---

---

---

Now.. to all that FMU/AFC stuff... pros and cons of each one.

First, 'the hack'.
Well, before I put my turbo on - I thought of going that way.. larger injectors, etc, etc...
Anyhow, got 310cc injectors from Honda Prelude, put them in, resistor box... put SMT5 to tune them.
Well, it ran... actually, due to 'hack' I got even little more power than before. How? 1st, I could run it a little richer... and 2nd hack advances timing.
OK, here's the *bad* thing about hack - timing advance. Why it happens?
First you need to understand how hack works/what it does.
Simply put - hack alters MAP signal. Since you put larger injectors, we need to lower duty cycle of 'em to keep mixture at same ratio as it would be with stock injectors. The way hack does it is to lower MAP signal - thus ECU thinks there is less air going to engine, and thus reducing duty cycle of injectors -> which results in approx same mixture as with stock injectors (if tuned properly).
But! reducing MAP signal did not only reduce ammount of fuel.. since ECU read there is less air, it also advanced timing!
Now that's where things get tricky.
As you know MAP reads ~0.9V in idle, at 0psi it reads 3V. At 3.1V (~0.5psi or even less) ECU goes in limp mode, since it doesn't have maps for boost.
At 5V MAP reads 10-11psi.
So... let's assume you got 440cc injectors, and have -40% set all way on AFC.
Now, what will ECU read: at 0psi it'll read (3V * 0.6) = 1.8V. So whis is what ECU 'sees' when you're running at 0psi. 1.8V for ECU is somewhat big of vacuum, and thus it also advances ignition. At 11psi you have 5V on MAP, and (5 * 0.6) = 3V ECU reading.
Now we can also throw in MSD BTM to make even more mess
What does it all come down to?
Well, it comes down to this: At vacuum you are advanced in igniton timing. At 0psi aswell. At 1psi, you are *stll* advanced even with MSD BTM - since ECU advanced rather much, and BTM just started to retard.
At some 4-5psi, if you'we set MSD BTM to 1 degree per psi, you would be to somewhere near stock timing at 0psi (remember at 4psi you still got advanced timing from ECU, and some retard by MSD). However at 11psi - ECU will finally read 3V (and put no timing advance), and BTM will retard to what it was set (like 11 degrees now due to 1degree per psi).

Another issue is part-throttle boosting.
Imagine 'cruising' on freeway at 4-5psi, at 50% throttle. Not hard to imagine, right? But imagine what yr engine thinks of it... or actually - ECU.
1st - it reads 50% TPS, 2nd it reads vacuum (due to hack) ... and end result - closed loop! Hmmm... I *don't* think at 4-5psi closed loop is such a good idea.... do you?

And last but not least - one *big* (?) advantage of AFC... you can 'tune' it! Yay! .. yes, you can set at what % you'll reduce MAP readings for ECU to read.. kinda neat to make that perfect A/F ratio at WOT... too bad at closed loop ECU does pretty good its thing
And that 'tuning' is why many people swear on AFC... too bad they always forget the 'hack' part when talking about AFC and why it actually stands there...

Uhh.... now that was lotsa text... hope you understand now what AFC does for timing....

Well, now we can cover FMU.
It's rather simple.. untill 0psi yr car runs like stock. When there is some boost missing link/FCD will fool ECU in not seeing boost, thus just making it see 3V. What does this mean? that at 0psi, as at 4psi and 8psi - your timing will be all the way the same, as opposed to advanced with AFC.
Whoa.... now that seems like FMU is *better* what AFC, doesn't it?
Well, partly - since FMU has it's downside... what it does is raise fuel pressure to give more fuel for more air. This makes lots of stress on injectors and fuel pump (inline is a must have for FMU!).
On a sidenote.. if using MSD BTM... you get that real deal. You'll timing retard will be exactly what MSD does, for each psi you'll have X degree retard and no advances from ECU.

Standalone management.. think there is no need to say anything.. as you can adjust just about everything with it... timing/fuel... and it *is* way to go if you got $$$.


Now, for conclusion.
As I said on beginning of post: I tried larger injectors... but as you see in my sig - I run FMU. Well, with larger injectors my car just didn't feel smooth as it was before... I really tried for some 2 months to get rid of all quirks... but was unable. So I went FMU way.
Many people also comment FMU on making 'jerky' boost transition. Well, I can only speak from my experience - I have *no* jerkiness at all, car runs really smooth, when going in boost/out of boost.. all the way!
Only thing that does kinda scare me is high fuel pressures thue to FMU (10:1 ratio)... and that I get boost creep to almost 9psi (0.6bar).
But, it runs (so far) great... I have stock timing and have no detonations... even at 5th gear pulls (when I creep to 9psi).

... and as for part throttle boosting... from what I could've read of A/F gauge - no matter how imprecise - at part throttle with FMU when going into boost it starts going to rich part... which *is* good.

All in all... FMU is good for lower boost setups. It works.
AFC does work too... but you should know what it does.

---