Quote:
Originally Posted by Old Mechanic
Load is better determined by MAP or the reverse vacuum. It is independent of throttle position as I stated in my previous post, if you go from flat ground to an uphill grade then the load increases and vacuum drops, while MAP (the inverse of vacuum reading) increases.
regards
Mech
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We are talking Gasoline engines here, not diesel. Rules are a bit different for a diesel engine.
Explain here how this happens in more detail, how is MAP Independent of throttle position? Obviously one of us has a misunderstanding. I say for a given throttle position, you are asking the engine to give you that much torque at a given RPM. MAP is going to be dependent on Throttle Position and RPM of the engine right? Going from flat steady speed to hill and not changing throttle will drop RPM obviously, but the torque the engine puts out will be relatively the same till you drop in RPMs below say 1700.
I think we are arguing the same point in different terms. When we look at a BSFC curve, it really has "Torque" as the Y axis (up & down one) and "RPM" on the X axis (side to side) with "grams per hour" ( or some given weight or volume of fuel being consumed over some period of time).
Since I don't think any of us has a "Torque" sensor, we need to rely on something that closely approximates torque for a given RPM of the engine and this would be the Manifold Pressure, or air pressure in the area above the intake valves. Again, since the only 2 things really affecting Manifold Pressure on a gasoline are Throttle setting and RPM, I don't see where my statement of throttle setting or position is wrong. The throttle setting will directly impact manifold pressure, and these are essentially 2 sides of the same coin. Since most folks don't have a scan gauge, and are able to detect MAP the only real way to gauge how much torque you are producing is by experience and feel for where your gas pedal is when you are creating about 70% of the rated torque of your engine.
If there is something I'm missing here, please educate and inform. Explain how it is wrong, or different, or if there is some third factor I do not understand.