maxbc wrote:
I don’t think the engine health has anything to do with that. If anything it means the engine is “pulling” too much, so shouldn’t be a problem.
Exactly. You need to look at it differently whether it is NA or TN/TC/SC .
IN all cases, a WOT condition will derive the minimum pressure loss through the throttle, but it will never be zero. I have not read what looks like a good AOPA mag article, (thx for posting) but 1" or around is normal. This will be zero with a stopped engine, of course, but once you have airflow, there will be some pressure loss, as with any fluid going through a pipe.
On NA it is suction form the cylinders that causes the airflow, so there must be lower MP than atmospheric press or else the flow would not occur.
On TN/TC/SC the compressor will increase pressure vs atmospheric, and at WOT (depending on the control system on each aircraft, not that easy, some are manually controlled and you can only only be WOT when at altitude), there may be higher pressure than atmospheric both upstream and downstream of the throttle, and it is the compressor that “pulls” air from the induction air filter and atmosphere, rather than the cylinders.
There will still be a pressure loss from atmospheric as air flows through the air filter and associated ducting , so that pressure at the compressor inlet will be a bit lower than atmospheric. This pressure loss will be amplified by the turbo, which . in electronic terms, works mostly as an amplifier of whatever comes in.
At high speed, say 160KTAS, and 8000ft, a quite optimal NA cruising altitude, a forward-pointing inlet will see almost 1" dynamic pressure which, when added to atmospeheric pressure of about 22" is a significant power boost. Hence a lot of aircraft are designed with such type of inlet (Mooneys M20J’s famously have an openable ram air inlet) .
If TC, then the turbocharger will amplify such dynamic pressure causing a significant boost.
On aircraft we have sensors for atmospheric static pressure (altitude) , dynamic pressure (IAS) , and on some, engine upper deck pressure (or compressor outlet upstream of the throttle) as well as MP (downstream of the throttle). A little graph below of our last take-off for your perusal:
