Whats the benefit for using this?

 

You avoid fuel cut and more timing. From; http://www.evotuners.net/forums/showthread.php?t=315


By leaning out the S-AFC (big injectors, more fuel pressure, or race gas) you decrease the amount of airflow that the ECU sees, and therefore you will get a bit more timing advance for power. This all assumes you have no knock, and also keep in mind that more timing advance will have an engine a higher propensity to knock.


Fuel Cut

Another issue involving the amount of airflow the ECU sees, and the correction factors of the S-AFC, is fuel cut.

For those of you who do not know, the ECU has a program that tells it to cut fuel when the airflow exceeds a certain amount. Now, this is with the final calculated airflow, not just the Hz signal, which means that temperature and barometeric pressure will effect fuel cut as well.

If you are to install, say, 660cc/min injectors, you will be able to pull the correction factors within the S-AFC down about -15%, perhaps more. This means that the ECU will see about -15% less airflow under a given amount of boost than it would have with the stock setup, which makes it much less likely for you to get fuel cut.



P.S.
Watch someone write back saying "AFC's don't control timing."

 

i heard somewhere that you need a wideband, or something like that?

 

With any tuning tool you need some kind of way to see your changes so that you aren't running blind. This means at minimum you need a Datalogger like the OBD2 pocketlogger and/or a wideband o2 signal in order to safely lean out your engine at various RPM points. These cars tend to need a different amount of fuel pulled out throughout the RPM range if you want to tweak the air fuel ratios for power.

With that said there are other ways to adjust for larger injectors but you must know exactly what you are doing. This weekend I ended up doing a few mods that carried over from my experience with DSM's. Dangerous info warning:

There is a MAS adjustment screw on the bottom of the MAS that if you back out all the way will lean the car out around 8% across the board. On a stock car I wouldn't back that out more than 1/4 to 1/2 (2-4%) and only if you have 93 octane or better gas. The car from the factory is likely as lean as it can be for 91 octane besides tweaking the low end for torque and upper RPM range for top end HP. Backing this out too far on a stock car will give you a ton of knock in the 4200-5600 range if you don't have a Super AFC to richen up certain RPM points but it's one way to lean the car out for larger injectors.

There is also a Barometric pressure sensor signal you can intercept on the ECU and lean the mixture out as well... enough to blow the motor sky high if you aren't carefull. This was termed the Dime Store fuel cut defenser and basically it's just a variable potentiameter of the proper range to reduce the signal a controlled amount. It's a good way to account for larger injectors so that your Super AFC doesn't have to be set for -50 across the board and gives some room to tune with the AFC when leaning out for race gas at the track.

Anything that reduces airflow signals will effectively advance your timing since it gets on more aggressive tables the less airflow the ECU sees. That's why when moving to larger injectors can also get you quite a bit of timing advance since you are fooling the car even more when leaning them out. This can be bad if you don't account for the change but if you know how to tune it means more power. If you don't have a logger and/or wideband to see your changes it would be very unwise to tinker with anything and you are doing so at your own risk.

 

Thanks a lot, Chris!!!!1 I just went out and blew my engine because of you!!32!#*$!#@!! j/k

I was going to see how low I can get with just an MBC and the S-AFC on race gas, but maybe now I'll try to see how low I can get with the MBC and injectors to utilize the S-AFC even more...

 

so you can use this as a supplement fuel cut aye... Does this monitor anything?