Intake

	Intakes/Throttle Bodies
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How you can make your 4.0 breathe in more easily.

The stock airbox and air filter (flows 370cfm @ 1.5inHg) are very restrictive. Replacing the stock air filter element alone with a K&N 33-2018 replacement (flows 455cfm @ 1.5inHg) will produce a gain of 3hp. Enlarging the front airbox opening and removing the trumpet-shaped restrictor from the airbox lid improves throttle response and adds a further 2hp. Insulating the airbox and tubing significantly lowers air intake temperatures compared with the stock set-up for further horsepower/torque increases. The next page shows how I modified my air intake in this fashion. Alternatively, there are aftermarket airtubes with open element K&N air filters available for the XJ 4.0 engine. Gains range from 5-8hp on a stock engine.

The stock 4.0 HO throttle body has a bore of 60mm that tapers down to 56mm below the throttle butterfly. Removing this taper to make the whole TB 60mm increases flow to ~505cfm @ 1.5inHg. The Turbo City is a stock TB that's been modified in this fashion. The XJ-Armor TB is bored out to 62mm and flows ~545cfm @ 1.5inHg for a 3hp increase on a stock 4.0 engine.
'87-'90 Renix 4.0 owners need not feel left out. The stock Renix throttle body has a bore of 51mm (2.0") and flows ~335cfm @ 1.5inHg. XJ-Armor can bore it out to 58mm. This increases flow by almost 40% to ~465cfm @ 1.5inHg resulting in an 8hp gain. Alternatively, you can remove the Renix TB and replace it with a TB (with taper removed) from the HO engine. Joe Attardo's HO TB to Renix intake manifold conversion article explains how it can be done.

The newer '99+ intake manifold is a superior design to the existing log-type manifold. The runners curve into a common plenum and the total manifold volume is much greater (4300ml vs 2600ml). Ram charge wave tuning is stronger resulting in more mid-range torque (6lbft) and top-end power (3hp). Gojeep wrote an excellent article about converting from a '91-'98 style manifold to a '99+ version.

Rusty's airtube and filter (left)
Rusty's Air Tube is one of the best things you can add to your vehicle. The air tube can be installed in about 10 minutes and will deliver 5 to 10 horsepower and will greatly improve fuel economy. Rusty's Air Tube is as simple as it gets but does the same job as the other guys that are priced 5 times as much. Rusty's offers two K&N filters to fit the Rusty's Air Tube which must be ordered separately. The 4.5" x 5" standard filters are plenty of filter for the 2.5 and the 4.0 liter engine. The 6" x 9" is recommended for the V8 engines and can be used on the 2.5 and 4.0 engines for a mean and muscle car look.

Airaid Intake (right)

AIRAID Intake System; QuickFit System Type; w/o Intake Tube; Installs In 30 Minutes;

Fits:

JEEP CHEROKEE (XJ) 1991-2001 L6 4.0L

Volant Performance Intake (left)

Jeep Cherokee

Product #: 27740

Engine: 4.0

Year: 91-01

K&N FIPK (right)

This Generation II Fuel Injection Performance Kit (FIPK) is now available for Jeep Cherokee 4.0 XJ's. Part # is 57-1519 for '91-'95 models, and 57-1518 for '96-'01 models. The filter flows 607cfm @ 1.5inHg and the FIPK produces a claimed 8hp gain.
A kit is also available for 1997-2001 Jeep Wrangler 4.0 TJ's. The part # is 57-1514-1.

Turbo City throttle body (left)

Turbo City Rock-It 60mm Throttle Body
4.0 L. Engine
Increases Air Flow!
Better Throttle Response!
Modified factory casting.
Direct fit, Easy Bolt-on Power.
Dyno-proven 3hp increase on stock 4.0 ZJ.

Fastman throttle body (right)

Bored to 62mm 2.440 bore
Custom Stainless Shaft
Feathered Edge Brass Blade

XJ-Armor bored HO throttle body (left)

These units are precision bored to 62mm. We also have available a restriction removal from the stock 56mm or so, to a full 60mm, the size of the original throttle plate.
Our TBs all come with brand new hardware and are available in powdercoat or glass-blasted finishes.

XJ-Armor bored Renix throttle body (right)

'87-'90 Bored Out Throttle bodies are enlarged from the factory 51mm to a much more pleasing 58mm.
Horsepower increase is easily noticeable, as well as an increase in mileage if the power is used in moderation. Throttle response is much crisper.
All throttle bodies are Glass bead blasted and precision bored. Custom made throttle plates are found in each of our throttle bodies.

Rubicon Express throttle body (left)

The new 62mm throttle body is an all new construction from 6061-T6 aluminum billet. Features include improved bearing and blade design, largest possible bore size, red anodized finish and easy installation. Installation can be done in less than thirty minutes. CARB EO# for no smog hassles. A high flow air filter is recommended for maximum benefit.
#RE1062

F&B Flometrics billet throttle body (right)

1x66/68J
Applications: 1991-2003 Jeep 4.0L straight 6 and stroked motors (4.2L - 5.0L)

F&B Jeep throttle bodies are available in 66mm and 68mm bore diameters (stock is 60mm necked to 56mm). Some intake manifold porting should be done to enlarge the manifold opening. These throttle bodies have a 3" inlet and are compatible with stock air intake systems (not recommended because of flow restriction) and most aftermarket air intake systems.