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.

Engine Blocks

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 2.5L engine.

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.

Oil Pumps

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 pages.

Oil Pans

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 crankshaft.


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.

Connecting Rods

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 pin design.

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.

Custom Rods

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 2.2L engine.

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 retainers.

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 shop.

Wrist Pins

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.
Return to the Mini-Mopar Turbo Performance page


This page is maintained by Russell W. Knize and was last updated 06/03/99. Comments? Questions? Email minimopar@myrealbox.com.

Copyright © 1996-2003 Russ W. Knize