Is running the stock 4BAR ok in this situation because of his 15 psi boost? So, if the K04 was boosting 20 psi would that then require something for fuel trim like a 5BAR? I finally had to order a k04 to replace my k03 on my 01, it's making the "sound"...250K so it doesn't surprise me. I'm running the Speedtuning mild K04 tune at 20 psi and stock injectors. Speedtuning told me the told was written for a 5BAR, but with my K03 the fuel trim readings via Vag-Com were right on the nuts. With that said, once I install my K04 next week, my assumption would be to install the 5Bar I purchased, however how was I able to run the K03 on the K04 tune at 20 psi without going lean?

Hmmmm....BTW...I was able to get a nice BW k04 cheap....thus is why I'm not going bigger.

 

The 5bar gives more overhead on fueling availability. A K04 may (and probably will) out-flow the stock injectors @ 4bar, which isn't a good situation to be in (lean fuel mixture). The 5bar FPR will give it just a bit extra fuel to better prevent lean situations. And let's assume the tune was written for 5bar (nobody in their right mind would write a 4bar/stock injector tune for a K04).

Just out of curiosity, have you done a boost leak test?
Normally if you have a boost leak, that is likely to cause a negative fuel trim (subtract fuel, AKA running rich). But if you have less fuel available, that could cancel out the negative fuel trim that should otherwise come up.
Just a thought.

 

I have not completed a boost leak test. However, my HG at idle is -21, and I was always consistently boosting between 15-21 psi with my k03, so I assumed there was no need to do so. With that said, would there still be a good reason to conduct a boost leak test?

 

There could be. Even with vacuum and boost leaks my car will still idle at 20-21 in.Hg.

 

Another suggestions someone on Audizine made was how poorly the stock injectors flow on a k04 tune and 5BAR, any input on this? He also suggested I buy some 315CC Red Devils, not sure what those are, but couldn't find anything red other than 315cc Bosch for about $225 or so a set. He said to determine how much fuel is flowing with the 315's. and from there adjust as needed to run virtually the same values as the stock injectors on the 5BAR.

I'm not even sure how to do all of this, or even know if it's worth it/good idea? Can someone please explain their thoughts?

 

I saw that, IMO it's not worth it. You wouldn't only need injectors, you would likely also need an adjustable fuel pressure regulator F(AFPR), and those start at about $80. You'd need a fuel pressure gauge as well. So you'd be out at least $300 for something that probably won't change anything.

It is totally doable though... I dunno how good you are at math, but here's a simple equation to determine the necessary new fuel pressure knowing your old pressure, new fuel flow (cc/min), and old fuel flow:

New_pressure = Old_pressure * (Old_flow / New_flow)^2
So let's say you went to 315cc, and stock injector fuel flow is 270cc/min:
New_pressure = 5.0bar * (270cc/min / 315cc/min)^2
New_pressure = 3.67bar

So you would most likely need an AFPR, or run a bit on the lean side with a 3.5bar regulator.

In any case, from what I've read online a 5bar on the stock 270cc/min injectors is fine with a K04 on a more mild tune (which yours probably is). The AEB stock injector is something like 210cc/min, and GIAC also offers a K04 tune which uses stock injectors and a 5bar regulator... so in that case there really isn't enough fuel. But that's not a problem you're having.