Jeep Liberty/Performance

Ignition systemEdit

The 3.7L engine was designed to use copper core spark plugs. NGK Vpower plugs are the best copper core plugs currently available for this engine. Precious metal or gimmick plugs will not do anything in this engine.

Performance Distributors carries their SOS ignition coils for the 3.7L. These coils release 10,000 more volts than the stock coils. This allows plug gaps of 0.065 which helps create a faster combustion.

TRQ ICA61506 coils also release 35k volts.


2005 Jeep Liberty Gasoline NGC PCM w/ integrated TCM

Computer modifications are needed to realize to full potential of any performance upgrades. The Jeep Liberty computer can be reprogrammed with a different flash image, tricked with a different intake temperature sensor, or tricked with a performance chip.

The B&G Jeep Liberty Flash (JTEC-NGC) permanently changes the timing and fuel tables, raises the rev limit and speed limit, and removes torque management. A different intake temperature sensor tricks the engine into adjusting the fuel mixture.

Jet Performance's stage 2 Jetchip can help increase power by adjusting fuel and spark tables as well as shift points, these are accomplished by tricking the computer with an altered signal. It cannot raise the redline, speed limiter, or remove torque management. This should only be installed after installation of a less restrictive intake and exhaust. The use of 91 octane fuel is required to prevent detonation.

The 3.7L gas and 2.8L diesel are very different engines with very different computer modifications. SP Diesel makes a chip for the diesel engine. The ECU on the 2.8L CRD is made by Bosch, and at this time there are two companies offering a re-flash for the CRD ECU, Green Diesel Engineering and INMOTION TUNING. Both vendors offer choices between ECO (economy) and Performance tuning programs.

HP Tuners software is now available for JTEC and NGC ECUs. This allows full control of all parameters and maximum efficiency of your setup when professionally tuned.

Mufflers and HeadersEdit

Many different companies manufacture cat-back exhaust systems for the Jeep Liberty. Borla makes a split pipe dual exhaust system. The Borla single side and Gibson Performance systems aren't preferable for off-roading because their larger mufflers hang more vulnerably below the lower control arm mounts. Rusty's Offroad offers a Flowmaster Delta Flow based system with a 2.5" clamped mandrel bent tail pipe.

A good off-road or muffler shop should be able to fabricate an off-road friendly exhaust system around a universal aftermarket muffler. Just remember, it's illegal to remove the catalytic converter. The Flowmaster 40 and 50 SUV mufflers are common choices, the latter being more quiet and durable. Flowmaster has also released a strengthened diamond plate off-road muffler. Generally, MagnaFlow mufflers offer more performance but less aggressive sound than Flowmasters. MagnaFlows are built from stainless steel while Flowmasters are built from rust susceptible aluminized steel. Aeroturbine and Gibson also manufacturer exhaust options. A 2.5" center in/side out muffler works well with the stock 2.5" mandrel bent tubing. A short restriction in the tubing, immediately upstream of the stock muffler flange, can be removed to increase flow. A new muffler can be welded in its place or, if disassembly is required, a DynoMax flange adapter. Increasing tail pipe diameter will deepen tone and most mufflers will get louder as they break-in. Exposed tail pipe tips should be avoided in off-road applications.

Contrary to popular belief, increasing backpressure will not increase low-end torque. On the other hand, decreasing pipe diameter will increase low-end torque. Decreasing pipe diameter increases velocity and thus the scavenging effect. The scavenging effect is most pronounced at lower RPMs where it affects low-end torque, but is negligible when using forced induction. The goal is to eliminate as much backpressure as possible while still maintaining sufficient velocity.

JBA manufactures stainless steel short-tube headers for the Jeep Liberty. Ceramic coated stainless steel versions, colored silver or titanium, are also available. These headers only work with 2005-2009 Libertys because other years have a different catalytic converter connection. Short-tube headers don't create as much scavenging effect because they don't pulse as well as equal length long-tube headers. On the other hand, short-tube headers pass emmisions testing, keep the catalytic converters, and are easier to install. The JBA short-tube headers include the "Firecone," which JBA claims increases scavenging. Regardless, all good aftermarket headers remove restrictions and increase efficiency.

Filters and IntakesEdit

2005 Jeep Liberty Gasoline Air Intake

There are a number of different drop-in air filters and replacement intakes available for the Jeep Liberty. The most popular aftermarket filters are made by K&N, who makes both drop-ins and a FIPK replacement intake. AEM Induction Systems and aFe also make a replacement intakes and filters. The CRD's turbo charger makes performance intakes and filters less advantageous for it than its gas counterpart. There is currently no FIPK available for the CRD. Another alternative is to install a snorkel, which by raising the air intake to roof height will keep dust out and allow for river crossings at the same time . At this time there are snorkels being manufactured for the Liberty. Aftermarket hood vents can help decrease underhood temperatures and making any of the intake systems more effective, especially at slow speeds while offroading.


Kenne Bell discontinued its supercharger for the Jeep Liberty's 3.7L engine. The relatively high piston rings in the 3.7L caused piston land weakness and failure, a problem correctable with forged pistons. A 4.7L supercharger can be installed onto the 3.7L, without issue, if a new tube and upgraded pistons are installed.

Throttle BodiesEdit

Stock (left) vs The Fastman (right) Throttle Body

The Fastman ported throttle body allows better flow than the stock PowerTech throttle body.

Airaid throttle body spacers can help increase throttle response be moving the throttle body further from the manifold. They will not add any noticible power increase on their own though.

Transmissions and Torque ConvertersEdit

The TransGo Shift Kit causes the Jeep Liberty's automatic transmission to shift more quickly. The same 45RFE PSK kit works with both 45RFE and 545RFE. The kit corrects the soft 1-2 and heavy throttle long 2-3 shifts and provides a firmer 4th and lockup.

The APS High Stall Torque Converter is an efficient torque converter that allows more power to be transferred from the engine to the transmission. It features additional stall, firmer lockup, increased torque multiplication, and 6% more efficiency than stock. It's only available for the 45RFE and not the more common 42RLE.

Suncoast Converters also has a 1200 RPM stall heavy-duty torque converter for the 2.8L CRD. This converter improves fuel economy and power delivery.

Sonnax produces many performance parts for the rfe transmission family. The most affordable being a line pressure booster module that plugs into the existing wiring.

The 2002-2004 545rfe TCM can be swapped into 45rfe equipped KJs of the same year. This provides a 5th gear overdrive that reduces the rpm by 200 after reaching 50mph.

To remove torque managments effects unscrew and remove the wiring harness from the TCM, then take the plastic cover off. Snip the #10 wire (it is yellow with a green tracer, make sure you are snipping the proper wire as some people have accidentally snipped the #17 wire (yellow w/ dark blue tracer). If you snip the #17 wire than the trans will shift way to hard. Reinstall the connector onto the TCM, reinstall the screw, then reinstall the plastic cover.

See AlsoEdit

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