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I was just curious as to how you are supposed to tune the air/fuel ratio on the car if the CPU automatically tries to tune it real time depending on the o2 sensor readings? Also, is there really a difference between a SAFC or a MAFterburner? I noticed that the MAFterburner has two settings, one curve for wide open throttle, and another if the throttle body plate is only partially open. My last question, is if you have a returnless style fuel system, would you be able to rely on one of those two products to take care of the fuel problems for a car running around 6-7 psi? Thanks alot!
 

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The stock returnless fuel system is fine out to around 300 horsepower. I dont know much about the Mafterburner but the SAFC is best tuned on a dyno with a wide band O2 sensor so you can add the fuel or remove it accordingly to reach the optimum fuel ratio.
 

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i don't know anything about the Mafterburner, but the AFC also has high and low throttle position settings. It works by splicing into the harness between the O2 sensor and the ECU and allowing you to change the voltage the computer sees from the O2 sensor. The ECU then adds or subtracts fuel accordingly.
 

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well generally....with narrow band o2 sensor cars (assuming thats what you guys have too)...when you go wot (only time you should be tuning) your car runs in closed loop...meaning that it just uses maf/map sensor readings to keep a preset tune in the ecu as far as a/f concerns..this is where the safc2 comes in..adjusting that signal before it gets to the ecu to acquire the a/f ratio YOU want...however when not at wot...you run in open loop meaning the ecu uses the primary o2(first sensor) and maf/map voltage to manipulate a/f ratios (ecu attempts to keep the car around 14.7 a/f ratio during this mode)...so its best to leave that alone...as the tuning is being done by the ecu constantly during open loop anyways.
 

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So what about the '04 XDs. The front O2 sensor is a linear (wide range) sensor.
 

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So the next question is, if the stock returnless fuel system can withstand a max of 300hp, what can the stock 2004 MAF handle?
 

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So, a 2004 could run a small 6psi system without any fuel or air measurement mods???
 

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you would want something to mod WOT conditions.

when you are at Wide open throttle the computer runs in OPEN loop and just guesses at what the timming and fuel should be.

i am not sure at what % of throttle position the car goes into OPEN loop, but on a dyno with a OBD-II logger you could figure that out.

i do know that someone above posted backword. CLOSED loop is when the comupter uses it's pre set fuel and timming curves and adjust based on MAF and Knock sensor info blah blah and at OPEN loop is when it just dumps gas and cranks up the timming based on it's preset program *basically guessing*

and i did not know our front O2 sensor was wide band! (i have an 04 elantra)wholy crap! that opens up a whole new world of tuning!!
 
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