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Jeep Wrangler Standard Equipment
 
  • 4 Cylinder Engine Information
  • 6 Cylinder Engine Information
  • AX-5 Transmission Information
  • Ax-15 Transmission Information
  • NP231 Transfercase Information
 

4 Cylinder Engine Info-

150ci (2.5L) I4
Bore
3.88"
Stroke 3.19"
Displacement
150ci (2.5L)
Compression Ratio
9.1:1
Horsepower (net)
123@5250
Torque (net)
139@3250
Main Bearings
5
Valve Configuration
OHV
Fuel
MPI
   

The 150(2.5L) I4 engine was used in mid 80s CJ-5s and CJ-7s, YJs, XJs, MJs, and TJs.

The 2.5L inline 4 (I4) engine used in Jeeps today was first introduced in '84 when Jeep was owned by AMC. Originally, the engine used a carburetor, later versions used throttle body fuel injection, and the current version uses multi-port fuel injection. The fuel induction has been the major change with this engine over the years. The 2.5L uses over head valves with hydraulic lifters and a cast iron block and cylinder head.

The current version of the 2.5L I4 engine uses multi-port fuel injection. This engine is the standard engine used in the Wrangler (TJ) and Cherokee (XJ). It was the standard engine in the Wrangler (YJ) since 1991. The XJ version of the 2.5L has a slightly higher output.


6 Cylinder Engine Info

4.0L I6
Bore
3.88"
Stroke 3.41"
Displacement
242 (4.0L)
Compression Ratio
8.8:1
Horsepower (net)
180@4750
Torque (net)
220@4000
Main Bearings
7
Valve Configuration
OHV
Fuel
MPI

 

The 242(4.0L) I6 engine is used in late 80s XJs and MJs and in 90s YJs, ZJs, and TJs.

The 4.0L inline 6 (I6) engine was introduced in the Cherokee in the late 80s and in the YJ in 1991. The cylinder design is based on the changes made to the fuel injected 2.5L I4 engine. The block and cylinder head are cast iron. It uses 7 main bearings and hydraulic lifters. The HP and torque gains are substantial over the older carbureted 258, but the peaks come at higher RPM. The fuel injected engine performs much better in off-camber, bouncy, and steep situations. It also calibrates better for changes in altitude. Fuel economy is also improved. If you have ever been in a carbureted vehicle on a steep incline then you know just how important fuel injection is.

A good way to embarass yourself in front of your Jeeping friends is to refer to it as a V6. It isn't a V6, it is an inline 6 or I6. The "V" in V6 refers to the configuration of the pistons in the block. The only two V6 engines ever available from the factory in a Jeep are the 225 "Dauntless" Buick V6 in the late 60s and early 70s and the 2.8L GM V6 in 80s Cherokees and Comanches. If you are shopping for a Cherokee or Comanche, make sure you get the 4.0L and not the 2.8L engine, there is a world of difference.


AX5 Transmission Info-

AX5 Tranny Gears
1st
3.93
2nd 2.33
3rd
1.44
4ty 1.00
5th .79
Rev.
4.74
   

The AX5 is a light duty five speed transmission. It looks similar to the AX-15, but smaller. It is manufactured by Aisin in Japan. The input shaft is 1" 14 spline and the output shaft can be 21 spline or 23 spline. The AX5 has only been used in 4 cylinder Wranglers (YJs and TJs).


AX-15 Transmission Info-

AX5 Tranny Gears
1st
3.83
2nd 2.33
3rd
1.44
4ty 1.00
5th .79
Rev.
4.22
   

The medium-duty AX15 is a surprisingly strong five-speed overdrive gear box. It was introduced in Jeeps in 1989. It is used in XJ Cherokees and MJ Trucks with the six-cylinder. Its only year in the ZJ Grand Cherokee was 1993, and only with the six-cylinder. It was also the transmission of choice in the 1989-present YJ and TJ Wranglers. The AX15 is also found in Dakota trucks.

The AX15 is closely related to the Toyota R154 as found in the Supra Turbo and Four Runner, though the case rear halves and gear ratios vary.

The AX15 is compatible with the New Process style transfer cases with a 23 spline input. It is also adaptable to the popular Model 300 transfer case. It is strong enough to be adapted to most V8 engines.

Identification
The aluminum-cased AX15 has a length of 16.5". The case is generously ribbed and features the shifter in the rear quarter of the assembly. In the vein of newer transmissions, the AX15 uses dowel pins for bellhousing alignment. The AX15 was used with an internal slave/throwout assembly up through the 1994 model year. In 1995, a more conventional slave cylinder and cross-arm were used. Input shaft is a 10 spline and its stickout length is 7-1/2".


NP231 Transfercase Info-
AX5 Tranny Gears
Low Range
2.72
High Range 1.00
*Tera Low*
4.00
   
The NP 231J was introduced at the 1988 model year in both the XJ Cherokees with the Command Trac option and the standard YJ Wranglers. Later to be called the NV (New Venture) 231J, this transfer case has continued in the trend of chain-driven cases. Its low gear is a respectable 2.72-to-1 (the lowest of all the Jeep transfer cases) and is direct-drive in high. It has a driver's side front output.

This transfer case is identified by its red and silver tag on the rear of the case. There are also very similar versions of the 231 for the downsized Chevy Blazers and Dodge Dakota trucks. Heavier-duty HD and DHD units are available in ZJ Jeeps and Dodge trucks, respectively. OEM 231 transfer cases are capable of transferring from 1600 to 1900 ft. lbs of torque.

The NP231 transfer case has turned out to surprise us in its strength, gearing, upgradeability and servicability. Most of our customers choose to retain the 231 with their conversions, though they do often opt to strengthen the case by switching to a 23 spline input (if currently 21 splines - common with the four-cylinder engine/transmission combos) and doing a heavy-duty tail shaft conversion. Wide chains are also available if even more strength is desired. With such upgrades, a transfer case capable of handling 2300+ ft. lbs. of torque is attainable. This is a result of good engineering and refinement. As such, we and the majority of our customers keep their 231's when performing a conversion.

One easily conquered drawback of the 231 is its length. With the introduction of the planetary reduction assembly and long tail sections, the 231 can be a mild hindrance when performing some swaps with long engines and/or transmissions. This problem is exacerbated by suspension lifts and resulting u-joint angularity. It is recommended that a heavy-duty short tail shaft conversion be performed to reduce the length of this unit. Another thing to be aware of is the tendency of the slip-type yoke to pull and separate from the transfer case during extra articulation of the rear axle. Unless you own a TJ model 231, you will lose the ATF lubricant from the case if this occurs.

Input Gears and Compatibility
The important variations to look for in this transfer case when planning a conversion lie in the input gear. It comes in 21 spline and 23 spline versions with long, medium (rare) and short variations.

The long shafts protrude 2.1" from the front mounting face of the transfer case. The short version protrudes 1.2". The rare medium shafts protrude 1.7". You should be careful when swapping any of these gears due to different bearing widths and gear teeth. The following chart shows how to determine which input gear you should have by transmission. It is always good to verify first hand if possible.

Because of differences in the cut of the gear, as a general rule; one should not interchange pre-'95 gears with post-'94 gears. These years are not hard and fast delineations. If one is not absolutely certain, disassembly and inspection is required.

21 Spline 
23 Spline
Short Input
Aisin-Warner 4
AX4
AX5
Earlier (pre-'95) AX15
Medium Input
Jeep ZJ's '93 to '95 only
Long Input
Peugeot BA 10/5
Later (post-'94) AX15
TF904 TF999
Peugeot BA 10/5

 

Dana 30 & Dana 35

 

 

The dana 30 is standard in the front of the YJs and TJs. The Dana 30 in a YJ is a High-Pinion while in a TJ it is a low Pinion. The Dana 35s are both C-Clip. Some TJ's have a Dana 44 in the rear from the factory.