The great fuel controller debate

** DISLCAIMER: I'm just thinking out loud here. I have no knowledge with engines. **

The traditional wisdom is that
a) modern engines run relatively lean from the factory due to emissions standards
b) installing aftermarket parts that allow for more airflow will make the engine run even leaner

When reading various motorcycle forums you will usually find a lot of people saying that if you will change only one (either exhaust or air filter) to a "performance" model you will be fine, but if you do both the engine will run too lean and suffer damages. For the record, this has been my understanding too.


The thinking behind this is that:
a) changing only one will still allow the ECU to adjust the fuel mixture enough to prevent the engine from running lean
b) changing both will be such a big change, that the ECU will not be able to adjust to the changes

Supposedly, and according to traditional wisdom, a fuel controller will:
a) prevent the engine from running too lean
b) prevent backfiring (that is caused by a lean running engine)
c) improve horsepower by adding more fuel
d) improve handling by removing some of the twitchyness present on many modern motorcycles (especially at low speeds)

HOWEVER...

I have recently read several writings by apparently educated and professional people saying that the traditional wisdom is not correct.

The claim is, as shocking as it sounds, as follows: the Bolt (and similar engines) WILL NOT run any leaner regardless of aftermarket pipes or air cleaners.

Why? Because while the FLOW of the air to the engine (by using a performance air filter) is indeed increased, the VOLUME of the air is NOT. In other words,all you are doing is changing how FAST the air enters and leaves the engine, not how MUCH air is entering.  Therefor the fuel mixture remains unchanged. This is an acceptable theory to me, because the stock air filter is not restrictive enough that it would actually deprive air from the engine.  In other words, the engine is filling to maximum cylinder capacity on each intake stroke.

Turbochargers are the only way to cram more air into the engine than the capacity of the engine allows when the air is unpressurized.

When I first heard this a few questions came to mind and I found the answers to them:
a) But free flowing intakes are PROVEN to give more horsepower! How do you explain this?
-- The horsepower increases are the result of the engine working easier with a less restrictive intake. Not because added air.
b) What about the popping with aftermarket pipes? It went away with a fuel controller!
-- The popping most likely was there all the time, but became audible when the aftermarket pipe was installed. FC corrected the engine running slightly lean and thus eliminated popping. In other words, the engine did not become any leaner by installing an aftermarket pipe

Now what does this all mean?
If you buy into the new wisdom it means that you don't need a FC on a Bolt because you have changed the exhaust and/or intake

HOWEVER:
a) a fuel controller CAN help with a twitchy throttle*
b) a fuel controller CAN reduce exhaust popping (commonly during deceleration)
c) a fuel controller CAN produce more horsepower

* the twitchyness is often a result of the ECU programmed to meet emissions standards. What happens is that the ECU cuts off the fuel too aprubtly especially at low speeds. This in turn leans to an ON/ OFF type throttle response.

Whats the truth?

I have no idea, but looking at THIS makes me think that maybe there is some truth to the new wisdom at least when EU bikes are concerned.