Hey, If i was to get a S-Afc would it be able to compensate down low for 720cc secondarys? I know that if was just to whack some 720 secondarys in with the stock ecu i'd have all sorts of backfiring problems etc but if i was to run a S-Afc and have it leaning it out at low rpm say to 5000rpm then just brought it back to 0 after 5000 would this work ok. Ive got a mild ported S4 with a S5 turbo and ported wastegate and a walbro fuel pump and a rising rate malpassi regulator

 

it would work but you should tune it with a wideband, if you bring it back to 0 after 5000RPMs you will be running excessively rich and losing power.

 

Ok cheers. does the injecton system in these cars work similar to the carby set up where the primarys will run by them selves to a certain point then the secondarys will kick in later on or do all the injectors run from the word go?

 

if im not mistaken the secondary injectors kick in at 3500 rpm below that only the primarys are working

 

anyone care to back this statement up??? Im not taking the **** i just have no idea so am asking for confirmation

 

That would be correct, with stock ecu . secondaries come on at 3800rpm,
thats where u get the hestation sometimes from them coming on.

 

up to ~3650RPMs the primaries fire only, after that stage point they all 4 fire together splitting the duty cycle.

 

Cheers guys, thank you very much.
One more question. if im not running more than 12psi are the 720cc inj necessary?

 

anything over 10PSI on the stock fuel system is a hazard waiting to happen, yes i would install the 720's, the SAFC and do some rough tuning with a wideband.

you will also need a FCD or Rtek to combat fuel cut if you haven't already thought of that yet. stock fuel cut is at 8.6PSI.

 

yea ive got a FCD already and im on my seconf motor now. Had a stock t2 motor with 3" exhaust and inlet with a pod filter and no ported wastegate adn a FCD adn it went boom very shortly after i got the 3" exhaust and it boosted 14psi. Trying to do it better adn smarter this time around

 

I had the same setup on my 91 t2 & after it was tuned I had no problems, go 4 it. I have since went to some radical upgrad so I sold mf S-AFC & is now running a Microtec ECU to complement the upgrade. I was making 261.7 rwhp on a stock motor with the afc & some minor add ons. With the new upgrade I am aproaching 400hp + @ the wheel

 

Check my sig for the training manuals. They'll tell you pretty much everything you want to know about the fuel control system. You'll need to lean out the upper RPM range, not the lower RPM range.

-=Russ=-

 

yea, Cheers russ,
I fuguired i might even lean out down low abit for fuel comsuption and then i'll have to lean it out even more up high to get the 720's hummin along nicly with the 550's with higher boost so it should all come together nicely. Now just to find low impedence 720cc for the S4