ORIGINAL: mach2
ORIGINAL: ahicks
This is wandering off topic a little, but maybe that's got something to do with the reason the engine is pretty much ''all in'' prior to it even getting the throttle plate to 3/4 open?
''Vacuum pressure'' is a term used only in avaition to my knowledge, and it's always made me crazy as well.
My dad is a pilot and I flew a bit when I was younger, Im a car guy and and an engineer for a fire department (dont think im smart; engineer just means Im a firefighter who drives the engine and pumps water out [img][/img]) so I understand a bit about pressure and vacuum. I never could understand why there is an instrument in aircraft (piston planes) that is turbocharged that reads ''manifold pressure'' and it's measured in inches''. At cruise, it usually flies at ''23 inches of pressure''.....what the heck is that????
Vacuum is standardly measured in inches and pressure is measured in PSI. I dont understand why they have it this way. A forced induction engine like a turbo or supercharged engine running with the throttle open on the high end is going to be getting pressure from the turbo chargers. So it would make sense to have the gauge read manifold pressure....in pounds per square inch (because it's positive). I actually think that is should be a compound gauges that reads both psi and vacuum. Anyway, nobody has ever be able to explain this to me. I should ask one of the aircraft mechanics.
I installed a supercharger on my Camaro. While driving around easy its just like a regular engine. The intake is under vacuum, but once the throttle plate is opened and its allowing the forced air from the supercharger into the intake manifold the gauge needle goes from the vacuum reading side to pressure (compound gauge).
Ive acutally got a video of it because I was trying to watch my air to fuel ratio but it was hard to watch that and my RPM while I was driving; so I used my camera.
www.youtube.com/watch
anyway. It is off topic. I think we have given more than our two cents for Jordan about tuning. He can take which ever one he thinks works best for him....
Jeremy
I will attempt to explain it. The confusion comes from the fact that an automotive vacuum gauge reads zero at rest, when in fact it is under atmospheric pressure, which is of course around 14.7 psi, or 29.92 inches. (Atmospheric pressure, stated in psi, or barometric pressure). The automotive vacuum gauge then indicates anything LESS than atmospheric pressure as a "vacuum". The gauge one finds in an aircraft, and NOT only turbocharged aircraft, is called a "Manifold Pressure Gauge". It is very similar to an automotive vacuum gauge, with one important difference; it shows
atmospheric pressure instead of zero when at rest. If you look at one with the engine not running, it will show barometric pressure; somewhere around 29.92 inches, depending on altitude and local weather. When the engine is running, the gauge measures actual pressure in the intake manifold. At wide open throttle, it will show a bit less than atmospheric pressure due to inefficiencies and restrictions in the intake tract, but it will show a high pressure, indicating that the throttle is wide open. Correspondingly, lower throttle settings show lower manifold pressure, and indicate lower throttle/power settings. This, along with rpms, provides a good way to determine how much power the engine is producing, in order to determine performance, fuel consumption, etc. In the case of a turbo or supercharged engine, the manifold pressure gauge can indicate pressures higher than atmospheric, due to the pressure boost provided by the turbo or supercharger.
AV8TOR