I have heard some say a 5bar FPR compensates for stock injectors and some say with larger injectors you don't need a 5bar FPR. There must be a limit after which you need bigger injectors. Anyone know what that limit is? Any other pros or cons I should know about?

 

i have both installed 5Bar FPR and 72lb injectors, car runs great except for the higher fuel consumption especially after removing the cells from the cats.

 

Question ,why do you think the fuel consumption went up after you went catless???When I went from 200 cell to 100 cell ,I got a tad better milage and performance........For injector Pros,,safety cushion and a little more fuel for a little more power,Cons the added cost,,,,,For 5 bar Pros,,fast ,cheap and with most pump gas applications with modest turbo upgrades it will do the trick....Cons,Lean is not mean and could starve with out the extra cush when things change,,,,,IMO......Good Luck

 

Larry, It really depends an what brand of injector you are using, impedance-wise. I've had 58lb Bosch injectors and a 5bar for the last couple years and have been right up to the limit as far as safety. Still safe, of course, but NO room for improvement. I have recently went to 72lb injectors and what I believe is a stock FPR. We plan to tune soon and I believe I should be good with this setup. I also still have the Meth injection which helps a little on the A/F, probably why I don't need the 5bar, but Tony can elaborate if he sees this.

 

k24 straight you dont need a 5bar FPR....k24/18g at 1,2 bar i would recommend a 5bar FPR.....k24/18g over 1,3bar you need injectors and all more, at this point ask your tuner he knows exactly what you need

 

I've seen one vendor, whose opinion I trust, state that stock injectors are at 100% maintaining an acceptable AFE at about 545 HP.

More pressure doesn't mean more flow if the cycle is maxed out.

 

sure it does, IF the pump can keep up with the pressure increase. 100% duty cycle is an open injector, if you have enough pump margin to increase pressure, more fuel will be delivered out of the injector. The extra pressure may even bring duty cycle down from 100% (or some other high number), the whole point of a 5 bar. The issue with the 5 bar is that pump flow drops with increased pressure demand.

 

Earl, is the stock fuel pump up able to keep up?

 

The stock pump can keep up with max duty cycle on stock injectors with a 5 bar FPR. A flashed K16 car will usually hit 100% duty cycle with the 3.8 bar FPR (stock) so a 5 bar is a nice upgrade if you want to bring duty cycles back down. Its hard to speak in terms of hard limits since everyone's dyno/conditions are different -best way is to log injector time, calculate duty cycle and see where it lies. Some logs will show the DME commanding >100% duty cycle in an futile attempt to hit target AFRs -not good. My own rule of thumb: if you're upgrading your turbos (be it K16s+new compressors, K24s+new compressors or something else), do the injectors. Cons: They're a bit of a pain to install.

The stock pump cannot keep up with bigger injectors at 100% duty cycle (or even less duty cycle depending on how much bigger the upgraded injectors are) and 5 bar of pressure. Since the stock fuel pump is now the limiting factor with larger injectors, the less pressure you run, the more the pump can flow and the more headroom you have -this is why tuners do not recommend a 5 bar if you have a stock fuel pump AND upgraded injectors. Of course you'll also eventually hit the pump limit with the stock regulator as well if you keep increasing fuel requirements.

 

I know I am gonna get flammed for this, but here goes....

I know many people run 5 bar FPRs without issues, but why risk it? A fuel pump failure can be catastrophic to your engine. Running a 5 bar can stress your pump more than stock fuel pressure. Higher fuel rail pressure adds much more stress to the pump than bigger injectors. I have seen it in other cars numerous times. In a perfect world with a perfect new pump you would probably never see an issue at 5 bar fuel pressure. But these cars are getting up there in age and increasing fuel pressure is asking for trouble. And a pump failure at full boost is not a good condition. It isn't that difficult to upgrade injectors. I would go with bigger injectors.

 

??? It sure does. The injector is tested wide open, no pulse to get its flow. The more psi the more flow.

 

What about the added stress on O-rings and fuel lines? 5bar(regulator) plus 1bar (boost) is about 88 psi on the rails.

 

Not throwing flames here but just futhering the discussion, I don't think a fuel pump failure would likely lead to catastrophic engine failure even at full boost. No fuel, no power, engine shuts down, call tow truck.

 

HAHA. Complete failure engine don't run. Lower capacity because of pump failing will kick out those head gaskets. Or melt something

 

Zakly...lean is mean!!!