The Mopar 2.2 Liter and 2.5 Liter Turbo Engines
The high torque of the 2.2 turbos sets them apart from many competing engines; the ability of the 2.2 to push out 224 horsepower, as far back as 1990, was exceptional, especially considering that they were not engineered with this type of output as a goal.
Turbocharged versions always had multiple-port fuel injection in the US.
There were four distinct turbo setups, and Mopar fans usually refer to them as the Turbo I, Turbo II (an intercooled version of the Turbo I), the Turbo III (DOHC, 16 valve), and Turbo IV (VNT). In each case, the turbochargers and fuel injection systems were computer controlled by an adaptive logic module that could compensate for changes in operating conditions (including altitude changes). Two other setups, less well-known, were used in the Cosworth-head M4S and in the TC by Maserati.
In 1984, the first year of the turbocharged 2.2, the engine produced 142 hp at 5,600 rpm and 160 lb-ft of torque at 3,200 rpm, around 30 hp and 30 lb-ft more than the best power made by the standard 2.2. The compression ratio was dropped to 8.5:1, using deep-dished, strutless, lightweight pistons. To make the engine more durable under power, Chrysler added high-strength valves, higher pressure springs, better-sealing rings, a special cam, select-fit bearings, and special exhaust manifold; they also used a diecast aluminum cylinder head cover for looks. Initially, Chrysler used a Garrett Research T-3 turbocharger, including an integral wastegate, with a maximum boost of 7.2 psi; the wastegate was controlled by a mechanical assembly, which used the pressure difference between the compressor outlet pressure and the throttle body vacuum. When the outlet pressure got too high, the wastegate would be moved so exhaust gases went directly through the exhaust rather than into the turbine.
The compressor itself was aluminum, driven by a turbine wheel in an iron housing with liquid-cooled bearings. The shaft bearing on the exhaust housing side was water-cooled, to reduce hot shutdown bearing failures. Turbocharger bearings were pressure lubricated with oil. Partly as a result of Pete Hagenbuch’s arguments, premium fuel was required; a detonation sensor allowed people to use regular gas with lower performance. The system used Chrysler-engineered and built electronic controls.
In 1986, fuel injection systems were controlled by a pair of computers, the Logic Module and Power Module; the logic module controlled ignition timing, the air/fuel ratio, emissions control devices, and idle speed, while the power module translated the logic module's demands for air/fuel ratios and timing into signals sent to the fuel injector (altering the length of its pulse) and the distributor. Input from the knock sensor allowed the computers to retard timing as needed to avoid damage to the engine with (for example) low-octane fuel (on turbocharged engines, engine knocking was dealt with both by reducing boost and by retarding timing for the knocking cylinder — and only that cylinder). The logic module was adaptive — it could compensate for changes in operating conditions, including altitude changes (this had been introudced in 1982).
Stefan Mullikin noted:
The boost level is based off of the volume of exhaust the engine produces. The more load, the more exhaust volume is produced the more quickly the paddle wheel gets turned the more boost gets created. Depending on what the various sensors are reporting, the computer decides whether the wastegate lever is open or closed.
The stock ECU is rather sophisticated, it monitors the oxygen, coolant, manifold pressure and throttle position sensors, battery and intake temperatures, A/C relay, Engine RPM, knock sensor and vehicle speed, etc to determine what values to use to control the engine. It varies when the fan comes on by monitoring the speed sensor and the coolant sensor.
There is a sensor the engine uses for determining the amount of vacuum or boost in the intake system. Its called the Manifold Absolute Pressure Sensor (MAP) The computer monitors it very closely, it also uses it to determine the barometric pressure of the ambient air (the slight miss at idle you might notice) it does this by briefly opening the MAP sensor to ambient air using the Baro-read solenoid.
Granted, the stock ECU does limit boost at low speed/throttle opening on many models to preserve the transaxle for the duration of the warranty (the 86/87 Shelby GLH-S for one) but there's not a load sensor as such.
The computer controlled boost (air pressure coming out of the turbocharger) via the wastegate, which opened to allow exhaust gases to power the turbocharger. The system allowed overboost during “snap acceleration” for up to ten seconds, and generally tried to keep a balance between engine responsiveness and gas mileage/engine life.
The turbocharger itself was cooled partly by the fresh oil circulated through its bearings, partly through a water jacket around the bearings and turbocharger itself, and partly through the air flowing through the engine compartment.
2.2 liter engine: never designed for turbocharging
One interesting tidbit is that the 2.2 was never designed for a turbo, according to Chrysler engineer Pete Hagenbuch; but its durability must have made engineers happy when they chose to force the air in. Pete wrote:
(The following are Pete's words, but we have combined two messages sent at different times so they read chronologically.)
I was the guy responsible for the performance of the 2.2 and later 2.5 turbos. We had no one in-house who knew much more than the very basics. It was pretty much learn as you go. The electronics folks at Chrysler were not any better off. Engine designers had one thing right; mount the turbocharger as close as possible to the exhaust manifold to reduce heat losses.
We learned a lot about turbocharging and, yes, the 2.2 responded to everything we did.
Our biggest difficulties lay with detonation, or the detonation sensor which was, I think, unreliable. Given this, the specified fuel could not be regular octane. I fought this battle and eventually won something in the owners' manual saying better performance and longer life could result from the use of high octane fuels. This was a big breakthrough. I had several different turbo lease cars and they were fine; they never tasted low octane fuel.
As to Mitsubishi, they became the production source sometime after my retirement. And up till then, their only contact with us was regarding their turbos and nothing to do with future designs.
After working with the improved 2.2 turbo (not Turbo II) with the long branch intake manifold, we picked up a nice gain in output which came from both the tuning effect and the improved fuel-air ratio distribution which allowed a better spark advance curve without detonation problems.
As to the variable geometry turbo, it was still being developed with Garrett when I retired. My right hand man, Dick Winkles, was deeply involved with the Turbo II, which was supposed to have both a charge cooler and the variable geometry turbocharger. Dick was the overseer of the LeBaron coupes which paced the 1987 Indy 500. They ended up without the variable geometry, but were really impressive just due to the charge coolers. Dick had a ball at Indy. All the drivers wanted a drive in it. And they loved it..! Of course it wasn't sellable. Oh, yeah, it was a LeBaron convertible.
[Of the production engines], the 1988 version with the longer branch tuned intake manifold was the best. I was driving an 1988 Daytona when I retired. The Turbo IV, with Garrett's switch-the-pitch turbine, was a bear, but I understand the thing froze up with a little carbon buildup. And then I retired! And anything I can tell you after that would be guessing.
One other thing I mention only because I am still disappointed that I couldn't even do a quick and dirty job setting up a car using the EYT Rootes-type supercharger for a demo. CHRYSLER WANTED A TURBO.
The 2.2 was not designed for a turbo. Turbos are for racing. Too much heat for normal driving. We should have gone with that Eaton Rootes-type supercharger. We had a [supercharger] unit, from Eaton, but I couldn't even get permission to do a quick 'n' dirty job with it. I begged for a test cell and six months to produce something that would counter the high friction and make decent economy. Nope, they were fixated on the turbo. After all, it was good enough for Formula 1.
Burke Brown, leader of LX engineering, added: “... I lived through the variable-nozzle turbo, and [exhaust rust and dirt clogging] was an issue there too. But what we would do with that is every time you start it up, we’d swipe them back. You’d flip the nozzles back and forth a few times to kind of clean off any deposits that were built up.”
The 1986 fast burn head helped; dyno tester Ed Poplawski wrote, “I worked on this a little bit. We ran Fast Burn heads on the 2.5L and the big advantage that I remember was that with the Fast Burn head, wide open throttle spark timing was lower than with the standard head, so you didn’t have to worry about spark knock too much and you didn’t need premium fuel. That made a big difference for the turbocharged engine.”
What Chrysler said about their engines in 1988
A small, stainless steel turbine wheel, in a housing which is bolted to the exhaust manifold, is driven at tremendously high speeds by hot exhaust gases and it rotates a small aluminum compressor on the other end of the same drive shaft. The compressor is located ahead of the intake manifold where it rams air-fuel mixtures into the combustion chambers under pressure to produce greater power in each cylinder when the spark plug fires.
For 1988, the turbocharger on the Turbo I engine is smaller and has less rotating inertia to overcome, thus achieving faster throttle response.
The single-module engine controller continuously monitors eight parameters in order to maintain the proper boost level and fuel-air ratio under all engine operating conditions. If the boost pressure were not limited, the engine would be subjected to higher pressures and higher temperatures than the engine could tolerate. The maximum boost level is physically controlled by a wastegate which is a valve that permits some of the exhaust gases to bypass the turbine wheel. This regulates the turbine and in turn the air compressor, thus preventing unwanted air flow into the engine. Controlled transient overboost is permitted during snap acceleration for up to 10 seconds.
The wastegate actuator solenoid is located in the pressure signal line leading from the turbocharger to the wastegate actuator. This solenoid receives a signal from the computer and, in turn, controls the position of the wastegate through the actuator.
A new wastegate power source is used for 1988-pressurized air from the turbocharger instead of manifold vacuum. This allows for a leaner fuel mixture and increased spark advance which enhances fuel economy.
Boost control was, starting in 1985, computer controlled; the computer monitored eight parameters. Calibrated pressure limits were programmed into the system, which worked by actuating the wastegate via the wastegate actuator solenoid (on the pressure signal line, leading from the intake manifold to the wastegate actuator.) Higher boost pressures compressed a spring connected to an actuator rod, opening the wastegate (which bypasses the turbocharger). Detonation control was also handled by the computer; when knock was detected in a cylinder, it retarded timing in that cylinder only, and lowered boost into detonation stopped.
The various turbocharged engine types
|2.5 T||2.5 TBI||2.2 T III||2.2 T I (1987)||2.2 T I (1989)|
The most common, and generated a respectable 142 hp (better than the 3.0 V6, or, for that matter, the late-80s 318). It was relatively reliable and had good fuel economy. The turbo was quite well suited for the 2.2, which had good (for the time) low end torque but did not breathe well at higher rpms; the turbo evened it out nicely. (142-150 hp depending on application). The engine computer was hooked up to a knock sensor to allow for the use of regular gas if needed; the computer changed the timing to match the fuel type.
When introduced in 1989, the 2.5 liter turbo engine replaced the original 2.2 Turbo I; its higher displacement provided faster initial acceleration, covering 10% more distance during the first five seconds of full-throttle acceleration. The longer stroke produced more turbulence for faster, smoother combustion, and the balance shafts helped damp out firing pulses, for a smoother idle. The block had diagonal cross-drilled coolant passages between cylinders, matching similar passages in the head, a feature common to the Turbo II engine; indeed, it was the same block as the Turbo II and base 2.2 and 2.5 liter engines. (This required a new head gasket with the passages built in.) The crank was a high hardness ductile iron, modified from the 2.2 for piston and block clearance; new aluminum alloy pistons had steel struts cast in, to control expansion. They had a dished crown to adjust the compression ratio.
The wastegate control strategy was revised, providing initial boost at a lower speed, and more boost at medium and high speeds. The engine had 150 horsepower at 4,800 rpm, with 180 lb-ft of torque (measured on premium gas). Boost calibration changes in 1991 added 2 horsepower and a full 30 lb-ft of torque, so the motor produced 152 horsepower and 211 lb-ft of torque at the same speeds.
A low intertia turbine and compressor resulted in fast reactions; internal changes to the turbocharger assembly were made to increase airflow, but otherwise it was similar to the original unit. The engine used the same connecting rods as the Turbo II, double weight sorted before assembly for accurate balance. In addition, the air cleaner was changed from round to oval in shape.
The next most common engine after the Turbo I, it added an intercooler, forged crank, and other performance touches, including a heavy duty transmission. An astounding 174 hp came from this reliable engine - not bad considering the original was only 93 hp - and that it came with 200 lb-ft of torque. The intercooler dropped the charge air temperature by up to 120° Farenheit, allowing boost to go from 7.2 psi to 12 psi. Small tubes drilled between the cylinder bores at the top deck were added to cool the engine more effectively, an important modification.
The Turbo II was only made for three years, from 1987 to 1989; in its first year it was only used on the Daytona Shelby Z, and in its second year it appeared as an option on Lancer ES and standard on the TC automatic. For its final year, it was on the Daytona Shelby, Shelby Lancer, Daytona C/S, LeBaron GTS, and optional on the LeBaron.
In 1989, the Turbo II (and Turbo I) gained a new throttle body with more reliable throttle levers; these automatically locked the cables into place, eliminating separate clips, and included a larger idle air control passage.
Generating 224 hp from 2.2 liters, this engine was a thrill to drive. The heads were designed by Lotus.
The Turbo III was a DOHC engine with distributorless ignition and four valves per cylinder at a time when few engines had distributorless ignition and no other Chrysler engine had four valves per cylinder.
One Chrysler engineer wrote: “Incredible engine, not many left around here, but lots still in Mexico. Heads cracked in the 1991 version because some dummy decided to use cast iron plugs in the water jacket holes instead of aluminum.” (There was a recall for this and many were retrofitted with the aluminum plugs.)
Michael Royce, of Lotus Engineering, wrote that development of the Turbo III (designated the A-522) started with a contract signed on March 1, 1985, by Bob Sinclair (Chrysler VP of Engineering) and Mike Kimberley (Managing Director of Lotus Cars Ltd). Royce was the program manager on all three of Chrysler’s programs with Lotus Engineering. Work on the Turbo III started before the Turbo IV (which came out earlier), hence the name.
Some interesting aspects of this engine, Chrysler’s first dual overhead cam production model, included putting the cams alongside the valves due to height restrictions; and putting the spark plug at the center of the combustion chamber. The pistons were forged aluminum, with scalloped tops for valve clearance; boost was set to peak at 11 psi.
Redline was 6,500 rpm; the 16 valve dual overhead cam engine was rated at 225 hp at 6,000 rpm, 210 lb-ft at 4,800 rpm. It had cross-flow porting, individual intake runners and divided ports, shallow pentroof chambers with central plugs, 1.4 inch intake valves, and 1.28 inch exhaust valves.
A 2.2/2.5 engineer wrote: "I'm amazed that the Turbo III ever saw the light of day. Too bad some people thought that V-6 was the answer ... we had supercharged 2.2s running in the dynos in the mid 1980s and it looked like a go for a while. But the 2.2 and 2.0 have "siamese" bores (no cooling in between) and sealing them with o-rings would be necessary, which is money. By the way, some of us fought to have cooling between cylinders when the 2.0 was being developed, but the Neon was to be cheap at all costs, so the same bore spacing (87.5 mm) was carried over so Trenton Engine wouldn't have to retool everything and could use the existing line with same machinery."
Michael Royce noted that the problem with timing belts was that:
The timing belt tension had to be set so high to overcome "tow roping" of the timing belt, i.e. the timing belt going into negative tension. Tow roping is a belt killer. We found that this problem was caused by the extremely low valvetrain friction from using roller rockers combined with the DOHC set up. As soon as an exhaust valve rocker goes over the nose of the camshaft, there is no friction to slow it down and it tries to close the valve even faster, causing the exhaust cam sprocket to rotate clockwise faster and decrease the tension in the belt span between the sprockets. With a bucket tappet, which is used on most DOHC 4 cylinders, there is friction. On the 8 valve SOHC engine, there is an intake lobe on the same camshaft coming up to help out! So we had to crank up the initial belt tension to solve the problem.
An automatic belt tensioner would probably have helped. However, belt life is probably improved if people watch their belt tension and keep it within spec.
Dyno operator Ed Poplawski wrote, “We evaluated a Lotus 4-valve head and a Maserati 4-valve head. If I remember right the power output of both heads was the same but one head was cheaper to make if it went into production. One head had direct acting buckets to actuate the valves (Lotus) and the other head had some sort of complicated rocker arm system that was complicated and expensive to make (Maserati).”
Directions on centerlining the Turbo III cam (you'll need them!).
See our Spirit R/T page for more details on this engine.
Even more rare; this engine used variable-nozzle technology (VNT) to increase boost at lower rpms, and made 174 useful horsepower; balance shafts helped smoothness. Torque was relatively high (225 lb-ft rather than 200 in the Turbo II). It was used in the CSX. A defect in early-production turbochargers gave this engine a poor reputation for reliability, but the technology was advanced for its time, and has since come into common use, particularly on diesels.
Lotus Engineering and “what might have been”
Lotus’ Michael Royce wrote:
On March 1st 1985, Bob Sinclair, the Chrysler VP of Engineering, and Mike Kimberley, The Managing Director of Lotus Cars Ltd, signed a contract for three inter-related programs:
- A 2.5L Naturally Aspirated 16 Valve Engine (program A-516)
- A 2.2L turbocharged Intercooled 16 Valve Engine (program A-522),
- A 4 Wheel Drive System (Vehicle) for the G-24 Daytona using the 2.2L Turbo (program A-544).
In the fall of 1986, the 2.5L NA Program was cancelled due to engineering budget constraints. The unusual combination of a long stroke (104 mm) with the 16 valve head fixed the 2.5L's breathing problems, and gave a nice smooth engine that would rev easily up to about 7500 rpm. It gave about the same performance in a vehicle as a Turbo I. The last example I know of was in a P-Body with a manual trans with the emissions people out at the Chelsea PG about 15 years ago.
The 4WD G-24 program was cancelled in November 1987, again due to budget constraints, just as we were getting the car to perform and handle as well as the Audi Quattro, the target vehicle. John Miles, from Lotus, was leading the chassis development. Doug Shepherd, our esteemed rally driver and DC exec., when he drove one during some Goodyear tire evaluations at Chelsea, said "it needed much more power!"
The Turbo II program continued with the objective of putting it into the Shelby CSX, and we even got so far as to facilitize the Saltillo Engine Plant to build the engine for Shelby in about 1989. I have forgotten what
caused it to be cancelled, as about that time I handed the program over to another program manager, Greg Boznyck. But the engine did make it into production in the 1991 Spirit.
General 2.2 and 2.5 stuff
There are several different 2.2 blocks. They feature siamesed cylinder bores, a short crankcase skirt, and partialopen deck; it was designed to be machined by milling to achieve lighter weight, but uses a cast iron (rather than aluminum) block because aluminum technology at the time was not what it is now. The oil pump is mounted internally. Turbo blocks weigh about 90 lb. Pistons are aluminum with steel struts, and rings are iron. Different years and engines (e.g. turbo I, turbo II) used different pistons.
2.2 liter engines are all noninterference designs, so they generally are not damaged when the timing belt breaks. Turbo III owners generally know this from experience.
Chrysler common block
Starting in 1989, all 2.2 and 2.5 liter engines, including the Maserati-built 2.2 used in the Chrysler TC by Maserati and the longitudinal engine in the Dakota, used the same engine block. This saved money and gave base engines a stronger block; so starting in 1989 the engines had stronger main bearing supports and caps, thick cylinder walls, balance shafts (on the 2.5 and late turbo 2.2), and cross drilling between the cylinders. Without a lengthened deck, the 2.5 liter engine maintained its displacement with a shortened piston.
The new block was not as high as the 2.5. Casting details were added to increase rigidity and integrity. An acoustical oil pan was added on all passenger car versions of the 2.2 engine, cutting noise; the 2.2 pan had a deep sump for uninterrupted supplies of oil during rapid cornering, braking, and acceleration (this was originally to be used only on turbo models). Crankshafts for all four cylinder engines were designed to use the old 2.5 engine's front seal and retainer; crankshafts were still cast, except on the forged Turbo II (and, later, Turbo III and IV). All engines also now used the old 2.5's camshaft and accessory shaft drive belt and sprocket system, with rounded teeth; a new water pump was driven from the back of the alternator Poly-V belt, increasing traction.
An acoustic cylinder head was set up as a running change on throttle body models; turbocharged engines already used an aluminum cylinder head cover with better acoustic quality.
Key 2.2 - 2.5 turbocharged engine links
- Mopar 2.5 / 2.2 Turbo Engines Performance and Common Repairs
- Interview with engine designer Pete Hagenbuch , which covers the 2.2 turbos and other topics.
- Interview with engine designer Willem Weertman
- Turbo bleeds (to increase boost)
- Turbo boost spiking and boost creep
- Sensors and computer fault codes: what they all do, what they all mean
- Interview with a Garrett turbocharger engineer (at acarplace.com)
- http://www.thedodgegarage.com/turbo_intercooling.html which discusses charge air cooling.