Torque or Horsepower????

CBX said:

Great topic!

Torque = Force
Horsepower = Rate of work

Torque is King. Ride in or a Drive a 500 Hp Corvette and then do the same in a 500 Hp Duramax or Dodge Cummins.

Then load them equally. The corvette wont be impressive once loaded equally to the truck.

Is it a fair comparison, No. But both have 500 right. Lets assume 500 at the wheels even.

Now take a 500 hp at the wheels Kenworth. Even with the theoretical gearing to get the corvette or the pickup to do equal work of the Kenworth it still wont happen.

Torque is king. As far as vehicles are concernd, Horsepower tends to create speed. Torque creates " the muscle" if you will.

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Thats a good way to think about it i think. the reason a big rig can pull even though it has the same hp as a corvette is because of where the hp is at. A corvette motor could pull a load up a hill, but it would have to be at 7,000 rpm all the time to be making 500hp, where the truck is only at 2,000? to make the same hp.

RKT said:

Torque is the entity that does work to the crank train... Like stated above, HP is calculated from the torque...

My goal here is to NOT get into a huge Physics debate and keep it very simple.. Once the equations pop out..people generally lose interest..
In any case...The area under the toque curve or the "shape" of the curve is whatreally dictates the engine's personality and performance ..

If you have a very wide and flat TQ curve, then you have an engine that is very linear in its power delivery and will not be to sensitive to rpm fluctuations.. These are the good engines.. If you have an engine that has a big PEAK TQ number but ....before and after this peak point is very steep in the curve's profile.. you have an engine that makes big peak HP but is very sensitive to rpm drift.. These engines usually hit very hard and usually fall off just as hard..

As far as turbo's making "X"% of torque multiplication at "X" boost.. With all due respect, this is simply WAAAY too general and simply not a correct assessment IMO.
There are way too many variables in play to state that any turbo can and will produce "X%" torque @ "X" Boost..

Kelsey

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Sweet post!! I would actually welcome a little physics into the discussion.

And just to add to your turbo statement, turbo efficiency/compressor mapping has everything to do with boost to power ratios as does the engine being turbo'd. Depending on the turbo's efficiency, X turbo @5 psi could/may be more efficient and produce more power than Y turbo @10 psi.

Man, You guys are allot of fun, nice be on a site that has intelligent discussions about irrelevant things !!!! LOL

this discussion is fun and meaningful , helps those who don't see the picture as clearly or have they had the access to a dyno and its wonderfull learning curve.

When operating a manual load valved water brake , the operator becomes adept at "feeling" the tuning of a given engine package.

ones with lower / flatter curves are very 'fun' to run as they are easy to follow with the load valve to throttle input.

Those with higher rpm 'in phase pro stock pipes' are just as easy if not ever easier, when carbs are tuned well.

its the poorly tuned ones that we FEEL are resistant to continue to build rpm AND take water, they tend to not be as ''broad shouldered ''.

I believe running the manual valve lets the operator identify tuning issues and just plain POOCHES quicker than a servo and just data files..



oops, off on another tale..
the moral,,,, TORQUE is what I think I feel when a good motor is on the pump..and just making me smile..

Gus:beer;:beer;

Torque is what you feel, and always will feel, it is the acceleration. Torque is how hard you are pushing down on the piston and thus turning the crankshaft. Horsepower is how many times you can push down on the piston. A big rig engine pushes down really hard but cant spin fast because of design limitations, but as an opposite an F1 engine cant push down very hard but can push down many times a second, actually 133 power strokes a second@16000rpm VS 16 a second@2000rpm for the big diesel! Too bad we couldnt have an electric sled, peak torque from 0rpm till the rated rpm!

I see snow on the hills!

old drag racers answer..torque acelerates the vehicle..hosepower makes it run the big mph............

brycter said:

This is great you guys. Lets throw in some calculations. I think everyone is learning something. There were a couple coments that i8 had to ponder on a few time but definantly a great thread?

So when i put a turbo on does my torque at 10 psi always stay the same? or can this be change with altitude? air density? or temp?

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Torque will change even if the boost gauge reads 10psig. Altitude, Atmosphere and temperature will all be factors.

Boost is reflective of load. The particular sled in discussion may be able to produce 10lbs wide open down the trail, but it also may do it at a lower rpm with a much greater load (say climbing a hill).

Without the engine loaded, the machine wont build very much boost, if any.

Another factor is compressor speed.

Compressor speed, ambient pressure on inlet side of the turbo, absolute pressure on the compressor outlet and exhaust drive is what makes the turbo run, and determines how efficent it is, which also determines how much "air" you can stuff in the engine.

I dont know how to attach an idividual page out of a pdf. file. but on page 9 and 10 of Garrett's 2009 catalog, there is the best sum of info and equations on determining how much boost and air you need to get to your target horsepower.

here's the link to the file http://www.turbobygarrett.com/turbobygarrett/images/catalog/catalog_common/Garrett2009Catalog1of2.pdf

One detail i noticed. All of the math formula's seem to focus on horsepower. Anyhow a fantastic read on turbo's. part I like is there isn't a slant on the info, just good straight up how it works.

As stated before

Torque = amount of work
Hp= how fast work can be done.
Boosts is relative to atmospheric pressure = 14.7psi (at sea level)
15 psi of boost means twice as much air(15 +14.7) in the motor
Twice as much air means twice as much fuel can be used (roughly) = twice as much (theoretical) HP

A turbo works on engine load, not speed. The more load, the more exaust gas to spin the turbo.

You can't (fairly) compare gas to diesel because diesel has a higher btu value thus 1 pound of diesel has more energy than 1 pound of gasoline.

Torque

brycter said:

Can you ever have a situation when torque falls or levels off and hp still rises?

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That would appear to be exactly what happens in big rig diesel engines.

My Volvo D16 engines produce peak torque at 1100 to 1450rpm in their specific application. Peak torque falls off dramatically after 1450rpm but peak horsepower is achieved at around 1900rpm. For big loads on these types of engines it seems its big torque, not big horse power that gets the work done. Torque can also be changed in the ecm without changing hp. When the engine exceeds peak torque, the ability to do the job is compromised even though hp will continue to climb.
So how does this compare to a sled engine application?

tranquillicer said:

That would appear to be exactly what happens in big rig diesel engines.

My Volvo D16 engines produce peak torque at 1100 to 1450rpm in their specific application. Peak torque falls off dramatically after 1450rpm but peak horsepower is achieved at around 1900rpm. For big loads on these types of engines it seems its big torque, not big horse power that gets the work done. Torque can also be changed in the ecm without changing hp. When the engine exceeds peak torque, the ability to do the job is compromised even though hp will continue to climb.
So how does this compare to a sled engine application?

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Thinking out loud.....with most vehicles you are shifting gears and falling below....and then going past peak tq/Hp rpm several times depending on how many gears you go through.....in a sled you are able to "clutch" to run at any desired RPm at full throttle...and to get the best resiults you must run near peak HP and not fall below peak tq. So a sled can run a narrower curve than most vehicles and still perform.

brycter said:

Can you ever have a situation when torque falls or levels off and hp still rises?

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Yes, in every snowmobile ever manufactured. In fact clutching depends on this. The hp curve leads the torque curve by a few hundred rpm after about 5200 rpm or so. If you clutch for peak hp at wot, then at wot if you load the drive train, rpm will drop off. As rpm drops off you will be climbing the back side of the torque curve, belt tension will rise, and the helix will screw the shieves back together causing a back shift and a return to peak hp.

Actually the equation of HP = T (ft lbs) x rpm/5280 is an approximation. Power is is simply how much work is done in a given amount of time and Work is Force applied through a distance...and the true defintion of horsepower is 33,000 ft lbs/minute

If:

P = power
F = Force
W=Work
t = Time
d = distance

So from above W=F*d And P = W/T substituting the defintion of work into the second eqation we get

p = F*d/t What is torque? Torque is force at a distance to T=F*d...

so what is power

P = T/t

Now is is where everyone will get confused. We think of engine speed in revolutions per minute. We don't think of engine speed in degrees per minute or radians per minute. What is a radian? it is just an engineering unit for angle measurements just like angles in degrees. It is a defintion thing. As a crankshaft revolves once it will rotate 360 degrees right? Well it just happens that as a crank rotates it will rotate 2*pi radians. Here is the really tough part. Radians are dimensionless degrees and revolutions are not. It is a math thing...you will have to trust me on this. It's kinda like "dems da rules"

so say we have a motor on a dyno and it is running at 1 rpm and measuring 1 ft lb of torque

P = 1 ft/lb*1rev/minute = 1 ft*lb*rev/minute...uh oh...what is a revolution in mathematical terms?...we can't have that...let's convert it to radians....

P = 1ft*lb* 1 rev/minute*2*pi radians/1 rev...as per our defintion of radians above

If you notice the 1 rev cancels out in the above equation and you get

P = 2pi ft lb radians/minute or P = 2pi ft lb/minute because radians are dimensionless.

lets use our defintion of 1 hp = 33,000 ft lb/minute to convert to horsepower.

P = 2pi ft lb/minute* 1 hp/33,000 ftlb/minute notice that mathematically the units cancel to get

P =2pi/33,000 hp or finishing the math on a calculator....

P =1/5252.1 hp...

So Power is simply Torque times RPM and the 5250 is just 33,000/2pi to convert from ft lbs rev/minute to horse power....

Confused?

Ok....lesson two...snicker What is better more torque or more hp? the anwer is not clear.

Let's not get into calculus...but I can...if you want...my guess is that just like the last post I will get negative comments and you won't want me to.

but anyway for the die hards...Imagine a Torqe vs rpm curve just like we are used to seeing. In my previous post I essentially derived the equation for horse power and it turned out to be essentially Torque times RPM. Now imagine our curve again....well torque times rpm is essentially the area under the torque curve.

Now imagine two torque curves from two sleds. They both have equal peak hp but one's torque curve is very high rpm and peaky and the other has a very broad shape. Which one will have more area under the torque curve? The answer is they will be the same...But what does this mean for sleds in a drag race? If it were a perfect world we could have an infinite gear ratio at the start and both sleds would be at peak hp when the hat dropped and both would tie in the drag race because torqe at the track would be HP/rpm and they would be the same..but it is not a perfect world.

Because both sleds start out at engagement at 5000 rpm, or there abouts, they have to accelerate to 7000 rpm, or there abouts, without the clutch shifting. The clutches will not shift until peak hp rpm. They are starting in first gear and the ratio is stuck at about 8:1 until they reach their shift rpm. What does that mean with the peaky sled? Well he is stuck accelerating more slowly since he has less torque at 5000 rpm than the sled with broader shoulders. What does this look like? The sled with more torque at a lower rpm will jump out 1 or 2 sled lengths until they both hit their shift rpm and depending on gear ratio...that will be about 20 or 30 mph track speed...and then they will accellerate up the hill at exactly the same speed. Why? because they have equal hp and therefore equal torque. Who will win? The sled with more torque, but it will be all done at the start.

This is illustrated nicely in the example of my ultra big bore lined up with 900 AC twins at the bottom of little Monte in Utah. I have an honest 10 more hp than those sleds but I simply cannot compete with the torque of the big twins with exhaust valves at the start. They put a sled lenght on me at the start but i am closing fast at the top. Who wins? depends on the length of the race. Their ET's are lower, but my top speed is higher.