ft-lb, hp...please help
#11
12-09-2011, 07:10 PM
Elite HDF Member
I was just about to post this. All things being what they are, and CVO/SE aside, I would put my money on the Dynas. Same engine and ratio (stock), but much lighter than a dresser, and somewhat lighter than a cruiser like a Softail or Fatboy. When all the drivetrains are equal, you have to put the money on the lighter machine. That is, of course, considering the all important rider factor.
#12
12-09-2011, 07:12 PM
Elite HDF Member
BTW, due to the power to weight ratio as well as the power curve, I would not rule out the Sportsters either. Let the flaming begin.
#16
12-10-2011, 12:59 AM
Club Member
HP=(torque X rpm)/5250...That is the magic formula...
On a Sporty you got a lightweight advantage..I've seen many an EVO Sporty on the dragstrip put a B-T to shame...HP to weight, and cubic inches is the answer.....The I-4's have the RPM advantage for HP so keep that in mind!
On a Sporty you got a lightweight advantage..I've seen many an EVO Sporty on the dragstrip put a B-T to shame...HP to weight, and cubic inches is the answer.....The I-4's have the RPM advantage for HP so keep that in mind!
#17
12-10-2011, 01:26 AM
Ultimate HDF Member
Torque is the rotational force at the drive shaft at a specified RPM. HP is the work the engine can do to say accelerate the bike. See above formula.
Consider two different engines, a 600cc inline four engine typically found in a super sport bike and a 1200cc vtwin found in a HD. The 600cc engine produces less torque at a given rotational speed, but because it can spin up to 13,000RPM produces 100 HP, slightly more than the HD engine. The HD VTwin can only produce about 80HP because it is unable to spin faster than its ~5500 RPM redline due to it's unbalanced design. Having only two valves per cyl instead of four also limits how well the engine can breath at higher RPMs.
In two bikes of the same weight, under max acceleration, the bike with the 600cc inline four will accelerate quicker than a bike with the HD 1200cc vtwin because of the higher peak horse power. The HD engine however produces more torque at much lower RPMs so with both engines running at say 3000RPM the harley motor will produce nearly twice the horsepower due to greater torque at this speed. If you typically only accelerate at part throttle and shift at 3000RPM the HD motor will feel more powerful. When driving a bike like a super sport the rider needs to change their riding technique and cruise/shift at the higher RPMs these engines are designed to run at.
In another example Ducati produce a 1200cc Vtwin that makes similar torque at similar speeds to the HD 1200cc Vtwin but because the Ducati engine is a 90 degree Vtwin it has better balance than the more compact 45 degree HD engine (the wider v angle allows for naturally balanced rotational forces and a more even firing order which means less vibration and stress on the engine and therefore a higher redline) and because of this can spin up to its 10,000 RPM redline without tearing itself apart. It also has 4 instead of 2 valves per cyl which allows it to breath better at higher RPMs. Having only a single inlet valve and single exhaust valve starts to limit how fast the cyl can fill up with air/fuel and expel combustion gasses at higher RPMs (<4000RPM) but is not really a disadvantage an lower RPMs. Because of this the Ducati VTwin puts out almost double the HP (150HP) as the HD engine at max throttle. Between idle and ~5000RPM power output would be similar between the two engines.
From what I've read Harley originally went with a 45 degree VTwin engine design because it was the most compact engine design possible and fit inside the bicycle frames early motorcycles used. The look and sound of the narrow angle VTwin is now part of their corporate identity so I doubt they will ever change their fundamental engine design even though other engine layouts vibrate less and can produce more power. Making a harley with say an inline triple would be giving up the brand identity.
Consider two different engines, a 600cc inline four engine typically found in a super sport bike and a 1200cc vtwin found in a HD. The 600cc engine produces less torque at a given rotational speed, but because it can spin up to 13,000RPM produces 100 HP, slightly more than the HD engine. The HD VTwin can only produce about 80HP because it is unable to spin faster than its ~5500 RPM redline due to it's unbalanced design. Having only two valves per cyl instead of four also limits how well the engine can breath at higher RPMs.
In two bikes of the same weight, under max acceleration, the bike with the 600cc inline four will accelerate quicker than a bike with the HD 1200cc vtwin because of the higher peak horse power. The HD engine however produces more torque at much lower RPMs so with both engines running at say 3000RPM the harley motor will produce nearly twice the horsepower due to greater torque at this speed. If you typically only accelerate at part throttle and shift at 3000RPM the HD motor will feel more powerful. When driving a bike like a super sport the rider needs to change their riding technique and cruise/shift at the higher RPMs these engines are designed to run at.
In another example Ducati produce a 1200cc Vtwin that makes similar torque at similar speeds to the HD 1200cc Vtwin but because the Ducati engine is a 90 degree Vtwin it has better balance than the more compact 45 degree HD engine (the wider v angle allows for naturally balanced rotational forces and a more even firing order which means less vibration and stress on the engine and therefore a higher redline) and because of this can spin up to its 10,000 RPM redline without tearing itself apart. It also has 4 instead of 2 valves per cyl which allows it to breath better at higher RPMs. Having only a single inlet valve and single exhaust valve starts to limit how fast the cyl can fill up with air/fuel and expel combustion gasses at higher RPMs (<4000RPM) but is not really a disadvantage an lower RPMs. Because of this the Ducati VTwin puts out almost double the HP (150HP) as the HD engine at max throttle. Between idle and ~5000RPM power output would be similar between the two engines.
From what I've read Harley originally went with a 45 degree VTwin engine design because it was the most compact engine design possible and fit inside the bicycle frames early motorcycles used. The look and sound of the narrow angle VTwin is now part of their corporate identity so I doubt they will ever change their fundamental engine design even though other engine layouts vibrate less and can produce more power. Making a harley with say an inline triple would be giving up the brand identity.
Last edited by fat_tony; 12-10-2011 at 02:51 AM.
#18
12-10-2011, 04:03 AM
Club Member
Torque is the rotational force at the drive shaft at a specified RPM. HP is the work the engine can do to say accelerate the bike. See above formula.
Consider two different engines, a 600cc inline four engine typically found in a super sport bike and a 1200cc vtwin found in a HD. The 600cc engine produces less torque at a given rotational speed, but because it can spin up to 13,000RPM produces 100 HP, slightly more than the HD engine. The HD VTwin can only produce about 80HP because it is unable to spin faster than its ~5500 RPM redline due to it's unbalanced design. Having only two valves per cyl instead of four also limits how well the engine can breath at higher RPMs.
In two bikes of the same weight, under max acceleration, the bike with the 600cc inline four will accelerate quicker than a bike with the HD 1200cc vtwin because of the higher peak horse power. The HD engine however produces more torque at much lower RPMs so with both engines running at say 3000RPM the harley motor will produce nearly twice the horsepower due to greater torque at this speed. If you typically only accelerate at part throttle and shift at 3000RPM the HD motor will feel more powerful. When driving a bike like a super sport the rider needs to change their riding technique and cruise/shift at the higher RPMs these engines are designed to run at.
In another example Ducati produce a 1200cc Vtwin that makes similar torque at similar speeds to the HD 1200cc Vtwin but because the Ducati engine is a 90 degree Vtwin it has better balance than the more compact 45 degree HD engine (the wider v angle allows for naturally balanced rotational forces and a more even firing order which means less vibration and stress on the engine and therefore a higher redline) and because of this can spin up to its 10,000 RPM redline without tearing itself apart. It also has 4 instead of 2 valves per cyl which allows it to breath better at higher RPMs. Having only a single inlet valve and single exhaust valve starts to limit how fast the cyl can fill up with air/fuel and expel combustion gasses at higher RPMs (<4000RPM) but is not really a disadvantage an lower RPMs. Because of this the Ducati VTwin puts out almost double the HP (150HP) as the HD engine at max throttle. Between idle and ~5000RPM power output would be similar between the two engines.
From what I've read Harley originally went with a 45 degree VTwin engine design because it was the most compact engine design possible and fit inside the bicycle frames early motorcycles used. The look and sound of the narrow angle VTwin is now part of their corporate identity so I doubt they will ever change their fundamental engine design even though other engine layouts vibrate less and can produce more power. Making a harley with say an inline triple would be giving up the brand identity.
Consider two different engines, a 600cc inline four engine typically found in a super sport bike and a 1200cc vtwin found in a HD. The 600cc engine produces less torque at a given rotational speed, but because it can spin up to 13,000RPM produces 100 HP, slightly more than the HD engine. The HD VTwin can only produce about 80HP because it is unable to spin faster than its ~5500 RPM redline due to it's unbalanced design. Having only two valves per cyl instead of four also limits how well the engine can breath at higher RPMs.
In two bikes of the same weight, under max acceleration, the bike with the 600cc inline four will accelerate quicker than a bike with the HD 1200cc vtwin because of the higher peak horse power. The HD engine however produces more torque at much lower RPMs so with both engines running at say 3000RPM the harley motor will produce nearly twice the horsepower due to greater torque at this speed. If you typically only accelerate at part throttle and shift at 3000RPM the HD motor will feel more powerful. When driving a bike like a super sport the rider needs to change their riding technique and cruise/shift at the higher RPMs these engines are designed to run at.
In another example Ducati produce a 1200cc Vtwin that makes similar torque at similar speeds to the HD 1200cc Vtwin but because the Ducati engine is a 90 degree Vtwin it has better balance than the more compact 45 degree HD engine (the wider v angle allows for naturally balanced rotational forces and a more even firing order which means less vibration and stress on the engine and therefore a higher redline) and because of this can spin up to its 10,000 RPM redline without tearing itself apart. It also has 4 instead of 2 valves per cyl which allows it to breath better at higher RPMs. Having only a single inlet valve and single exhaust valve starts to limit how fast the cyl can fill up with air/fuel and expel combustion gasses at higher RPMs (<4000RPM) but is not really a disadvantage an lower RPMs. Because of this the Ducati VTwin puts out almost double the HP (150HP) as the HD engine at max throttle. Between idle and ~5000RPM power output would be similar between the two engines.
From what I've read Harley originally went with a 45 degree VTwin engine design because it was the most compact engine design possible and fit inside the bicycle frames early motorcycles used. The look and sound of the narrow angle VTwin is now part of their corporate identity so I doubt they will ever change their fundamental engine design even though other engine layouts vibrate less and can produce more power. Making a harley with say an inline triple would be giving up the brand identity.
The I-4's get the HP from lighter engine parts, slower piston speeds, less heat and higher RPM's...The I-4's go thru the traps with a higher speed compared to the faster 30-ft and 60-ft times by the Twins...Reaction time is also a factor.
#19
12-10-2011, 04:55 AM
Novice
I think the following video illustrates the difference between off-idle torque and top-end Hp a little:
http://youtu.be/jXsoAdh5P5g?t=3m
Enjoy!
http://youtu.be/jXsoAdh5P5g?t=3m
Enjoy!
Last edited by 6ft4in; 12-10-2011 at 05:04 AM.