s-afc and fmu Q

[babyblueMX3]

hi guys..I'm trying to gather all parts now and thinking...do you need an fmu if you have a s-afc because basically the s-afc controls the amout of fuel and the fmu does the same thing excpet you can adjust on the s-afc the fuel on different rpm range...Am I just out of the track now or this makes sense??

[curtklze]

FMU controls fuel pressure.
S-AFC controls injector pulse, they are not the same and dont do the same thing.

F.M.U = Fuel Management Unit.
also known as a RRFPR, Rising Rate Fuel Pressure Regulator.

this is the easyest way to add a proportional ammount of fuel to boost.

eg. a 8-1 RRFPR will add 8PSI of fuel pressure for every 1 PSI of boost pressure.

so at 10 PSI of Boost the RRFPR will add 80 PSI of Fuel pressure ontop of your stock fuel pressure (usually around 40 psi) so you would have a total of about 120 PSI of fuel pressure.

this is what adds the extra fuel needed for all the exter air pumped into the cylinders.

it works off of a pressure "signal" to increase pressure ONLY in resonse to BOOST PRESSURE.

the S-AFC modifies the signal from your MAF/VAF/or MAP sensors to trick your stock computer into giving a little bit more or a little bit less fuel for a given throttle posistion and RPM.

It can be set up so that insted of using RPM and Throttle POS, it can use RPM and boost (wire in a MAP sensor insted of your Throttle sensor)

BUT it can only increase/decrease injector pulse by + or - 50% also if your max fule pressure is 40 psi and you run 40 PSI of Boost then they cancel each other out and no fuel will flow regardless of how long the injector stays open.

so you have to raise the fuel pressure whenever you add boost PSI.

A popular thing to do with boosted imports these days is to use a RRFPR to increase the fuel pressure in proportion to the boost so that the car runs a little rich under boosted conditions, then use the S-AFC to fine tune the fuel delivery and lean it out a little to optimize the A/F ratio under boosted conditions.

This way durring normal (non-boosted) driving the stock computer can handle eveything by its self, when the boost comes on the FMU will raise the fuel pressure to provide the added fuel needed and the S-AFC will fine tune the injector pulse as needed to keep a constant A/F ratio.

Now for low boost applications 4-8 psi the stock FPR is usually good enough to increase the fuel pressure (its a 1-1 ratio, 1 psi boost = 1 psi Fuel pressure) so if you add 6 psi of boost to a stock system you will have 46 psi of F/P, but since the 6 psi of boost is pushing up on the fuel stream you actually still only have 40 psi of F/P getting past the injector. so if 40 PSI was good for 0 boost it wont be good enough for 6 PSI of boost.

This is where people go to larger injectors and S-AFC. the larger injector will allow more fuel to flow durring the same ammount of "on" time at 40 psi than a smaller injector, and the S-AFC will fine tune your system to make the injectors pulse less when there is no boost and more when there IS boost.

however on the MAZDA V6, our ECU does not use the VAF for air flow readings at WOT. when the VAF reaches it MAX reading it relies on a set fuel and timming map in its memory, so the S-AFC is useless on the Mazda K series ECU since it modifys the VAF signal going to the ECU.

(as far as I know.)

The RRFPR is used more often when the stock injectors are to be used or for high boost levels (14+ psi)

It will raise the fuel pressure in responce to boost pressure so that more fuel is forced into the cylinder when the injector opens.

This way the stock computer will pulse the injectors the same as its always done, but the needed fuel will still get into the cylinder.

The best way to set all this stuff up is with a chassis dyno with a wide band O2 sensor so you can see EXACTLY what is going on with the A/F ratio.

AND REMEMBER, start off too rich (too much fuel) and lean it out (less fuel) bit by bit, too lean and you melt your pistons. its better to be a little rich than a too lean.

<small>[ January 27, 2004, 12:21 AM: Message edited by: curtklze ]</small>

[curtklze]

that was the long version, this is the short answer.

V6 K series You NEED!! a FMU (RRFPR). You HAVE to have one.

BP 4 cylinder + custom turbo, FMU, injectors and S-AFC would all be good to have.

4 cylinder mazda including, BPT, B6T you dont need to have a FMU but if upping the boost maybe swap injectors and get a S-AFC.

<small>[ January 27, 2004, 12:27 AM: Message edited by: curtklze ]</small>

[thebox]

I just have one question... i could probably find this info somewhere else....BUT im gonna ask here anyway. Since the K series ECU doesn't read VAF signal at WOT how the hell do you use a computer to deal with that situation? Can you use a computer at all at that point, or do you just run enough fuel through injectors+RRFPR to run properly at WOT, and then use a computer to correct for all the rest of the throttle position? Did that make sense or did I say that badly?

[maldo]

however on the MAZDA V6, our ECU does not use the VAF for air flow readings at WOT. when the VAF reaches it MAX reading it relies on a set fuel and timming map in its memory, so the S-AFC is useless on the Mazda K series ECU since it modifys the VAF signal going to the ECU.

(as far as I know.)

This was believed to be the case with the M1 Miata but was found to be unfounded so I don't know the truth behind that statement in regards to the K series engine. There had been some tests done, they may apply to the K series, I will see if I can find them.

[babyblueMX3]

thanx curt for all the infos...
so basically if I'm going to run 7-8psi on my ze there's no need to use a s-afc..just a fmu like the vortech 12:1 fmu would be fine, right?

[curtklze]

the problem with the V6 K series is that they use a VAF, it has a mechanical plunger, under High air flow it WILL reach its limit.

It WILL physically stop moving. So since it is at its limit the signal will be say 5.0 V, the computer sees WOT, and the VAF hit 5.0V, so it makes no sense to try to modify a stedy signal

I dont know waht the best ratio FMU is to use.
8-1 10-1 12-1 ?

I would call vortechs tech support line ask them, also they have ones where you can swap out plates and change the ratio your self. go big check how rich you are then go 1 step down and check again ect ect.

<small>[ January 27, 2004, 02:29 PM: Message edited by: curtklze ]</small>

[babyblueMX3]

k thanx I'll do that

[curtklze]

I just read that you want to run 8 psi on a ZE. I think that this is a bit high for the ZE. I will be boosting my own ZE this year and I plan on only 3-5 psi. this will provide an aditional 50 H.P.

to run more boost like 8-10 psi I would recomend going to larger injectors (2.3 millenia supercharged injectors) or get R.C. Engineering to make you a set, and going to a stand alone ECU like SDS, Haltek, or something simmlar.

The main reason for this is because the stock ZE/2.5L injectors can only flow enough fuel for approx 250-260 H.P. at approx 80-100 PSI.

since we cant use a S-AFC on a K series engine the only way to compansate for the bigger injectors is to go to a stand alone ECU.

[BATTOSAI]

On my turbocharged K8 I ran the Vortech 8:1 fmu, s/afc, and Kl injectors combo and run it perfectly at 10 psi with a good A/F ratio.(with a 255 walbro fuel pump) I suppose that maybe the same setup can be applied to a Kl(or ze) with the Millenia injectors. I didn´t use any afpr for lowering the base pressure in order to not running rich, I had the S/afc for that mission. I had all the disks for the FMU and realized that both 12:1 and 10:1 were way rich!
If you divide the millenia injectors size, by the stock Kl ones (280/220) you get a 1,27 and if you divide the Kl inj. size by the standard K8 (220/175) you get 1,25. The comparison of the two values is quite similar, so maybe you can have a succesful result as I did. Start with the 10:1 disk and adjust it with the S/afc. I would be sure that you can´t fail! (for what I have experienced on my K8) and if you are too rich swap to the 8:1 disk (purchasing all the caliber disks is advisable)

[curtklze]

Originally posted by BATTOSAI:
On my turbocharged K8 I ran the Vortech 8:1 fmu, s/afc, and Kl injectors combo and run it perfectly at 10 psi with a good A/F ratio.(with a 255 walbro fuel pump) I suppose that maybe the same setup can be applied to a Kl(or ze) with the Millenia injectors. I didn´t use any afpr for lowering the base pressure in order to not running rich, I had the S/afc for that mission. I had all the disks for the FMU and realized that both 12:1 and 10:1 were way rich!
If you divide the millenia injectors size, by the stock Kl ones (280/220) you get a 1,27 and if you divide the Kl inj. size by the standard K8 (220/175) you get 1,25. The comparison of the two values is quite similar, so maybe you can have a succesful result as I did. Start with the 10:1 disk and adjust it with the S/afc. I would be sure that you can´t fail! (for what I have experienced on my K8) and if you are too rich swap to the 8:1 disk (purchasing all the caliber disks is advisable)

Im suprised that the S-afc would work. what are your air flow readings from the VAF when you are at full boost?

[babyblueMX3]

curt you said i won't be able to use the kl injectors over 250hp...I read in many places on probetalk that many people are running stock injectors and have around 240-250WHP so that's more than you said..i was thinking too of getting the millenia 280cc injectors...
my_probe_is_faster on probetalk runs over 9psi on his ze and don't have any problem with it...i read many times too that 7-8 is prolly the max boost for the ze..I mean i don't plan to start with 8 psi but I'll owrk my way to it

[curtklze]

I would find out exactly what he is using on his car. I havent turboed my car yet so I cant speak from experiance, I can only go by the info I have collected.

The H.P. rating for the injectors may have been for naturaly aspirated (non turbo) but I cant remember.

The Key is Tuning the Air/Fuel ratio and keeping it safe.

all it takes is 1/2 a second of beeing too lean and you will melt a piston. and I have seen MANY A/F ratio graphs of turbo cars that start out safe then around 4500 go either very lean or very rich then go to almost normal again. Its in that dip that damage can happen.

I remeber the Turbo Matrix a magazine put together, they made like 275 WHP on the stock engine with the stock 11-1 compression and 91 pump gas. they drove it for about 6 months and 3000 miles before they melted the thing.

not to good for our needs.

I dont know everything but I can give you the basics and some starting points to keep your car running strong for a long time with out self destructing.

1 more thing, I know that honda ECU's can compansate for about a 5%-10% larger injector with out modifactions. the computer will just lean out the pulse to compansate for the extra fuel flow. I dont know if our ECU's can do this or not.

It seems that bossati is using the S-AFC only for non boost conditions to control the larger injectors and using the FMU and incombo with the KJ(millenia) injectors for when its on boost.

This is a very good Idea, since the S-AFC is usless when the VAF reaches its limit inder boost.

good job battosai.

But I would still like a way of fine tuning the injector pulse when under boost at high RPMS.

any Ideas?

<small>[ January 29, 2004, 08:03 AM: Message edited by: curtklze ]</small>

[BATTOSAI]

It seems that bossati is using the S-AFC only for non boost conditions to control the larger injectors and using the FMU and incombo with the KJ(millenia) injectors for when its on boost.

that´s the key!!

[BATTOSAI]

As many of us are using boost dependant fuel enrichers, why can´t we put a travel restrictor on the VAF and let it throw a value in which the ECU doesn´t get on WOT and adjust the TPS to do the same thing? we will be working always on open loop, so we can use the s/afc on any time! I suppose that the VAF would tell the ecu the WOT condition at something before 100% VAF travel, so maybe we should ask to those guys who have studied the VAF-ECU relationship in deep if this can be done, and what negative effects it would have on driveability or performance. I have a good friend here in Spain, which used to be a Mx-3.com member who was involved in MAF conversions with Mike P and Andrew Brownsword, if I recall the names correctly, so maybe he can throw us a good hand on it!! If you have any suggestions or ideas , we could make the awesome S/afc work on all RPM and TH% ranges!!!

<small>[ January 30, 2004, 10:17 AM: Message edited by: BATTOSAI ]</small>