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      02-24-2011, 12:22 PM   #36
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roninsoldier83's Avatar

Drives: E90 BMW 335xi N54 6MT
Join Date: Oct 2010
Location: Denver, CO

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Originally Posted by Morpheus View Post
Good post. Were the subarus you mention closed loop all of the time? Because if not, then you can't compare the two. I know the rx7s weren't, and you had to rely on user maps. These types of piggybacks would never have worked on an rx7. Just like the S-afc would not work-safely, that is. Maybe that's the reason for the confusion here?
Fueling is closed loop on these cars compared to open loop on most other cars thanks to employing WB02 sensors from the factory and having an ECU smart enough to address AFR quickly. However, there are still timing tables for these cars with base values that should be determined by load, just like any other modern turbo car (well, most NA cars as well).

Originally Posted by Morpheus View Post
It's also the reason you can't just slap on DPs an exhaust, and an intake and make 50hp with no tune. With an rx7 there was the 3 mod rule. Ever heard of that? Three airflow mods: intake, exhaust, downpipe. Any more than that and BOOM. Actually sometimes not, and sometimes even with less than three the engine went boom anyway. All it took was a hot day, or a bad tank of gas. Why? Because the ECU wasn't able to react. That's not the case here.

You're also incorrect in saying that the knock sensor is setting the BASE timing map. BMW sets the base ignition map and it does indeed look similar to the one you posted and does decrease timinq with load. I may be oversimplifying things here and somebody correct me If I'm wrong because I'm only repeating what I've read here, but it's my understanding that the flashes rely on the knock sensor as well, but with a 3 degree "head start".
Maybe there was a misunderstanding (we're on an open forum, it happens ), but I agree the base timing map (unless altered) is set by BMW from the factory. Sorry, I thought it was implied.

IMO, the knock sensor is meant to be a failsafe, and under the wrong circumstances it is a crucial tool in saving your motor. However, rather than relying on it as a means to altering timing, the base timing values should be set as a maximum, which should be under the knock threshold. Ultimately, the goal when tuning should be be set timing values (as well as AFR & boost of course) to a value that allows WOT operation without knock under most normal conditions.

Originally Posted by Clap135 View Post
However the goal should to set timing so the max value at any given rpm is below the knock threshold. you should only rely on the knock sensor to pull timing in bad conditions not everytime you floor the car.

^^^ Apparently you beat me to it


While you and I see to have different styles of communication, on a technical level, we seem to have a similar mindset.

I've seen numerous OTS maps for multiple cars... I'm not a big fan, as they typically leave much to be desired. Hell, I'm not even a big fan of many supposedly conservative factory tunes (I've seen some pretty atrocious logs on stock cars of various makes over the years!! We're talking LTFT's around ~15%, AFR's deep into the 9:1 range under WOT, knock/timing correction all over, cars that won't hit peak targeted boost, you name it). Ultimately, these maps are made/tuned by someone else in another part of the country, and like humans, among cars there will always be variances. Manufacturers try to be overly conservative and make maps that will be safe in a variety of conditions, but there are so many variables from car to car that this is rarely optimum. I've seen cars with the same mods, running the same OTS maps, under the same conditions (elevation, fuel grade ect) make WOT pulls, and the logs/torque curves are vastly different.

Personally, I would rather tune my own car, for my own conditions (fuel grade, elevation, variances specific to my vehicle, ect, preferably under harsh conditions..) to ensure that my car is knock free while pushing peak boost/timing/under full load. I'm a big fan of optimum performance, consistency and safety when at all possible

That's just my $.02 though, YMMV.
Current- 2015 Subaru WRX

Former- E90 BMW 335xi 6MT N54 - SOLD

Last edited by roninsoldier83; 02-24-2011 at 02:19 PM.