i've did a search but no answer yet..well i just installed the sfmu(stock injectors,2.72 disk,hard spring,stock fmu removed ),50psi idel fuel pressure and i get about 90psi at wot(7lb of boost).my question is that when it goes into boost my air/fuel ratio guage goes down to red(2nd last red bar)then goes all the way up(rich).i was wondering if that was normal for it to go from lean(2nd last bar)then rich? also when i'm in boost it feel like i'm loosing power at around 4500 rpms(like its falls flat around that rpm range).

my setup: hrc stage 2 kit with 20g turbo,howell long rod kit(8.6.1),sfmu,spec stage 4 clutch.

man, with your set-up i'd be REAL careful about only using a blinky-light A/F meter. THey aren't realy all that helpful anyway with true A/F readings. i know that before i blew my motor i was reading 1.02-1.05 on my meter and i was lean in real life.... get a wideband!

Yes get a wideband and an EGT gauge. If you have that setup, you should get some larger injectors. Stock ones simply cant handle crap.

Then, call Vortec and get the calbration kit for the SFMU. In the calbration kit you will find a vacuum resistor. Put the vacuum resistor in line between your vacuum source and the SFMU. That should clear up your small lean condition. Install the resistor with the larger end toward the SFMU.

Originally posted by siueclipse
Yes get a wideband and an EGT gauge. If you have that setup, you should get some larger injectors. Stock ones simply cant handle crap. Then, call Vortec and get the calbration kit for the SFMU. In the calbration kit you will find a vacuum resistor. Put the vacuum resistor in line between your vacuum source and the SFMU. That should clear up your small lean condition. Install the resistor with the larger end toward the SFMU.

I would say that you are running lean. I have the Hahn stage II with the 16G and I am running 6 psi of boost on the stock injectors at 110 psi at full boost. With this setup I can only get it as rich as 12.2:1 at WOT.


(Hopefully my Megasquirt will come soon)

Originally posted by siueclipse
Yes get a wideband and an EGT gauge. If you have that setup, you should get some larger injectors. Stock ones simply cant handle crap.

/\/\/\/\/\ Yeah exactly...
Your engine is like a ticking timebomb with a 20G and those tiny ass injectors...

the wideband and larger injectors is next on the list of things to buy.i do have an egt guage and at wot its a lil under 1500. should i change the disk in the sfmu to the larger one?would upping the idel fuel pressure to 55 help?

You should be using the largest disk(uses NO ring) in the SFMU for stock injectors. The 2.72 is the second to largest disk. At 7 psi boost, you should be at at least 100 psi fuel pressure, if not a bit more.

Originally posted by XtremeRS
You should be using the largest disk(uses NO ring) in the SFMU for stock injectors. The 2.72 is the second to largest disk. At 7 psi boost, you should be at at least 100 psi fuel pressure, if not a bit more.

i swaped out to the largest disk on the sfmu, 55 idel fuel pressure and it worked.i'm a lil over 100 psi at wot and it feels great..thanks for the advise XtremeRS.boost is alot smoother now but it still seems to fall flat at 5500rpms(my plugs are gaped @ 032).

I was thinking your idle pressure is a wee bit high. Am I wrong? I was always under the impression that it should be no higher than 40ish after vac has been connected.

Originally posted by DJ420a
I was thinking your idle pressure is a wee bit high. Am I wrong? I was always under the impression that it should be no higher than 40ish after vac has been connected.

In the instructions with the Hahn kit, it says to set the idle pressure at 55 psi (that's where I have mine set).

so try the largest disk and same hard spring?what should my idel fuel pressure be set at?i always thought it was 45-50 for stock injectors.

The power loss is likely due to improperly gapped spark plugs. Try changing the gap and you will see a difference. I gap mine @ 030 and seems to work great for me. I would try several different gaps to get it right for your car.

I dont think plug gap is the issue here really..I've run .032 on mine at 15 psi without any issues at all. What exhaust are you running? The stock exhaust and muffler? If so, then thats prob why power starts to fall off at higher rpm. Stock exhaust is just a bit too small to flow well when boosting at higher rpm, esp if you are running the stock muffler too. You also may want to be sure your boost is not falling off at high rpm eigher..just pay attention to your boost gauge.

i have a custom exhaust.. 2.5 inch pipes all the way to the muffler(aftermarket muffler). it pulls hard til about 5500rpm and it seems fall flat beyond that rpm range,boost guage says 7lbs.

100+ psi fuel pressures....

Man, I would strongly suggest getting larger injectors before even worrying about anything else...until then just run 5psi or so..

That's what I would do.

i have a set of high Impedance bosch injectors(#30)(0 280150 218)laying around.i was wondering if u guys know if those injectors will work on the 420a motor.if they do,what idel fuel pressure should i be at with the sfmu?

They are still too small...312 cc/min are not enough. You need at least 550 cc/min to use that turbo effectivly.

isn't the star turbo(t3/t4) bigger than the hahns 20g?don't star kit runs 8psi with stock injectors?i know i need larger injectors and will be geting some next week but whats the largets injectors i can use with the sfmu without the safc?