: Can someone please explain to me the performance gain by going above 30" MP
: (say, during takeoff) on a turbo'd engine.

Lots.

: How much better performance are you getting from the engine at say 35"MP on
: takeoff vs a non-turbo'd engine that's going to max out around 29"?

As was mentioned before, try taking off in with a regular engine at less than
full throttle.

: Is it worth the strain put on the engine? I understand the turbo being able
: to maintain power at high altitudes, but I haven't heard it explained to me
: why I would need such a high power setting on takeoff/climb (assuming sea
: level field).

There are two different types of turbo systems. The former that you're
familiar with is a "turbo-normalizer." It allows for sea-level manifold pressure at
altitude. That does not add much more "strain" to the engine, although the inlet air
temperature and cylinder cooling in the thinner air at altitude will still make it run
hotter. That *can* be detrimental to longevity.

The other type is "full-time turbo." With that, the engine is designed to
withstand the additional stress of a larger load of air/fuel per power stroke.
Basically, you get more power per cubic inch of engine. These types tend to run even
hotter than their turbo-normalized siblings since they are producing more power.

Unfortunately, in order to prevent a turbo'd engine from destroying itself due
to detonation, the compression ratio of full-time turbo'd engines must be lowered.
That reduces engine efficiency.

For example, my mechanic's turbo Arrow has an TIO-360 Continental that's rated
at 210hp at something like 35" MP. My carb'd O-360 Lycoming is rated at 180hp. If it
were fuel-injected with angle-valve cylinders, it'd be rated at 200hp. That extra
10hp is all that is gained from 6" more MP because the compression ratio was lowered
from 8.5:1 to 7:1. That's not a tradeoff I would be willing to make for any aircraft
I owned. Turbo-normalized, yes... full-time turbo, I don't think so, but to each
their own.

-Cory

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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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