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Chrysler PT Cruiser engine and suspension

The 2.4 liter turbo engine

2.4 liter engineA turbocharged version of the 2.4 liter engine was already used in Mexico at the time the PT Cruiser GT started development. However, the Mexican and American turbo-fours were developed independently (thanks, Paul Holmgren).

While the turbo-four engine was used in the Neon SRT4, it was, according to Chrysler engineer Garry W. McKissick, created specifically for the PT Cruiser GT. They were at first going to do a supercharged engine, but switched to the final turbocharger with a charge air cooler (usually referred to, loosely, as an intercooler). The result was a joint effort of numerous groups; and while it was mostly the same on GT and Neon SRT4, the intake manifold was different, with the PT Cruiser people having to fit the tight space, and the SRT group engineering their own intake. The development of the engine is detailed in this SAE paper.

The 2.4 turbo in the Neon SRT-4 produced 205 horsepower and 220 lb-ft of torque, but propelled it from 0-60 in 6 seconds, stock. The PT Cruiser Turbo produced 215 horsepower and 245 lb-ft of torque (until the 2006 models increased power) with the peak at a surprisingly low 3,600 (torque) and 5,600 rpm (horsepower). Details and photos.

A reduced power (180 hp) “light boost” turbocharger was also sold for those who wanted more power but not the higher cost and stiffer suspension of the GT.

PT Cruiser transmissions (details)

Suspension and handling

The PT Cruiser’s suspension mounting, body structure stiffness and suspension calibrations are tuned to minimize noise, vibration and harshness, and body lean. The MacPherson strut front suspension features a high-roll center that contributes to responsive steering while reducing body lean during brisk cornering. Low-lean geometry achieves the desired suspension handling performance. A stiff front suspension cross member attaches the front suspension to the body structure and supports the steering gear. Stiffness helps to control noise.

In the rear, coil springs support the twist beam layout. Trailing arms and a Watts linkage provide longitudinal and transverse location of the axle, respectively. The rear suspension’s transverse beam causes the tires to remain vertical relative to the road during cornering, contributing to stable handling even under loads. The rear suspension’s coil springs and jounce bumpers mount above the beam, in line with the wheel centerline, to prevent after-shake when the wheel hits a bump.

The Watts linkage is used for lateral location of the axle and includes two transverse links pivoting on the body structure at the outer end and on a third link at the inboard ends. The third link pivots at its center on the axle, moving in a vertical plane relative to the body. This system controls lateral movement of the axle. Compared to the more commonly used track bar, the Watts linkage:

Also contributing to the solid ride and handling characteristics is the rigid support of the PT Cruiser’s body structure.

Body structure bending and natural torsional frequencies or vibrations are separated from steering column, powertrain and suspension input frequencies to enhance strength and soundness. The transmission of natural noise and vibration are reduced at each one of the 47 points between the body and these systems. Tuning each local area individually to separate its natural frequency from the input largely eliminates noise and vibration paths to the passenger compartment.

The tightly sealed body shell lowers wind and road noise as well, resulting in quiet ride through all driving ranges. This is achieved through precise dimensional control of door and liftgate openings and their sealing systems and through attention to detail on sealing body seams and other openings.

Details on the 2.4 liter engine

In North America, the front-wheel drive PT Cruiser is powered by a 2.4-liter, DOHC, 16-valve engine. The engine produces 150 horsepower @ 5,500 rpm and 162 lb.-ft. torque @ 4000 rpm. It uses counter-rotating balance shafts for smoother performance.

The 2.4 entered production in December 1994 for minivans and cloud cars. It is similar to the 2.0-liter (Neon) engine in design and construction but has a longer stroke, taller block, a dual overhead camshaft cylinder head, and dual counter-rotating balance shafts that reduce engine vibration.

Displacement 148.2 in(cubed)(2429 cm (cubed))
Bore 3.44 (87.5)
Stroke 3.98 (101)
Bore-to-stroke ratio 0.87
Block length 16.43 (417.3)
Block height 9.36 (237.8)
Rod length 5.94 (151)
Connecting rod L/R 2.99
Compression ratio 9.4:1

 * All dimensions are in inches (millimeters) unless otherwise noted.

The cylinder head is a low profile aluminum casting with pent-roof combustion chambers that house four valves per cylinder. The valve included angle is 48 degrees, allowing large valves.

Dual camshafts run in six bearings with removable caps that are machines in the head base material. Powdered metal valve seat inserts and valve guides are pressed into the head. Spark plugs thread into the center of the combustion chamber through wells cast into the head.

Ports from each valve merge in the head, leading to a single branch (runner) in their respective manifolds. To provide turbulence in the cylinders that contributes to the rapid combustion necessary for low emissions and efficient operation on regular-grade gasoline, the ports cause incoming air to "tumble" from top to bottom of the cylinders. The degree of tumbling action was balance against the conflicting need for high air flow to obtain high power output.

Made of die cast aluminum, the cylinder head cover features an isolated mounting with an O-ring type, silicone perimeter gasket. The DIS coil-mount is built into the cover.

The PCV system is different on PT Cruiser engines than on minivan and cloud car engines, due to space issues.

The block and bedplate are similar to those on the 2.0-liter engine. The primary difference is that the block is 9.36 inches (237.7 mm) high to accommodate the longer stoke.

The one-piece, cast aluminum intake manifold has a runner length of 15.7 inches (400 mm). The intake manifold combines tuned individual runners for each cylinder with an integral plenum chamber.

 Made of thin-wall cast nodular iron, the exhaust manifold has a four- into-one runner design. The four-bolt outlet flange mates with a sealed flex coupling flange on the exhaust pipe.

Dual overhead camshafts actuate four valves per cylinder. Valve diameters are 1.40 inch (35.5 mm) intake and 1.20 inch (30.5 mm) exhaust. All valves have 0.24 in. (6 mm) chrome plated stems. Valves have a 48-degree included angle. The exhaust valves are on the right (rearward) side of the head. Each valve is operated by an end-pivot rocker arm that has a 20 mm roller cam follower to reduce low speed friction and cam wear. Rockers pivot on inboard-mounted, fixed hydraulic lash adjusters. Barrel-shaped single valve springs provide control of valve actuation to 7200 rpm.

Camshafts of post-hardened nodular cast iron provide a 236 degree intake duration and a 240 degree exhaust duration. The intake cam centerline is 113 degrees ATDC, the exhaust is 110 degrees BTDC, with 15 degrees of overlap. Intake valve lift is 0.33 inches (8.25 mm) and exhaust valve lift is 0.26 inches (6.5 mm).

Camshaft drive is similar to the 2.0-liter SOHC engine but the intake and exhaust cams have separate drive sprockets. A three-piece molded plastic cover, with inspection plate, completely encloses the belt to prevent damage from foreign matter.

Cast aluminum, single-size pistons have pop-up tops with valve cut outs allows broken-belt valve clearance. Piston pins are held in place by press fit to the connecting rods.

Crankshaft

Cast of nodular iron, the lightweight crankshaft has eight counterweights and a 75 percent balance ratio. Counterweights straddle each crank pin to balance the bearing loads for smooth, quiet operation. Counterweights straddling each crank pin also allow smaller, narrower bearings. Smaller diameters reduce friction and, therefore, increase fuel economy and power. main bearing diameter is 2.36 inches (60 mm), rod bearing diameter is 1.97 inches (50 mm). The crankshaft main bearing journals are 1.0 inch (25.5 mm) wide for low friction.

 A torsional vibration damper is used. The damper has two poly-V pulleys that drive accessories.

Balance shafts

The 2.4-liter engine operates very smoothly because of a system of counter-rotating balance shafts which counteract second-order unbalance, the predominant reason for four-cylinder engine vibration.

 The two counter-rotating, eccentric balance shafts, interconnected by gears, are driven by a short chain from the crankshaft. They turn at two times engine speed to offset the reciprocating mass of the pistons and connecting rods and to achieve the desired balancing effect. The balance shafts are enclosed in an aluminum housing mounted beneath the crankshaft in the oil pan. The housing is bolted to the bottom of the main bearing webs of the bedplate and rest in the oil supply. When the engine is running, the balance shafts pump oil out of the housing to minimize parasitic drag which could occur if the shafts spun in the oil.

More stuff

The camshafts need no bearing inserts. They operate directly in the cylinder head. Main and rod bearings have bi-metal inserts.

The powdered metal gerotor oil pump mounts in the front of the block and is driven by the crankshaft.

 The system that returns oil from the head is designed to prevent aeration during high-rpm running. The block is inclined to the right (rearward in the car) to allow the oil to drain from the head along the right face of the clock. The crankcase is ventilated through and opening on the left side of the head. Oil capacity is 4.5 quarts plus filer. SAE 5W-30 oil, grade SG/SH is recommended. A half-quart oil filter mounts horizontally to an extension of the oil pump body providing easy access for service.

 The oil pan is stamped of a sound-deadening metal-plastic-metal laminate material to minimize transmission of noise. A windage tray, integral with the oil-pan gasket, minimizes aeration of the oil.

To reduce complexity, the base of the water pump housing is part of the block. The body of the pump is die cast aluminum, bolted to the front of the block. The pump is driven by the timing belt. The thermostat, radiator nipple, cooling system filler neck and overflow nipple are combined in a single unit.

Fuel injection and ignition

The returnless, sequential multi-port injection (SMPI) uses four dual-spray injectors to provide balanced fuel delivery to all cylinders. Sequential injection improves throttle response and overall driveability compared to single-point injection. The returnless fuel injection system, which is similar to that on the 2.0-liter engine, is less complex than customary systems.

The 2.4-liter engine features a direct ignition system (DIS), without distributor. DIS offers important advantages over a conventional distributor systems: quicker starts, reduced complexity, more accurate firing, smoother idle, lower maintenance and higher reliability.

 The PCM determines idle speed. It actuates a stepper motor and valve in the throttle body to change idle air flow. An idle speed control sensor has been added to signal loads from the power-steering system. A switch on the power steering high pressure hose detects an increase in hydraulic pressure from steering action and increases idle speed when the steering wheel is turned.

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