S.A.F.C. / Power FC Tune and Boost

[AndyMac]

If you increase boost pressure after a S.A.F.C. or Power FC has been tunned, do you stuff up all the fuel maps ?

I know that increased boost would load up the fuel system more, would this mean that a tune set to 12psi would lean out if you increase boost ? Or can the S.A.F.C. or Power FC sense this and adjust the fuel maps accordingly using the extra pressure/air flow sensed ?

Thanks...

Andrew

[predator]

Interesting question..

I think the S-SAFC is pretty dumb, and just has the one range of settings per rev-range. Therefore I'd imagine that there would be no ideal setting for both high and low boost??? What is too rich for low boost (say 7psi) may be just right for high (say 12psi)? So if its set to xxx, if you run low boost regularly and its really mapped for higher boost, it will be very inefficient. Can somebody explain what could be the best balance?

Low-throttle and high throttle settings can be set however - i assume they are just based upon the %THR sensed, i.e. foot to the floor? Mine are all zeroed out on lo-throttle (e.g. no adjustment) - is this good or bad? I'm getting very bad fuel economy even for a skyline (around 100km per 18L or so) and would adjusting the settings do me better?

Basically all i really know is that the SAFC adjusts what the standard ECU "sees" from the air system, and the ECU adjusts to suit. So you give it a -15% airflow reading and it pumps up the fuel by +15% at that rev range.

The powerFC should be a bit more smart about it and be able to adjust A/F settings according to the boost sensed. Will a PowerFC give me any better economy if tuned correctly? The rate i'm going on petrol would my engine be running much more efficient with a PowerFC over an S-AFC as a daily driver?

[Steve]

Peak RPM - I really dont think boost pressure has much of a bearing on fuelling - what does is the air flow - this is the beauty of afms - they tell the computer how much air is coming in, and the computer delivers the fuel. This is a simplistic analogy as other factors are taken into a count, temp, revs etc.

But I cannot see why upping the boost pressure would cause a problem, unless you run out of fuel pressure. I have done this on my car (tuned at 0.85bar, I gave it a squirt at 1 bar - amazing what a difference 0.15 bar makes!) and didnt notice a problem - or more accurately, the power fc didnt tell me of one.

Steve

[R33NT]

I think you have got the wrong idea about the Power FC.

The apexi power FC uses load points. The load points represent different levels of pressure in the manifold as such if your car is tuned and it has been tuned upto the load point representing 12psi (and above) then all should be good. Remember that the PowerFC is a complete replacement and doesnt JUST control fuel.

In essence it doesnt adjust the fuel maps the person tuning the car sets the fuel maps and the car senses it has hit 12psi and uses the according values in the fuel and timing tables.

Fuel economy!!!!

You are driving a turbo charged car, trying to extract more power and you are worried about fuel economy!!!!

Simplest thing is to drive it off boost in which case you might as well go and trade your skyline in on an Accent then bolt on a F40 rear wing and a 2.5inch exhaust with a turbo tip. :whackit:

I dont know what the SAFC is, i assume it is a piggy back fuel trimmer which in my opinion is dodgey, either do it properly (PowerFC) or dont do it at all.

[Nismodified]

for around 450(?) for the safc, its a pretty good, but limited way to gain from the air/fuel mixtures. Im interesting in gettin one, can any body tell me what i could expect from installing and tuning it to my car, i know it would depend on how rich the car runs when stock.

im not lookin for a massive amount of power, just enough to justify its purchase instead of saving for something more substantial.

[AndyMac]

I realize the Power FC is a full replacement computer. But if you don't know what a SAFC is then how can you can it dodgey ???

Not everyone wants to replace the computer and have the hassles of tunning one fully, its not as straight cut as it seems.

A Apexi SAFC is a great air/fuel intercpetor to get an extra 18-20rwkw's. If your not going injectors/coolas/turbos, whats the point of a PFC ??? An exhaust, bleed valve and SAFC can produce pretty good results.

If the car was tunned to use 12psi that isn't a problem, since going down in boost would richen the mix...messy and still screws with performance, but if you actually go the opposite way you can lean out which is a problem.....piston gets a little too big for the hole.......thus must question (and lack of understanding - yes!) on if the load points or fuel map will sense the extra boost..

it has been somewhat answered yes....

[predator]

yes, yes, i know what a PowerFC is R33NT and so do most people here... what we were getting at (i think) was whether there was as a best balance state between the a/f ratios to cater for both low and high boost and whether the S-SAFC is adjusting for that or not.

And what i was trying to ask is, seeing as the S-AFC is really just controlling the A/F ratios, and that is only half (or well, a big part of) the equation. Will a PowerFC do a more efficient job of the fuel tuning (compared to S-AFC), as well as the other benefits it gives?

nismodified: with the S-AFC you're probably looking at 20-30rwkw depending on your other mods (exhaust flow, air intake, etc). Its good value mod for the money. The cheapest option however is altering the maps directly on the ECU via editing the EPROM chip (r32 can easily, r33 i think is a bit harder).

[Steve]

Originally posted by R33NT

I think you have got the wrong idea about the Power FC.

The apexi power FC uses load points. The load points represent different levels of pressure in the manifold as such if your car is tuned and it has been tuned upto the load point representing 12psi (and above) then all should be good. Remember that the PowerFC is a complete replacement and doesnt JUST control fuel.

In essence it doesnt adjust the fuel maps the person tuning the car sets the fuel maps and the car senses it has hit 12psi and uses the according values in the fuel and timing tables.

Using Manifold pressure is MAP, using airflow is MAF. I understand that the power fc uses load points, 20 x 20 of them, but uses rpm (load points) and cross references airflow, not air pressure - or it would not need the afm? I think the only way you run into trouble is when the afm has reached max flow voltage, when dyno tuning is compeleted off the o2 sensor that would be attached to the exhaust. If you dont run out of air flow resolution, or upgrade to a Z32 or Infiniti afm, and have airflow resolutioin, this wouldnt be a problem.

Just my understanding, and I am really sorry if it is completely wrong and misleading.

Steve

[JimX]

Originally posted by R33NT

I dont know what the SAFC is, i assume it is a piggy back fuel trimmer which in my opinion is dodgey, either do it properly (PowerFC) or dont do it at all.

You have an uninformed, arrogant opinion.

[Ustasa]

Originally posted by R33NT

"I dont know what the SAFC is, i assume it is a piggy back fuel trimmer which in my opinion is dodgey, either do it properly (PowerFC) or dont do it at all."

I believe he is spot on. A S-AFC is what is known in the industry as a "sensor bender". It doesn't have the capability to differentiate between different load settings like a Power FC does. A S-AFC will just chop the signal coming from your afm (or map sensor). When you turn up the boost in a stock ecu’d car the air/fuel ratio richens up and your ignition is retarded. When you use an S-AFC, you lean out the fuel by modifying the signal the stock ecu sees but at the same time you change the amount of ignition advance as well. Instead of retarding you can advance the timing which at high boost levels will kill engines quickly especially if you aren’t used to detecting detonation.

[predator]

so the standard ECU basically advances or retards the timing based upon the A/F ratios sensed?

Ustasa: this may seem a silly question, but how to do you detect detonation or close to detonation while just driving?

[Ustasa]

Predator666

It doesn't advance/retard based on a/f ratio but on rpm and load sensing which in this case would be from the AFM. The S-AFC changes the AFM signal the stock ecu sees. What this then does is change the fuel and ignition set for a certain rev and load point. You might be running 12psi but the stock ecu is only "seeing" say 8psi. At 8spi you will run less fuel and more advance then the stock ecu would have ran for 12psi.

You know you have damaging detonation when you can feel the vibration through the throttle. It's akin to a misfire like fouled spark plugs but the harshness is more pronounced and you will hear a tinkling similar to a can of spray paint being shaken.

[ed]

Ustasa, so would you class the emanage in same class as the SAFC?

[T0nyGTSt]

If you are detonating, you check engine light will be flashing quite furiously.

T.

[ed]

and how would YOU know that Tony?

[SlowGTS-t]

Originally posted by PeakRPM

If you increase boost pressure after a S.A.F.C. or Power FC has been tunned, do you stuff up all the fuel maps ?

I know that increased boost would load up the fuel system more, would this mean that a tune set to 12psi would lean out if you increase boost ? Or can the S.A.F.C. or Power FC sense this and adjust the fuel maps accordingly using the extra pressure/air flow sensed ?

Thanks...

Andrew

More boost means more airflow, so the ecu puts more fuel in.

It isnt as bad as you think. I think in most cases it ends up getting richer with more boost (until you run out of fuel system capacity)

[Ustasa]

If you only wired in the basic harnes of the E-manage then yes it would be nothing but a sensor bender. Albeit a better one then the S-AFC since you can have 10% increments of the throttle position on the y-axis which is still better then the S-AFC. Buttry tuning a car with forced induction based on tps lol

But if you wired in the optional Injector and ignitor harnesses it would be akin to a Power FC where you have rpm on the x-axis and the afm voltage on the y-axis. We did a S15 200sx like this and it turned out to be a half-decent solution. Although on a turbo charged car you would want a map based load sensor to help you correlate your tuning with the boost not afm voltage.

[Steve]

Why does boost pressure give better results than air flow? I was of the understanding that boost pressure does not take into account things like air density due to temp, altitude or change in airflow from a slowly degrading air filter whereas airflow does. I know the differences here arent huge, but would be significant when extracting peak performance vs driveability?

[T0nyGTSt]

Well it seems to be that a MAF PowerFC would work better than a AFM PowerFC.

Unfortunately a MAF PowerFC only exists in SR20 or PowerFC Pro version.

The above could be slightly inaccurate.

T.

[Steve]

tlai909 - if you mean MAP, the power fc comes in a version called the DeJetro, which uses MAP on skylines