Topic: torque vs. HP

[Ryan 550k]

My head just exploded

[sangyo soichiro]

Consider this..
 you have a Sportster 1200cc with a 100 hp at rear wheel.
 and a CB 750 1000cc with 115 hp at the rear wheel..

 given that both bikes are set up for 1/4 mile, have decent clutches and good riders..same reaction time.. for arguments sake.. same (experienced)rider on each.

 Which (do you think) will win in a 1/4 mile race, and why?

 Its not a trick question, but it illustrates a point..

Are those hp numbers you give the peak hp numbers or the average hp numbers?  It's not a trick question, but it illustrates a point.   

See, the bike with the highest average^* hp over the RPM range used in the 1/4 mile will win.  Of course, the bike with the highest hp at, say... an RPM of 3000 (or pick your favorite RPM) also has the highest torque at that RPM.  So it's kind of a silly argument talking about peak hp and peak torque because we ride through a broad range of RPMs, not just where it peaks.

(* It's actually a 'weighted' average; weighted over the RPMs used during the 1/4 mile.  This accounts for more time spent on the most used RPMs.  I won't bother with the math.)





As far as the math (that so far seems to be a turn off to most people) 
The first thing I posted was just to show where that formula hp = torque*RPM/5252 comes from.  It's nice to understand that it's not just pulled out of thin air.  The other stuff I did was because paulages asked if I would show mathematically why hp peaks after torque.  The first is just algebra.  The other stuff involves calculus.  I knew that it was somewhat advanced, but if anyone understands the math, it really is the easiest way to show it.  After all, math is supposed to make our lives easier, it just seems to be a subject too many people run away from though.  Blame the education system I guess.   

[mlinder]

1 + 1 = 11

[sangyo soichiro]

As far as what the other guys have, numbers dont matter, what happens on the track does..

If done properly, the numbers and what happens on the track will be the same. 

What about comparing the area under the torque curve taken over the used RPM range?  I have heard this is the best way to compare two different engines...  Anyone...

They make pretty accurate computer programs that will tell you an E/T if you input all of the relevant info like mass, overall gearing, time lapse to shift gears, torque curve, aerodynamic drag, etc.

Kenolds

You are right.  The engine with the most area under the curve has, not only the greatest torque, but the greatest overall (not necessarily peak!) horsepower. 

[paulages]

sorry, i guess i did  hijack my own thread asking for the math explanation. I think all this information goes well in this section though, and it does help do dispel common misconceptions.

[sangyo soichiro]

Paulages, I appreciate the chance to play with the math.  In fact, I was unaware that hp peaked after torque until you mentioned it here.  I would wish that no apologies were necessary though.  When I get a chance to learn something, I am very grateful.   

A lot of people have a fear of math.  And that is not a good thing.

I'll never forget this:
A long time ago I worked in a tool and die shop.  One of my coworkers needed to fabricate and weld up something that involved compound angles.  His solution was to cut up some cardboard and tape it together, repeating with different angles, until it came out right.  He had been working on it for maybe a couple hours. 

After talking to him, I went to use the restroom (when you gotta go...).  I suppose I always had a knack for math (or at least, I wasn't afraid of it).  I took a piece of paper, a pen, and my calculator, and sat on the toilet.  When I came out of the restroom I had calculated the angles the guy needed to cut his sheet metal for it to work and gave him the info. 

Then it dawned on me; I had accomplished more while taking a #$%* than he had accomplished in the last couple hours.  Only because I knew how to do the math.  That's when I realized the power of knowledge.

[Ryan 550k]

Paulages, I appreciate the chance to play with the math.  In fact, I was unaware that hp peaked after torque until you mentioned it here.  I would wish that no apologies were necessary though.  When I get a chance to learn something, I am very grateful.  

A lot of people have a fear of math.  And that is not a good thing.

I'll never forget this:
A long time ago I worked in a tool and die shop.  One of my coworkers needed to fabricate and weld up something that involved compound angles.  His solution was to cut up some cardboard and tape it together, repeating with different angles, until it came out right.  He had been working on it for maybe a couple hours.  

After talking to him, I went to use the restroom (when you gotta go...).  I suppose I always had a knack for math (or at least, I wasn't afraid of it).  I took a piece of paper, a pen, and my calculator, and sat on the toilet.  When I came out of the restroom I had calculated the angles the guy needed to cut his sheet metal for it to work and gave him the info.  

Then it dawned on me; I had accomplished more while taking a #$%* than he had accomplished in the last couple hours.  Only because I knew how to do the math.  That's when I realized the power of knowledge.

Jesus, my head just exploded again

[MJL]

1 + 1 = 11

1+1=10, duh.   

[paulages]

Paulages, I appreciate the chance to play with the math.  In fact, I was unaware that hp peaked after torque until you mentioned it here.  I would wish that no apologies were necessary though.  When I get a chance to learn something, I am very grateful.   

A lot of people have a fear of math.  And that is not a good thing.

I'll never forget this:
A long time ago I worked in a tool and die shop.  One of my coworkers needed to fabricate and weld up something that involved compound angles.  His solution was to cut up some cardboard and tape it together, repeating with different angles, until it came out right.  He had been working on it for maybe a couple hours. 

After talking to him, I went to use the restroom (when you gotta go...).  I suppose I always had a knack for math (or at least, I wasn't afraid of it).  I took a piece of paper, a pen, and my calculator, and sat on the toilet.  When I came out of the restroom I had calculated the angles the guy needed to cut his sheet metal for it to work and gave him the info. 

Then it dawned on me; I had accomplished more while taking a #$%* than he had accomplished in the last couple hours.  Only because I knew how to do the math.  That's when I realized the power of knowledge.

that's a brilliant story. i use basic algebra in the shop quite frequently (basic formulas to find percentages, etc), but calculus is another story... haven't thought about it at all since high school. you're right though. knowledge is power. i think about knowledge this way: memorizing facts will only solve the exact problem you've memorized the fact about, whereas understanding the concepts involved will give you the wisdom to apply those concepts to other challenges. i used to make my algebra teachers so mad when i'd ask "why" formulas would work...

[754]

Wel I certainly heard a NEW TERM today....Average HP..
 Anyone care to explain that in laymens terms

 Back to my question, will explain better

 Both bike made a max HP of 100 at rear wheel. I dont care when or where RPM wise that occurred..
 Now to fill in the blanks cuz it seems a few on here are more familiar with either 4cyl hp/torque, or 2win cyl hp/torque, not both.

 I general term a H-D (that makes)  100hp will make near that in ft/lbs torque.. the Honda 4 will make around 68-70ish ft/lb  if it makes 115 hp.. the torque and HP max readings do not occur at the same rpms.. so now who do you think will win in the 1/4 mile.. equal rider, bikes prepped properly.. is that a bit easier?

 The problem with hp figures is, unless you see a dyno sheet its hard to know if they are truthful, and motor is still the same, but at the end of the day, are you interested in numbers?.. or results..
  Myself I care about results not the dyno sheets..

 I just came back from 2 trips to Bonneville this summer..
 this is what you see..
 a Truimph with around 120 hp doing 170mph
 Busa's with STOCK 150 or + doing the same speed.. I saw a local 1 cyl HD do 160 mph, and it dynos maybe 110 hp..

 Ack Attack with 2 Busa engines set the abolute Bike record last year at 350 ish (2 way average)... yet Wheeler with EZ Hook did a 350 one way at least 3 years ago with a single Kawi engine!.. do you think it makes more HP than Ack?.. I doubt it, but yet it got great results..

 So what I am trying to point out is that HP  does not always win, sometimes it is a combo of HP & torque, sometimes other  variables come into play..  All the HP in the world wont help if you cant put it to the ground..


 All the math in the world does not always put it in simple, everyday context..

[mlinder]

1 + 1 = 11

1+1=10, duh.   

There are 10 kinds of people in the world. Those who know binary, and those who don't.

[mlinder]

Aerodynamics, 754. Aerodynamics.
Drag increases exponentially. What did the single cylinder HD look like?

[Joel]

Wel I certainly heard a NEW TERM today....Average HP..
 Anyone care to explain that in laymens terms

 Back to my question, will explain better

 Both bike made a max HP of 100 at rear wheel. I dont care when or where RPM wise that occurred..
 Now to fill in the blanks cuz it seems a few on here are more familiar with either 4cyl hp/torque, or 2win cyl hp/torque, not both.

 I general term a H-D (that makes)  100hp will make near that in ft/lbs torque.. the Honda 4 will make around 68-70ish ft/lb  if it makes 115 hp.. the torque and HP max readings do not occur at the same rpms.. so now who do you think will win in the 1/4 mile.. equal rider, bikes prepped properly.. is that a bit easier?

 The problem with hp figures is, unless you see a dyno sheet its hard to know if they are truthful, and motor is still the same, but at the end of the day, are you interested in numbers?.. or results..
  Myself I care about results not the dyno sheets..

 I just came back from 2 trips to Bonneville this summer..
 this is what you see..
 a Truimph with around 120 hp doing 170mph
 Busa's with STOCK 150 or + doing the same speed.. I saw a local 1 cyl HD do 160 mph, and it dynos maybe 110 hp..

 Ack Attack with 2 Busa engines set the abolute Bike record last year at 350 ish (2 way average)... yet Wheeler with EZ Hook did a 350 one way at least 3 years ago with a single Kawi engine!.. do you think it makes more HP than Ack?.. I doubt it, but yet it got great results..

 So what I am trying to point out is that HP  does not always win, sometimes it is a combo of HP & torque, sometimes other  variables come into play..  All the HP in the world wont help if you cant put it to the ground..


 All the math in the world does not always put it in simple, everyday context..

Average HP is simple.  HP is Work/Time.  If you do 550 lb-ft of work in 5 seconds, the average power is 0.2 HP.  Unless the power is constant over the entire 5 seconds, there will be short periods during that time that are higher or lower than the average.

It would be similar to average speed.  It may take me 70 minutes to make a 50 mile trip.  For part of the trip, I travel at 60 mph.  However, my average speed for the trip is about 43 mph.

[754]

I know aero comes into play bigtime, so do other factors..


 He single was a bike with fairng, homebuilt, 950cc with a blower.

[mlinder]

Drag increases exponentially. Having more torque did not allow him to go faster with 110hp than less torque and 160hp.
What did his fairing look like?

[754]

You are missing the point, HP alone does not make it go down that track.
 The bike had a handbuilt aluminum fairing, first Full one he ever built.

 Have you ever compared HP between V twins & fours with the same 1/4 mile ET?

[mlinder]

You are missing the point, HP alone does not make it go down that track.
 The bike had a handbuilt aluminum fairing, first Full one he ever built.

 Have you ever compared HP between V twins & fours with the same 1/4 mile ET?

Only thing that makes you get down the salt at top speed is power.

And you say he had a full fairing? Like, fully enclosed?

You are using a VERY small sample to try to describe what power is and does.

Again, horsepower IS torque. It's how many times it's putting available torque to the ground in a given amount time.
Soichiro up there tried to explain why a high torque engine makes it down the VERY short 1/4 mile track a bit faster than a high horsepower four.
The big twin makes within 80% of it's peak power (doesn't matter if it's torque or HP you are measuring, because, again, they are the same thing) for a much larger percentage of it's rev range than a high revving four.
Therefore, the four must shift many more times to stay in the powerband. Drop that down to a 8 to 11 second pass, and that's an issue. If you wanted to use a larger control set, to really see what 'power' does, put the same bikes on a mile long stretch. Then what happens?
The reason the big twins do so well in the quarter mile is because the nature of such a short track and it plays well to this configuration.

You are ascribing a generality to a situation from a tiny control set.

[paulages]

i think there needs to be a different term to describe "torque" in the manner in which it is often spoken. skimming past the math, it's easy to continue the misunderstanding that torque=low end grunt and HP=top end speed. i'm not sure exactly how to translate it, because i think at the end of the day we're saying similar things, just talking different languages.

maybe this analogy works: in the common misunderstanding of the terms, "torque" is one guy who can lift a boulder up a hill. "HP" is 10 weaker guys who can do the same work, but it takes all 10 of them to get it done. the math is just saying that the same boulder is getting moved either way, and 754's experience is just saying that they sure as hell don't look the same doing it. 

[754]

I was part of the tiny control set that enjoys drag racing.. the very short track is probably the 1/8 tracks or the ones shorter than that , and hillclimbs and dirt drags.

  I never had a problem understanding torque or horespower, in everday situations that most can understand.

 I find that people that prefer to ride multi cylinder bikes vs Twins, (and have not ridden/worked on them) often dont understand torque & need it explained..

 The more I hang around racetracks, the less I rely on hp figures to give results..

 Back to the fairing, it ended ahead of the riders legs, and did not cover the front wheel.

[mlinder]

I was part of the tiny control set that enjoys drag racing.. the very short track is probably the 1/8 tracks or the ones shorter than that , and hillclimbs and dirt drags.

  I never had a problem understanding torque or horespower, in everday situations that most can understand.

 I find that people that prefer to ride multi cylinder bikes vs Twins, (and have not ridden/worked on them) often dont understand torque & need it explained..

 The more I hang around racetracks, the less I rely on hp figures to give results..

 Back to the fairing, it ended ahead of the riders legs, and did not cover the front wheel.

Funny, the more I hang around race tracks that aren't just 1/8th or 1/4 mile long straights, the less I rely on torque figures to give results

/edit: I was kidding! In all honesty, I need them to make as much torque as possible... in the top end of the rev range, because, more torque equals more HP. ... cus they are the same thing....

Also, please don't misunderstand me when I say the control set is too small. I don't mean the number of people doing it. I mean the conditions of the sport itself.

[w1sa]

All over Good Read.

Improved my appreciation of  'Horses for Courses'....

[sangyo soichiro]

If you only remember one thing I've said in this thread, remember this:
The numbers for peak hp and peak torque are almost worthless. These peak numbers only give the value at one RPM.  We do not ride at just one RPM.  You need to maximize the horsepower over the most used RPM range to get the best acceleration.  You maximize the horsepower over this RPM range by maximizing the torque over this same RPM range.  Hp and torque go hand in hand.  At any particular RPM, the bike with the most horsepower will also have the most torque at that RPM.  With all else equal (weight, aerodynamics, etc.) the bike with the highest average power (weighted over the used RPMs) will have the fastest acceleration, (and the highest average torque over the used RPMs). 




Okay... I've said in practicality we need to maximize torque to maximize power.  The key is that we need to maximize these quantities over the RPMs we use the most.  That is the practical part of this discussion.  Now I just want us to understand enough to use the proper language to describe what we're doing.  The proper language is this:

'We need to maximize the power over the most used RPMs in order to get the best acceleration.  In order to maximize the power over this RPM range, we need to maximize the torque over this same RPM range.' 

At this point, I'm only advocating the understanding of these words we've been using.

To understand that it's the "power" and not "torque" that is the correct word, here is another equation.   

Let's say we're doing a 1/4 mile.  It takes some amount of work to move our bike that distance.  Power is work divided by time:

power = work/time.

Solving this equation for the time, we get

time = work/power.

To minimize the 1/4 mile time, you must maximize the power (over the RPMs used, not necessarily peak hp!).  And I've already mentioned how we do this in practicality.

The reason why it is more correct to say we must increase the power is because it is the power that defines how much work we can do in a given amount of time.  It just so happens that power is made from a combination of torque and RPM for an engine with a revolving crankshaft.  Rockets, for example, increase power by increasing thrust, and torque plays no role. 

[ealanm]

What about comparing the area under the torque curve taken over the used RPM range?  I have heard this is the best way to compare two different engines...  Anyone...

What really matters is the area under the power curve.  The area under the power curve is proportional to energy.  If you compare two bikes of the same weight between two RPMs that represent the same speed on each bike, the curve with the greater area under it will be for the bike that got from one speed to the next in the shortest time.

If you shift so that you go straight across (from, say, 70 HP at 8000 RPM to 70 HP at 6000 RPM, with peak power being somewhere in between) you'll get the maximum acceleration in that gear.  (The math gets a bit funky, but with calculus you can show that this maximizes the area under the curve.)

[sabres7th]

apples to oranges. low end speed,  mid range and high end are all different areas of a power band. you can not have them all so you pick one area and build from the area you want to travel fast in. when you want to go fast in low end you advance the timing. in the high end you retard.one is for torque and one is for rpm breathing sustained power.

[MRieck]

apples to oranges. low end speed,  mid range and high end are all different areas of a power band. you can not have them all so you pick one area and build from the area you want to travel fast in. when you want to go fast in low end you advance the timing. in the high end you retard.one is for torque and one is for rpm breathing sustained power.

Welcome sabres. I didn't really get into this topic but it sounds like you are coming from a "cam" perspective. I agree with your premise for sure.