Syonyk

*plugs ears* I don't want to know, I don't want to know...

Well, as DigitalSynthesis pointed out on IRC, a SAFC-II really is a gateway drug. I said I'd be content with it, he said something along the lines of "Eh, right. I'll give it 3 months until you're looking at a full standalone." Well... 2 months later... anyone selling a Haltech?

I'm curious as to just how bad the stock S4 NA ECU is compared to a standalone. I know the S4 ECU has a rather slow processor, and from a ECU analysis website I ran across ages ago, apparently can only fire the spark plugs accurately up to 7700 RPM or so. The S5 ECU has a faster CPU and some other improvements, so I suspect it's not quite as bad.

I've heard that the NA ECUs will sometimes dip down into high 9:1 AFRs at high RPM/load, where optimum power is somewhere around 13:1 - 13.5:1. Is this accurate?

Also, I've heard that advancing timing rather significantly can provide some response & power gains, but tweaking the CAS too much leaves a subpar idle from the timing being too far advanced. Plus, the ECU advance maps assume the CAS is set properly.

From what I've been able to determine by goofing around with my SAFC and the stock O2 sensor voltage, the ECU does run really quite rich throughout most of the power band. I have to pull out 30-40% around 4000 RPM to get the mixture back to stoich, and I haven't been able to pull out enough fuel up high (6000-7000 RPM) to get the mixture to stoich. I know that's not the best place for the fuel mixture to be, but it's what I can detect...

Finally, it seems that doing some significant leaning up high has a MAJOR impact on how much fuel I use "canyon running" - without the SAFC, I could chew through a quarter tank of gas without even trying by just keeping the RPM above 4000 and my foot on the floor. After leaning things out, it seem I use a lot less fuel doing the exact same runs (and arguably going slightly faster as well).

Has anyone done detailed analysis of the ECU performance in the car (AFRs, actual advance, etc)? And, if so, how does it end up comparing to a well tuned standalone?

-=Russ=-

NZConvertible

The rich mixtures have nothing to do with the ability of the ECU itself; that's just Mazda's very conservative tuning, which is perfectly normal for a mass-produced car that has to be designed to survive anything thrown at it during the warrantee period...

You can't compare the tuning of the stock ECU to a programmable one as you suggest in your last sentence. A programmable ECU can be tuned for high-risk max power, or high economy, or low emissions, or exaclty the same as the stock ECU if you really want. A well-tuned ECU for a street car will be a compromise of all of those things. A programmable ECU can make an engine run as well or as poorly as the tuner wants.

Comparing raw computing power is pretty pointless too. Put your current PC next to a Commodore 64 (just a little older than the FC) and you'll have a pretty good idea...