Homebrew Stage 3 Idle Information....

[PSmalls::DoggieStyle]

Now that more and more people are doing homebrew setups, I thought I'd post some more info as questions arise. I recently had a request to log idle airflow, injector on time, and 02 voltages. Thinking that it would be helpful for others to see as well, I decided to post it......



Airflow at fully warmed up idle hovers between 3.8x g/s and 4.0x g/s, injector on time stays at 1.7ms, and 02 voltages rocket back and forth across stoich range. Note that this is with RS4 MAF housing modified to use Hitachi MAF.

YMMV, but felt like sharing. Would be interesting to see same info from different homebrew cars. Happy motoring.

[S4mig@PEB tuning]

[PSmalls::DoggieStyle]

[Hal_TT::CBP]

I need to get you some data, hoping to have a mod day with Zold-man over the holidays to install my pump and such. Want to validate my theories after as well.

[Snow Trooper Is Numb]

[Mike2kS4]

What kind of % are we talking about? The only RS4 Y'd car I've tinkered with also has some really odd fueling trims/curve.

I thought the Y might have had a small effect, but not a significant one due to it being considerable distance from the MAF element.

[Mike2kS4]

That's about .6g/s lower than my larger 90mm Bosch MAF and with greater fluctuation (4.5-4.6), but I run 20rpm more idle speed, but that *shouldn't* increase g/s by 10%. I'm running stock idle now, I'll recheck it.

[Hal_TT::CBP]

the RS4 Y(still on stock pump, wanted to measure some things with higher hp) and the idle is definitely cleaner. S4 Y does ok on the APR v2 Stg3 stuff and boost/throttle transitions respond quicker with it however idle suffers and part throttle vacuum/boost transitions stumble occasionally, like there is a hole in the intake charge or a cyl misfires(feeling wise, have not caught this condition in a log).

O2Vs were .86s pretty much under all conditions/gears with the stock Y. OXS temps ~795-800s. With the RS4 O2Vs are .87s with a .88 here and there and OSX ~820-840 tops so far. MAF readings are down slightly at idle but by a few 1/10ths at most. Hardly enough to draw a trend line against. Idle is smooth, no missfires to speak of now. Before with the stock Y cyl1 would missfire ~6-8 times a min but I was writing that off to a plug diff or other flow issue(has that PCV tube right across the velocity stack in the mani). doesn't miss now. Temps on measurements are fairly constant at 45deg, pressure fluctuating at 995-1001B as measured on the car sensor.

Guess the findings so far are (1) its getting more air with the RS4 Y(or my fuel pump decided to start dieing at the same time, filter is 5K old) and (2) subtle differences in run characteristics between the two when taken into account the programming on the fuel loop. Although I won't pass final judgement on the fueling questions until after I measure with the RS4 pump I'll say this code is *likely* tuned to whatever the characteristics are of the RS4 pump delivery(or I hope so). As-is I think my car would have some edgy fuel issues when it gets hot here.... left alone w/o tweaks that is.


Edit:

My desired AFR is 11.5:1, actual is 13.3:1 at 6800 rpms. I'll leave this post here but don't want to confuse anyone(as I was last night) on possible leaning. My O2Vs are a little richer overall. IDC at 130% in some cases though. That is not normal for this code. I'll repost at a later date with more fueling data to clarify for both me and others. Sorry for the confusion.

[PSmalls::DoggieStyle]

[PSmalls::DoggieStyle]

When my idle was above 1,000 RPM on cold start, my airflow was more than double (9.xx g/s) what it is at fully warmed up idle (760-800 RPM).