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Safc??

skyr31

By skyr31,
in Engines & Forced Induction

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Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi guys, this looks like an opportune time for a bit of SAFC, ITC and ECU information dumping......

An SAFC modifies the signal from the AFM to fool the ECU into thinking there is less airflow (this leans out the mixture) or more airflow (this richens the mixture).

An SAFC does nothing for correcting the ignition timing, in fact I have seen cases where it actually does the wrong thing. An example, if you have somewhere in your RPM range where the mixtures are too rich. The SAFC can be adjusted to have the ECU lean this out by telling the ECU that there is less airflow, so it reduces the amount of fuel. The A/F ratios are now good, but what happens to the ignition timing? Well the ECU thinks there is less airflow (than there really is) so it advances the ignition timing to what the ignition map says is correct for that (lower) amount of load.

In my experience that's too far advanced quite often, so I have 2 choices. Either, retard the static ignition timing, which affects all rpm ranges. Even though it might be OK at some RPM's and even (already) too retarded at others. Or, compromise on the A/F ratios and balance it out so I get close to what ratio I want, but don't affect the ignition timing too much.

Now to fix this ignition timing problem you can get an ITC. This sits between the CAS and the ECU and modifies the ECU's firing of the spark plugs. But again this is a compromise as the ITC only has a small number of correction points and it extrapolates in a straight line between them. This is particularly a problem at times (in the RPM range) of rapidly changing boost levels.

As you increase the amount of power and/or boost this "compromising" just gets worse. With an SAFC and an ITC you have (sort of) fixed the A/F ratios and the ignition timing, but you also have the problems of boost mapping, idle stability, load correction for air con, power steering, electrical load, rpm limiter, speed limiter, cold start and run etc etc

If you add up the costs of all the "trickers" it works out more than a Power FC and still doesn't give anywhere near the quality of result. So for a modest power target, an SAFC is not a bad thing, but if you are serious, then an ECU upgrade is the go.

Hope that helps

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MJ Mentor

MJ

Posted
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Thanks for that reply Sydneykid, my car is also auto and i have a s-afc. But when being tuned on the dyno the tuners had problems with the timing as it caused the car to misfire when they leaned out the s-afc. So if i get my hands on a ITC it will fix my problems? I wish i could get a power fc but im stuck with this problem.

Or would you recommend me to sell the s-afc and buy a e-manage with igniton harness? The only info i havent been able to find out is if the ignition harness will work on the auto with no problems. I dont want to throw any more money around trying to solve it, i just want the cheapest, easiest option which the ITC sounds like it can do.

Cheers,

Matt

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Sydneykid Grand Master

Sydneykid

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Hi Strutto, if your power targets are modest, then an SAFC is the go. We are getting an auto Stagea shortly and I will stick an SAFC in that. I have a ball bearing hi flow RB25 turbo to go on it, a split dump, 3" exhaust, panel filter, CAI, Autospeed (Norgren valve based) boost controller and an OK intercooler. Should give a nice torquey 200 rwkw to tow the race cars with.

If it doesn't end up meeting my expectations, I might try a piggy back manual Power FC. Leave the inputs to the standard ECU and the outputs from it to the auto. Parrallel up the inputs to the PFC and use it to run ignition, fuel, boost and idle control. I have seen an R33 with a Link piggy backed similarly, it was OK but a little rough on the gearchanges.

Have a chat to Steve-SST, I think he has done a Wolf into an auto.

Hope that helps

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Sydneykid Grand Master

Sydneykid

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Well once i get the ecu issuses sorted out i plan on doing the fuel pump, fuel pressure regulator, cam gear and then finally highflow the T3. I think that will be enough power for me so is a safc and itc good enough for this setup? Thanks again, Matt

Yep, sure it's a compromise, but not that bad. I had a friend with an SAFC and ITC and he was happy for 3 years, driving everyday + some drag and circuit work.

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