The AMC 258 was introduced in 1971 in J-series pickups and Wagoneers and in 1972 in CJs. It continued to be used through 1990 in the Wrangler. It is basically a stroked 232 engine. The great thing about this engine is it reliable, inexpensive, and has horse power and toque peaks at low RPM.

The 258 inline 6 (I6) engine always came from the factory carbureted any many people complain about the Carter BBD carburetor and the maze of emmissions vacuum hoses. There are a couple articles below that can help you sort through those hoses and tune the Carter BBD. For a carbureted engine, the 258 with the Carter BBD performs very well off road. The 258 always came with a cast iron block and cylinder head, hydraulic lifters (with non-adjustable rockers), and 7 main bearings.

The 258 used in '87-'90 Wrangler YJs uses a computer controlled Carter BBD. It is very simlar to the 258 used in '82-'86 CJs, but performance suffers due to emmission controls.

 

AMC 258 I6
Bore x Stroke	3.75" x 3.90"
Displacement	258 (4.2L)
Compression Ratio	9.2:1
Horsepower (net)	112@3200
Torque (net)	210@2000
Main Bearings	7
Valve Configuration	OHV
Fuel	2bbl Carter BBD

The 258 used in '82-'86 CJs used a computer controled Carter BBD. The computer controls mixture based on an O2 sensor and other sensors.

 

AMC 258 I6
Bore x Stroke	3.75" x 3.90"
Displacement	258 (4.2L)
Compression Ratio	9.2:1
Horsepower (net)	115@3200
Torque (net)	210@1800
Main Bearings	7
Valve Configuration	OHV
Fuel	2bbl Carter BBD

The 258 used in '79-'81 CJs, some used a 1bbl carb and some used a 2bbl carb.

 

AMC 258 I6
Bore x Stroke	3.75" x 3.90"
Displacement	258 (4.2L)
Compression Ratio	8.3:1
Horsepower (net)	110@3500
Torque (net)	195@2000
Main Bearings	7
Valve Configuration	OHV
Fuel	1bbl and 2bbl

The 258 used in '72-'78 CJs, J-series pickups, and Wagoneers, some used a 1bbl carb and lower compression than later 258s.

 

AMC 258 I6
Bore x Stroke	3.75" x 3.90"
Displacement	258 (4.2L)
Compression Ratio	8.0:1
Horsepower (net)	110@3500
Torque (net)	195@2000
Main Bearings	7
Valve Configuration	OHV
Fuel	1bbl

The 258 was introduced in 1971 as the standard engine in J-series pickups and Wagoneers.

 

AMC 258 I6
Bore x Stroke	3.75" x 3.90"
Displacement	258 (4.2L)
Compression Ratio	8.5:1
Horsepower (gross)	150@3800
Torque (gross)	240@1800
Main Bearings	7
Valve Configuration	OHV
Fuel	1bbl Carter or Holley

Other Information

	258 Primer : Are you lost in a maze of vacuum hoses? Are having problems passing your state smog check? This article covers everything you need to know to fix and understand your 258.
	Learning to Love Your 258: An easy fix for the most common idle problems with the 258(4.2L) engine used in Wranglers(YJ) and CJs.
	Computer By-Pass: John Nutter's alternative ignition modification for the 4.2L engine.
	Mopar Ignition Upgrade: Ignition upgrade for a more powerful 4.2L Jeep Engine.

Contributors

Some photos courtesy Rick Boiros.

Last modified Monday, 08-Nov-1999 19:11:38 PST