blowngasket
Automotive
First let me say that I'm not a professional. I'm more of a hobbiest, but that wasn't on the list when I signed up, so you'll have to excuse my lack of knowledge.
1) My first question is how horespower (and torque) are measured, exactly. I don't know exactly how a dyno works, but to calculate power I would think that you would measure how fast the engine can accelerate a known mass and in what amount of time it takes to do so. If this is this correct, what's the formula here? The next thing is torque. It's measured in ft/lbs, so I'm thinking it is a measurement of force? If that were true and I have an engine that produces 300ft/lbs of torque, is that to say that it produces a force of 300 lbs one foot away from the center of rotation? I don't really know, but that doesn't seem like very much to me. Also, I have a friend who thinks he read somewhere that all horsepower and torque curves cross at 5,250 rpm because of the forumla's used to compute the two. My logic arugment for this was what about engines that don't rev to 5250, such as diesels. Is there any truth to this, or is it just an invalid conclusion based similarities in observed data?
2) The next question is where it is measured. There seems to be something about gross and net horsepower measurements. I understand that before 1971? they measured it terms of gross and after that it was net. Gross being without accessories and net being with all the accesories (such as alternator, water pump, fan etc). So, are these measurements taken at the flywheel, output shaft of the transmission, at the wheels? If the measurements are taken at the same place, what is an average loss throughout the drivetrain system? It seems to me that both of these measurements would be greatly affected by gearing. So, if it's measured anywhere other than the flywheel how is that considered in any formula?
Lastly, it seems (through my experimentation) that an engine produces more torque if the exhaust is restricted or has more back pressure. However, I'm at a complete loss to figure this out. I would think that the easier the piston can move up during the exhaust stroke, the less loss there is and therefore would produce more torque and horsepower. What's up with that?
I know this is a lot to answer so I'm greatful to anyone willing to take some time to explain what might be the "basics" to you.
Thanks in advance.
1) My first question is how horespower (and torque) are measured, exactly. I don't know exactly how a dyno works, but to calculate power I would think that you would measure how fast the engine can accelerate a known mass and in what amount of time it takes to do so. If this is this correct, what's the formula here? The next thing is torque. It's measured in ft/lbs, so I'm thinking it is a measurement of force? If that were true and I have an engine that produces 300ft/lbs of torque, is that to say that it produces a force of 300 lbs one foot away from the center of rotation? I don't really know, but that doesn't seem like very much to me. Also, I have a friend who thinks he read somewhere that all horsepower and torque curves cross at 5,250 rpm because of the forumla's used to compute the two. My logic arugment for this was what about engines that don't rev to 5250, such as diesels. Is there any truth to this, or is it just an invalid conclusion based similarities in observed data?
2) The next question is where it is measured. There seems to be something about gross and net horsepower measurements. I understand that before 1971? they measured it terms of gross and after that it was net. Gross being without accessories and net being with all the accesories (such as alternator, water pump, fan etc). So, are these measurements taken at the flywheel, output shaft of the transmission, at the wheels? If the measurements are taken at the same place, what is an average loss throughout the drivetrain system? It seems to me that both of these measurements would be greatly affected by gearing. So, if it's measured anywhere other than the flywheel how is that considered in any formula?
Lastly, it seems (through my experimentation) that an engine produces more torque if the exhaust is restricted or has more back pressure. However, I'm at a complete loss to figure this out. I would think that the easier the piston can move up during the exhaust stroke, the less loss there is and therefore would produce more torque and horsepower. What's up with that?
I know this is a lot to answer so I'm greatful to anyone willing to take some time to explain what might be the "basics" to you.
Thanks in advance.
