FAQ: SAFC error

[Evil Z31]

http://www.redz31.com/pages/fuel/afc.html

Most units can run +/- 50% of your stock injector size. This means the Z's stock 260CC/min injectors can be replaced with up to 390CC/min injectors.

This is incorrect. An SAFC will take 50% off your "new injector" size you're running. Therefore, you can go up to twice the size of stock injectors, or 520cc's, not 390cc.
For the Z, when programming the SAFC, you plug in -50% all the way across on the low map. That turns your new 520cc injectors into 260's again.


In my Tib, I had been running 440cc injectors in place of stock 245's using the SAFC at -45%.

[simply86T]

I am curious to see some wideband A/F ratio logs with SAFC, just to understand how effective is SAFC. If the logs are from on a dyno, will be even more interesting. :roll:

[Evil Z31]

If you donated an SAFC to me, then I could log it on my wideband. lol

Actually, the SAFC is great on some cars as long as the stock ECU "lets go" of the AFR's and closed loop mode. Most cars are supposed to enter open loop when going WOT and ignore AFR's. That's where the SAFC takes over. However, the SAFC didn't work well in my Tib because the stock ECU didn't fully exit closed loop and wanted to pull the AFR's lean all the time. Perhaps the "older" (and hopefully dumber) ECU in the Z won't be so complicated. If so, then I may try it out.

But like the FAQ says, the more you subtract from the stock MAF readings with bigger and bigger injectors, the more timing you're adding. Boom!
However, you could also get an aftermarket ignition system to pull the timing.
But cost of SAFC + ignition controller = cost of something better

[Jason84NA2T]

As I recall that's the way it was explained for the SAFC (50% larger injectors) and how I had them tuned for the car I installed it in (323GTX, not Z31), is the SAFCII different allowing 200% larger injectors?

That just means they are cutting the maf signal voltage curve by as much as 50%...

I would really like to hear from anyone running a SAFC in a Z31 to see how a stock ECU handles the altered maf voltage input, specifically at idle.

[Evil Z31]

You need to think about it from the other way around as already having the injectors installed. If you have 520cc injectors in the car and you use the SAFC to cut them by 50%, then you are making them pulse half as much = 260cc.

[Jason84NA2T]

Evil Z31 wrote: You need to think about it from the other way around as already having the injectors installed. If you have 520cc injectors in the car and you use the SAFC to cut them by 50%, then you are making them pulse half as much = 260cc.

Did both the SAFC and SAFCII offer the same injector size increases? I have only used SAFC.

Right, but you have a (TTPMIN) minimum plusewidth and maf voltage thresholds (limpback) in the ecu to account for. Despite decreasing the input maf voltage and trying to get the pulsewidth lower, I dont think you would be able to get it low enough for that big of an injector anyway. I had to decrease my ttpmin 2 dec (about 30% lower pulsewidth) to run 550cc injectors in place of 260's and still get it to idle correctly.

I will make the corrections on that page based on your info, but I've heard so many reports of poor and crappy running when people tried AFC's with stock Z31 ecu's that I would not recommend it. I still want to hear from someone who has done it without any drivability issues.

[Evil Z31]

Both versions correct to 50%.

I'm not sure about the z31 liking it at idle or not. It would be an expensive test if I were to try it. I've never heard of any car having that issue though.

[Russ84na]

Jason,
I just removed a SACFll from my NA 2+2 and replaced it with NisTune in the 84 ECU. It was what I was using when I got to 164WHP. It ran fine at idle and through out the rpm range. When I get back to the dyno I want to see if I can improve on the 164whp

[Evil Z31]

That's not really what he was asking. I'm fairly certain you didn't replace your injectors to have a -50% decrease in MAF voltage. What was your low throttle corrections set to?

He wants to know who has the SAFC, and very large injectors (probably 440's and up).

[simply86T]

Russ84na wrote: Jason,
I just removed a SACFll from my NA 2+2 and replaced it with NisTune in the 84 ECU. It was what I was using when I got to 164WHP. It ran fine at idle and through out the rpm range. When I get back to the dyno I want to see if I can improve on the 164whp

What was your number before SAFCII?

[Russ84na]

[quote]simply86T wrote:

Jason,
I just removed a SACFll from my NA 2+2 and replaced it with NisTune in the 84 ECU. It was what I was using when I got to 164WHP. It ran fine at idle and through out the rpm range. When I get back to the dyno I want to see if I can improve on the 164whp
What was your number before SAFCII?

I can't say exactly.
The base line before mods was 130. After the intake and exhaust mods and with the Apexi SAFCll it was 150. Then I retarded the cam gears and went to 164. I have to get back on the dyno and see what I have when I set the timing back to stock, then retune using NisTune and see how much more I can get. My dyno sheet is on Z31parts.com under the adjustable cam gears.

[TODD03412]

Im running a SAFC and have for a few years (transplanted it from my nx I autox) and after an indepth conversation with someone on another board...it was pretty much determined that the safc is probably good for a rough 10% adjustment before you run into control issues. Im still running stock injectors and only adjust it in small amounts.

With the Safc and as much as I have used it, most other can tell you like I can....its never the same thing. The cars ecu always tries to adjust for something that is a ghost in the machine (refering to a piggyback).

Like it was said, with the money put into making it work for BIG applications like most guys here run its just smarter and better to run a totally different ecu and program it instead of using a "trick"

All this is just my ineducated opinion......and Im a total Apexi whore...no joke.. I love their products and used to sell the crap out of them locally (I think mostly out of my charism for the product) and I still run their stuff.. BOV/ RSM I use for autox and my SAFC.....

:shock: