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AutoWeek's Test - Merc S600


RUFDRAFT

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Autoweek - May 15th - Article on the MB S600.

 

Car weighs 4960lbs.

 

Horsepower: 510 (V12 - TT)

 

Torque: 612

 

0-60: 4.5 secs.

 

Now - I'm not an engineer - but it seems odd that a car which weighs 1,000 lbs more than the Shelby and has only 10 more hp can click off a 4.5 to 60.

 

Comments?

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Everyone focuses on horsepower, but it's torque that does the work. Look at those ricers that have 450Hp and 179 Lb Ft of torque (well, yes, I'm exaggerating). They're getting the horsepower numbers by winding the crap out of the engine. It's what I call thin horsepower. Look at the horsepower v. torque for tractor-trailer rigs. Torque is usually the bigger number.

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whew.

 

I keep having this problem with the difference between hp & tq.

 

And - no one yet has provided me with an understandable explanation of how the two differ.

 

If torque is what's important - why does Ford advertise 500 HORSEPOWER?

 

Sleepless in Washington! :shift:

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whew.

 

I keep having this problem with the difference between hp & tq.

 

And - no one yet has provided me with an understandable explanation of how the two differ.

 

If torque is what's important - why does Ford advertise 500 HORSEPOWER?

 

Sleepless in Washington! :shift:

 

Because HP is what you want to hear about.

 

HP and torque do not differ they are related. I cannot remember the relationship exactly, but the easy rule is that torque will get a load moving (acceleration) while horsepower will keep the system moving.

the reason the MB performs well is due to 12 cylinders and twin turbos as much as it is the 'hp or torque ratings"

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whew.

 

I keep having this problem with the difference between hp & tq.

 

And - no one yet has provided me with an understandable explanation of how the two differ.

 

If torque is what's important - why does Ford advertise 500 HORSEPOWER?

 

Sleepless in Washington! :shift:

 

 

Man, there's so much to this question and there's no short answer, but I'll try.

 

Horsepower gets you going fast but not necessarilly quickly

 

Torque gets you going quickly but not necessarilly to a high speed.

 

Gear ratios use torque curves and max hp ratings to marry the two to get the best performance.

 

When you accellerate in 1st gear you're going to have to shift into second at some point to go faster. The torque to keep the gears spinning and the car moving forward is still there in 1st gear, but at some point the engine can't turn any faster. You just ran out of horsepower. In order to keep accellerating you have to change gears which will get you moving faster eventually. The torque you have at the lower rpm after you switch gears is going to determine how quickly you can get up to speed, the more torque, the quicker you will reach max hp. Low torque and you accellerate like a snail (kinda like starting from a dead stop in high gear - you'll get there eventually but it's gonna take you longer because you don't reach peak torque until the engine gets up to speed.) High torque and you get to your max rpm (i.e, horsepower) much quicker. The more torque you have the quicker you can accellerate. So torque gets you up to max hp. The heavier the vehicle the more you need high torque to have the power to get it accellerating quickly.

 

Another way of thinking about it, think of torque as the amount of twisting force you have at the shaft or the wheels and think of HP as the maximum speed at which the engine can turn.

 

I hope I didn't confuse you more.

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I can tell you that @ 5252 rpm's torque and hp are ALWAYS the same. Thats why its part of the formula to figure one out if you have the other.

 

To person who says you HAVE to have lots of torque???? Not always! Have you ever seen the torque curves & peaks on a Ferrrari?

 

 

Yes, at 5252 rpm torque and horsepower curves always cross.

 

BTW - This is why big rigs have so many gears. They are designed for high torque but low RPM. They can pull very heavy loads but have to use more gears to get up to faster speeds. It's also why a 6 speed transmision with closer gear ratios will give you better accelleration than a 4 speed (as a general rule,) provided they have the same final gear ratio.

 

I have not seen the torque curves & peaks on a Ferrari. It must be a very short stroke high revving engine, which is not the best for street use and might explain whi it has to go in for service every 1000 miles.

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Torque accelerates a mass. HP is a calculation of torque at rpm (HP=TQ x RPM / 5252). HP is not measured, it is calculated from torque.

 

The capacity of the engine and efficiency determine max torque produced - a very efficient engine makes 93 lb-ft per liter. I have seen very few engines make more TQ/L than this.

HP is simply where the torque is produced and how well the engine flows air beyond peak torque rpm.

Gearing is a torque multiplier. Lower gearing multiplies the torque to the ground, higher gearing allows for more mph with the same max rpm. Selecting the correct gear spacing allows the engines torque to be used effectively. And more gears allow more top speed.

Example: current Nascar engines only make slightly more average torque than they did 20 years ago (mostly due to reduced friction), but because they make this torque at a much higher average rpm, they make more HP. As a result, more gearing can be used to accelerate and go faster than in the past.

 

The mass of the vehicle determines the inertia required to be overcome to accelerate the vehicle. The frontal area and coefficient of drag determine the amount of torque required to reach and/or maintain a given speed.

 

Torque to weight ratio gives a fairly accurate representation of acceleration for a vehicle. HP to weight ratio means nothing if rpm and gearing are not known.

 

Manufacturers quote HP numbers because that is what people ask for. People ask for HP numbers because that is what they have been trained to talk about by magazines and automotive society.

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Well, we've all pretty much got it here. The simple way to remember it is that Torque is the amount of 'twist' that is applied to the crankshaft. It is a function of the design of the engine or motor or whatever. An electric motor produces the most torque at stall speed - zero RPM! An IC engine produces it at higher RPM so you have to slip the clutch to get started without stalling the engine.

Horsepower is a measure of the time-rate of doing work. For example, if you hitch a person to a sled with one hundered pounds in it and have him pull it up an incline, he will do the same amount of work if he takes five minutes or five hours to do the job. He must produce more Horsepower to do it in five minutes as compared to five hours, however, because Horsepower is the time-rate of doing work. Torque is measured in units of Lb-Ft. Notice there is no mention of time in the units. Horsepower, however, it is a function of revolutions PER MINUTE. This is a time-rate function.

At any RPM, if you measure the angular velocity of the crankshaft ( 2 Pi X rotational rate(or we say RPM)) and multiply it by the Torque at that same RPM you get the engine's Horsepower at that RPM. A Ferrari has a narrow torque curve so you have to keep it in a more narrow RPM range with the gearbox to achieve the greatest resonse to the throttle. That's why smaller displacement (and lower torque) engines have been coupled to five or greater speed transmissions since the sixties - keep the engine near the narrower torque peak. Truth is, the GT500 doesn't really need a six-speed because of its wide torque band. The T56 is used because it is the only U.S. manufactured (yes, I know some are made in Mexico) mass-produced manual transmission able to handle the required Torque (there's that word again!).

By the way, large diesel trucks have so many speeds because the diesel engine operates over a much narrower RPM band than a spark-ignition engine.

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The simplest explaination I have ever heard for Torque vs HP as applied to a car in the real world was as follows:

 

Torque is the force pushing you forward at any given instant.

 

That torque applied over a period of time is Horsepower (a measure of work not force)

 

Therefore an increase in torque will provide an increase in acceloration.

 

An increase in HP will decrease the 1/4 mile time.

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Threecobras,

Very good details. As you said, Torque is a force in angular movement (rotation). Power is a force and movement (work done) over time.

 

The 6060 trans (T56 variant) is used to improve CAFE mpg ratings - lower rpm at the same mph. We still get to pay the GG tax, just not as big as if it only had a single OD 5-speed trans. There are several 5-speeds available that can handle the torque load. (also, the torque capacity of a trans (or any drivetrain/chassis part) varies with the weight of the vehicle)

Diesel tractors use many gears in order to get mph. Since they only turn a very limited rpm, more gears allow more mph. If the weight of the tractor and trailer loaded was less, the gear spacing could be larger and use less number of gears since the torque/acceleration/time demand would be less.

 

This topic is always a good discussion, with lots of good input and details - always something to learn (for me anyways). ;)

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DVS -

Just out of curiosity, what five speeds do you mean? Mass production, that is. I'll show my ignorance here. I was looking for a tranny for my 93 Cobra with a Turbo R302 in it and I could only find the T56 to handle about 600Hp/TQ.

jc -

Not to split hairs, but torque is always a rotational - twisting - force. It is converted into forward motion by twisting the tires which resist the twisting because they are gripping the road. Horsepower is the rate of doing work, not just the act of doing work. Moving X amount of weight along a distance D requires the same amount of work (neglecting speed-related things such as wind resistance) no matter how long it takes (the speed). Changing the amount of time it takes to do that work affects the horsepower required. Since Force = mass times acceleration (F=ma), the faster you want to accelerate the same mass, the more force is required.

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Most performance enthusiasts are into acceleration first and foremost. Then why aren't we mainly high fiving and celebrating torque instead of HP? Doesn't make sense.

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Tremec makes several 5-speeds that are as strong or stronger than the T56 and its variants, just no demand for them from OEM's due to CAFE - so no mass production. They don't build what they can't sell. For the individual, there are many aftermarket 5-speed units that can handle well over 600 hp/tq.

 

On torque/power, work is force applied to an object regardless of movement..we are just repeating each other now, trying to clarify each others wording. ;) I think others are getting the idea now...maybe not. :beerchug:

 

An example of high HP with very low torque is a turbine engine. The M1 tank engine moves over 80 tons (very well in fact), but requires LOTS of gearing to multiply the available torque in order to do it.

 

150man,

Torque at higher rpm allows gearing to be used to amplify acceleration.

 

The Honda S2000 makes about the same power as a buick GN (just at a much higher rpm, with a lot less torque). The torque of the GN moves the heavier weight of the Buick much better than the S2000 which has to be driven like you stole it.

 

A broad torque band is F-U-N and easy to drive. RPM stands for "ruins peoples motors".

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If you can hook up the torque, shift so it stays in the highest average power range. Depending on ratios, this is generally 300-400 rpm after peak power. Some (stock) rev limits on forced induction cars do not allow this. And traction will always be an issue. DO NOT hit the rev limiter or you will slow down.

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DVS -

Yup, we're both locked up and providing traction. I didn't remember seeing any of the T5 variants able to handle that big a load. Thanks for the correction. In any event, look at some of the internal views of the GT500's T56. I've seen them posted, maybe over on SVTPerformance. The gears are definitely noticeably wider than the earlier Termy and Viper T56s, and the sychros are beefier as well. So even the T56 wasn't originally strong enough.

150man -

I think it's just something to do with human nature. A rating of XXX Horsepower is easier to grasp than XXX Lb-Ft. Remember the stock cars in the 60s that used to paint the horsepower and cubic inches on the hoods? Can you visualize 425 Lb-Ft written on the hood instead? Me either.

Harley -

I'm sure DVS is about right. The redline is there to prevent engine damage, not indicate best performance. If you look at the torque curve for some of these engines, it is nearly flat from, say, 2000 RPM to, say, 4500 RPM. So the peak torque is achieved over a wide RPM range. I wouldn't shift at 2500 even if the peak torque is there (and up through 4500). In straight line acceleration, I would think the key isn't as much what RPM you shift from, say, second gear to third gear as it is where the engine RPM will be in third at that speed. You would want to drop it into third so that the engine RPM still in that peak torque band, not below it. I don't make any claim to being a world-class drag guy, so others may know more on the shift points.

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