|
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
|
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.
|
|
© rwp may. 2000