Interesting point about modifying intake or exhaust

[macx]

Started out looking for info or products on ECU code scanning,
ran across this observation in one of the threads that came up.

Being the efi system is a speed density versus mass air and there
fore does not measure the actual air mass coming into the engine
but rather is set by the factory to provide fuel in response to inputs
such as from the tps, increasing airflow via a freer flowing intake
setup or filter or via reducing backpressure in the exhaust via an
aftermarket exhaust setup essentially leans out the already lean
air fuel mix because the system does not recognize nor does it adapt
to or compensate for additional airflow over that of what is programmed
by the factory with a totally stock configuration.

I've just gone thru a "what if" exercise on possibly eliminating the
airbox (just to avoid the hassle of R&R when doing trans / clutch
work) and was educated to a considerable degree regarding these
types of issues on these bikes.

I have removed the oem muffler (not the cat) and installed just a
short downturn, but have not experienced any lean running indicators
probly because when I bought my bike (an 04 I bought in summer
of 08) it already had the code plug removed which I understand
richens the mixture some.

I just had never thought of intake or exhaust modification in specific
terms of it's relation to the factory tune and the Motronic's inability
to compensate for additional intake airflow or reduced exhaust back
pressure, at least not in stock form (i.e. without one of the piggyback
tuning devices available which are designed to compensate by enriching
the oem programmed fuel mix)

My "hot rod" (car) was initially a speed density system which of course
I learned had basically the same limitations. After converting to a mass
air system, which was available in subsequent models so was the same
basic system just adding a mass air meter and a different ecu all of which
conveniently plugged into the speed density system) I was able to
considerably increase power thru a larger engine displacement, a much
freer intake including throttle body size, intake manifold, heads, and cam,
and freeing up exhaust flow via headers and a much freer flowing catback
setup. Per the dyno I added about 100 hp and 75 lbs of torque and, due
to torque-curve matched components designed for good street torque in
the mid rpm ranges, suffered no loss of mpg's at steady cruise rpms.

Sometimes one just has to think thru the whole process to understand
how a given modification can help - or hurt - performance.

[boxermania]

macx

Your research is pretty much dead on regarding the capabilities of the Motronic 2.4 ECU fitted to our bikes. This is a good time, specially for the new breed of owners, to re-visit what I have posted before.

Engine tuning by the OEM is at best a compromise, not only dealing, with design constraints, economy, emissions and last but not least the fact the the bikes will be sold and operated in all climates, hot, cold, rainy, sea level and high altitudes.

To this end the BMW engineers have managed to circunvent most of the issues by the following:

1) There are half a dozen A/F ratio maps incorporated in the ECU. These can be accessed by the CCP (Code plug) and satisfy the majority of the conditions addressed above.
2) All of these maps are a bit on the rich side to avert potential ambient/operational issues that could affect the engine reliability.

Note: US bikes fitted with the CCP run a specific A/F map to deal with economy and emmissions, however, removal of the CCP selects a slightly richer A/F map. Early on, when owners complained about engine surging, BMW dealers removed the CCP as a matter of course, many dealers removed the CCP's prior to the sale of the bike

With the above as a starting point and assuming the engine is in a satisfactory state of tune one ould make the case that selective mods of the intake and exhaust can improve the operation of the engine as one would be tunnig to the existing ambient conditions

Engine power is a combination of air, fuel and the ability to remove the spent gases (everything else being constant for this purpose). A less restrictive filter or exhaust can will certainly help out, without exposing the engine to any damage, based on the fact the that A/F map is on the rich side, more so if you are running without the CCP.

In closing, it is important to recognize what are your expectations and keep a system of checks and balances as you go along, such as reading the plugs or using a wide band O2 sensor to log the A/F ratios during operation or buying an engineered kit.