What gives diesels their strong low-end torque characteristics?
- Thread starter NFS4
- Start date
Are diesels more inclined to bore rather than stroke? IIRC, a longer stroke gets you more HP but a larger bore gets better torque.
Higher energy capacity? Lower RPM?
PM Tominator.
-PAB
Higher energy capacity? Lower RPM?
PM Tominator.
-PAB
Hayabusa Rider
Admin Emeritus & Elite Member
- Jan 26, 2000
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Hayabusa Rider
Admin Emeritus & Elite Member
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Sorta yeah. It goes like this:
Long Stroke = Higher Torque, Lower RPM.
Short Stroke = Higher RPM, Lower Torque.
Widening the bore helps with Torque which also helps with Horsepower, since HP is a function of Torque and RPM. It's sorta both.
But since the High RPM gives you Horsepower, if you take the same displacement and widen the bore and shorten the stroke, you'll likely get higher horsepower (at a higher RPM), however with less torque.
Edit:
Diesel, if it wasn't answered already, has a long stroke, so you get lots of torque out of each revolution, but the max RPM is lowered. Also they tend to be pretty big, so they probably have a fairly wide bore to. Making them have lots of cylinder face to press against, and a nice long stroke for lots of torque.
Diesel helps because it burns slow, so the force against the cylinder lasts through the long long stroke, but alot of the high torque/low RPM comes from the engine build shape. If you ran gasoline in an engine with the same stroke and bore as a diesel, you'd get alot of the same characteristics. It wouldn't be quite as powerful because the gasoline would burn off faster, so the force against the cylinder wouldn't be and constant for the whole stroke. But a good portion of the torque is just from the shape of the cylinders.
Edit #2: Reworded that a bit sounded kinda contradictory before...
It's not just the stroke. It also has to do with the speed at which the fuel burns. Gasoline burns much faster than diesel. Imagine a weaker, but constant force on something versus a very quick and strong force. Analogy: A rubber band wound around your finger for a few days would probably cut off blood supply and cause severe damage with little discomfort (diesel engine). Now, imagine your finger gets slammed in a door (gas engine). Even though it hurts worse to get you finger slammed in a door, less work is actually done on your finger. It's also like different powder charges in firearms. If you have a long barrel and quick burning powder, your barrel is going to be jammed. If you have a short barrel and slow burning powder, you waste a lot of energy. A more technical explanation of dynamics is not within the scope of this thread. This is also why diesel engines are marginally more efficient than gas engines. A slower, more complete burn yields more energy put to work rather than wasted heat.
Useless info tidbit #28
A deisel engine requires no eletrical system, other then the starter to start it. No battery, no alternator, no spark plugs, no distributor etc etc.....
A deisel engine requires no eletrical system, other then the starter to start it. No battery, no alternator, no spark plugs, no distributor etc etc.....
Pliablemoose
Lifer
- Oct 11, 1999
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About the lack of electrical components-no maintenance of an ignition system, so the state of tune stays relatively constant, another nice plus for the diesel engines
Well, there's still the timing of the injection system to deal with.Originally posted by: Pliablemoose
About the lack of electrical components-no maintenance of an ignition system, so the state of tune stays relatively constant, another nice plus for the diesel engines
2 of the most simple reason's
1:More Massive internal parts making more Kenetic energy, and 2: 2-3X higher compression ratio's
1:More Massive internal parts making more Kenetic energy, and 2: 2-3X higher compression ratio's
The slow burning fuel is good info that I never thought about. I didn't read the link, I don't have time at the moment, but does the fact that diesels don't have a throttle also have anything to do with it?
BTW, the shorter the stroke, the lower the peak linear speed of the piston is at a given RPM, hence the capability of a short stroke engine to rev higher without self destructing.
The longer the stroke, the more torque you can get with a given bore, because there is more leverage at the crankshaft. Think of when you're loosening a bolt. The longer the wrench you use, the more leverage you have, so more torque can be applied to the bolt with your muscles.
BTW, the shorter the stroke, the lower the peak linear speed of the piston is at a given RPM, hence the capability of a short stroke engine to rev higher without self destructing.
The longer the stroke, the more torque you can get with a given bore, because there is more leverage at the crankshaft. Think of when you're loosening a bolt. The longer the wrench you use, the more leverage you have, so more torque can be applied to the bolt with your muscles.
just remember you can put diesel in a gas car and it wont blow up but dont ever put gas in a diesel engine or else you might not be around for us to see you!
You should see the Diesels guys have up here, I know one guy that runs Propane, Nitrus and Nitro Methane all on his, it takes it all and keeps on tickin. 8MPG from a Diesel though so he pays for it.
You are correct, and I probably phrased my question wrong.Originally posted by: Garfang
Not in a really big engine. Big bore X big stroke = big displacement.
I thought that the OP was equating a long stroke with high torque, which is probably true but really has little to do with a Diesel engine.
Don't most diesels generate higher torque numbers due primarily to their much higher compression ratios which greatly improve thermal efficiency?
Lithium381
Lifer
- May 12, 2001
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Zenmervolt
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Well, sort of. Since the incoming air is un-throttled (ie, non-restricted) the pumping efficiency of a diesel engine is always at its maximum. When a gasoline engine is at anything less than WOT the engine must work to force air in through a restricted opening (the throttle butterfly) which takes away some of the power. Since a diesel always has a free-flowing intake, its pumping losses are minimised. Remember, an engine is basically an air pump, the more efficiently air flows into and out of an engine the more power you will get if all other things are equal.
ZV
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