YACT Diesal engines?
- Thread starter gregshin
- Start date
olds
Elite Member
- Mar 3, 2000
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i dont want TORQUE vs. HP discussions...i wanna know why diesal engines produce gobs of torque but little HP
Reda the damn article I posted with the knowledge that "Deisel engines do not rev to very high RPMs".
Horsepower is NOT a stupid number.... and engine torque CAN be a VERY stupid number. Power (or energy, if you prefer) is the ONLY thing conserved through a gearset (minus losses in a non-ideal world). Torque, on the other hand, is not.
Example. Engine A makes 200 ft-lbs of torque, but puts it through a 4:1 gearset. Engine B makes 400 ft-lbs of torque, but puts i through a 2:1 gearset. How much is at the wheels? its identical.
Torque is THE important number (I'll definitely give you that)--but only the torque AT THE WHEELS. So engine torques mean VERY little unless you know the differential ratios. But this is all oversimplified anyway.... a LOT of poeple say "my car has XXX horsepower" but neglect to inform you that it weighs 5000 lbs, too.
As far as diesels are concerned, they're knock-controlled ignition (that is, compression ignites the fuel-air mixture). Hence they're not capable of high RPMs (and like the others have said, HP=torque*RPM). BUT, knowing this limitation, most diesels are designed for high torque (long stroke, for example) and APPROPRIATE gearboxes are affixed to the engine (see earlier remarks).
I liked the article, notfred... should have read it before my previous post. Very "simple" way to explain to people the difference of the two... and why both numbers are important (or why torque as a function of RPM is important--not to mention gearing).
Yeah, mine started doing that today. :| I hope it's easy to fix...it seems like the gas pedal/thottle/whatever is getting stuck. It's running way too fast at idle and then dieseling when I turn it off. I have a 1988 Toyota Corolla FX.
HP = torque * RPM /5252Originally posted by: HokieESM
Horsepower is NOT a stupid number.... and engine torque CAN be a VERY stupid number. Power (or energy, if you prefer) is the ONLY thing conserved through a gearset (minus losses in a non-ideal world). Torque, on the other hand, is not.
Example. Engine A makes 200 ft-lbs of torque, but puts it through a 4:1 gearset. Engine B makes 400 ft-lbs of torque, but puts i through a 2:1 gearset. How much is at the wheels? its identical.
Torque is THE important number (I'll definitely give you that)--but only the torque AT THE WHEELS. So engine torques mean VERY little unless you know the differential ratios. But this is all oversimplified anyway.... a LOT of poeple say "my car has XXX horsepower" but neglect to inform you that it weighs 5000 lbs, too.
As far as diesels are concerned, they're knock-controlled ignition (that is, compression ignites the fuel-air mixture). Hence they're not capable of high RPMs (and like the others have said, HP=torque*RPM). BUT, knowing this limitation, most diesels are designed for high torque (long stroke, for example) and APPROPRIATE gearboxes are affixed to the engine (see earlier remarks).
LOL @ this thread...
Horsepower is a "stupid" number. Torque is what puts you in your seat when you accelerate. Horsepower is just another method of measuring energy output.
It's basically already been covered. The massive torque is a function of the extremely long stroke. The extremely long stroke is a cause of the very low redline.
Let's take an old Hit and Miss engine, for example.
The Stover 6HP gasoline engine made in 1922 makes full power @ 550RPM.
5 3/4" bore and a 8" stroke. That means it's producing 57ftlbs of torque at 550RPM, yet only 6HP.
Horsepower is a "stupid" number. Torque is what puts you in your seat when you accelerate. Horsepower is just another method of measuring energy output.
It's basically already been covered. The massive torque is a function of the extremely long stroke. The extremely long stroke is a cause of the very low redline.
Let's take an old Hit and Miss engine, for example.
The Stover 6HP gasoline engine made in 1922 makes full power @ 550RPM.
5 3/4" bore and a 8" stroke. That means it's producing 57ftlbs of torque at 550RPM, yet only 6HP.
this is definitely a newb question....
if hp doesnt matter, how can cars with low torque and high hp be fast at all? is it all gearing?
the engine or car i am referring to is the rx7.. rotary engines... super low torque, great hp..still fast and will out you back in ur seat..
if hp doesnt matter, how can cars with low torque and high hp be fast at all? is it all gearing?
the engine or car i am referring to is the rx7.. rotary engines... super low torque, great hp..still fast and will out you back in ur seat..
Demon-Xanth
Lifer
- Feb 15, 2000
- 20,551
- 2
- 81
Diesels are low revving due to the fact that the fuel is slow burning, and since it CAN'T rev high, it's torquey. If an engine can't hit 5252 then it's torque will ALWAYS be more than it's power. Gasoline on the otherhand, is much faster burning. Both are some of the best fuels for energy density.
Low revving is right. I remember driving trucks for the family beer warehouse. The Mitubishi Fuso FKs redlined around 2,900RPM. Peak torque was around 1,500 - 1,600RPM. Lots of grunt to get a heavy load going off the line. The larger Internationals had redlines around 2,300 - 2,400RPM. The HP ratings were really funky and would shock people. The Mitsus had something like 200HP but around 450lb/ft of torque and the Internaltionals has 250HP and had around 650lb/ft of torque. Believe it or not, when those trucks were empty, they could really fly off the line.
Windogg
Windogg
It's not ALL about the stroke length. It's also those moonlight walks on the beach. OOPS! Sorry I got distracted.
howstuffworks is usually pretty good, but if you think about it, a long stroke gasoline engine would have the same torque advantage as a diesel. And, in fact, they do. There have been lots of long stroke truck and tractor gas engines built. The real difference is in the cycle MEP (Mean Effective Pressure). This defines the average force pushing the piston down. That force, acting through the lever arm (varies from 0 to 0.5 x stroke) gives the torque. Since diesels usually have compression ratios of 15 to 22, the MEP is much higher for a diesel. Stroke limits the maximum engine speed due to inertial speed of the internal components. This is especially critical for diesels with the heavier pistons and rods required by the higher MEP. However, the diesel is also limited by ignition speed due to the compression ignition design and the low volatility fuel, so the compromise is usually a long stroke engine.
Industrial diesel design like tractors and construction equipment are usually limited to about 2000 rpm, as much for long term reliability as anything else. Gas designs for these vehicles usually are governed to about 2500 rpm. Trucks and buses may rev to 2800 or so. Small diesels (3 to 4 liter) in autos and light trucks will usually rev to 4000 or so. Mercedes built some racing diesels and I think they got up to close to 6000 rpm.
Horsepower and torque are both very meaningful. Ultimately horsepower is energy and that's what moves the car. The problem is that it is usually not practical to operate an engine at constant maximum horsepower but relatively easy to operate it at the torque peak. That's why a high horsepower car will be faster but in day to day driving a torquey car will be easier to go fast with. When Honda first entered small motorcycle racing (50cc, 125cc, etc.) they quickly dominated because they had way more horsepower than anyone else. However the narrow power band (for example, no real horsepower outside of a band from 15,000 to 18,000 rpm) meant they needed things like 8 speed transmissions and the riders had to be exactly right on the gear shifts every time.
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