the injector pulse width. The amount of pulse width change depends on how far the short term fuel trim value is from 0%. The short term fuel trim is rich when the scan tool indicates (up to )-25%. The short term fuel trim is lean when the scan tool indicates 25%. The short term fuel trim changes the pulse width by varying the Closed Loop factor of the base pulse width equation. As the ECU monitors the oxygen sensors input, it is constantly varying the short term fuel trim value. The value is updated very quickly, therefore, the short term fuel trim only corrects for short term mixture trends. THe correction of long term mixture trends is the function of long term fuel trim. Long Term Fuel Trim Description
The long term fuel trim is a matrix of cells arranged by RPM and MAP. Each cell of the long term fuel trim is a register like the short term fuel trim. As the engine operating conditions change, the ECU will switch from cell to cell to determine what long term fuel trim factor to use in the base pulse width equation.
While in any given cell, the ECU also monitors the short term fuel trim. If the short term fuel trim is far enough from 0%, the ECU will change the long term fuel trim value. Once the LTFT value is changed, it should force the STFT back toward 0%. If the mixture is still not correct (as judged by the HO2S), the STFT will continue to have a large deviation from the ideal 0%. In this case, the LTFT will continue to change until the STFT becomes balanced. Both the STFT and LTFT have limits which vary by calibration. If the mixture is off enough so that LTFT reaches the limit of its control and still cannot correct the condition, the STFT would also go to its limit of control in the same direction. If the mixture is still not corrected by both STFT and LTFT at their extreme values, a Fuel Trim Diagnostic Trouble Code (DTC) will likely result.That being said, lets adapt to an intake and a subaru
so you put on an intake
and your STFT goes to lets say +7% (adding 7% to achieve 14.7:1)
after driving arounf the LTFT will ty to correct that and the TLFT will be +7%
so while cruising in Closed loop the 02 corrects for the intake.
THEN YOU FLOOR IT
LT AND ST trims go to 0% (thats what they do) and the car runs off the maps
Here lies the problem that 7% that was needed is now gone
and your afr will be Off due to the fact the intake causes a lean condition.
All of a sudden you are 7% off and AFR is important!
The other problem is
the loads can be affected by an intake. If the internal diameter and flow is not like stock.
Lets say the stock LGT intake is 72MM and your new intake is 75MM
Its just 3mm right? WELLLLLL
that will change the load a bit (not as much as say a big maf) but a bit
so now the timing is slightly advanced and the mixture is leaner.....
w00t you make more power (thats what happens when u do that )
BUt you lose that saftey
The subaru ECU is WAY smarter than you are, so it combats knock and impending knock by retarding the knock advance (knoch correction, Dynamic advance)
but that reduces power......
i could go on but i wont....
There is so much involved just slapping on parts whilly nilly can and WILL affect things, and the ecu may adjust , just not the way you thinkit will.
I have tuned intakes, lots, APS, Cobb, K&N , AEM, Custom, Blow thru MAF
and many more.
I can say that a cobb intake = GREAT GET ONE if you want an intake
I can say that a K&N intake = MEH , on an sti i did it made his life horrible, on an LGT it was ok, on another lgt it was a PITA.
Perrin = Confused me, i ordered one For an LGT (72MM inlet) they sent me a 68 MM wrx in a LGT box, I called explained and they claimed it was fine.........
no thanks. I put it on an Sti and got a differnt one for the LGT
APS= whacky , needs a tune
AEM = needs a tune
Perrin big maf = the bain of my existance, ask Christian or Scans about that
im rambling now
PM or IM if u have questions
