Horsepower, Torque, and how to use it properly on a motorcycle. - ZX6R Forum
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post #1 of 35 Old 07-11-2015, 03:46 PM Thread Starter
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Horsepower, Torque, and how to use it properly on a motorcycle.

Hey all! Welcome to the next installment in my series of writings.

I have often heard the words 'horsepower' and 'torque' tossed around and I got the sense that maybe the person using those terms was not 100% sure of their definition.

To many, horsepower means nothing more than 'my bike is fast'. Torque is 'that other thing that means my bike is fast', and bigger numbers means that I am cooler than the guy/girl next to me. While this may be a fine definition for some, let's take a little more in-depth look at horsepower and torque to see exactly how it applies to our real-world riding.

To begin, lets define both those words but to do so requires a little further delving into one of my favorite subjects; physics. DISCLAIMER: This will be a simplified viewpoint as it relates to our subject. If you are a physics nut(job) please do not become offended by my shorthand.

Horsepower and torque are both units of measure for power produced by an engine. Ok, so how do you define power? Power is simply the rate of doing work. Well...what the heck is work? The rate of moving an object. So power is the unit of measure for moving an object. For motorcycles, we measure this with torque and horsepower. Stick with me, it gets easier, I promise!

First, let's quickly clarify something. If you are discussing the power plant of a MOTORcycle (misnomer) or any internal combustion vehicle, you are talking about an engine. An engine converts fuel to power. A motor is an electrical device. Lets get those terms straight, shall we?


Torque

Put simply, torque is a unit of measurement of a twisting force and is measured in foot pounds or pounds-per-foot (lb-ft). If you have a foot long wrench on a bolt and set a 10lb weight on the end of it, you are exerting 10 lb-ft of torque on the bolt head.

Torque is most easily understood by motorcyclists as the force exerted on the rear wheel and it is directly related to acceleration. More torque=faster acceleration.

Horsepower

As it applies to the motorcycle world, horsepower is a unit of measure equal to the force necessary to move 550lbs one foot in one second. Who came up with this? Not a clue, but it doesn't matter. For the point of our discussion think of horsepower as 'top end' speed. The maximum velocity that you can travel is directly related to your horsepower (we are removing gearing from this discussion for the sake of simplicity).

The equation for measuring horsepower is pretty easy: (torque * RPM)/5252. So, if we are putting down 50 lb-ft of torque, at 10,000 RPM we would be producing 95.2 horsepower.

What the heck does all this mean?

Ok, ok. In very simple terms if your top speed is 180mph, that is a function of your horsepower. How quickly you reach your top speed is determined by your torque. There is some overlap of course but that is far beyond the scope of this discussion.

So which is better?

The simple answer: both. Ideally you want as much of both of them as possible but to answer this you need to determine what your use for the engine is.

In a technical track where you are spending lots of time accelerating through the gears, the more torque you can produce the better. In a longer, high speed sweeper type track, a higher horsepower engine will serve you better.

Have you ever watched a WSBK or MotoGP race and heard the announcers say that this particular track favors the Yamaha or Aprilia? The Yamaha is an inline 4 engine...they generally produce higher horsepower but less torque. The Aprilia is a V4 engine and produces more torque and less horsepower. If you look at the track layout, the longer tracks will favor the Yamaha and the shorter, more technical tracks will favor the Aprilia. The Yamaha has a higher top speed but the Aprilia reaches its top speed quicker

Ok, so now that the remedial learning is done we can now focus on how the heck do we make use of this information?

Well, first we need to measure our torque and horsepower, and that is done on a dynamometer or 'dyno' for short.

The six reasons why you need to get your bike to a dyno

The dyno is a lot more than just a tool for measuring horsepower. It is also a tuning instrument used to get the absolute most out of your engine. Ever have your bike stumble in lower gears? The dyno can cure that. Ever feel like you were going fine but at certain RPMs the bike kind of falls flat on its face? Yep, the dyno can fix that.

I have never understood why people will spend $1000 for an exhaust and $800 for a power commander but not spend the $200-300 for a custom tune from a dyno so that you can actually make the best use of that shiny new exhaust and PC. That is like buying a HD television but not paying for HD cable service. Sure, it may work but you aren't getting your moneys worth.

1) Your bike will have more power after visiting a dyno. Getting a custom map done fine-tunes your power commander or bazzaz unit to your riding conditions (temp, humidity, riding style) and really 'wakes up' the motor.

2) Your bike will run smoother after visiting a dyno. From the factory our bikes are tuned to pass emission standards which unfortunately takes precedence over actually running right. Power delivery is easier to manage and makes the bike more fun and friendly to ride.

3) You can cause harm to your bike if you do certain modifications and do not get the bike tuned. As I just said above, bikes are tuned from the factory to meet emission standards which means they already run lean (fuel to air ratio...less fuel, more air). If you install an aftermarket air filter (still more air) and an exhaust system (still more air) then you are making the bike even more lean. The leaner you make the fuel/air mixture, the more heat it generates and any engine builder can tell you that heat is the enemy. Unchecked it has the potential to do bad things to your internal engine components. THIS IS NOT A SCARE TACTIC. It doesn't mean that if you do not get this done your bike will suddenly explode. It does mean that you are shortening the lifecycle of the engine and adding increased wear into your system.

4) You can get improved fuel economy. Even though we generally create more power by adding more fuel into the mix, you will usually end up with increased fuel economy due to the increase in power. If you needed to run 20% throttle to maintain 70mph on the highway, you may only need 15% throttle after having it tuned. That translates into fuel savings.

5) You know how accurate your tachometer is. Every bike that I have seen has been off with the tachometer. On a dyno you will know what your true RPMs are compared to your displayed RPMs. This information will be useful when you start looking at dyno charts to get the most out of your engine.

6) You cannot get the most out of your bike without knowing exactly where your power and torque is. This may not be relevant for street riding but for track riders and especially racers, this is the most important benefit of dyno tuning.



How to use your power

So, now that we have established some definitions and gotten our bike to a dyno, we get the dyno results sheet which looks something like this below.



This is an exact graphical representation of the power created by our engine, in this case my own Kawasaki ZX6R race bike.

The top line is the horsepower that the engine creates. The line below it is the torque that is generated. On the bottom of the chart you will see numbers 3-16, that is your engine RPMs x 1000.

This gives us a matrix to look at. Go to the 6 on the RPM scale and look up that horizontal line. You will see that the torque is somewhere around the 39 mark which means our HP is ~44. Well heck, that's not a lot! We can clearly see that there is more horsepower as we move to the right of the chart, which means that as our RPMs climb, we produce more and more power to a point. This gives us an idea that this particular engine needs to be kept in the higher RPM range to get the most out of it and that is true if we are talking about top end speed.

Lets take a moment and look at that torque line. You can see that the highest amount of torque is right about 11,000 RPMs. Since we have already established that torque=acceleration, if our goal is to accelerate we want to be keeping our RPMs in a range where we have the highest torque...and ignore the HP numbers for now. I know this goes against all the internet-tough-guy-forums and bro-science thinking where all they throw around is large horsepower numbers in an effort to seem ultra-cool. Trust me on this. Torque is where it is at unless you are in your top gear and pulling down a long straight.

So, since the goal is to accelerate as quickly as possible, where do we want to keep our engine RPMs? Right here:



For this particular motor, there is a 'sweet spot' where the torque is nearly perfectly flat. That means tons of available power to accelerate between the 11,000 and 13,000 RPM range. You can see that after 13,000 the torque starts to fall off. What this means is that you want to shift this motor at 13,000 RPMs to drop it back into the sweet spot. You keep doing this until you are in 6th gear and then you have no choice but to continue to rev the motor.

This is what I mean when I say 'short shifting'. It means that you do not continue to rev your bike until you hit the rev limiter. You shift earlier than the limiter to keep the bike in that sweet spot. If you have ever watched any of my videos that show the dash, you will see that I always shift earlier than the rev limiter.

**NOTE** This is where knowing your displayed RPMs vs actual RPMs is critical. On my particular bike we discovered that the tachometer reads about 1000 RPMs higher than actual. What this means is that even though I want to keep the engine between 11,000-13,000 actual RPMs, the numbers displayed on the tach would be closer to 12,000-14,000. Those numbers are what I shift with when looking at my tachometer.

So, we know that to get the fastest acceleration we want to keep the RPMs in that sweet spot shown above. What about when I am in 6th gear on a long straight? This is where horsepower becomes more important than torque. How much actual power is there to push you and your bike through all that wind resistance?



About 12,500-14,000 RPMs is the ideal range when I am looking for top speed as that is where my peak horsepower is made. If the track that I am at requires me to rev past that 14,000 mark, it is time to look at changing your gearing to keep your bike in that rev range for top speed.

You will note that after 14,000 RPMs the horsepower starts to fall off drastically...and so is the torque! What that means is that under no circumstances do you want to rev this engine past 14,000 RPMs. You are just not making the power that you want to make.

One final note: All bikes are different!

Here is a dyno chart from an older Yamaha R6.


Looking at this chart you can see that it really doesnt make good power until much higher in its RPM range, but that the power continues right up until redline. That means this engine is one that you want to take to the rev limiter on every gear.

This is why it is critical for you to dyno your own engine. Even in the same make, year, and model the engines can vary in how they deliver power.

So, I hope that you stuck it out to the end of this as it has gotten quite long and that you have found the information useful!
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post #2 of 35 Old 07-11-2015, 07:50 PM
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I have a question - I'm assuming the rpm gauge on the power commander (when you have it hooked up to your computer) is tied to your bike, so if your bike is wrong, the power commander will be wrong as well? I've never thought about the possibility of the tach being off. Is that why my dyno chart falls off at 15.5 when the bike revs to 16.5?



Fantastic read. Thank you!
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post #3 of 35 Old 07-11-2015, 08:30 PM Thread Starter
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Originally Posted by exalted512 View Post
I have a question - I'm assuming the rpm gauge on the power commander (when you have it hooked up to your computer) is tied to your bike, so if your bike is wrong, the power commander will be wrong as well? I've never thought about the possibility of the tach being off. Is that why my dyno chart falls off at 15.5 when the bike revs to 16.5?



Fantastic read. Thank you!
You are correct in that you are displaying 16.5k rev limit but the actual, real hard limit is 15.5k. More revs is not necessarily better, what matters is that you know where your power is in relation to what your tach is displaying =)

I honestly cannot answer the question regarding the power commander with any authority. I *assume* that it reads the same as the ECU/tach but do not know that for a fact. I will shoot that question off to my dyno tuner and let someone with the right knowledge fill in that blank before I take a guess.
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post #4 of 35 Old 07-11-2015, 08:34 PM
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So based off my dyno chart, I should be shifting when my bike's tach says 15k to get the most out of it? Would that change on long straights?
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post #5 of 35 Old 07-12-2015, 12:03 AM
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Sorry PS, but there is some misinformation in your post. Power is simply the work (energy) done over time. If power is higher, it will do more work in the same amount of time or the same work in less time. The result of more work is more acceleration.

What this means is you will ALWAYS accelerate fastest by maximizing HP. While the engine may make more torque at a lower RPM than where HP peaks, by staying in a lower gear so that HP is higher, you actually make more torque at the wheels, which means you accelerate faster.

A simple way to analyze this is to use a theoretical engine/motor that has a perfectly flat torque curve. HP will continue to rise at a constant slope. Pick any wheel speed you want and use several different gear ratios. You'll find that despite having the same torque output at the engine, the torque at the wheels will always be highest in a lower gear.

You can also flip the analysis and use a theoretical engine that has constant HP. The torque curve will have a constant slope but be negative. But what you'll find is that at any given speed, the torque output at the wheels will be the same no matter what gearing you use.

So what does this mean? HP is the more important number as far as acceleration is concerned. Want to accelerate the fastest? Choose shift points that give you the most area under the curve on the HP curve. You can actually do this using torque as well, but you would need to do it with the raw wheel torque curves for each gear.

Another interesting exercise is to take the torque at the engine and whatever engine RPM that correlates to and calculate the torque at the wheel in any given gear mathematically. Then calculate the resultant wheel RPM. Then calculate the HP at the wheel using the resultant wheel torque value and the wheel RPM. You'll find that the wheel HP number is exactly the same as the HP calculated at the engine. Use that same HP and engine RPM and do the same with every gear and the result will be exactly the same. And what this tells us is that HP is the same at the engine and wheel for any given RPM (assuming WOT and ignoring losses in the drivetrain) regardless of gearing. And this makes it a much easier number to compare across gearing with.

I'd be happy to provide some visuals at some point, but its late on a Saturday night and I think I'd prefer to sit under the stars and enjoy a stiff drink and a cigar instead. Plus its better for everyone to digest this themselves. If you want to really dig into this, use Excel and go through the analysis I explained above. And if you need clarification or help, please ask.
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post #6 of 35 Old 07-12-2015, 03:08 AM Thread Starter
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Originally Posted by CKwik240 View Post
Sorry PS, but there is some misinformation in your post. Power is simply the work (energy) done over time. If power is higher, it will do more work in the same amount of time or the same work in less time. The result of more work is more acceleration.

What this means is you will ALWAYS accelerate fastest by maximizing HP. While the engine may make more torque at a lower RPM than where HP peaks, by staying in a lower gear so that HP is higher, you actually make more torque at the wheels, which means you accelerate faster.

A simple way to analyze this is to use a theoretical engine/motor that has a perfectly flat torque curve. HP will continue to rise at a constant slope. Pick any wheel speed you want and use several different gear ratios. You'll find that despite having the same torque output at the engine, the torque at the wheels will always be highest in a lower gear.

You can also flip the analysis and use a theoretical engine that has constant HP. The torque curve will have a constant slope but be negative. But what you'll find is that at any given speed, the torque output at the wheels will be the same no matter what gearing you use.

So what does this mean? HP is the more important number as far as acceleration is concerned. Want to accelerate the fastest? Choose shift points that give you the most area under the curve on the HP curve. You can actually do this using torque as well, but you would need to do it with the raw wheel torque curves for each gear.

Another interesting exercise is to take the torque at the engine and whatever engine RPM that correlates to and calculate the torque at the wheel in any given gear mathematically. Then calculate the resultant wheel RPM. Then calculate the HP at the wheel using the resultant wheel torque value and the wheel RPM. You'll find that the wheel HP number is exactly the same as the HP calculated at the engine. Use that same HP and engine RPM and do the same with every gear and the result will be exactly the same. And what this tells us is that HP is the same at the engine and wheel for any given RPM (assuming WOT and ignoring losses in the drivetrain) regardless of gearing. And this makes it a much easier number to compare across gearing with.

I'd be happy to provide some visuals at some point, but its late on a Saturday night and I think I'd prefer to sit under the stars and enjoy a stiff drink and a cigar instead. Plus its better for everyone to digest this themselves. If you want to really dig into this, use Excel and go through the analysis I explained above. And if you need clarification or help, please ask.
I certainly appreciate your input and I am familiar with the math you are using. My intent in this post was to give people a workable range of RPMs to use when riding the bike so as I said in my original post, this is an abbreviated version of the very in-depth physics required to fully understand the subject...a sort of cliffs-notes if you will.

I respect your position. The entire reason I posted this was to start a discussion but will respectfully differ. There are most definitely two camps in the engine building world and I can just as easily find well-known builders that swear one is better than the other for both horsepower and torque.

On our I4, small displacement bikes, torque never comes on strong at lower RPMs (at least not in my experience) so it is a much easier method to watch the torque curve to discover that usable RPM range where a rider will get the most bang for his buck.

As with all things, I do not know everything. This is my understanding of the subject which has served me well in the racing world but I am always open to learning something new. When you have the chance I would love to have an intelligent discussion regarding your position.
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post #7 of 35 Old 07-12-2015, 07:50 AM
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I think it might be easier to say that the ideal setup for any track has the engine in the optimum peak output for as much of the lap as possible. Maximum acceleration, tapped out at the end of the longest straight.

It all comes down to what is the 'sweet spot' of a given engine configuration. How wide is it, and how much does it 'roll off' above and below that point?

Close ratio transmissions have significant overlap in useable RPM, so that the engine can be kept near the 'peak' output point even when shifting. The step 'down' in RPM as you go 'up' in gears is typically about 1,000 RPM.... much tighter than necessary in a street bike, and realistically wider than required with anything approaching a 'street' tune.

The 6 speed transmission makes it possible to be at peak power in first, roughly 11-13K, at something like 60-75 MPH on stock gearing. Bang into second, dropping to 12K, and romp to 13 again and it's nearer to 90 MPH. do that, and the motor stays near the 100 HP 'peak'.

Short of maximum power, the area that has enough to provide adequate acceleration rather than that max, is more broad..... useable power is on the order of 5-13K. That probably spans 60-100 HP. If your timing is off, and you are around 60 HP and your competitor is closer to their 100; you will lose the drag race.

The reason this is relevant to this conversation is that the calculation for torque, and the calculation for HP produce the same value at 3750 RPM. A motor that has it's peak power output (greatest efficiency) within a couple of K of that value is more accurately assessed with a torque number, vs. a HP #.

When engines could not readily exceed 5K RPM due to mechanical limitations displacement ruled. Mo' bigger meant mo' power. I've seen tugboat motors that have pistons that are feet across. Ships main engines have strokes measured in feet, and bores which are significantly 'under square'. Efficiency in that realm has to do with the best atomization of fuel, to extract as much heat as possible for each engine cycle.

Now that we have increase the rate of firing by going smaller, it's all about the efficiency of the pumping action.... the faster in and out, the more firings that can occur, which adds up to a higher average power. The actual atomization and burning of the fuel is still important, but it is not the sole emphasis. More bangs in a unit of time, even if they are less effective individually will trump an efficient single event of the same displacement.

Honda spent a great deal of time and money on researching ways to increase RPM in the past 60 years. The 8 valve per cylinder NSR oval piston race motor was probably the most extreme example. Jaguar's V-12 350 CI motor is another example of increasing valve area for more RPM.

The goal of the NSR was to increase valve area further than what could be done with 4 valves per cylinder, or the 5 valves per that Yamaha was having some success with. Oval cylinders are harder to maintain a ring seal with, compared to a circle.
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post #8 of 35 Old 07-12-2015, 10:33 AM
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this entire thread has made my day. Thank you

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post #9 of 35 Old 07-12-2015, 10:43 AM
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Excellent write ups Mr. PainfullySlo. I've enjoyed the series of articles you're written and the projects you've posted. Thanks for sharing this useful knowledge.
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post #10 of 35 Old 07-12-2015, 12:52 PM
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Originally Posted by PainfullySlo View Post
I certainly appreciate your input and I am familiar with the math you are using. My intent in this post was to give people a workable range of RPMs to use when riding the bike so as I said in my original post, this is an abbreviated version of the very in-depth physics required to fully understand the subject...a sort of cliffs-notes if you will.
The physics here is quite simple as concepts of power and force are the fundamentals. Its really a macro view.

Quote:
Originally Posted by PainfullySlo View Post
I respect your position. The entire reason I posted this was to start a discussion but will respectfully differ. There are most definitely two camps in the engine building world and I can just as easily find well-known builders that swear one is better than the other for both horsepower and torque.
The physics is not subject to interpretation. The problem is that there are just too many people who simply do not understand what HP and torque actually are and how they are applied. In an engine, the HP and torque are inherently tied together by RPM [HP = (T * RPM) / 5252]. An engine simply does not make one without the other. In an electric motor, it is possible to have torque without HP if the torque is not enough to overcome the load. In this case the motor stalls or is spun backward but will still provide torque so long as there is current. An engine will simply stall. This is actually why I say Power is a more important figure. Torque is a meaningless number in IC engines without RPM. You don't need to know the RPM to make such a comparison if you use HP.

Quote:
Originally Posted by PainfullySlo View Post
On our I4, small displacement bikes, torque never comes on strong at lower RPMs (at least not in my experience) so it is a much easier method to watch the torque curve to discover that usable RPM range where a rider will get the most bang for his buck.
You're describing an engine with low end torque deficiencies. Which means you are describing an engine with low end HP deficiencies as well. This is actually where I believe the confusion stems from. Engines with strong low end torque tend to be thrown into trucks where hauling heavy objects is important. Being able to comfortably pull a load from a start is an important feature. The reality is a small displacement motor that revs high and makes the same HP can pull just as much weight with a larger one that revs motor at their respective peak HP RPM. It would make little sense to apply such a motor as the higher revving motor would be totally uncomfortable to haul a load with in this manner over long distances. Imagine driving a semi across the country screaming along at 8000 RPM.

Quote:
Originally Posted by PainfullySlo View Post
As with all things, I do not know everything. This is my understanding of the subject which has served me well in the racing world but I am always open to learning something new. When you have the chance I would love to have an intelligent discussion regarding your position.
Here's a quick example. I used the dyno chart you provided. Its basically the wheel torque plots that would occur if a Continuously Variable Transmission were used and held at the peak torque and peak HP RPMs. What it shows is that at all wheel speeds, the wheel torque at all wheel speeds is always higher where peak HP occurs. The plot starts at 60 wheel RPM only because the torque multiplication occurring at lower speeds is so high that it makes it hard to distinguish the lines at higher wheel speeds due to scaling. But I included the tabular data and you can clearly see that the RPM at which peak HP occurs is always higher.

Horsepower, Torque, and how to use it properly on a motorcycle.-wheel-torque-peak-hp-peak-torque-cvt.jpg

The reason for this is that the peak HP can take advantage of the mechanical advantage provided by the transmission. Ultimately, so long as you have both the torque and RPM data, you have the same information as having just the HP data. The beauty of having the HP data is that you do not have to adjust for torque multiplication to figure out how to maximize acceleration. As long as you pick the shift points that gives you the most HP at all times, you are doing just that.
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post #11 of 35 Old 07-12-2015, 01:13 PM
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I just think it's cool that all engines make the same hp/tourqe at 5252.
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post #12 of 35 Old 07-12-2015, 01:28 PM
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Fantastic write up, thanks for taking he time to do so.
i read all your articles and enjoye it every time,
there is so much to learn from you.
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post #13 of 35 Old 07-12-2015, 02:04 PM
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This discussion brings me back almost 20 years...when I bought a TL1000 instead of a GSXR750 because of the TQ myth. I learned then that for max acceleration it's all about HP. For road race engines, maximum area under the curve is important due to the variety of corners we encounter.

There was a time prior to electronics that with a few rules advantages big twins dominated Superbike racing. This was because the power delivery of the twin was better for traction coming out of corners. With better tires and TC systems it's the high HP multis which have made the broad TQ twins almost obsolete.

YMMV Great info here thanks both of you for taking the time to discuss.

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post #14 of 35 Old 07-12-2015, 03:57 PM
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Horsepower, always power.

Power is the unit that measures the rate of energy being delivered to the wheels to propel you; torque only plays half the role in delivering that energy. It's largely irrelevant whether the engine produces torque low or high as long as you maximize power. Hence you stay in the 'power band' despite torque dropping off from its maximum.

It goes back to those anecdotes where the torquey Mustang accelerates fast off the line but ends up croaking at high speeds. When the actual truth is it made all of its power off the start and that power was never really sufficient to propel it past its speed barrier.

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post #15 of 35 Old 07-14-2015, 10:46 AM Thread Starter
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Sorry, wasnt able to get to the forums yesterday for more than a moment.

Again, I appreciate the intelligent discussion of all involved. I am certainly no scholar. What I wrote above is the result of my experience and learning from others over the years so if I need to make a correction I will be happy to admit that I was wrong and make the changes.

I have a sincere question for those who are in the horsepower camp as I do not wish to be spreading misinformation.

A motorcycle dyno works by measuring torque delivered to the rear wheel and then performs the basic mathematical equation that we have both mentioned using RPM as work over time (leaving out the proprietary equation for correction) to arrive at the horsepower number. Can we all agree on this?

Please walk through my logic with me; The force driving the dyno drum is torque. The higher the value, the more force is exerted on the drum. Agreed?

Under that assumption, lets take a look at my original dyno sheet just so we are working with the same variables.

Let's now take a snapshot of the engine at 11,000 RPMs. We would be producing a constant 51 lb-ft of torque...the computer then performs the math and arrives at 106.81 hp.

Now lets take a snapshot of 15,000 RPMs and call it 42 lb-ft of torque. Again the computer performs the math and arrives at 119.95 HP. The mathematical HP result is higher than the first example, despite the fact that the force driving the dyno drum (TQ)is lower. Obviously this is the result of the work over time (RPM) variable.

Am I missing anything so far?
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