SFMU Tuning Help

[dsm9]

i've been tryin to tune my car for a week now and i cant get it any leaner....
when i first hit boost my car goes way too rich but as i build boost it starts to lean out and take off but at first it dives rich and boggs for a second or two...
on my safc my 450s are turned as far negative as they will go (for the first couple thousand rpms) so now im gonna buy a sfmu and keep the safc to fine tune it

my question is what static pressure do i need to run between 7-10 psi? i understand the equation i read on 2gnt but he was only talkin bout 8-9 pounds.
also if anyone is running a similar setup (450s & 255 walbro) what size fmu works for you?
(it does not have to be perfect because i will use the safc to fine tune)

Thanks for your help
Brandon

 

[96TurboGS]

With a safc you can get away with 20-30 psi idle fuel pressure and still manage good millage with a 14.7:1 idle.

Here was my old set up:
Idle fuel pressure: 30psi
Size Disk: 6:1 (i believe the second largest)
Ring: largest
Spring: silver (if it doesn't work for you try the black one)

With 450's you are good for ~16 psi depending on the size of your turbo.

Make sure your bleed valve isn't left open (this sounds like the prob), when you blow into the vac line you shouldn't hear any air coming out of the sfmu (make sure its screwed all the way in). Make sure you have the correct disk. (6:1)

 

[dsm9]

well i dont have a sfmu yet
im tryin to see what the best one is for my setup
but thanks for the response

 

[rstare]

If you get an sfmu you don't need the SAFC at all.
Chris is using 450's, he's in the mid teens for idle fuel pressure.
The sfmu would be the best way to go, not counting MS or PF.
SAFC's really arn't very good on boosted 420a's, read below.
http://www.dsmtuners.com/forums/dsm...ons/272661-why-s-afc-iis-dont-work-420as.html

 

[chris712vt]

Yeah I've got an SFMU + 450s setup right now. I had the boost at 15-16psi without any problems. I had my idle fuel pressure somewhere around 18-20, but I had to run a larger return line in order to get it that low (the lowest I could get with the stock return system was like 40psi).

 

[dsm9]

will the sfmu really get the afr's that perfect?
i already have the safc so i was just plannin on keepin it to get them perfect
chris- what size disk were you runnin on your setup??

i have a safc I not II so i dont know if theres a difference but it def. works on my car
i just have too much fuel for the low boost right now and im tryin to even shit out

 

[dsm9]

im guessing 6.1 7.1 or 8.1??
any suggestions?
best place to buy one??

 

[rstare]

SAFC can only be used to alter fuel out of boost. Once it goes into boost you need to have something else. I assume right now you also have an fmu, or something else of the sort?
The reason some people get an SAFC with a fmu is because the fmu cannot control idle fuel at all, so bigger injectors is going to run you super rich at idle. So, some people get an SAFC to alter the idle fuel in conjunction with the fmu.
The sfmu can do both of these. It drops the idle fuel pressure so you can use bigger injectors without worrying about running super rich. Once you do this the purpose of the SAFC has been taken over by the sfmu and the SAFC is no longer needed.

You can get the sfmu pretty close to exactly where you want it. It has multiple disks for different rising rates and it also has a bleed valve so you can slightly alter whichever disk you choose.

Vortech sells them on their site, I would suggest looking around for a used one though.

 

[dsm9]

well right now i only have the safc...
my car is fine when i get up to about 5 or so pounds but for the first few pounds if boost it is not enough air for the amount of fuel(too rich) so my car boggs for a second or two


i just want to know what size disk (6.1 7.1 8.1 etc) i should get for my setup of 450s 255 pump and 8-10pounds of boost.
thank you

 

[dsm9]

ok i realize now that a sfmu and a fmu are 2 totally different things...my bad
but right now i dont have enough money to get a sfmu
so i guess i plan on keepin the safc and gettin a fmu to help lean things out under boost
so i guess a 6:1 disk would be good for a fmu?

 

[silvreclips]

I would save up for the SFMU. The FMU sucks compared to the SFMU. You will be able to control your fuel much better. I wouldn't risk my motor by going cheap on a fuel system. Everyone I know that started out with a FMU has upgraded it not long after. It would save money in the long run. Used SFMU aren't that expensive either.

 

[dsm9]

yeah man i agree but i dont boost every time i hit the gas
and i could get the sfmu eventually...
i just wanna know opinions for like short term
thanks for the concern

 

[dsm9]

so im just gonna get a 6:1 fmu for now
ill get the sfmu later
anyone had success with this setup (450s, 255 pump, 6:1 disk on 10 pounds)
and i can also lean things out with the safc if need be
just lookin for suggestions/comments

thanks

 

[dsm9]

??? anyone have any input? i plan on tryin out this setup within the next week

 

[rstare]

Go with the sfmu, that's my input. It's not much more expensive.

 

[dsm9]

ok man.
then i can get rid of the safc too?
thanks.

 

[dsm9]

oh yeah what size disk for the sfmu (10 pounds 450's and 255 pump) and best place to find one?

 

[rstare]

I'm using the 3.62" disk with 315cc injectors. With the bleed valve closed I hit ~ 10.5:1 AFR at 10 pounds of boost. I use the bleed valve to lower the rate, but I should probably try switching to a smaller disk and see if that gets me closer, without using the valve.

Edit: Yes, you can get rid of the SAFC. I would check 2gnt FS section, they come up pretty often on there.

 

[dsm9]

does it come with all different kinds of disks and shitt??

 

[rstare]

It should come with a few different size disks as well as a few different springs.
Super Fuel Management Unit | Vortech Superchargers