Lets talk about Load
02-09-2002, 10:31 AM
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Lets talk about Load Ok, I think I've got a pretty good foundation on the basics of engines, but I've never really understood the concept of load.
How is sitting with the tranmission in neutral and revving it to 5000 rpm different than spinning the rollers on a dyno and taching 5000? I've heard its very bad to rev and engine when its not under load, bad on the rods/rod bolts especially. Why is that? What is the definition of load and what does it do?
Why wont turbos spool with the clutch pushed in? The answer is because the engine isn't under any load, but what does that mean? If the throttle blade is wide open, and the engine is spinning at 5000 rpm, isn't the engine pumping air regardless of what the tranmission is doing?
J.
How is sitting with the tranmission in neutral and revving it to 5000 rpm different than spinning the rollers on a dyno and taching 5000? I've heard its very bad to rev and engine when its not under load, bad on the rods/rod bolts especially. Why is that? What is the definition of load and what does it do?
Why wont turbos spool with the clutch pushed in? The answer is because the engine isn't under any load, but what does that mean? If the throttle blade is wide open, and the engine is spinning at 5000 rpm, isn't the engine pumping air regardless of what the tranmission is doing?
J.
02-09-2002, 10:53 AM
#2
TECH Enthusiast
Re: Lets talk about Load This make me think of a toy steam engine that
I had as a kid. It had a device that the faster
that it spun the more the blades would extend,
as to give it some load and prevent it from
over speed. I guess this was a govener(sp?).
Intrested to see an engineering reply here.
Terry
I had as a kid. It had a device that the faster
that it spun the more the blades would extend,
as to give it some load and prevent it from
over speed. I guess this was a govener(sp?).
Intrested to see an engineering reply here.
Terry
02-09-2002, 11:13 AM
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Re: Lets talk about Load [quote]Originally posted by Crazyquik:
<strong>Ok, I think I've got a pretty good foundation on the basics of engines, but I've never really understood the concept of load.
How is sitting with the tranmission in neutral and revving it to 5000 rpm different than spinning the rollers on a dyno and taching 5000? I've heard its very bad to rev and engine when its not under load, bad on the rods/rod bolts especially. Why is that? What is the definition of load and what does it do?
Why wont turbos spool with the clutch pushed in? The answer is because the engine isn't under any load, but what does that mean? If the throttle blade is wide open, and the engine is spinning at 5000 rpm, isn't the engine pumping air regardless of what the tranmission is doing?
J.</strong><hr></blockquote>
OK - here is my shot at it, and I will shut up on stuff I don't know about.
I do not know the precise definition of load, but suspect that it is some variant of the amount of torque that an engine must exert to maintain its speed (angular velocity of the crank, etc.).
One big difference between an engine spinning at 5000 RPM with no load and a heavy load is the amount of cylinder pressure required to maintain that RPM. If the only work an engine does is to keep itself spinning as opposed to keeping itself spinning plus hauling a 3500 pound car, it is going to require a lot less cylinder pressure to maintain the engine only case. But less cylinder pressure = less combusted fuel = less exhaust gas. That should be the reason why turbos won't spool up as well with a no load high revving engine.
My $0.02. Anyone else know more?
<strong>Ok, I think I've got a pretty good foundation on the basics of engines, but I've never really understood the concept of load.
How is sitting with the tranmission in neutral and revving it to 5000 rpm different than spinning the rollers on a dyno and taching 5000? I've heard its very bad to rev and engine when its not under load, bad on the rods/rod bolts especially. Why is that? What is the definition of load and what does it do?
Why wont turbos spool with the clutch pushed in? The answer is because the engine isn't under any load, but what does that mean? If the throttle blade is wide open, and the engine is spinning at 5000 rpm, isn't the engine pumping air regardless of what the tranmission is doing?
J.</strong><hr></blockquote>
OK - here is my shot at it, and I will shut up on stuff I don't know about.
I do not know the precise definition of load, but suspect that it is some variant of the amount of torque that an engine must exert to maintain its speed (angular velocity of the crank, etc.).
One big difference between an engine spinning at 5000 RPM with no load and a heavy load is the amount of cylinder pressure required to maintain that RPM. If the only work an engine does is to keep itself spinning as opposed to keeping itself spinning plus hauling a 3500 pound car, it is going to require a lot less cylinder pressure to maintain the engine only case. But less cylinder pressure = less combusted fuel = less exhaust gas. That should be the reason why turbos won't spool up as well with a no load high revving engine.
My $0.02. Anyone else know more?
02-09-2002, 11:18 AM
#4
FormerVendor
Re: Lets talk about Load Load means how close to peak cylinder pressure you are and is controlled by your throttle position and manifold pressure. The more manifold pressure or less vacuum the more load you are putting on the engine.
When you are free revving your engine in neutral you are only opening the throttle for a tiny sec or it would blow up. In neutral you can barely crack the throttle and send the engine to 7500 or run it and keep it there. In gear or pulling a trailer you'd have to keep the throttle wide open to let full atmospheric pressure into the manifold and into the cylinders and then you'd truly be under full load or WOT.
When you are free revving your engine in neutral you are only opening the throttle for a tiny sec or it would blow up. In neutral you can barely crack the throttle and send the engine to 7500 or run it and keep it there. In gear or pulling a trailer you'd have to keep the throttle wide open to let full atmospheric pressure into the manifold and into the cylinders and then you'd truly be under full load or WOT.
02-09-2002, 11:34 AM
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Re: Lets talk about Load [quote]Originally posted by racer7088:
<strong>You beat me to it Weather guy. You are correct.</strong><hr></blockquote>
Wasn't a race <img src="gr_images/icons/wink.gif" border="0"> Actually, glad that I was right - did not know the actual definition, but had a good idea from basic physics.
<strong>You beat me to it Weather guy. You are correct.</strong><hr></blockquote>
Wasn't a race <img src="gr_images/icons/wink.gif" border="0"> Actually, glad that I was right - did not know the actual definition, but had a good idea from basic physics.
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02-10-2002, 12:14 AM
#9
FormerVendor
Re: Lets talk about Load NastyC5,
Sinces there's very little cylinder pressure the rods see a lot of tensile force from the piston swinging hard through TDC. Under load the compression from the higher cylinder pressure "cushions" the pistons abrupt change in direction at TDC. Most Rods get thrown when you let off at high rpm becasue of this, few come off on the way up under load.
Sinces there's very little cylinder pressure the rods see a lot of tensile force from the piston swinging hard through TDC. Under load the compression from the higher cylinder pressure "cushions" the pistons abrupt change in direction at TDC. Most Rods get thrown when you let off at high rpm becasue of this, few come off on the way up under load.
02-10-2002, 01:32 AM
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Re: Lets talk about Load Is this why automatic Supras are faster in a straight line than manuals...because they can "power brake" off the line and put the engine under load so the turbos spool, while a manual can't launch under boost?
02-10-2002, 08:59 AM
#12
Re: Lets talk about Load [quote]Originally posted by racer7088:
<strong>NastyC5,
Sinces there's very little cylinder pressure the rods see a lot of tensile force from the piston swinging hard through TDC. Under load the compression from the higher cylinder pressure "cushions" the pistons abrupt change in direction at TDC. Most Rods get thrown when you let off at high rpm becasue of this, few come off on the way up under load.</strong><hr></blockquote>
Thanks. Makes perfect sense now! <img src="gr_grin.gif" border="0">
<strong>NastyC5,
Sinces there's very little cylinder pressure the rods see a lot of tensile force from the piston swinging hard through TDC. Under load the compression from the higher cylinder pressure "cushions" the pistons abrupt change in direction at TDC. Most Rods get thrown when you let off at high rpm becasue of this, few come off on the way up under load.</strong><hr></blockquote>
Thanks. Makes perfect sense now! <img src="gr_grin.gif" border="0">
02-10-2002, 09:06 AM
#13
FormerVendor
Re: Lets talk about Load Yes the turbos benefit from some load because as your intake manifold pressure rises it generates more cylinder pressure which in turn generates more exhaust pressure which in turn gets the turbos spinning even before you have taken off. This is a viscious cycle on a turbo engine and the waste gate controls it from making too much boost or increasing too much.