I went out for a few runs yesterday to determine what SAFC settings are needed to bring the afr down to a safe level when running an A32 ecu with a Z32 maf. My earlier experiments with this setup resulting in pinging at anything over about half throttle.

Test conditions:

• 55 F, 70% humidity
• dry, open road

SC and engine configuration:

• V1 blower with 3" pulley (10 psi @ 6400 rpm)
• 370 cc/min injectors at oem fuel pressure (43 psi, 34 psi base fp)
• Z32 maf
• A32 ecu
• functioning MEVI

First run SAFC settings:

2 krpm: 0
3 krpm: +7%
4 krpm: +11%
5 krpm: +13%
6 krpm: +13%
7 krpm: +13%

Here is a run I did in second gear all the way to redline:



In this run the afr hit a low of 12.9:1 at 4520 rpm and gradually rose from there to a high level of 14.36:1 at 6000 rpm. The weirdness at time=6.5 seconds is when I hit the rev limiter. I have gotten used to shifting at 7000 rpm with the JWT ecu, and the rev limit caught me by surprise. At first I thought I had toasted the engine. Boost pressure was 10.3 psi at redline. I didn't hear any pinging, probably because the air was nice and cool, but I didn't like the high afr at 6000 rpm, so I did another run with lower SAFC settings.

Second run SAFC settings:

2krpm: 0
3 krpm: +10%
4 krpm: +15%
5 krpm: +20%
6 krpm: +25%
7 krpm: +25%
8 krpm: +25%

Second and third gear run:



The afr at 6000 rpm is now 13.05:1 in second gear, and 12.4:1 in third gear. Much better. Why the lower afr in third compared to second gear? I don't know, but I've seen that trend in every run I've done where I shift gears during data collection. Maybe the ecu and the safc perform better when the rpm is changing at a slower rate.

One other interesting note is that I have added an air intake temperature gauge with a peak hold feature. I saw a high temperature of 165 F at full boost, with normal steady-state non-boosted temperature at about 105 F (heat soaked engine and blower), so a 60 F temperature rise due to 10 psi boost.

Conclusions:

• The combination of the A32 ecu and Z32 maf with 370 cc/min injectors can be made to work along with SAFC corrections
• Boost levels higher than 10 psi may not be possible, since the SAFC can only correct a maximum of 25% (I believe, correct me if I'm wrong).
• The ecu maintained a perfect 14.7:1 afr at idle and partial throttle operation

 

Good news for those of us who don't have the option of a JWT ECU.

If you wanted to run a little richer, or to tune above 10psi, could you run a FMU with a 1:1 or 2:1 disc, then lean it out using the SAFC?

 

Good point. It would take greater than 1:1, since that is what I was using. The oem fpr is 1:1 boost sensitive.

 

Stephen,

You can adjust the correction ratio to a higher amount which will allow you to do more than just the standard 25%. Like lets say it was set to 3%, then the max you raise is 25% based on 3% correction factor. If you raise that 3% to a 6 or 9 or even 15, then you wouldnt need to go as high as 25% anymore, probably less than half of that.

I forget where the option is, believe it is in the setting, I dont have the SAFC anymore, but I do remember that one.

Dixit

 

hes using the stock FPR which already is 1:1

this is very good news for alot of peolple and an oportunity to save ALOT of money

 

Oh, okay, thanks. I didn't know if the aftermarket unit ran 1:1 on top of what the OEM was providing, or if it actually replaced the OEM, but it sounds like the latter is the case.

 

Thanks, Dixit. I'll look into that. By the way, I have your SAFC, remember?

 

Hahhha, I completely forgot. I remember I used to have an SAFCI before I sold it to get the new SAFCII which I dont have anymore either.

Good deal.

Dixit

 

Actually, correct me if I'm wrong, but wouldn't it take a 4:1 or higher for a JWT ECU and a 5:1 or higher for the stock ECU?

With stock 1:1 FPR at 10psi, fuel pressure would be 53psi(43psi at WOT+10psi FPR).

So, for the FMU it's 1/2(static fuel pressure at idle) + (FMU ratio*psi).

With JWT at OEM fuel pressure that would mean:
1/2(34)+(4*10)=57psi for a 4:1 FMU ratio

WithOUT JWT you have to lower base fuel to ~26psi:
1/2(26)+(5*10)=63psi for a 5:1 FMU ratio

Correct?

 

Also, I'd feel MUCH safer subtracting fuel with the S-AFC vs. adding.

 

You don't need the fmu with the JWT ecu unless you are maxing out injectors. At 10 psi (actually I'm at 11.5 psi at 7000 rpm) I'm only seeing 80% duty cycle on my duty cycle meter. So there's still some headroom (well, only if you're comfortable with going higher than 80%).

With the A32 ecu you can use the fmu along with the SAFC, but you can keep the fuel pressure at the stock 34 psi if you are using the Z32 maf and 370 cc/min injectors.

 

That would be the safe thing to do, no doubt about it.

 

Augh..very good clarification. I was intending to point out for more head room....not that it was required. Thanks.

Good point.

 

ok, so on the chart with the 2-3 shift when the a/f ratio drops, does that mean that you are running extra rich because of the shift in rpm?

im still a little hazy about the fpr calculations.

steve

 

If the BOV is after the MAF withOUT a recirc tube, it releases already metered air into the atmosphere causing the ECU to add fuel for air that is no longer there.

 

so stephen max has a bov after his?

im still runnin na because stillen is giving me trouble on the warranty with bracket #2, so i havent experienced it with mine


its an old picture

 

Yes, the MAF is on the CAI now.

 

yeah, i know

but stephen, did you relocate the z32 maf farther away from the blower inlet? i know that you were having trouble with the MAF when it was mounted next to it. did you put it next to the filter in the wheel well?

 

Yes, I had a lot of trouble with the maf in the wheel well because of back flow from the blower whenever the throttle closed at anything above about 1500 rpm, such as during shifts. It made the engine run momentarily super-rich - to the point that my plugs were completely soot covered after only a couple hundred miles. It also occurred during low throttle cruising when modulating between, say, 5% and 0% throttle. I could tell it was happening because my duty cycle meter would light up to 10-20% whenever I let off the gas.

Against JWT's recommendations, I have been running the Z32 maf between the bov and the throttle body - back in the normal place the Stillen kit provides. All problems have disappeared and it drives normally. I've had it in that position since November with no ill effects to the maf.

The reason the afr momentarily lowers during shifting is that just before the shift the injectors are dumping fuel based on WOT and massive airflow. Letting off the throttle shuts off air flow fairly instantaneously, and it takes a fraction of a second for the ecu to detect the overly rich condition. The same situation happens in reverse (i.e. momentarily lean) after completion of the 2-3 shift when suddenly it's at WOT again.

 

Might it be possible to create some kind of cylindrical sleeve to slide into the Z32 maf to partially fool the sensor via changed flow area and get a little closer ratios without so much electronic correction?

 

Yeah, that might work. But it would be hard to get a uniform afr that way, methinks, without some electronic correction. Plus, blocking airflow just doesn't set well with me.

 

so your maf is where mine is? or is that too close to the bov?

Steve

 

Mine is closer to the throttle body:

 

yeah, but my air to water after cooler is where yours is

 

I think you should be okay where your maf is, regardless, since it's not going to see any backflow from the SC.

 

yeah, but im still waiting on that new s/c bracket from stillen, so it doesnt matter right now.

im just trying to do some more research for when it IS up and running.