| N ow I
don't know if anyone ever noticed it, but I am not a big fan of diesel
engines. I still prefer a spark to gracefully ignite the mixture instead
of using the raw power of high compression ratios to force the mixture
igniting itself. But alas, it still is a very
economical proposition and for people more interested in economy than
performance Rover had a nice diesel engine available in our beloved SD1.
It wasn't an engine developed by Rover itself however but was bought in
by Rover from the Italian VM company.
VM Motori is a well established Italian firm founded
in 1947 by Vancini and Martelli (VM) and is specialised in air and water
cooled diesel engines. Since 1995 it is a part of the Detroit Diesel
company.
The diesel engine we are talking about here came into
life in 1978 and is produced until this day, however much has been
improved during the years off course. The engine was built in three,
four, five and six cylinder configurations for various companies like
Alfa Romeo, Ford, Jeep, Toyota , Chrysler and off course Rover.
Now this diesel has some unusual features which we
will look closer at in this page.
The concept might be a bit old fashioned at first, no
overhead camshaft but a pushrod engine with the camshaft located low in
the cylinder block. However as a diesel doesn't like to be revved not
having an overhead cam is not an important point. It makes it possible
to drive the camshaft, waterpump, and oilpump directly from the
crankshaft by gears instead of using a chain or belt drive.
The cylinderhead is different from any engine on the
market. Where a normal engine has one head for all the cylinders, or two
in case of a V or boxer construction, this in-line engine has a separate
cylinder head for every cylinder. This unusual setup has been chosen
because it allows one cylinder head casting to be used for all engine
configurations, be it a three or a six cylinder. Every cylinder head is
bolted onto the main block with six bolts. The chances of getting a
warped cylinder head are very small with this setup.
The combustion chamber was based on a design by the
British Ricardo firm, one of the leading engine designers in the world.
The chamber design, called Ricardo Comet V, was optimised for maximum
swirl effect. A further strange thing about the head design, the inlet
and outlet manifolds are both located at the same side of the head. This
sure makes it easier to place a turbo on the engine.
And if the cylinder head isn't strange enough, how
about a diesel engine with a tunnel carter... Normally an engine has
main bearing caps which are bolted to the cylinder block. Not so with
the VM diesel. A Tunnel carter looks more like the picture below, it's
from an old Ferguson engine but it shows the tunnel carter setup very
good. And if you look close you can just see it in the picture above, of
the VM diesel as used in the Chrysler Voyager. The engine of the Voyager
is the same engine as used in the SD1's with improvements in the
combustion chamber and diesel injection system
The entire crankshaft can also not be installed from
underneath but has to be put into the engine through the tunnel. However
this construction makes the engine very very stiff and the crankshaft is
fitted without any stress by main bearing caps. A very nice and elegant
solution only found in exotic race engines.
The VM diesel was equipped with a KKK turbo charger,
The engine was designed right from the beginning for use with a turbo.
Despite the turbo, power isn't really impressive the
2.4 litre delivering 90 bhp at a lowly 4,200 rpm. Nowadays you can
expect around 136 bhp at 4,400 rpm from the Range Rover 2.5dt Turbo
diesel engines. However when the diesel SD1 appeared on the market in
1982 it was the fastest diesel saloon in the world with 100 mph, how
times change.
The VM diesel was used in the SD1 from 1982 towards
1985. Special modifications for the installation in the SD1 were:
- V8 9.5inch clutch
- larger diameter propeller shaft from the 2000
- 3.9 final drive ratio also from the 2000
- 5-speed with raised fifth gear from 1:0,79 to 1:0,77
- oil cooler ahead of the radiator with electric fans. (standard
SD1's have them integrated into the radiator)
- Stiffer front suspension
- second 12V battery
- equipment level as the 2600S
Over the 1982-85 period Rover managed to sell 10,081
of these 2400 SD's mostly in LHD form. |
Rover and
Diesel's death
Rudolf Diesel was born in Paris on
March the 18th in 1858. His parents were Germans living in Paris
where his father had a leather factory.
He studied mechanical engineering in Munich and set up a
laboratory in Paris in 1885. At Augsburg, on August 10, 1893,
Diesel's first model, a single 10-foot iron cylinder with a
flywheel at its base, ran on its own power for the first time.
The Diesel engine was born. By 1898 he had become a millionaire
from the franchise fees.
On the 29th of September 1913 he shipped on the "SS Dresden"
for a short trip to the Rover factories in England. Rover was
interested in the Diesel engine and had arranged a meeting.
However Rudolf Diesel never showed up and Mr. Noble who was
ordered to pick up dr. Diesel in his 12 hp Rover waited and
waited.....
The body of Rudolf Diesel was found a couple of days later by
a coast guard boat. As it was usual at that time, the seamen
only took his pasport and other papers and threw the body back
into the sea.
As a result Rover had to wait for a while before it finally
got its Diesel engine. Well sorry for Rudolf, but it certainly
delayed Rover in using this rough running unelegant design,
let's be honest the Diesel's only virtue is its thermal
efficiency! (Or am I rude and biased?) |
VM Code
The VM engine in our SD1 is coded
HR 492 HT This code can be broken as follows.
- HR High Revolution (yeah, sure....)
- 4 4-cylinder
- 92 Bore of 92 mm
- HT Watercooled engine with Turbo
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Why a Turbo
loves the diesel engine
Turbo's and Diesel engines have
made a very good couple the last decade. Off course a normal
aspirated Diesel engine doesn't give very much power and hanging
on a turbo can bring it's performance up to petrol engine
standards and in some cases even better them. But give a petrol
engine a turbo and it blows every diesel into the weeds.
However putting a turbo
on a Diesel is easier than putting one on a petrol engine. The
main reason is turbo lag. Push the throttle and it takes time
before more gases flow through the engine and the turbo picks
up. Manufacturers have tried to eliminate these effects with
various design tricks:
- Smaller turbo
- Two turbo's
- The wastegate
Still turbo lag remains a
problem and is one of the reasons the supercharger is becoming
quite popular as an alternative. However on a Diesel engine you
seldom see a supercharger and the turbo has become almost
standard equipment on the Diesel.
There are two reasons:
- The exhaust gases of a Diesel engine are 200 to 400
degrees Celsius cooler than from a petrol engine this makes
the setup easier and cheaper to design and built and also
gives a longer turbo life.
- The Diesel engine has less variations in flow over the
entire speed range than a petrol engine.
Now what do we mean with
that last reason?
Well when we want more speed on a petrol engine we press the
accelerator and a valve in the carburettor or injection inlet
manifold opens and lets more air pass, presto the engine speeds
increases.
Not so with a diesel.
When you want more speed with a diesel engine you press the
accelerator which makes the diesel pump inject more diesel into
the engine and as a result it sucks in more air.
As you can see with a
petrol engine you control the engine speed with the air
quantity. with a diesel engine you control engine speed by
varying the fuel quantity. The diesel doesn't have a throttle
valve!
Because it doesn't have a
throttle valve the gases can always freely enter the engine. The
diesel doesn't have the big underpressures in the inlet system
like a petrol engine.
This means where the
density of the gases is almost constant in a diesel engine, this
isn't the case with a petrol engine where the density of the air
is smallest when the throttle valve is closed. As a result the
turbo on a diesel engine receives more exhaust gases under
partial load than a petrol engine under the same conditions. In
practice the flow ratio between full power and low power at the
same rpm is around 1:30 to 1:40 for the petrol engine and a
lowly 1:5 to 1:6 for the Diesel.
This effect makes the
diesel engine far less sensitive to turbo lag than a petrol
engine and also partly accounts (together with more expansion on
the power stroke) for the cooler exhaust gases. |
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