Just wanted to share some thoughts I had today regarding Stage 3- w/ bigger compressor wheels.

[PSmalls::DoggieStyle]

As some of you know, I am planning on going stage 3- with K16 or RS6 compressor wheels. Just to clarify for those who aren't aware, stage 3- is bigger turbos with k03 software, stock fueling, 5 bar FPR (fuel pressure regulator), and the use of an MBC(Manual Boost Controller) either in place of the N75 valve (Controls boost via the ECU) or in parallel to somehow alter boost levels.

From what I have seen, K04s on stock fueling and 5 bar FPR start to max out the fueling at ~16.5 psi (~1.15 bar)near redline. With the bigger compressor wheels (K16/RS6) flowing more air at the same amount of boost, I assume that the same fueling setup will be maxed out at around 14.5 psi (~1 bar) near redline.

So far, people have taken two different approaches to altering boost levels from the normal K03 software levels. This is done in order to take advantage of the bigger compressor wheels' ability to flow more air in the upper RPM ranges (K03 software tapers to ~.85 bar after 5500 or 6,000 rpm because the K03s run out of breath, but the K04, K16, and RS6 compressor wheels can flow quite a bit more up there).

One approach is installing an MBC in series with the N75 valve. With this setup, the MBC is used *only* to alter the initial spike when you go WOT (wide open throttle). This does not in anyway increase boost levels in the upper RPM ranges, where the bigger compressor wheels have an advantage over the tiny K03s. The power increase is negligible IMO.

The other approach, which has shown better results in the power deparment and is more common among Stage 3- people, is replacing the N75 valve with the MBC. This allows you to set the MBC at a specific boost level, which the car will sustain throughout the RPMS while going WOT. This allows you to take advantage of the bigger compressor wheels' ability to flow more air in the upper RPM range. However, you do this at the expense of less airflow throughout the 2500-5500 rpm range along with reduced driveability (due to the removal of the N75 valve).

Because both setups have their downfalls, I have continually been trying to think of a way to get the best of both worlds. I think I found a way, but I'd appreciate some input. I'm sure others have tried this before and it may not be new, but I truely think it is the answer for those of us wanting Stage 3- with compressor wheels larger than K04s (because they won't be able to flow more than 1 bar near redline with stock fueling + 5 bar FPR) and would like to share. Here is a quick diagram of my idea (using hypothetical figures based on GIAC X chip) followed by an explanation.....



The black line represent the normal boost levels created by the ECU via the N75 valve when using a k03 chip, such as GIAC X, with a MBC in series to set the initial spike at ~18 psi (~1.25 bar).

The blue line represents the boost level when using an MBC in place of the N75 valve, set at 1.1 bar (It really should have been shown at 1 bar, but I fvcked it up . IMO, 1 bar near redline is about all the stock fueling can handle with the larger compressor wheels flowing so much air).

The white line is hypothetically what my way of doing this would look like. First of all, the MBC is in series with the N75 valve to cause an initial spike of ~18 psi (~1.25 bar). Then, with some tinkering, get the N75 set so it will only taper to ~14.5 psi (~1 bar) and sustain that to redline instead of the normally requested ~12.3 psi (~.85 bar). IMO, this creates the best of both worlds, MBC in parallel and the MBC alone, by taking advantage of the larger compressor wheels' upper rpm range flow while keeping stock like driveability.

Sorry for boring you guys. I didn't realize how long it was until I was done. Hopefully, someone got something out of it. Any input is welcome. I'd love to discuss this with anyone willing

[BUFFALONOGAROpebFATS]

and do you think that you will have enough head room with the injectors at that flow rate just in case you accidentaly run too much boost? ie adjusting the n75 for 14.5 and making a mistake oops.


thought you might want to think about/talk about that.

joe

[PSmalls::DoggieStyle]

FWIW, the 16.5 for k04s is with headroom also. Some people run 17 without the slightest problem.

[VerrÜckt]

redline.

[PSmalls::DoggieStyle]

I say start at 12 and move up slowly. Just replace N75 with MBC to get a sense of the limit.

[VerrÜckt]

[Mark P]

if you don't get bigger injectors. You're shooting yourself in both feet. If you put in a bigger turbo, you'll get more lag down low. If you don't give the engine more gas (since you've already stated the injectors are maxed out), you're not taking advantage of the positives of the larger turbos. You're ending up with a slower car.

Get some bigger injectors to support the higher airflow of the bigger turbos, then let's talk. Otherwise, you'll never get any good use out of bigger turbos.

My feel is that "Stage 3-" is K04's with K03 software, with whatever supporting stuff one adds - not specific to a 5bar FPR, stock injectors, etc.

[PSmalls::DoggieStyle]

[PSmalls::DoggieStyle]

[VerrÜckt]

more lag than standard K04's and will be more reliable and produce lower IAT's. We're talking minor changes in compressor wheel size.