Robert M. Gary wrote:

Am I missing something?

-Robert

The intake manifold pressure to ambient pressure differential is
probably the least important value in the equations you are discussing.

This comes down to the total generated power of the powerplant. The
engine is rated to make "X" horsepower. Lets say "200". At sea level. On
a standard day. As you climb, the higher pressure altitude (and
presumably higher density altitude) results in not being able to develop
that full 200 hp.

Pressurizing the plenum with a turbocharger or supercharger allows that
power to be generated at higher altitude.. but you already knew that. If
you go boosting the engine to 2-3 ATM you can make a BUTTLOAD of power
but the reliability will be in the toilet. WWII piston fighters and
bombers used to run MAP's in the 40-50-60" range.. but long term
reliability wasn't the primary issue for them.

Turbo-normalizing is a limited form of turbocharging that results in the
power being generated being limited to about what a normally aspirated
engine makes at sea level. The Crankshaft, prop, pistons, rods and other
"stuff" in the engine is subjected to no more stress than the engine
would be at sea level (with some limitations - the turbocharged air is
warmer, so there is a power loss and potential for detonation.. the air
at altitude for cooling is less dense, so its cooling ability across
intercoolers and cylinders is lessened... you get the drift).

Heavily turbocharged engines dont have short TBO's because of inlet
plenum failure due to air pressure fatigue.. they have short TBO's (when
operated improperly) due to cracked cranks, overheated cylinders,
excessive wear type stuff.

So.. no.. its not a marketing gimmick. Turbonormalizing an engine isnt
as big a deal, because the engine is not intended to exceed its original
"normally aspirated" sea level power rating.

Make sense?
Dave