from their lies you will know them.

[stuofsci02]

Let's see if I can clarify this. The ONLY torque that matters in accelerating a car is the torque at the REAR WHEELS. That is determined by gearing as well as the engine.

How fast the car accelerates is determined by how fast the wheels can be spun at that torque-------------------------WHICH EQUALS HP!!!

Again, a gas turbine, that only generates 100 ft-lbs of torque, will accelerate a car rather rapidly because it is also turning 30,000 rpm and generating 570 hp.

OR:

Accelerating a car requires work to be done as a car at 50 mph has a lot more energy than a car at 25 mph. Work per unit time, by definition, is hp. You can accelerate a car from 25 to 50 mph with a low hp engine---------if you aren't in a hurry. The quicker you get from 25 mph to 50 mph, the more hp you will need in that engine.

+1... This is exactly right..

HP is a measurement of power (obviously). Power is the amount of work that can be done in a unit of time.

To take your Prius example a step further, if at 1200 rpm it makes 67 HP. Then at that exact point it would accelerate the same as a gas engine that makes 100 lb-ft TQ at 3,518 rpm.

A 2008 F1 Engine only produces between 200 and 240 lb-ft across the RPM range but produces over 750 HP because you can rev it to 19,000 RPM. This would provide faster acceleration than a 500 lb-ft motor that makes 500 hp, providing you are operating both motors in their peak HP range (which should be a given).

This is all very basic engineering...

 

[GenesisCaptain]

Again, a gas turbine, that only generates 100 ft-lbs of torque, will accelerate a car rather rapidly because it is also turning 30,000 rpm and generating 570 hp.

I should quit, but the math and theory are intriguing...

That turbine engine at 30,000 RPM may only produce 100 ft-lb of torque. However, to get that power to the wheels, you would need a final drive ratio about 5 times higher than a typical car would have. So, you effectively multiply the torque threefold more through the transmission than a normal gasoline engine. That is why that high high RPM turbine can accelerate well-- it is producing a moderate amount of torque at a very high RPM. When that torque is geared-down to a useful RPM for our application, the available torque at the wheels is dramatically higher.

HP is irrelevant . HP is a made-up number that is a mathematical derivative of torque, nothing more.

This is all very basic engineering...

I am an engineer. I have lived through many painful multi-dimensional physics, calculus, statics, dynamics, and deformable bodies calculations in my lifetime.

 

[stuofsci02]

stuofsci02,
I think your missing the Captians point.

You can not measure HP. It is a derivitive of measured torque divided by RPM's.

So even to say that TQ and acceleration are only related by HP is inaccurate. TQ is acceleration. The HP number is simply a product of TQ and RPM's.

The main problem is that everyone relates to HP even though they really don't understand it.

If you take a look at a dyno graph, you will see that HP and TQ curves will always cross at 5252 RPMs. Why? Because of the formula for calcualting HP = TQ/5252.

I don't think I am missing the point. I know that HP is calculated through TQ as you will see in my posts above.

The point is that acceleration requires power. The more power you have the faster you will accelerate. This is independent of torque.

Obviously the more TQ your have at an RPM the more HP you will have at that same RPM. I am not disputing this. But ultimately the engine that has the most total HP in its operating range will accelerate the fastest. That is a low TQ motor that makes hi HP will be faster then a hi TQ motor that makes low HP.

 

[stuofsci02]

I am an engineer. I have lived through many painful multi-dimensional physics, calculus, statics, dynamics, and deformable bodies calculations in my lifetime.

Yes, as am I. In fact I do this stuff for a living. Not with gasoline motors and cars, but with electric motors and pumps. Same physics though...

 

[stuofsci02]

I should quit, but the math and theory are intriguing...

That turbine engine at 30,000 RPM may only produce 100 ft-lb of torque. However, to get that power to the wheels, you would need a final drive ratio about 5 times higher than a typical car would have. So, you effectively multiply the torque threefold more through the transmission than a normal gasoline engine. That is why that high high RPM turbine can accelerate well-- it is producing a moderate amount of torque at a very high RPM. When that torque is geared-down to a useful RPM for our application, the available torque at the wheels is dramatically higher.

HP is irrelevant . HP is a made-up number that is a mathematical derivative of torque, nothing more.

If you are going to include gear ratios then the whole discussion is moot because you can gear two hypothetical engines with different specs to produce the same output with gearing. We are talking about crank HP and crank TQ as cars are rated.

 

[Midnightsun]

Nah... That's not true.. Acceleration is almost all HP.. Low end TQ only plays in for the first second. After that RPMs are high and HP is king..

You are kidding right? Both come into play all the time. If that were the case then how come the latest SL 550 with exactly 429hp (coincedence?)and 516lb of torque will do 0-60 in 4.5. The same 429 HP Genesis will do it in 5.3 however there is only 376 lbs of torque available. Weight difference is only minor as the Genny is only about 300lbs heavier.

 

[stuofsci02]

You are kidding right? Both come into play all the time. If that were the case then how come the latest SL 550 with exactly 429hp (coincedence?)and 516lb of torque will do 0-60 in 4.5. The same 429 HP Genesis will do it in 5.3 however there is only 376 lbs of torque available. Weight difference is only minor as the Genny is only about 300lbs heavier.

That is easy to explain... Because the TQ is higher (presumably across the RPM band) which will mean the area under the HP curve will be more.

The Genesis will peak at the same HP, but the area is less.

While you might think that this proves your point, it actually proves mine. The SL 550 has more available HP then the Genesis and hence faster acceleration.

 

[Crusty Old Shellback]

That is easy to explain... Because the TQ is higher (presumably across the RPM band) which will mean the area under the HP curve will be more.

The Genesis will peak at the same HP, but the area is less.

While you might think that this proves your point, it actually proves mine. The SL 550 has more available HP then the Genesis and hence faster acceleration.

It has more available HP at a given point due to the actual measured TQ at that pont being higher. As stated by others as well, HP is the product of TQ/RPM. TQ is what is actually measured. there is no measurment for HP. It's just that you are to accustomed to using the HP number than the TQ number. Without TQ, you have no HP.

As as for your gas turbine example, here's a little info for you.

Gas turbine driven ships use a high speed, RPM, low TQ gas turbine engine and pass that RPM thru a set of reduction gears that turn it into a high TQ/low speed, RPM, to move a 9000 Ton ship thru the water at 35 Knts. It makes 80,000 shaft HP because of the high TQ/low RPM. But as in your example, the engine is only actually making about 100 TQ.

 

[stuofsci02]

It has more available HP at a given point due to the actual measured TQ at that pont being higher. As stated by others as well, HP is the product of TQ/RPM. TQ is what is actually measured. there is no measurment for HP. It's just that you are to accustomed to using the HP number than the TQ number. Without TQ, you have no HP.

As as for your gas turbine example, here's a little info for you.

Gas turbine driven ships use a high speed, RPM, low TQ gas turbine engine and pass that RPM thru a set of reduction gears that turn it into a high TQ/low speed, RPM, to move a 9000 Ton ship thru the water at 35 Knts. It makes 80,000 shaft HP because of the high TQ/low RPM. But as in your example, the engine is only actually making about 100 TQ.

It has nothing to do with what I am accustom to using and everything to do with the physics.

Once an engine produces a certain amount of HP you can always gear it to produce varying levels of TQ at the output while reducing or increasing RPMS.

HP is as real as the BTU or the WATT. It is a measurement of the rate at which work is done.

Here is the million dollar question.

If you are driving a sports car and you want peak acceleration do you:

a) shift so that the area under the TQ curve is maximized

or

b) shift so that the area under the HP curve is maximized.

 

[Crusty Old Shellback]

a.

if you choose B, then you are out of RPM's and must shift to acheive a and still have RPMS left to accelerate. Max HP is at the upper RPM end while max TQ is in the middle. But you can build the engine to have a almost flat TQ curve from 1500 RPMS up to 5252 when the HP and TQ cross.

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[stuofsci02]

a.

if you choose B, then you are out of RPM's and must shift to acheive a and still have RPMS left to accelerate. Max HP is at the upper RPM end while max TQ is in the middle. But you can build the engine to have a almost flat TQ curve from 1500 RPMS up to 5252 when the HP and TQ cross.

The correct answer is "b".

You shift such that the area under the HP curve is maximized for best acceleration. This may not mean shifting at redline, but for most car gasoline engines this is the case. Not all engines peak HP at redline, but you would still want to shift there so that you are making more HP at whatever the RPM is in the next gear.

BTW you can design an engine to have varying TQ curves. Flat TQ curves are very nice to drive for everyday use because they provide predictable linear HP increase with RPM.

 

[Top Gear]

Honestly, none of it matters without thinking about the weight of what is to be accelerated, as well as the drivetrain loss from crank to tarmac.

Anyway, the bashing you're getting about the awesome Sedan is nothing compared to those bashing the Coupe, including a fair number of supposed Genesis Coupe enthusiasts on other forums. Apparently it's cool to bash your own car's platform, thus "proving" it needs to be modded up (but to those of us above 25, it just proves daddy bought them their car). Even on this forum there is a basher review of the Coupe that surely reads like paid copy from a rival forum or manufacturer.

Maybe we should sorta revel in the fact that these cars get enough attention to be bashed by snobs, or those with something to lose (like a race). People are mostly just jealous because they paid two or three times more for a logo and got nothing better. The old days of brand snobbery seem basically over, or greatly reduced, and that irks brand snobs to no end

 

[427435]

This is getting to be fun (even if it is way off topic)!!!!

First, I "are" an engineer too. Did a lot of work with matching engines to off-highway vehicles. Both hp and torque (especially torque back-up were considerations). As a result, I am very cognizant of the difference between Hp and torque-------and what both can do for a vehicle's performance.


Second, Hp is indeed measured (check any modern dyno) because it is a result of measuring BOTH torque and rpm and applying the correct constant. There is a reason that Hp was defined the way it was-------a method of measuring the work capability of early steam engines was needed. It was related to what a single, good horse could do (raise 550 lbs one foot in one second). Thereafter, people could determine how much work different engines could do, compared one to another. The more work you wanted done, the higher Hp engine was needed.

Third (and again), work is done when a car is accelerated. The faster a car is accelerated, the more work is being done. The more work that is being done, the more Hp is required.

Whether that Hp comes from a high torque, low rpm engine or a low torque, high rpm engine is not relevant. The cars will accelerate the same (as long as there is gearing that accommodates the rpm range of the engine).

End of story.

Oh yes, here's a picture of one of "my" machines:

And another:

No, that's not me standing by the tractor.

 

[Billfz1]

Honestly, none of it matters without thinking about the weight of what is to be accelerated, as well as the drivetrain loss from crank to tarmac.

Anyway, the bashing you're getting about the awesome Sedan is nothing compared to those bashing the Coupe, including a fair number of supposed Genesis Coupe enthusiasts on other forums. Apparently it's cool to bash your own car's platform, thus "proving" it needs to be modded up (but to those of us above 25, it just proves daddy bought them their car). Even on this forum there is a basher review of the Coupe that surely reads like paid copy from a rival forum or manufacturer.

Maybe we should sorta revel in the fact that these cars get enough attention to be bashed by snobs, or those with something to lose (like a race). People are mostly just jealous because they paid two or three times more for a logo and got nothing better. The old days of brand snobbery seem basically over, or greatly reduced, and that irks brand snobs to no end

Ok guys and girls,
I'm the original poster, and yesterday I couldn't even spell engineer, now I are one. I find the digression into the torque/horsepower discussion interesting but futile. The poster I quoted above got my point. If you have caused the "competition" to start telling tall tales about you or your vehicle you are already "there". The Genesis has the kind of performance only seen in the top level of quality machinery. And it does it for a lot less money. I plan to just enjoy mine for some years to come. It is funny to see all the talk. When it comes to simple acceleration I have a 1000 cc motorcycle that will hit 60 in less than 3 seconds, but it isn't as comfortable as the Genny on any day, just more exciting. The important thing is to understand what kind of performance you are after. I have had fun watching the thr0ead run pretty far into the weeds. ( I even helped once or twice. ) ENJOY your car I certainly will!
Bill

 

[EXBMWGUY]

^ I'm pretty much where Bill is. Actually, I just wanted to end the story!

 

[Ruissimo]

Ok guys and girls,
I'm the original poster, and yesterday I couldn't even spell engineer, now I are one. I have had fun watching the thr0ead run pretty far into the weeds.

Understatements of the year right thur.

 

[Crusty Old Shellback]

I think I'll join you Bill. Just like throwing a little gas on the fire every once in a while.

I'm also with you on the motorcycle, but mine's a little more comfortable than yours.

Love my Genny.

 

[Top Gear]

Well, on a busy forum, I would agree, but I liked the "horsey" exchanges above, and frankly, this forum could use more discussion beyond those Sedaners who just bought and can't find the settings in the nav. I LIVE for an exchange like the one above that only comes around once every few weeks or months. The other extreme is the howling turbo cabal of double standards and moderator abuse on the mod-kiddie Coupe forum across the interwebs. Maybe if more grown-up Coupers would join in for balance, and if we let our hair down just a bit, we could have a number of cool discussions going on regularly. How's that for a thread-jack?