Robert M. Gary wrote:

I"m still confused...
1) Why not just put a regular turbo on and agree to not over boost it?

It IS a regular turbo. There is a device attached called a wastegate to
limit the boost. A turbonormalized application has a wastegate that is
set to limit pressure to what would be found at sea level on a standard
day.. approx 30 inches. Some are automatic, some are manual and some are
fixed. Deakin's colums explain this. They have pictures too.

2) If compression increases inside cylinder pressure about 8 times
wouldn't taking MP up to 30" cause a MUCH higher inside cylinder
pressure than 20" (its a mutiple scale). If the outside of the cylinder
is 20" its going to have a significantly higher difference in pressure
than running out the outside 20" in MP. I just don't see how a cylinder
could crack and stress relative to 30" when its only 20" outside. Isn't
the cabin of the space shuttle under more stress when in space than
when sitting on the ground at sea lever?

Throw this line of thinking out the window... its not doing you any
good. The forces inside the cylinder are the same for a given power
setting. If you are making 200 hp, the forces are ESSENTIALLY the same
at sea level as they are at 20,000 feet with turbo-normalization. Yea,
you went from 30 inches ambient to somewhere in the mid-teens (like 15"
ambient)... but when you look at the pressures the cylinders endure on a
POWER stroke (not a compression stroke, like you are describing, the
pressure difference is miniscule.

The Shuttle analogy is a poor one. Fatigue is the result of pressure
cycles. Launching an orbiter into space, then orbiting for a week, and
then landing is ONE cycle. I want to say they run around 10 PSI or so,
not the 15 PSI ambient that we experience here at sea level. A four
stroke engine undergoes one cycle per two rev's (a compression and power
stroke.. im "ignoring" the intake and exhaust strokes for this
argument). At 2000 rpm, that engine cylinder has just exceeded the
entire shuttle program's accumulated cabin pressure cycles in a FEW
SECONDS. And the pressure differential is MUCH greater (exponentially
so, in fact), especially on the power stroke, immediately after combustion.

Looking at the graph ( http://www.avweb.com/news/columns/182084-1.html )
on Deakins article that I mentioned shows that simple compression
without ignition (compression stroke without spark/burning) causes the
combustion chamber pressure to approach 350 PSI. Ordinary, properly
timed combustion results in a combustion chamber pressure of close to
800 PSI. A detonation event in the combustion chamber event can push
this pressure to over 1000 PSI. Now.. compare those pressures.. 350...
800.. 1000... to what the atmospheric pressure is at sea level (30"/15
psi) and in the low flight levels (15" or so/7.5 psi or so) and you see
how little a difference 7 or 8 or 9 inches really is.. and that 800 psi
is where your POWER generation is.. 800 psi is 800 psi is 800 psi. It
doesnt really matter (in a statistically significant kind of way) what
altitude you are at when you generate it.

Which brings us back to where the problems with turbocharged
installations lie: The crankshafts, the bearings, the turbo itself
sometimes, the lubrication breaks down due to high heat in the turbo,
the engine makes more power than can be adequately air-cooled and you
scorch a cylinder or two..etc... If you dont exceed the rated power of
the original engine, but only use the turbo to GET that rated power at
altitudes you couldn't before... you are getting the best of both worlds
- power AND some semblance of reliability as compared to the normally
aspirated version of that engine. BTW, The earlier limitations/
disclaimers I mentioned about cooling air mass still apply at altitude.

Dave S