Pulled a ~5.0sec uphill (~4.7 flat) FATS @ 11psi today :-P Boost isn't everything <long>

[BoneStockS4]

So now that I have ECUx and MarkP's templates I can't stop logging. After my first logging session it was apparent that I was running out of injector in a bad way (injector duty cycles were pegged at 120% from ~5500rpms up). Based on this I decided to play it safe and cranked my Piggie MBC down a half turn, ending up with about 14.8 max boost. The car actually felt noticably more responsive, and the logs show the MAF kissing the 300g/s mark. Unfortunately, there was almost no difference in injector duty cycle and my O2's were all over the place, dipping into the 0.83V's.

Scared by this, I gave the MBC a full turn down, not really knowing where this put me boost-wise but figuring less is better for safety. The car felt slower, but still pulled fairly hard. Imagine my surprise when I checked the log and saw 11psi! Sweet!

Now imagine my surprise again when I saw 4.9, 5.0, and 4.6 FATS times! Woah! This is very close to my previous runs linked above.

Just for reference, these logs were taken on the same exact stretches of road, in the same manner, with the same amount of gas in the tank. Ambient temps were 31degF vs. 38degF previously, and lemmiwinks remained unchanged at +0.0 timing, 97.7% accel and decel, and +4.88% primary. Also, see my last note about intake at the bottom of this post (doubt this was much of a factor though)

Here are the graphs, with my interpretation below them:













In short it looks like I picked up some very decent timing with the lower boost levels and very low 31deg F ambient. Also, I'm MUCH mre comfortable with where the injector duty cycles are at now. That said, my O2 values look very lean throughout the run compared to most of the GIAC cars that I've seen.

My car has always run its fastest with the O2 voltages around 0.84V. I'm starting to wonder if APR just likes to run a little on the lean side compared to GIAC.

I'm still unsure as to whether I should be worried about running this way for the long term. Part of me wants to get those voltages up to 0.86V so I can be like the other Homebrew boys. The other part of me just says F' it... Get stage 3 fueling :-P I'm positive my car is basically limited right now by the amount of fuel its able to deliver. I guess until I can afford fueling my goal is just to keep it safe

Oh, and I should mention that over this past weekend (after the ~16psi logs) I swapped the modified upper airbox with ITG filter (stg2 Darintake) for my stock upper airbox with stock paper filter, leaving the bottom portion with airholes in place. After my last oil analysis came back with high silicon levels I suspected poor filtration and decided to go back to the stock paper filter to play it safe. So far I haven't seen any ill effects performance wise. I think the holes in the lower airbox housing are responsible for most of the performance benefit. FWIW, there is probably nothing wrong with the ITG, except the fact that I'm the one who oiled it last and I probably didn't oil it right.

Phew... and I'm spent...

[Mike2kS4]

140% is the new 100. Once your afr starts declining with RPM, get worried.

Looking at your MAF numbers, timing and CF's you're *super* safe.

[BoneStockS4]

Hmmm... 140% you say? Interesting...

Curious... what does the ideal AFR graph look like per the MarkP format? My AFR graph from these 11psi runs looks like this:



It does kind of dip with rpm :-/

[Mike2kS4]

Nothing below 12.2 or so. The optimal AF changes with boost pressure and such, so do the leanest mixture you go fast with.

I'm an insomniac

[DAP@EPL]

I wouldn't rely on ECUx's AFR data as that is the ECU's requested AFR. It won't tell you if the car is actually achieving that.

Best to verify with a wideband.

But I agree with Mike that duty cycles over 100% are not a problem if you aren't leaning out up top.

-Dave Pramanik

[Hal_TT::CBP]

am I out of fuel?

[DAP@EPL]

I'd prefer to see actual AFR stay in the 12s.

-Dave Pramanik

[Hal_TT::CBP]

Was going to try to show stock vs aftermarket/RS4 pump capacities but I forgot about pressure/capacity differentials at high volumes. Think its pretty obvious that this kit requires a higher flow/pressure pump now with the RS4 injector.

[BoneStockS4]

Oh, and thanks for all the help!

[DAP@EPL]