Fuel injector Question

[orangedsm]

So I bought my S-AFC today and got it all hooked up just fine. Main reason I bought it is to aid in delaying fuel cut. Tell me if my math and logic is correct:

550cc injectors flow 18% better than 450cc (450 divided by 550). So this would raise my fuel cut rpm by 18% (right?) as long as I lean it out on the S-AFC.

660cc injectors flow 32% better than 450cc. Same deal, lean S-AFC by 32%, 32% later fuel cut.

Does this all make sense? Right now I am hitting fuel cut at about 5000-5300rpms at 15-16psi (depending on how cold it is). So 18% higher fuel cut would take me up to 6250rpms (5300 x 1.18, still not at redline). 720cc injectors would raise fuel cut by 32% taking me all the way to 7000rpms (where I shift when racing).

I am just trying to think logically. So to raise my fuel cut to redline I have to get 720cc injectors (or larger) right?

Any input would be appreciated.

Thanks,
Jason

 

[dsmkilla]

whoa this fuel cut is weird!!!!!!!! i drove my bro stock bone stock tsi awd turbo and i didnt get fuel cut until like almost redline or 500 rpm befor redline.......and that was all gears.....i dont kno man maybe u guys have some kind of mechanical.....prob.....or soemthin aint right

 

[KenTSIII]

Fuel cut is dependent on how much air the MAF is seeing. If you turn up the boost... the more you'll hit fuel cut. The colder it is outside.. the more you'll hit fuel cut..

 

[steve]

This is a little outside my experence level but from what I've read I believe you address fuel cut three ways. Hacking the MAF to bypass more air and then tune as needed with the SAFC. Switching to a 2G MAF which generated a lower count for the same airflow and again tuning with SAFC. Getting the TMO ECU upgrade which removes the fuel cut. I would assume you could bump the injectors up and cut back the air count but as some point you wind up with injectors that deliver too much fuel at their minimum duty cycle and your low rpm response goes bad. You can also play games with the base fuel pressure to make your injectors act like bigger ones and again cut back the seen air count with the SAFC. I'd start by doing some basic MAF hacking and work up the chain. What size turbo are you running?

Steve

 

[insane147]

if your brothers car is hitting fuel cut in evry gear, you better tell him to save for a new engine soon, and read up on how to get by it. most factory turbo cars if not all have fuel cut, the rx7s are very picky, the supra is too ive heard.

 

[jw]

Orangedsm, the first part of your post make sense but the part about fuel cut is rpm dependent does not. Like Ken said, fuel cut is airflow dependent. Fuel cut condition is programmed into the ECU. The condition go something like this, if x airflow (i think it's air mass but anyways..), perform fuel cut. As you can see. Air mass is dependent on airflow, temp and baro pressure. So as airflow increase, mass increase and it reaches fuel cut easiler. Steve already mentioned you can delay fuel cut using bigger injectors (with an AFC to trick the ECU by reducing airflow aka leaning it out), hack the MAS by allowing more bypass air therefore delaying fuel cut OR, you can use TMO mod that totally eliminate the fuel cut condition. I believed they did it by making the fuel cut condition almost impossible to reach or do a no-op operation for fuel cut. Out of our context but you get the idea.