Well I am upgrading to a 3.12 pulley this weekend. I have a begi adjustable fmu, inline fuel pump and a safc2 will this be enough or will I also have to upgrade my injectors? Also I was running 265 hp with out the safc2 I was very rich with some tuning with the afc2 and the 3.12 pulley and test pipe I am also installing do you think I will be able to hit 300 hp??

 

You will be fine without the injectors. I Ran the 3.125 w/ stock injectors for a year and no ill affects. I think with a good tune and a ypipe, test pipe, and catback, you will be at 300hp.

 

Using a stock base fuel pressure of 34psi, the 3.125" pulley generates ~11psi, Stillen kits 8:1 FMU standard disc, and Vortechs FMU equation for calculating fuel pressure shows:

1/2(base fuel)+FMU ratio*boost = 0.5*34+8*11 = ~105psig of fuel pressure.

105psi(94psi actual) through 290cc injectors(stock) is equivalent to having ~426cc injectors. This would support:

426cc@80%DC = ~301whp<~~~UNSAFE fuel pressure
426cc@100%DC = ~376whp<~~~UNSAFE FP+NOT recommended DC

If you drop down to a 6:1 FMU disc, you'll see a safER fuel pressure of 83psi(72psi actual) making your stock injectors flow ~373cc/min and that would support:

373cc@80%DC = ~264whp<~~~HIGH fuel pressure
373cc@100%DC = ~330whp<~~~NOT recommended DC

Now, if you were to pick up a set of Power Enterprise 380cc P-N-P injectors(~$450 used/$870new) and run a super safe stock fuel pressure with the 1:1 OEM FPR, you'll see 54psi(actual still 43psi), which would support:

380cc@80%DC = ~269whp<~~~SAFEest possible setup
380cc@100%DC = ~336whp<~~~NOT recommended DC


In short, people HAVE run 100+psi through stock injectors for decent periods of time although it will prematurely kill the injectors and is pretty risky. So, first I'd drop down to the 6:1 FMU disc IMMEDIATELY, since you don't need that much fuel pressure for 275-300whp. Second, I'd try and find a set of PE380cc injectors and run a 4:1 FMU disc. Unless you're going to run an eManage or you can control the additional fuel during coldstarts with your AFC, you'll need to drop down base fuel pressure a bit so that's why you'll want the 4:1 FMU ratio still. *OR* you might just get away with a Walbro GSS342 HP pump and toss the FMU, however I'd carefully try this only with a WB02 dyno.

FINALLY, don't just do this blind on my GUESStimations. Make sure you monitor your actual fuel pressure and do some WB02 dyno tuning to find the optimal setup for your car.

 

I have a begi adjustable fmu so no need to change disk. I do plan on tuning the car as soon as its together. (prematurely kill the injectors and is pretty risky) kill the injectors I understand and can deal with PRETTY RISKY? as in what ENGINE DAMAGE,FIRE? I AM NEW TO BOOSTING AND TRYING TO LEARN AS I GO 426 cc@80%DC = ~301whp<~~~UNSAFE fuel pressure. Could you break this down for me. I think I understand how you get to 426cc and @80% is the injector cycle? What dose DC stand for? What would be a safer way to tune raise fuel pressure with the begi fmu and then back down with the safc2, or try to keep the pressure low as possible and tune more with the afc? thanks for any input

 

Engine damage. Supposedly, if you run that high of pressure and injector Duty Cycle(DC), ie time injector is open/on, it can stick open or worse closed. That means not enough fuel and you will go lean.

Good, then I'd drop it back to 7:1 and then 6:1 or possibly lower.

As for which is safer...raising fuel pressure or increasing duty cycle? I'd say do both. Keep fuel pressure around 80psi preferably below 80psi and duty cycle at a max of 90%, however you probably don't have a way to easily measure duty cycle. Basically, I'd adjust the Begi until the air/fuel ratio was ~11.5-12:1 on the RICH side across the board, and then REMOVE/pull fuel using the AFC to whatever AFR you feel comfortable with. Depending on your whp and these GUESStimates, that point should happen around 75-85psi of fuel pressure.

You'll need a fuel pressure gauge and a few dyno runs with a wideband 02 to properly determine this.

 

This is so confusing! So it's unsafe to run stock injectors, 3.125'' pulley, and the stillen 8:1 FMU? Even if you have the walbro HP pump too? I may never understand .

 

The Walbro just provides greater fuel volume then OEM even at higher fuel pressures to the fuel rail/injectors. The FMU increases the pressure to the injectors according to boost pressure. The more boost you run, ie smaller pulley, the more fuel pressure.

If you increase fuel pressure too high, ie 80+psi, it is not safe. If you don't have enough fuel pressure, then you must increase injector duty cycle(time injector is open) to flow more fuel. However, both of these methods are only bandaids to the real problem, which is the stock injectors are too small.

In short, you can get more fuel through the stock 290cc injectors by raising fuel pressure and running more injector duty cycle, however there is point you pass where you risk injector failure.

Any better? I'm trying man...I'm just not able to explain things for ****.

 

So basically if you're running around or over 300hp, no matter what pump or FMU you have, you need bigger injectors?

 

To SAFELY support 300bhp, IMHO yes.

Many others here will disagree probably, but for $500 or less for a used set of PE380cc injectors, you'd be wise to upgrade when pushing those power levels.

 

Guess I have to get injectors . Is ebay the best place to get used injectors?

 

They show up every now and then, but I'll PM you some links.

 

Thanks! I appreciate it.