HP vs Torque

[marcelm]

I would like to understand better, how do you feel the difference between torque and HP, when riding.

Let’s imagine we have two bikes :

1st one :  80 HP and 102 lb-ft (about like our stock Raider, OHV engine)

2nd one : 80 HP and 80 lb-ft (a smaller engine size than 1st bike, which needs a higher rpm to reach his max 80 HP, likely a DOHC engine)

Due to the fact that both engines has same power, 80 HP, the question is : when and how do you feel that difference in torque ?

[Ares X]

Good topic.

[Bill L]

With the higher torque the engine is going to pull much harder and pretty much sustain equal performance throughout the entire pull.

I saw a great analogy on Utube.  Think of a body builder, and a sprinter, they both have the same power, (HP) but the body builder has a lot more stamina, (Torque).  Put a 50 pound pack on the back of both the body builder and the sprinter and have them run 100 yards.  The body builder with it's high torque will run the same time with or without the pack.  The sprinter with the lower torque will run two very different times because he doesn't have the stamina, (Torque) to maintain the same speed with the 50 pounds on his back.

[Paladin]

Because the engine with the higher TQ rating developes its TQ at a lower RPM, it will travel a measured distance (1/4 mile) quicker than the same displacement engine that developes less TQ, but the same HP. You'll also feel the TQ reaction from the higher rated engine sooner.

A simple way to look at it would be: TQ = the time it takes to travel a measured distance. HP = the top speed atained while traveling that same distance.   

[Ares X]

Because the engine with the higher TQ rating developes its TQ at a lower RPM, it will travel a measured distance (1/4 mile) quicker than the same displacement engine that developes less TQ, but the same HP. You'll also feel the TQ reaction from the higher rated engine sooner.

A simple way to look at it would be: TQ = the time it takes to travel a measured distance. HP = the top speed atained while traveling that same distance.

That makes it very clear.

[Capt_Zoom]

I would like to understand better, how do you feel the difference between torque and HP, when riding.

Let’s imagine we have two bikes :

1st one :  80 HP and 102 lb-ft (about like our stock Raider, OHV engine)

2nd one : 80 HP and 80 lb-ft (a smaller engine size than 1st bike, which needs a higher rpm to reach his max 80 HP, likely a DOHC engine)

Due to the fact that both engines has same power, 80 HP, the question is : when and how do you feel that difference in torque ?

Its easier if you compare a 4 cylinder crotch rocket to a v-twin.  There are a lot of factors involved.
-HP
-Torque
-RPM
-Displacement
-Piston Stroke
-Power to weight ratio

As I understand it, and I'm no expert is as follows

A 1300 or so CC bike like a hyabusa has more cylinders moving at a smaller stroke at a faster RPM.  THe bike produces massive HP (near 200hp) at very high RPM (RPMs a raider could never reach.  However, the torque of such a bike isn't like that of a raider.  Hyabusa produces somewhere around 95ftlbs where a raider produces around 115-120ft lbs.  Because the busa has a very high power to weight ratio (same for the torque to weight ratio, you can feel the torque when you hammer it.  You can wheelie the bike easily because the HP and torque are matched well with the weight of the bike.

A raider on the other hand, 1854cc with its stroked twin design produces massive (for a twin) power at a very low RPM with a nice flat HP and torque curve.  This means that you feel the power and torque all the way up the the rev limiter at 5400RPM.  Because a V-twin's pistons move further, especially if stroked, than a 4 cylinder crotch rocket the raider can never reach the RPM levels of the busa.  Torque in the raider is felt off the line and during hard accel gear shifts.  Feels like the bike is pulling you or throwing you back in the seat trying to pry your hands off the bars.

In your example you provide look deeper into your question.  If the second bike has a smaller motor it is also likely lighter.  so my guess is that the difference you would feel in the torque would be negligible.

Its kinda funny though. I can compare two very different bikes like my raider vs my wife's 1980 xs650.  Power to weight means everything.  My raider 97hp 120 torque pulls harder, and has a more consistent pull right through entire RPM range.  My wife's xs650 on the other hand (55hp and 50ft lbs torque) it doesn't pull consistently to redline (9000RPM) but has spots where you hit the power band in each gear where the bike take off on you.  Oddly enough, because we stripped the bike down to 380lbs it is nearly as quick in the 1/4 mile as my raider, and I even used a sproket to reduce acceleration and increase cruising speed.  This is Especially apparent if my wife is on it.  With her on it the xs has nearly the same power to weight ratio as the raider with my 200lbs on it. 

Read this
http://www.largiader.com/articles/torque.html



 

[Capt_Zoom]

With the higher torque the engine is going to pull much harder and pretty much sustain equal performance throughout the entire pull.

I saw a great analogy on Utube.  Think of a body builder, and a sprinter, they both have the same power, (HP) but the body builder has a lot more stamina, (Torque).  Put a 50 pound pack on the back of both the body builder and the sprinter and have them run 100 yards.  The body builder with it's high torque will run the same time with or without the pack.  The sprinter with the lower torque will run two very different times because he doesn't have the stamina, (Torque) to maintain the same speed with the 50 pounds on his back.

This would greatly depend on creatine levels of both athletes.  Also if you look at olympic sprinters or All American sprinters...they are bigger (leg wise than the body builders now a days.  This is easy to see in the NFL since most of the best running backs were also national class sprinters.  30+ inch legs are now the norm rather than the exception.

[jim]

And here I explain it this way... the crotch rocket may outrun a bus... but I will be able to pull it.... 

[Pudge]

Because the engine with the higher TQ rating developes its TQ at a lower RPM, it will travel a measured distance (1/4 mile) quicker than the same displacement engine that developes less TQ, but the same HP. You'll also feel the TQ reaction from the higher rated engine sooner.

A simple way to look at it would be: TQ = the time it takes to travel a measured distance. HP = the top speed atained while traveling that same distance.

That makes it very clear.

Great topic and thanks also Paladin. Describes it perfectly for me.

[Bill L]

With the higher torque the engine is going to pull much harder and pretty much sustain equal performance throughout the entire pull.

I saw a great analogy on Utube.  Think of a body builder, and a sprinter, they both have the same power, (HP) but the body builder has a lot more stamina, (Torque).  Put a 50 pound pack on the back of both the body builder and the sprinter and have them run 100 yards.  The body builder with it's high torque will run the same time with or without the pack.  The sprinter with the lower torque will run two very different times because he doesn't have the stamina, (Torque) to maintain the same speed with the 50 pounds on his back.

This would greatly depend on creatine levels of both athletes.  Also if you look at olympic sprinters or All American sprinters...they are bigger (leg wise than the body builders now a days.  This is easy to see in the NFL since most of the best running backs were also national class sprinters.  30+ inch legs are now the norm rather than the exception.

Capt, it's just a simple basic comparison, not meant to dig into the physics of it.  The example gives both at the same power but different torque, or in the case of humans, stamina.  But even today's Olympic sprinters are not going to run a 100 as fast as they do with 50 pounds on there back.

[PhysicsDude55]

The best comparison I like to use is to compare it to a ratcheting socket wrench.

A big ol' ratchet with a 3 foot handle would have amazing torque, you could loosen very stuck bolts, but if you have a long loose bolt, you wouldn't be able to loosen it very fast.

A little ratchet with a 3" handle could work very fast, you could loosen loose nuts very quickly, but you'd have a hard time loosening anything which is decently tight.

Its really a pretty literal comparison to HP/Torque of engines, because ratchet handle length is analogous to the length of the connecting rods and the stroke of an engine.

An advantage high HP/low torque engines have is that with a very large bore compared to their displacement, it allows for bigger valves, so a high revving 1000cc engine might be able to breathe as much air/fuel as a low revving 2000cc engine.  Also, remember that HP is (Torque X 5252), so an engine that revs to 15,000 RPM, even if its only producing 50 ft/lbs of torque in that range, will make 142 horsepower, while low revving engines (such as the Raider's 5300RPM redline) will never make more hp than their peak torque.

Really, it all depends on the torque curve.  A smooth flat curve will produce more total power than a peaky curve.  The area under a curve indicates how much total power that curve creates over time.

EDIT:  Horsepower = (Torque * RPM) /  5252

(thanks theurbanlegend)

[Capt_Zoom]

With the higher torque the engine is going to pull much harder and pretty much sustain equal performance throughout the entire pull.

I saw a great analogy on Utube.  Think of a body builder, and a sprinter, they both have the same power, (HP) but the body builder has a lot more stamina, (Torque).  Put a 50 pound pack on the back of both the body builder and the sprinter and have them run 100 yards.  The body builder with it's high torque will run the same time with or without the pack.  The sprinter with the lower torque will run two very different times because he doesn't have the stamina, (Torque) to maintain the same speed with the 50 pounds on his back.

This would greatly depend on creatine levels of both athletes.  Also if you look at olympic sprinters or All American sprinters...they are bigger (leg wise than the body builders now a days.  This is easy to see in the NFL since most of the best running backs were also national class sprinters.  30+ inch legs are now the norm rather than the exception.

Capt, it's just a simple basic comparison, not meant to dig into the physics of it.  The example gives both at the same power but different torque, or in the case of humans, stamina.  But even today's Olympic sprinters are not going to run a 100 as fast as they do with 50 pounds on there back.

Sorry...got off topic there.  Sprinters don't like weight period.  they typically freak out if they have to switch to a heavier shoe let alone to wearing weight on their back.  As one sprinter once told me...."sprinters are the lazy track runners on earth...we go through life trying to conserve energy for our one big shot...we take elevators and escalators everywhere." 

 

[StrykerBilly]

Better answers here than my short and sweet attempt but not taking into consideration torque/HP curves and what rpms they are achieved at, power-to-weight etc. I used to explain it at a very high level this way:
Torque = Traffic(and by that I mean a torquey motor [low end torque] is very helpful in traffic.  Think small diesel
HP = Highway(and by that I mean more horsepower allows for higher speeds and better passing on the highway once at speed)

Like I said there are a myriad of other contributing factors that the "real" gear heads can explain better.  I just used this analogy back when engines were much whimpier and you didn't always get good torque and good hp in one motor.  You Raider folks are a little spoiled in that regard

[arrowdriver]

And this is why I also prefer v-twin sports bike, much more drive ability in every day traffic than a 4 cylinder.  More torque = more relaxed riding.

[jhow2133]

Torque throws you back in your seat, HP keeps you going faster. Good thread!