Stock ECU, Z32 MAF, 550's...explained
 

I have been getting alot of PM's and emails with questions regarding running just the stock ECU, z32 MAF, and 550's. There seems to be some confusion. I am a firm believer in uderstanding the dynamics of modifications. How and why they work, not just that they do. This is where I believe alot of people get into trouble with their cars.

This is a dumbed down vesion of things, and is certianly not technical.






The first thing to understand is why a Z32 MAF and 550's will work together so well without needing any sort of piggy back system or ROM tune.

An A32 MAF and Z32 MAF are both a 0-5V sensor. They have almost the exact same voltage curves as well. These two things are the main reason why this combination works.

The air flow detected by the MAF sensor is what the ECU uses to fire the injectors. So for every X amount of air metered by the MAF, X amount of fuel is delivered by the injectors.

I will use an example using arbitrary imaginary numbers to make it simple......

For example, in the stock configuration using a A32 MAF and stock 240cc injectors, lets say for a MAF voltage reading of "4" the injectors are fired at "10". (again, these numbers are just made up). This is a program written in the ECU to achieve the proper AFR. Nissan engineers tuned the stock ECU to know that to when it sees MAF voltage of 4 it fires the injectors at 10, and all is good. A nice 13:1 AFR is achieved. This being on a stock NA maxima.

Understanding how the above works is crucial to understanding how my set up works.

Ok, so now back to the Z32 MAF and A32 MAF comparison. Like I said, they are almost the exact same type of sensor. Both a 0-5v and both follow almost the same voltage curve. The difference is that The Z32 MAF can meter almost twice the amount of air that an A32 MAF can. Going back to our arbitrary #'s, this means that if the stock ECU metered an air amount of "4" a Z32 MAF would meter that same air amount as "2" because it is twice the size.

So if we were to just stick a Z32 MAF in a stock maxima and change nothing else then there would be problems. The air that an A32 MAF would normally meter as "4" would now be metered as "2" by the Z32 MAF (remember it's twice the size) and injectors fired at "10" would now be fired at "5". This would not be good because the motor would be getting half the amount of fuel it is supposed to at this particular air flow.

But what if we were to put in injectors that flowed twice the amount of the stock ones?

Then even though the Z32 MAF would only meter "2" instead of "4" and the injectors would only fire "5" instead of "10" the injectors would be flowing twice the amount of fuel so the motor would still be getting the proper amount fuel.

That is the very basics of why it works. But there are still a few other things involved.

For an FI application we don't want the ECU to still delivery the same amount of fuel is was designed to deliver for an NA motor. We want more fuel at every given point. This is why we don't use exactly twice the size injectors. We use injectors a little larger than twice the size....like 550's.

Remember when I said an A32 MAF and Z32 MAF had almost exactly the same voltage curve? "Almost" is the key word in that statement. They don't have exactly the same voltage curve and that will cause the AFR to fluctuate as a car goes through the RPM band. A nice straight AFR is not achieved with running A Z32 MAF, 550's, and the stock ECU. If you were to over lay the voltage graph of an A32 MAF and Z32 MAF they would differ in several areas. The biggest difference being at the higher voltage levels. At the higher voltage levels is where the A32 MAF and Z32 MAF differ the most.

This is why another device is needed to pull or add fuel at different points to achieve a fairly flat AFR. There will be peaks and valleys in the AFR that need to be corrected. That is where an SAFC comes into play. This set up still needs to be fine tuned. An AFPR would also be very useful as well in this situation.


There are down sides to running this set up. Although we can get a quality WOT tune out of this set up, the off throttle or cruising suffers. This set up simply runs rich at low throttle points. Gas mileage will suffer little in normal driving. To many of us that is not a big deal, but it is something that should be noted.


The last point to note for those who would like to run this set up is that there is no timing control involved. If one has aspirations to run high boost and HP then additional timing control devices will be needed. But great #'s can be achieved at low boost levels when you’re running sock timing. I was able to put down the highest known HP/TQ at the lowest boost. 375whp & 350wtq @ 9.3 psi.

Hey mike great read, I have also followed this route and have been very happy thus far. My dyno numbers will be released sunday as im getting dynoed with the same setup as mike is only with a bigger turbo and slightly bigger injectos from what he said rated at 615 i believe. Cant wait till sunday.

Awesome write-up Mike! Thanks for writing that in english, LOL, and not getting all technical. Very easy to understand.



nice write-up.

Mike, I would like to add a bunch of stuff about the z32 ecu language and how the injector pulse width is modified, but I don't have enough time right now. I'll supplement your information later.

Great write up Mike! I always though that way to about the injectors on the stock ecu but was not realy sure. But none the less great write up!

that's probably the most useful info i've read on this forum. up untill this write up, i didn't know what the SAFC was for. this is definitely sticky material. Thanks Mike!!!

Here's the thing. I know that Mike is turbo, which this application applies to most. You need much more fuel throughout the rpm band, which is why the 550's work the best. However, if you are supercharged, you do not have as much forced induction due to the rpm-based nature of a centrifugal supercharger. Many people are using 370's with a need of a fuel bump at the upper limit because of how the z32 maf interacts with the a32 ecu. I think that my 410's are closer to what a supercharger's needs are. Again, I only have a bump at the upper limit of the rpm band and its only about 8 psi more than oem (51 psi). It is fine tuned by safc within +/- 5%

Sorry to contradict you a little Mike, but the 550's are a little too big for my application. The 440's would probably be the best.

Great info Mike,this should be STICKY.Thanx. :)

That really shouldn't matter Steve. You can run this set up on a other wise stock Maxima and it will work. Actually, I think this has been ran on a bascially stock maxima and worked fine.

550's are too big actually. But IMO it is better to start off rich and be safe then pull fuel then to start off lean and add fuel. At least for those who won't be data logging AFR from get go.

SC, Turbo, or stock. It shouldn't matter too much. The MAF is still reading the amount of air and firing the injectors accordingly. Sure a turbo will see more air flow than a SC at a given point at the same boost, but the MAF will just read less air and lower injector pulse width.

What does come into play is how much of the 0-5v range one is using. Since the A32 and Z32 MAF differ the most at higher voltages, the closer one gets to the limit of the MAF the more the AFR is going to change.

Agreed. Also, I know that at least one other person is using a different type of MAF (mardi) which reads even more airflow. My question for that is what needs to be calibrated for even higher boost levels. I know that you're planning on upping the boost soon. Too bad you're moving.

Mardi is still on the Z32 MAF from what I know. He has talked about running a Cobra MAF but I don't think has tried it yet.

I am actually not planning on running anymore boost. I would have to build my tranny before any more power can be safely put down. I am a little above the power level where most guys lose 3rd gear.

From what I know, as the voltage curves of the A32 MAf and Z32 MAF get further apart it would cause a leaning out condition. And that is typical of the AFR I have seen of those who have this set up. So trying to run this set up and getting close to maxing out the Z32 MAF could get interesting. Alot of fuel may have to be added in the upper rpm's.

Thats why I went with the SFMU instead of just ditching an FMU all together. I like being able to tune the fuel curve very close. For those that don't know, the Cartech/BEGI and Vortech SMFU have tunable rising rate fuel pressure increases.