Another benefit of a flat torque curve is that shifting becomes a no brainer. It is easier to drive th ecar around town as it's making decent HP at lower rpm. Then, when letting 'er run, you don't have to be as precise about shifting at the torque peak. That's not to say you can get max performance by shifting at any 'ol rpm, but overall driving experience is better.

Remember that 300lbs-ft is what the driver can feel. That is the force that causes the car to move. HP is a measure of how long it can do it. That's why super peaky high rpm engines can accelerate cars so well. Remember the fictional car that makes 300lbs-ft at 1500rpm and at 4000rpm. It matters not what rpm you are at, you have the same force available to you.

This is where gearing becomes important. People stopped thinking about gearing when automatic became the number one choice, but it's not so simple. Making torque at high rpm is usefull because you can use gearing.

This summer in the Yukon we had a tour of a sternwheeler paddleboat from the goldrush era. A neat machine that took HUGE advantage of gearing. It took THOUSANDS of foot-lbs to twist that giant wheel through the water. How did they do it? A giant engine? Sort of. The thing didn't make tons of torque (as literally required) but used torque multiplication through gearing.

Suppose we go back to our 300 ft-lb MB engine. Could it run that boat? You bet! The boat ran the wheel at only 22 rpm. Take you engine that makes 300 lb-ft at 4000rpm and gear it down to 22 rpm. Thanks to the wonders of gearing, we can exert over 54,000 ft-lbs on that paddle-wheel. Of course, in cars we want speed and gearing that has the engine spinning at 4000rpm and the final drive at only 12 rpm wouldn't work too well. The lesson is that we can always use rpm and harness it with gearing.

That is how cruise ships use engines that are small (huge, but not considering the boat size) to run props that are so enormous it's insane.

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John Shellenberg
1998 C230 "Black Betty" 240K

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not to beat a "dead" horse but is safe to say that
1. torque is the engines ability to do work i.e. the ability to turn the drive shaft and hence the wheels

2. and HP is a reflection of how "quickly" the engine can do this work.

For example: is an engine has a 300ft/lb of torque from 1500rpm to 6000rpm, as the rpm rises the engine can do its work/torque quicker.
Is my analogy on target?

Also for a given torgue/hp curve where does the tranny gearing paly a role?

Although the popular press is always talking about HP, wouldnt it be more useful to talk about torque?

Horsepower is an expression of torque and means something when talking about a car's absolute ability to accelerate.

You analogy is right. Torque is how much work the engine can do. It's how much it can lift. The horsepower is how much it can lift, how fast.

Gearing plays a strong role. The higher you can have the engine rpm the more room you have for gear reduction. Gear reduction is a torque multiplier. Suppose we have that mythical Mb that makes 300lb-ft at 4000rpm. If we have such an unbelievably steep gear that the wheels are only turning 10rpm while the engine is spinning 4000, we have:

4000rpm/10rpm = 400 multiplication factor.

Take your 300 lbs-ft and multiply it by 400. That's 120,000 lbs-feet of force available. That's an amazing amount of force!! You are going very slow, but you couls push a huge vehicle along. This is the principle that boats and huge tractors (semi's) use. Super steep gears that allow enormous torque multiplication.

But, from the math, can you see why it's so important for an engine to make rpm? AND make that torque at high rpm? It allows greater gearing flexibility and torque multiplication.

Take our above example. Suppose that we operate that engine at 1500rpm.

1500rpm/10rpm = 150 multiplication factor.

Now we have only 45,000lbs-ft of torque available. We want the engine to be spinning fast and the final drive to be spinning slow if we're going to have huge force amounts available.

Why do you think that little Honda S2000 can rip off sub 6.0 sec 0-60 runs with only 240hp and a super peaky torque curve? RPM baby. Motocycles take advantage of the same thing that big trucks do. RPM and gearing. It is always prefereable to have an engine that makes high torque at high rpm and use gearing than an engine that makes high torque at low rpm. Of course, many engineers have spent tons of time trying to figure out how to have both. Variable intake runners, variable valve timing, variable exhaust baffling, etc.

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John Shellenberg
1998 C230 "Black Betty" 240K

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We want the engine to be spinning fast and the final drive to be spinning slow if we're going to have huge force amounts available.

[/B][/QUOTE]

But doesnt this makes a car like this tiresome to drive eg the Honda S2000.

It would seem to me that you want your power(torque/hp) down low so you dont have to rev the engine to get going or keep going. I guess this is the difference between Big V8 and smaller engines.

But doesnt this makes a car like this tiresome to drive eg the Honda S2000.

It would seem to me that you want your power(torque/hp) down low so you dont have to rev the engine to get going or keep going. I guess this is the difference between Big V8 and smaller engines. [/B][/QUOTE]

It can make the car tiresome to drive, and that is why engineers have tried to make engines that produce torque at low rpm as well as high.

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John Shellenberg
1998 C230 "Black Betty" 240K

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I did not read all posts, but I would like to add something here.

The development of the V6 did not begin for the purpose of smoothness, more power, more fuel mileage, more efficiency, etc., etc., The purpose was to create an engine that would fit into a shorter, lower engine compartment.

As with any evolution there have been some fabulous V6's produced and some that weren't worth a bucket of cold spit.

Don't buy the argument that they were developed for more HP, more torque or any other power or efficiency reason. The same bore and stroke with the same cam profile, combustion chamber arrangement, valve size etc, whether the engine is V or inline will produce VERY similar power/efficiency profiles.

My $0.02,

I think this thread discussion wasnt so much to argue for or against any particular engine. But for me was more to educate myself on a topic which i knew little about.
I think we all, including myself, at times throw around HP and torque numbers without a true grasp of their true meaning.
Once again this thread has helped me in understanding these numbers and what they mean.
My $0.02.

8MPG.. And the American car manufacturers wonder why nobody here buys their cars...


Still I think it's weak, I make about 24MPG city and 30MPG in the AWD A6. It has 8-15bhp less (depending on model) but is much much heavier.

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190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg

Inline 6 vs. V-6

Not Mercedes but the sound of a TR250/TR6 or Jag 3.4/3.8/4.2 at idle and speed

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Anders

1995 E300
2015 VW TDI Sportwagen 15K
1977 240D (197K)
2002 Subaru Legacy L Wagon (115k) (Wife's)
Gone but not forgotten:
2005 Buick LeSabre
1998 C230
1984 300D
1983 240D
1981 300SD
1974 240D
1974 Fiat 124 Spider
1968 Triumph TR250

Subaru 2.5/190e 2.6

MPG and HP about the same but Subaru gets cheap gas.
MB runs much smoother. Both seem to have head gasket
issues.

Actually, the M103 has nowhere the head gasket problem the M104 does. With Subaru, the Phase 1 DOHC 2.5L has a terrible rep for head gaskets, and it's a pricey job. The Phase 2 SOHC 2.5L is much better, but still has some external weeping issues. Luckily, it does not melt down internally like the Phase 1 gaskets. Often, the Phase 1 engines will overheat and suffer damage thanks to the HG going south. The Phase 2's usually just leak a bit and don't break themselves.

Both our Forester and OBW handlily beat the ol 190E 2.6 in the mileage race. But, the 2.6L M103 is much smoother (inline six!) and made nicer sounds. Gearing was awful though, with the engine revving at about 3000 at 100km/h. It really could have used a slightly taller first gear (so low it would smoke the tires) and fourth could have been much longer.

__________________
John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif