Posted for "marc" <cardmarc@charter.net>:

This is typically the way all stock aircraft 'turbo normalized' intake
manifolds are designed. The "pop off" or "blow off" or "prv" is set to
release the excess pressure relative to the absolute map the "upper
deck" is experiencing, regardless of pressure altitude outside. If you
want 34" map at 20,000 feet it will not release unless that is exceeded.
If you want 34" at sea level, the same goes. These safety devices are
generally not adjustable in flight, but have an adjustment on the ground
for the point at which you want it to 'relieve' your engine (within its
design range for hp).

Essential reading: the entire series of Light Plane Maintenance Mag's
turbo maintenance series. This mag is worth its weight in gold if you
have any aircraft, experimental or not.

There are several control schemes used in aircraft. The sloped density
controllers are neat. I don't have it all figured out yet, and wish GAMI
would come up with an electronic scheme better than the hydraulic
control schemes presently in widespread use. I do not have much regard
for any system using vacuum tubing controls.

One thought to remember regarding almost all wastegates: they aren't as
big as the open pipe straight from the engine. Most times they are about
half size. So unless you upsize the wastegate and assoc piping, you will
almost always be running some boost, even at sea level!

 

Marc Wiese