Question for the Motor Heads

[ATAG_Bliss]

Originally Posted by Blakduk

Just had a reply from an engineer who works on superchargers all the time- the boost gauge should not show higher boost when RPM drops regardless of whether the RPM decrease is due to higher loading of the engine. It relies entirely on what the supercharger is doing and it is directly linked to engine RPM.
It seems CoD is wrong.

Well no offense to your engineer buddy but he is wrong m8. I'm an engine builder (drag racer) and a mechanical engineer.

Take this analogy: Easiest way to test this would be with a supercharged car with a manual transmission. Say you are in 2nd gear winding up around 5000 RPMs - you are accelerating at the time, not crusing (with a 6500 redline). Now without changing the throttle, press on the brakes (create a load) that not only stops your acceleration but decreases your RPM's by say, 500. Your boost will increase. Now just for the fun of it, keep pressing the brakes even harder to really lug it down and floor the throttle. Boost is still not dropping, but RPM's are falling off. Now if you press the brakes hard enough while you are floored to essentially kill the engine, you will maintain boost up until a certain point (even more so than what you originally started with) until the engine dies. That scenario just shows you that boost (just like the definition of how a supercharger works) relies on both engine load and RPM.

If you don't believe me. Please go to a car dealership and test drive a supercharged car, borrow a supercharged car, steal a supercharged car, do w/e you want to get one. But do just what I said and you'll see the same thing. I don't claim to know anything about an aircraft engine, but if it's a V configuration, combustion engine, that has a gear driven supercharger going through a carb, it can't be that much of a different principle than a similar setup on a car.