Upgrading The Engine's Bottom End
Blocks | Oil Pumps
| Oil Pans | Crankshafts
| Rods | Pistons | Wrist
Pins | Rings | Bearings
This page describes the options available for upgrading the bottom end
on 2.2L and 2.5L engines. This includes the block, oil pan, crankshaft,
connecting rods, pistons, wrist pins, rings, and bearings.
There were basically 4 different blocks that were manufactured by Chrysler
throughout the years. Some are better than others in different ways.
The 1984 - 1988 2.2L Turbo I Block
This block was basically the original 2.2L N/A block with a few modifications
that include the 23/32" hole for the turbo oil return passage and a block-off
plate where the carbeurated fuel pump used to be located (next to the water
pump). This block is good for around 200 to 250 hp. Above that,
the block actually begins to twist and the result is usually a random bearing
failure or the #3 main bearing cap breaking. Many have successfully
used this block in 300hp applications, but it was not designed for these
kinds of stresses. Its longevity for such a use is questionable.
The 1986 and 1987 Shelby Turbo II engines (GLHS and CSX) also use this
block. Keep this in mind when upgrading your Shelby.
The fuel injected versions of these blocks can be identified by the
fuel pump block-off plate next to the water pump and the back of the oil
pan flange "bumps" outward at each oil pan bolt. You can identify
a turbo block by the coolant supply flange connection and oil return tube
on the back of the block. Also note that 1984 and 1985 Turbo I blocks
should be avoided because they use the weaker 10mm headbolts. Later
blocks used 11mm headbolts.
The 1987 - 1988 2.2L Turbo II Block
This block was only used for two years. It was a strengthened version
of the Turbo I block that has stronger webbing to support the main bearings
and thicker cylinder walls. Also these blocks were cross-drilled
to improve cooling. A cross-drilled block requires a cross-drilled
head because the hole for the cross-drilling is supposed to connect the
rearward facing waterjacket on the head to the forward facing water jacket
on the block. This design would be improved even more in 1989.
The 1986 - 1988 2.5L N/A "Tall Block"
I am mentioning this block because it has some interesting aspects.
It was also only used for a brief period. It is stronger than the
early 2.2L Turbo I block, but not as strong as the Turbo II block.
It has a taller deck height to compensate for the longer stroke of the
2.5L crankshaft, while still being able to use the 2.2L pistons.
It is also the first block to use counter-rotating balance shafts, to help
cancel out the additional vibration caused by the longer stroke of the
The reason why this is significant is because it opens the possibility
of a high-performance 2.2L long-rod engine, with a rod ratio of 1.8 (length
of the rod divided by the stroke of the crank) or more, for use in an all
out drag racing engine. The longer rods reduce the trust loading
of the piston skirt against the cylinder wall. For more details about
the long rod engine, see the 2.2L Long Rod
Drag Racing Engine page.
These blocks can be identified by the fuel pump block-off plate next
to the water pump and the back of the oil pan flange is straight with no
bumps for the bolts.
1989 - 1993 Common Block
This block was the strongest of all 2.2L and 2.5L blocks. It has
the strongest webbing and main bearing caps, with the thickest cylinder
walls and a cross drilled block and head for improved cooling. It
was used for the 2.5L N/A engine, the 2.5L Turbo I engine, the 2.2L Turbo
II engine, the 2.2L Turbo III engine, and the 2.2L Turbo IV VNT engine.
This is why it is called the "common block". The differences in the
block between the different engines are small. The N/A engine does
not have the oil return line and has a different distributor. All
blocks except the 2.2L Turbo II and the 2.2L Turbo IV had the same counter-rotating
balance shafts as the tall block installed. Common blocks without
balance shafts do not have the holes necessary to install them. All
2.5L common blocks had balance shafts, as did the 2.2L Turbo III engine.
This block will take you well beyond 300hp and will not suffer from
the twisting effect of the early Turbo I block. These block also
have huge main bearing caps and can easily support a cast crankshaft for
a very high-output application.
These blocks can be identified by the lack of a fuel pump block-off
plate next to the water pump and the back of the oil pan flange is straight
with no bumps for the bolts.
There were two stock oil pumps used on 2.2L and 2.5L engines. From
1983 through mid-1985, a lower-volume, high-pressure gear pump was used.
In mid-1985, the pump was changed to a high-volume, low-pressure design.
These pumps can be identified by the number of bolts that are around the
pump housing. The older style had 5 bolts, while the newer style
had 4 bolts. In general, the newer style, 4-bolt pump is the most
desirable. It provides ample oil pressure with less parasitic drag
on the engine. Mopar Performance sells a high volume version of this
pump (PP4286741), but it is unnecessary because the stock pump provides
more than enough oil and this pump only adds more drag on the engine.
Also, it does not fit 1986 and later blocks, for some reason.
Two very helpful modifications to the oil pump are to chamfer the round
bore in the block to match the oval-shaped output of the pump. This
helps reduce the drag of the pump even further, while allowing more oil
to flow into the main oil gallery. The second modification is to
open up the hole in the oil pump intake with a die grinder or dremel tool
so that it is round. You have to be careful not to damage the screen.
This will greatly help the intake of the pump.
When installing the pump, be sure that the intake is about 5/8" off
of the bottom of the pan. You can measure this by reaching into the
pan with your hand through the front end of the engine when the crankshaft
is out. You should be able to slip your index finger between the
oil pump intake and the pan. Also, use some anaerobic sealer to seal
the pump to the block.
Some other pages you may want to see are the Engine
Oil Choices and the Engine Oil Filters
There are a few differences in oils pans for the different blocks.
The 1987 - 1988 Turbo II oil pan should be the same as the early Turbo
I oil pan. The 2.5L tall block has a special oil pan that is straight
on the back side and has a different oil pickup area, while making room
for balance shafts. The common block also has it's own oil pan with
a straight back and larger area to fit balance shafts. There are
some additional differences in the shape of the pan's sump. The 1987
and 1988 oil pans have a deep sump feature to concentrate the oil and help
prevent the pump from going dry during hard turns.
The biggest improvement that can be made to an oil pan is to get a baffled
version, or to have your pan baffled. A good baffle features a screen
that collects oil and allows it to fall back into the pan instead of foaming
and hanging on to the crankshaft and rods. The one-way nature of
the screen prevents the oil in the pan from being whipped back up by the
The crankshafts used in turbo engines varied. 1984 through mid-1985
crankshafts used 6 bolts on the flywheel, while mid-1985 and later crankshafts
used 8 bolts. Turbo I crankshafts were cast while the Turbo II crankshafts
were forged. The forged crankshafts, though stronger, are significantly
heavier (about 43 lbs) than the cast ones (about 34 lbs). This adds
a lot of rotating mass which ultimately effects power output during acceleration.
The cast crankshafts are still very strong and can handle well over 300
hp, as long as it is not revved too high. You definitely want to
stay under 6000 rpm with a cast crankshaft on a high output engine.
The forged crankshaft will allow higher engine speeds, if you desire.
Generally, 8 valve heads do not perform well above 6000 rpm, so the forged
crankshaft is most useful with the 16 valve heads.
The 2.2L crankshafts had a 3.62" stroke, while the 2.5L crankshafts
have a 4.09" stroke. There is no forged 2.5L crankshaft available.
There were some changes in connecting rods throughout the 2.2L/2.5L engines'
history. There are basically 4 different stock rods available for
turbocharged engines. All of the rods listed below are of equal length
and are interchangeable between blocks.
The 1984 - 1985 2.2L Turbo I Rods
These engines featured big-beam forged rods to increase the strength of
the turbocharged engine. They feature a fixed-pin design, where the
wrist pin is pressed into the rod end. If you can find an engine
with these rods, grab them. They are perfect for just about any high
performance 2.2L application.
The 1986 - 1988 2.2L Turbo I Rods
The connecting rods for these engines were similar to the earlier rods
(forged, fixed pin), but were made from significantly less material.
Chrysler lightened the rods to reduce the engine's reciprocating mass.
They are more than strong enough for a stock Turbo I, and they are even
strong enough for a Turbo II (the 1986 and 1987 Shelby GLHS and CSX uses
these rods). If you want to upgrade your engine for over 200 hp and
you have these rods, they should be replaced with stronger units.
The 1989 - 1993 2.5L Turbo I Rods
In 1989 the Turbo I got its strong rods back. They the same rods
as the Turbo II rods, which were slightly stronger than the 1984 - 1985
Turbo I rods. They feature a brass-plated steel bushing for a floating
The 1987 - 1990 2.2L Turbo II Rods
These rods were similar to the 1984 - 1985 Turbo I rods. They are
somewhat stronger because of the additional material on the rod bearing
caps. They have a brass-plated steel bushing on the piston end for
a floating pin setup. The bushing is a slight weak point, and it
is worth the effort to replace them with a solid brass bushing. Even
so, they are considered to be an overkill for even 300hp applications.
If you plan on building a 16 valve engine, then I would definitely go with
these rods because they can handle the high revs. If you want the
security of not having to worry about your rods, go with these which are
available through Forward Motion and LRE.
Of course, you can always have rods made for you by companies such as Cunningham
or Venolia. This is necessary
if you plan on building a very customized engine, such as a 2.2L
long rod engine.
Piston design changed a few times throughout the 2.2L/2.5L history.
All stock pistons are cast and are not designed to high-output applications.
Though they will usually handle high boost without trouble, problems arise
if the engine detonates. One good knock and the upper ringland on
the stock piston will fail, cracking the ring. If you are going to
have a high performance engine, go with custom forged pistons.
The 1984 - 1985 2.2L Turbo I Piston
This piston was a standard cast aluminum piston that had a fixed-pin design.
It had a 8cc dish to reduce the compression ratio for the turbocharged
The 1986 - 1988 2.2L Turbo I Piston
This piston was the same as the earlier version, except that it had a dish
volume of 14cc because of the lower volume "swirl" head introduced in 1986.
The 1986 and 1987 Shelby Turbo II engines (GLHS and CSX) also use these
pistons. Keep this in mind when upgrading your Shelby.
The 1989 - 1993 2.5L Turbo I Piston
This piston was made by Mahle and featured
a higher-strength cast aluminum design. In addition, the rings and
wrist pin were all raised on the piston to make room for the 2.5L's longer
stroke. This had the effect of slightly increasing the compression
of the engine (because of the higher rings). Though slightly stronger,
it will still suffer the fate of a cast piston if the engine knocks.
The 1987 - 1990 2.2L Turbo II Piston
The piston was also made by Mahle and
featured the high-strength cast aluminum design. It also suffers
from the drawbacks of a cast piston. The rings and wrist pin of this
piston were arranged the same as the earlier Turbo I pistons, since it
had the shorter stroke of the 2.2L. This piston was designed to accommodate
the floating pin setup of the Turbo II by providing notches in the pin
bores for cir-clips. In high performance applications, these clips
have a tendency to get pounded out by the wrist pin, which destroys the
cylinder wall. Go with custom forged pistons because they use spiral-lock
Custom Forged Pistons
There are a few vendors that will custom-manufacter forged aluminum pistons
for our engines. These include J &
E Pistons, Venolia Pistons, and
TRW. The TRW pistons, seem to be of less quality than the J&E
or Venolia. J&E and Venolia's pistons are probably equivalent
in strength, but the J&E pistons are about twice as expensive.
If you need them fast, Forward Motion
stocks oversized J & E forged pistons.
With a custom piston, you can have it made any way you wish. They
typically have the blueprints for the stock pistons on file. As such,
you can have them make it to those specifications. The only things
they will need to know is your dish volume (8cc or 14cc, see above) and
pin diameter and type. Stock pin diameter is 0.900", but this pin
is known to flex in high output applications. Two other pin diameters
are popular: the 0.936" Chevy pin or the 0.912" Ford pin. While the
Chevy pin is stronger, the Ford pin is lighter. Either pin is better
than the stock pin. If you request floating pins, the manufacturer
will machine grooves for spiral-lock pin retainers instead of the failure-prone
cir-clips that the stock Mahle pistons use. There is usually an additional
charge for the extra machining required for a floating pin setup.
If you go with an over-sized wrist pin, then you will have to have your
rod end honed out. Because the bushings in the rod end are brass-plated
steel and not solid brass, often the honing will remove most of the brass.
If you can find a solid brass bushing, have it pressed in by the machine
There are really only two different stock wrist pins available. All
Turbo I engines feature a fixed 0.900" diameter pin that is pressed into
the rod. Turbo II, III, and IV engines feature a floating 0.900 diameter
pin that is held by retainer cir-clips. The Turbo II retainer clips
are prone to failure because they get pounded out by the floating pin.
Any custom piston and some new replacement pistons from Mahle feature a
spiral-lock design. These clips cannot be pounded out because they
sit in a square-shaped channel. To completely prevent the wrist pin
from moving, the spiral-lock clips can be doubled-up on each side.
If you are having custom pistons made, you can easily specify a different
pin size to strengthen it, since the stock pins are known to flex under
heavy load. Two other pin diameters are popular: the 0.936" Chevy
pin or the 0.912" Ford pin. While the Chevy pin is stronger, the
Ford pin is lighter. Either pin is better than the stock pin.
If you go with an over-sized wrist pin, then you will have to have your
rod end honed out. Because the bushings in the rod end are brass-plated
steel and not solid brass, often the honing will remove most or all of
the brass. If you can find a solid brass bushing, have it pressed
in by the machine shop.
If you will be using conventional rings on your engine, a set of Mopar
Turbo II rings will be more than sufficient. After market companies
such as Perfect Circle make good OEM rings as well.
Companies such as Seal Power,
Hastings, and Total
Seal make gapless rings for our engines. They virtually eliminate
blowby by having a gapless #2 compression ring. As the boost delivered
to the engine increases, so does the loss from blow-by. Quite a few
drivers have had good luck with these rings. They also provide special
#1 compression rings that work well for high compression, turbocharged,
and/or nitrous-fed engines.
Go with standard Mopar main and rod bearings for your engine. There
have been problems with a few of the aftermarket suppliers, but I have
had good luck with Perfect Circle.
This page is maintained by Russell W. Knize and was last updated 06/03/99.
Comments? Questions? Email
Copyright © 1996-2003 Russ W. Knize