Originally Posted by esracer

a few more months they will release their Accesstuner which lets do all the tunning you want by yourself.......

Originally Posted by Superdave17

I have a question...If you dont race your vehicle for money, why would you want to tune your car or have the ability to blow the the thing up??? And by adding horsepower have you heard of anyone grenading their transmission??? And is there an upgrade from these tuning companies that might help the transmission deal with the extra horsepower load?? Just wondering because I keep hearing of people breaking transmissions with stock horsepower load. Seems a little expensive if you ask me. And I know some people are just plain stupid when launching the WRX.

Originally Posted by ride5000

i will believe that when i see it.

people have trouble tuning a static fuel/timing curve with a utec/xede, nevermind the adaptable learning capacity of the oem ecu. i think it adds layers of complexity that most folks will never be able to comprehend. cobb knows this. it will probably be priced to make sure that those who buy it are professionals.

jm2c
ken

Originally Posted by esracer

Quoted from www.cobbtunning.com
Not too much trouble since you have the basemaps to start out with if you know what you're doing you just tweek them to what you want, just like tweeking a Utec map. It basically all comes down to if you know what you're doing......Accesstunner will provide the same amount of tunability (if that's a word) as the Utec, they are very much alike.

Originally Posted by sponaugle

Let me further expand on the method you mentioned, plus offer some explanation for those not familiar with the internal structure of the Subaru ECUs. The design of the fuel comp system in the ECU is based around the three direct input variables, plus a 2D map. The three input variables are the current MAF reading, the current RPM, and the 'injector scale' programmed into the ECU. In order to determine how much fuel needs to be injected, the ecu first takes the MAF and RPM parameters and calculates an estimated load per cylinder charge. That is simple the amount of air (in grams) that should be in each cylinder during the compression cycle.

This can be determined by taking the current MAF reading (which is in g/sec), and using the formula below to determine the charge:

Per Cylinder Charge = (CurrentMAF*120) / 4*RPM.

(Mathematically, Per Cylinder charge is the derivative of the MAF over RPM. PCC = (dMAF/dR) )

Once the ECU figures out how much air is in each cylinder charge, it uses that value as one of the axis in the 2D fuel map. These values are in the 0-7 grams range, depending on the size of the turbo, load, etc. With the RPM and Load vales, a 2D map of target AFRS is referenced.

This is the 'fuel map'. This map contains for each load and rpm a target AFR value, specified in real AFR (x:1) *see note1*. Once the ECU looks up the fuel map value, it has a target AFR it would like to hit.

From this point, the ECU now has the amount of air in the cylinder, the target AFR, the rpm, and the injector size. From this point, it uses simple math to determine what duty cycle to run the injectors at. Here is a quick sample calc, although this DOES NOT include all of the variables.

Let's start with the engine load at 1.25 g/charge/cylinder, and the RPM at 5000 rpm, and the injector size at 540ccs/min. *note2*. Let's assume the target AFR for this load is 11:1. AFRs are measured by mass, not volume, so we need to convert the volume of fuel (cc/min) into mass (g/min). Typical pump gas premium fuel is around .760 specific gravity, meaning it is .760 g/cc.

So, in order to get an 11:1 AFR, we would need to inject 1.25/11 = .11364 g of fuel. This equates to approximately (.11364/.760)= .1495ccs of fuel. Given that an injector can flow 540ccs/min = 9ccs/sec, we would need (.1495/9)=16.61 ms of fuel injector on time. 5000 rpm = 12 ms per rev, 24 ms per 2 revs. We have 24 ms total available time to inject. We need 16.61 ms on time, so we run the injector at (16.61/24)=69.2% duty cycle.

Once the above math is completed in the ECU, it can fire the injector for the correct amount of time, and continue it's calculations.

[big snip]

*note1*: Actually, the ecu does not use AFR, but a hex representation of relative fuel comp, which can be converted to AFR easily.

*note2*: The internal number for the injector scaling is not directly convertible to cc/min at 43.5psi. It appears to be a number with slightly different scaling. Stock WRX injectors, which typically flow at about 420ccs/min at 43.5 psi, are scaled as 380ccs, while 540cc/min Pink injectors are scaled at 500ccs/min.