I have always wondered about this.

If you are equating acceleration to horsepower, you are dead wrong. Horsepower is the ability to pull heavy loads, accelertion is the ability to achieve high speed.

If diesel engines didn't produce horsepower, they wouldn't be used in EVERY commercial application from Truck Transportation, to Heavy Equipment.

Go to any construction site, or quarry, What do you see there? Earthmovers, bulldozers, graders, & heavy trucks. Do they run on gasoline engines? No, they run on diesel, because diesel produces power, horsepower, to get the job done.

Diesel trucks regularly pull loads to a maximum of 80,000 Lbs. and more (under permit) across this country, over mountain passes, and with better efficiency than gasoline engines. Pulling those kinds of loads takes a lot of "horsepower", as much as 525 HP, measured at the drive wheels, not the flywheel..

A diesel Mercedes may not be the fastest vehicle, but it is efficient, and has the power required to pull a trailer or boat better than a gas engine, and will last many times longer.

Diesel power isn't just about acceleration, it's about economy, horsepower, and stamina...

And if you don't think that a diesel engine can achieve high speed, go for a ride with a professional truck driver who drives a V-12 Cat hooked up to an 18 speed transmission, and see if he can't make you pee your pants... There ain't nothin' like doin' 125 across east Texas with an 80,000 Lb. load behind you!

Of course, you understand that this is all contingent upon gear ratios as well...

__________________

Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."

I'll take a stab at explaining this in a simple way.

Horsepower is work performed over time. The key thing to
understand is that time is a factor in determining HP.

Gasoline engines have an advantage over diesel in
producing horsepower because they can run at higher RPMs.
Higher engine speeds fit more power strokes into the
same period of time. Hence gasoline engines have the
ability to burn more fuel in less time than diesels by
running at higher RPMs. This is why the maximum HP of
a gasoline engine is generally higher than that of an
equal sized diesel engine.

For example, the late E300 turbodiesel produces its
maximum of 174HP at 4400RPM. The maximum speed at which
a diesel engine can run is about 5000RPM - it's limited
by the (slow) rate at which the fuel burns. In contrast,
the E320 produces its maximum of 221HP at 5600RPM. The
diesel engine cannot even reach that speed.

Where the diesel has an advantage is at more common engine
speeds. At 2000RPM, the E300 can produce about 125HP,
compared with about 100 for the E320. At 3000RPM the
E300 can produce about 170HP vs about 150 for the E320.
This is why diesels are very responsive in normal driving.
(I'm reading these numbers from graphs in the 1998 E-class
sales brochure. The graphs are small, so my interpretations
are somewhat approximate.)

Class dismissed.

- Jim

Actually horsepower is mathematically derived from the measurement of torque. Torque is measured by engine or chassis dynamometers and converted over to hp via an equation, which explains why torque and hp always cross each other at 5252rpm, as displayed on dyno output sheets. Diesels rarely will rev beyond 5000rpm and that is why the hp output frequently appears lower than comparable gassers as they make peak hp at high rpm. In looking at 400+hp large truck diesels it is important to also note these engines often produce torque in the 1000+ft/lb range. What keeps a diesel from accelerating quickly is the burn time of the fuel, and the limitations this presents to advancing the injection timing. New technology such as direct injection, high-pressure common-rail systems and electronic injectors have changed this pretty drastically. Drive any new diesel pickup, vw or benz and I think you will agree. Currently there are manufacturers that are pushing light-truck Cummins and Powerstroke engines into the 300hp/600ft/lb range. The result is 8 second 0-60 times, not bad for a 6000+lb truck. Engine longevity is usually unaffected since these engines were medium-duty truck engines de-tuned for light truck use. RT

Horsepower is not a derived measure. It is a standard
in and of itself. Try http://www.lycoming.textron.com/support/publications/watts_horsepower.html
to see how far back the definition of horsepower goes.

Horsepower is the imperial (British) unit of power, now
replaced by the watt - the new SI unit. One horsepower is
the work done at the rate of 550 foot-pounds per second and
it is equivalent to 745.7 watts.

Simply put, one horsepower is the ability to lift 550 pounds
one foot in one second.

An internal combustion engines' horsepower can be calculated
if its torque is measured. To imply they are the same thing
is incorrect.

Just what was SV actually asking? The responses from you two gentlemen are both accurate and very well stated, but is SV asking about actual HP, BHP, or acceleration?

One of the factors affecting acceleration of diesel engines is the fact that no one to date has produced a "perfect" automatic transmission for diesel engines.

In a previous thread patsy posted a copy of an article about a new company that was developing a "constant speed" automatic transmission that would be the closest to an ideal for use with diesel engines.

In commercial diesel applications, there are a number of factors that influence both the speed and torque of a given vehicle when using a manual transmission. Those are: displacement of the motor, efficiency of the motor, where the horsepower is rated (Cummins and Detriot both take HP ratings at the flywheel, and Caterpillar uses the final drive application), the gearing (ratios) of the transmission, and finally, the gearing (ratios) of the differential.

So, SV, Just what did you want to know again?

[Edited by longston on 02-21-2001 at 11:45 PM]

__________________

Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."

I think this relates to your discussion about diesel power. Check it out, I think you will be surprised by the results they got on these diesel trucks will all bolt on mods.

http://www.crankandchrome.com/previous_shows/thisweek_1.27.html

and this
http://www.dieselperformance.com/preleases/prpage.php?d=2000-10-27

And check out these videos
http://www.dieselperformance.com/dynoday/index.php

I'm sure you diesel guys will enjoy it.

Alon

__________________
'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon

Diesels aren't normally considered for a hot-rod setup. There are not many aftermarket parts are available, because diesels don't respond to "hotter" cams, headers and larger carburetors like gasoline engines since they operate on a different priciple and use slower-burning fuel.

Diesels always use fuel-injectors. Not may hot-rodders even THINK of playing with mechanical FI, like on the original Corvette, and until recently the only diesel FI systems were mechanical. Newer diesel engines have electronic controls, so the potential to "chip" a diesel is growing. Not much, as diesels are still not popular by a long shot.

By the way, check out http://www.62-65-dieselpage.com/ for some good stuff on GM's diesels, including how-to's for the 6.2/6.5L series and featuring their new Duramax 6.6L. Note too that a lot of discussion on high-performance diesels is devoted to cooling! High-power engines make a lot heat, and given a chance any will gladly melt their pistons down into slag whether diesel, gasoline, alcohol or methanol fueled.

Did you know that MB diesels use an oil spray under the pistons to help the cooling? Keep that oil level where it belongs!

Anyway, I guess it boils down to "It's hard because it's difficult."

BCingU, Jim

I don't know if this is enough diesel horsepower for you:
http://www.geocities.com/MotorCity/Speedway/5350/v8cdi.htm
But I sure would love to drive one.


Dale Mitchell
________________

'84 300SD
'96 6.5TD GMC Suburban

Real engines don't spark!

I just meant that diesel engines usually don't have much horsepower. I know they have lower redlines, but the also have the aid of a turbo (most of them usually). I'm not talking about torque or acceleration here just horsepower.
OK, it comes down to this, my main question :is it harder to get horsepower out of diesel engine than a gas engine ? Anyways thats all changing with all the new technology we are seeing in MB diesels with their CDI engines.

Awesome picture and article on that engine there, Oil_burner! That baby's a far cry from our cars, eh?

And SV, you still sound confused. There are only two final applications of internal combustion engine power. Those are: Horsepower, which is, in terms if physics, the time rate of doing work, or of producing or expending energy. 1 HP=550Ft.Lbs. per second, or in metric terms, 746 watts. The other is measured as speed or acceleration.

If you are asking if it is easier to get horsepower out of a diesel, or gas powered engine, then your answer would be dependant upon your personal definition of horsepower. True horsepower is most efficiently produced by diesel fueled engines. If this were not true, tractor-trailers, buses, and heavy equipment would all be gasoline powered. But in terms of the other final application of internal combustion engine power, high octane gas, aided by N20 injection produces the fastest speeds in hybrid race cars built solely for speed.

Here's another approach to your question, The flash point, or the lowest temperature at which either fuel ignites are radically different between the two. If I remember correctly, diesel "flashes" at 167°F, and gasoline at -40°F.

You could always "Ask Jeeves"...

One small afterthought, commercial diesel truck and bus engines gon't have a "redline" they have a governor that controls maximum RPM on the engine. A 350HP Caterpillar engine is governed around 2100RPM. With those "restrictions", and given the appropriate gearing and differential that same vehicle is capable of both cruising at speeds above 90MPH, and ripping a 3,000 lb. car in half with sheer pulling power.

[Edited by longston on 02-24-2001 at 12:08 AM]

__________________

Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."