1.5l cutaway (view from rear)
One of the most well known facts about the NA (naturally
aspirated) or non-turbo diesel engines that the MK1 Rabbits were endowed with
was the agonizingly low horsepower figures displayed on the dynamometer. The
owners of the IDI diesel Rabbits traded acceleration for economy whether they
knew it or not, and if they did not know it they found out quickly.
There are two different models of diesels that VW utilized in their
Rabbit. When the first diesel option was introduced in 1977 it was a 1.5l
(1471cc) with a fuel efficient 48 horse power and 58 ft/lbs of torque. This
engine used the same style of head with an eight valve overhead camshaft as
their gasoline/spark engine counterparts. The profound difference in a diesel
vs. gas engine is a genuine contradiction. A diesel engine inherently runs off
of a high compression and lean fuel mixture that allows the diesel to combust
under intense pressure and heat without the need of an ignition source. On the
other hand a gasoline engine runs without the compression, less than half, of
which the diesel does and a spark is used to coax the gasoline into combustion
at a precise time within the engine cycle. This information is probably
elementary if you would consider yourself mechanically inclined at all but
nonetheless this is relevant in distinguishing the differences in the earlier
and later diesels and the difference in the gasoline and diesel applications for
the Rabbit. Also, in able to understand the differences in the 1.5 and 1.6l
(1588cc) engines more roundly we need to understand the basic
differences.
The 1.5l diesel engine was a higher revving motor for one reason, a
shorter stroke. The shorter stroke means that the piston does not have to travel
as far from point A to B thus it can repeat the movement faster. Diesel engine
produced from 1977-1980 has a stroke of 80mm (8cm) and the 1.6l produced from
1981-1984 has a stroke of 86.4mm (8.6cm), this difference of 0.6cm stroke length
attributed the maximum engine speed of the 1.5l being 5,600 rpm and only 5,300
in the 1.6l. Along with the diminutive differences in the internal
specifications there are also a few significant discrepancies involving the
head/top end of the two engines. In the 1.5l engine and the early model 1.6l
engines until 1981 there was an 11mm head bolt used to secure the head onto the
block. I mentioned earlier that diesel engines run on high compression that can
surpass 500psi, this high pressure is contained by the head bolts that hold the
top and bottom of the engine together. A 1.5l has a bad tendency if it overheats
up to weaken and cause the head gasket to fail which requires immediate
replacement. The later 1.6l diesel had a 12mm head bolt that was capable of much
higher clamping pressure which increased pressure and heat tolerances
significantly.
The two engines used parts that were interchangeable for the most part. A
common upgrade was to put a 1.6l head onto a 1.5l engine to alleviate the weak
head problems which can open the door to more modifications to the engine that
can increase power and MPG in many cases. Both engines used a fuel injection
pump that was built by Bosch specifically for this application and proved to be
a reliable and efficient method of fuel delivery. The 1.5l engine was capable of
45mpg city/ up to 57mpg highway. According to the EPA fuel mileage chart in the
February edition of Popular Science the 1.6l Rabbit diesel got 56mpg highway and
38mpg city. For all practical measures the 1981 debut of the upgraded diesel had
the same mileage capabilities as its 1.5l predecessor while adding more power
for better drivability.
aspirated) or non-turbo diesel engines that the MK1 Rabbits were endowed with
was the agonizingly low horsepower figures displayed on the dynamometer. The
owners of the IDI diesel Rabbits traded acceleration for economy whether they
knew it or not, and if they did not know it they found out quickly.
There are two different models of diesels that VW utilized in their
Rabbit. When the first diesel option was introduced in 1977 it was a 1.5l
(1471cc) with a fuel efficient 48 horse power and 58 ft/lbs of torque. This
engine used the same style of head with an eight valve overhead camshaft as
their gasoline/spark engine counterparts. The profound difference in a diesel
vs. gas engine is a genuine contradiction. A diesel engine inherently runs off
of a high compression and lean fuel mixture that allows the diesel to combust
under intense pressure and heat without the need of an ignition source. On the
other hand a gasoline engine runs without the compression, less than half, of
which the diesel does and a spark is used to coax the gasoline into combustion
at a precise time within the engine cycle. This information is probably
elementary if you would consider yourself mechanically inclined at all but
nonetheless this is relevant in distinguishing the differences in the earlier
and later diesels and the difference in the gasoline and diesel applications for
the Rabbit. Also, in able to understand the differences in the 1.5 and 1.6l
(1588cc) engines more roundly we need to understand the basic
differences.
The 1.5l diesel engine was a higher revving motor for one reason, a
shorter stroke. The shorter stroke means that the piston does not have to travel
as far from point A to B thus it can repeat the movement faster. Diesel engine
produced from 1977-1980 has a stroke of 80mm (8cm) and the 1.6l produced from
1981-1984 has a stroke of 86.4mm (8.6cm), this difference of 0.6cm stroke length
attributed the maximum engine speed of the 1.5l being 5,600 rpm and only 5,300
in the 1.6l. Along with the diminutive differences in the internal
specifications there are also a few significant discrepancies involving the
head/top end of the two engines. In the 1.5l engine and the early model 1.6l
engines until 1981 there was an 11mm head bolt used to secure the head onto the
block. I mentioned earlier that diesel engines run on high compression that can
surpass 500psi, this high pressure is contained by the head bolts that hold the
top and bottom of the engine together. A 1.5l has a bad tendency if it overheats
up to weaken and cause the head gasket to fail which requires immediate
replacement. The later 1.6l diesel had a 12mm head bolt that was capable of much
higher clamping pressure which increased pressure and heat tolerances
significantly.
The two engines used parts that were interchangeable for the most part. A
common upgrade was to put a 1.6l head onto a 1.5l engine to alleviate the weak
head problems which can open the door to more modifications to the engine that
can increase power and MPG in many cases. Both engines used a fuel injection
pump that was built by Bosch specifically for this application and proved to be
a reliable and efficient method of fuel delivery. The 1.5l engine was capable of
45mpg city/ up to 57mpg highway. According to the EPA fuel mileage chart in the
February edition of Popular Science the 1.6l Rabbit diesel got 56mpg highway and
38mpg city. For all practical measures the 1981 debut of the upgraded diesel had
the same mileage capabilities as its 1.5l predecessor while adding more power
for better drivability.