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      02-24-2011, 04:53 PM   #64
Mike@N54Tuning.com
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Quote:
Originally Posted by roninsoldier83 View Post
Interesting concept... Please enlighten me sir. Fuel is closed loop under light accel/idle on all modern cars. This is done through the use of either a narrow-band or wideband O2 sensor(s) that constantly monitor AFR/lambda & adjust fuel accordingly in order to try and target around 14.7:1 AFR. These cars (N54/55) are unique in that they apply this basic function under heavy load/WOT... they have x2 WBO2 sensors last I checked, and an adaptive ECU/DME, that combined with a more detonation resistant DI design (injectors point almost directly at the spark plugs), it's no wonder that they're able to run such lean AFR's under load, or run closed loop fuel under WOT.

Fuel is fully closed loop on these cars, there's no debating that.... but timing? If this is truly your belief, please breakdown how you believe this "closed loop timing" works. No sarcasm intended, I would truly like to hear your theory.

Are you implying that the DME is constantly attempting to advance timing with no maximum load based values? If so, that would mean that running something like VP 110 (or any other designer racing fuel out there) would advance timing with no theoretical limit... and there would be no extra power to be made by advancing timing (manually/tune ECU for more timing) when octane permits (via race gas, meth ect) as the DME should constantly max out timing values based on knock input with no load based limits at any RPM... is that what you're suggesting?

If so, do you happen to have a technical write-up of some sort we could take a look at?

If not, well, '07 AP support and ATR will be out soon... I suppose I'll find out for myself
As I said the N54 platform is pretty unique which is why people who come from other backgrounds always have your strong opinions until they do the tuning themselves. Fueling is closed loop during WOT using wideband sensors. Boost is vacuum controlled with a default open position. Timing is closed loop. It uses what we refer to as "maximum set points" and continually adds timing, listens for early knock, and removes timing, until it hits its maximum set point. Which are set so high that it would take race gas to hit them on a stock car. It uses short term trims (knock) and long term trims (octane) analogous to long and short term fuel trims. This is in addition to all the other factors that influence the timing mapping. If you add race gas you will automatically increase advance in a factory stock or tuned car as they are all running on this knock threshold system. As you get close to not being able to support your boost with your octane the DME logic starts overreacting with 3 degree drops instead of small 1/4 degree drops and you know it's time to dial back the boost. This is the basis for piggyback autotuning.

Mike
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