Good point. How much more flow with the 5BAR over stock and does that buy a bigger safety margin? If so, how much?

 

Melted parts don't mix well with a running engine. And fuel pumps don't always just stop pumping. Many degrade causing a reduction in fuel before they just stop. So if you are at 1.2 bar and 4000rpm and the pump starts leaning the Motronic has to try to dump fuel at it and/or pull your boost(limp mode) before the leaning leads to torching in the cylinders which happens really quick. It can cause an engine failure not will. It all comes down to what gives when the failure occurs. It is your engine, not mine. Do what you feel safe doing. But I would rather spend the extra 1k when the possible increase in pump wear from more fuel pressure may possibly cause 20k in repair bills. Even if the possibility is fairly slim. The difference in price between a new engine and having your engine torn down for a repair of internals is not much in many cases so call it a 20k bill.

 

A 5 bar will give you approx 14% more fuel over the 3.8 bar (if the pump can keep up).

Good points all around on the downsides of a 5 bar -one of the most common failure modes on the 996tt fuel system is a split feed hose right off of the pump, a 5 bar would likely accelerate that process.

 

For ease we will use a 500cc injector tested at 55psi (3.8bar) for a flow rate of 500cc, turn the psi up to 73psi (5bar) makes that injector flow 576cc. that's a 76cc increase. On the flip side the higher the fuel psi the less fuel the pump can pump. Think of it this way if you were to send a fuel line straight up the side of a building and the pump has a head pressure of 100 psi that it can pump and you put two taps on that line you can open and close one at a time, you would get more fuel out of the lower tap then the higher one. Same thing with 3.8 or 5 bar reg.

 

I agree with you if the fuel pump fails as you describe but my guess is that if it fails, another scenario in which the afr is way past "lean" would more likely occur which would make it less likely to melt anything. Knock sensors should help out as well.

 

So from what i have read do injectors and 5bar and upgraded pump what is the upgraded pump of choice?

 

the injectors you run will also dictate if you need a stock 3.8bar FPR or a 5bar fpr

you need to match the impedance(resistance) of the injectors with our german system and the rated FP that you will be running.

cant just grab injectors off the shelf and slap on a FPR.


the upgraded pumps generally are used are bosch 044 units they are inline pumps (piggy back in series with stock pump)

and when you get above the 750whp range people are running dual 044's to each rail with larger injectors

 

Absolutely no disrespect intended here, but I can't trust knock sensors at full boost. The computer is just not as fast as an explosion in your cylinder in many scenarios. I would rather take measures to prolong the life and health of my fuel pump than gamble on how it is gonna fail. Just my .02, but their is always two ways to skin cat.

 

do you run a 2nd fuel pump with that? 5 bar plus a 72lb should have a separate source, at least that's what I have been led to believe by my tuner

 

If there was any doubt, I would also add an upgraded fuel pump if I were doing the upgrade. I was just speculating on what might happen if the fuel pump failed. I was viewing it as similar to running out of gas at high boost.

 

To add to the confusion, what are the chances that the fuel pump will fail during the few seconds you are under full boost? For me, propbably 100% chance, but most likely not for most...

 

LOL---I hope you didn't just jinx yourself.

 

Yeah right? I hope to get on the dyno by the end of the week and finalize my tune after my upgrades. I could very well need more pump too.

 

Can't wait to hear about your upgrades. Any performance goals in mind, break the 5s barrier?

 

Nothing ground breaking...same old turbos, just better breathing with intake piping , Y pipe and bigger IC's. Also upgraded injectors from 58's to 72's. I'm guessing we might pick up 20-30 more whp at the same boost with a tad better spool?