• JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler

Jeeps Kick Ass Engine - The History Of The 4.0L

Posted in How To: Engine on April 1, 2006 Comment (0)
Share this
Jeeps Kick Ass Engine - The History Of The 4.0L
Photographers: Courtesy of Jeep

There are very few things Jeep enthusiasts can agree upon. Very few. But one thing is for sure -- the 4.0L, six-cylinder engine was a flat-out kick-ass engine. When the all-new '07 Wrangler debuts later this year, it will be minus that beloved ingredient and replaced by a 3.8L V-6, a minivan engine (for more details on the next-gen Wrangler, check out Dispatch on page 16 ).

To pay the engine its proper respects, Jeep let us dig through its archives, chat up its engineers, and send a lot of hate mail (signed with Pete's name, of course) regarding the end of an era. The finale comes mostly out of a need to produce a cleaner, more-efficient engine (send your hate mail to tree-huggers), but there's no denying the inline-six has led a charmed life. Some of you will be able to relate to its early days, like Hesco's Bennie Fulps, who says while in high school he ran around in a Rambler with the 199ci. Others will have experience with no other engine except the current 4.0L because it has a reputation of cracking 200,000 miles without as much as a hiccup. So flip on Green Day's "Time of Your Life" (isn't that the token farewell song?) and take a crawl down a rock-strewn memory lane as we look at the inline-six's beginnings, changes, and what went wrong.

1964The Rambler Classic "Typhoon" in yellow (with a black top) is the first AMC with the 232ci engine. It makes 145hp and 215lb-ft of torque with the one-barrel, and 155hp and 222lb-ft of torque for the two-barrel. Bore-and-stroke is 3.75x3.50-inch. The '64.5 Rambler American in red (with black top) gets a 199ci version with a shorter stroke (3.00 inch) that makes 128hp and 180lb-ft of torque.

The 199ci and 232ci combustion chamber switches from "quench" to "open" on account of emissions issues.Late '60s International Harvester starts buying up 232ci engines. Also during these years, Barney Navarro puts a destroked, turbocharged 199ci engine in his IndyCar. It supposedly makes more than 750hp. Overpowering the chassis, it crashes ... a lot.

This year brings a raised block height, and the 199/232 gets bumped to 232/258 (the latter making 150hp, 220lb-ft of torque). The 258-stroke becomes longer (3.90 inch); there's now a small port head with a higher flow than the large port head. The 258ci (4.2L) has a 12-counterweight crankshaft. Rocker arms are switched to an individual stud-mounted design rather than shaft-mounted. Additionally, Tocco-hardening starts for six-cylinder exhaust seats to make the engine compatible with unleaded fuel.1972

The 1972 model year brings molestation of the rear face of the block to "commonize" it with AMC V-8s. Early '70s The rotating parts are individually balanced and engine assembly balancing is discontinued.Also in the '70s Vehiculos Automores Mexico builds 252ci and 282ci versions of the 232ci and 258ci for cars in Mexico. The blocks have special castings with larger bores (31516-inch compared to 3 34-inch). They end up in racing engines (Don Adams' desert Jeep in 1985 and stadium Comanches in the late '80s and early '90s).

The Carter BBD two-barrel carb is optional on the 258ci. It's also the return of the "quench" chamber.

The 232ci ends production in the 1978 calendar year.

This model year brings with it a lighter-weight version of the 4.2L, with a plastic rocker cover, four-counterweight 258 crankshaft, 716-inch head bolts, thinner castings, and an aluminum intake manifold, oil pump, and water pump.

A prototype 4.0L makes an appearance in Don Adams' Class 3 SCORE HDRA desert Jeep (and is the only non-V-8 to win a Class 3 race). The happiness flows freely -- until Renault kills the racing budget. Hesco builds the race engines (for everyone sponsored by Jeep). At this time, fuel injection isn't allowed in desert racing.

Cherokee engineers don't want the GM V-6 anymore, they want an inline-six. Ta-da, a 242ci 4.0L six-cylinder arrives in the Cherokee and Comanche. The 177hp and 224lb-ft of torque inline-six has a multiport fuel injection and a high-flow cylinder head, plus a larger bore and shorter stroke than the 4.2L (3.88x3.19 inch). The 3.88-inch bore design borrowed from the 2.5L means the 4.0L can share rods and pistons; a new lighter weight crankshaft is added. Enthusiasts complain about the Renix fuel injection and the lack of low-end torque compared to the 232ci and 258ci. While people are whining, a 4.0L Comanche sets a speed record at Bonneville (stock pickup truck class).

This model year reveals a better-flowing Power-Tech Six High Output version of the 4.0L. Changes are made to the cylinder-head design, the camshaft profile, and the block castings. The YJ makes 180hp and 220lb-ft of torque while the Cherokee's mill has 190hp and 232lb-ft of torque (variation in numbers is due to differences in design of the exhaust and air cleaner).

The 4.0L gets some upgrades, including lighter pistons, new cylinder-head casting (to improve the exhaust flow), a new two-piece thin-wall cast exhaust manifold (that replaced the one-piece, tubular style), and steel valve covers (again).

The block is tweaked so that the oil-filter mounting can be relocated, meaning the Grand Cherokee no longer needs an adapter.

This is the last model year for improvements to the 4.0L, which include new direct-mount accessory drive bosses, a thrust washer added to the camshaft, a new chain oiling system, and larger-diameter casting between lobes (to stiffen the camshaft in "bending" mode). Also, ribs are added to the rocker pedestals and holes are tapped for the new coil rail system in the cylinder head.

The 4.0L ends production. The TJ is the last application.

* '87 Cherokees and Comanches were the first to get the 4.0L.
* '91 YJ was next.
* '93 is when the Grand Cherokee got it.
* '97 was the first for the TJ.

*AMC Advanced Engineering out of Detroit came up with the AMC/Jeep six-cylinder's design concept, but it was AMC Kenosha Engineering that handled final design and development.
*The Nash 196ci flathead engine was the inline-six in the AMC family prior to the 232ci. It continued to be in the Rambler American until 1965 because it was shorter and had A/C. The 199ci was too long to mount the A/C drive -- that is, until the 1966 model year, when the Rambler American gained 3.8 inches under the hood to accommodate the 199ci.
*The 232ci featured seven main bearings (solid as a rock, compared to the OHV 196's four) and hydraulic tappets, was sub-assembly balanced (crank, vibration damper, and flexplate/flywheel), and had shaft-mounted rocker arms.
*The 232ci engine was painted red, the 199ci in blue. In 1983, all engines became black (long live the French).
*Think the 4.0L was based off the 4.2L? Wrong. Its design actually stemmed from the 2.5L four-cylinder introduced in 1984, the first four-cylinder built and designed by AMC/Jeep (GM was responsible for the 2.8L V-6). Sure, it had the same valvetrain as the 258 (minus cylinders two and five), but it was then modified for performance (the design team took advantage of the new block, head, and crank).
*Speaking of making the switch from 2.8L V-6 to 4.0L six-cylinder, no one wanted to change the Cherokee's looks, so they had to make the new engine shorter. They eliminated the normal fan mounted to the water pump, which allowed the water pump to be shortened. A single electric fan was attached to the radiator along with a smaller mechanical fan for a total of two cooling fans.
*When the 4.0L Cherokee was being finalized, management had planned for the volume split to be 60 percent 2.5L and 40 percent 4.0L, but after dealers got behind the wheel of the peppy Cherokee it was switched to 20 percent and 80 percent, respectively.

Flip through the pages of Jp and you'll find plenty of companies offering upgrades for the inline-six. Just because they are not mentioned here doesn't mean they aren't worth checking out. We've simply included some of the most-talked-about upgrades over the years.
* 258ci cranks from the 1972 to 1980 model years are often considered the best to use in 4.0L stroker motors because they are stronger and smoother.
* The 4.2L launched with a reputation of being torquey and for also having a weak cylinder head that didn't flow with an unlikable carburetor. Extensive porting has been a solution for some, but a more common modification is to convert the 4.0L cylinder head onto the 4.2L block. Hesco has used the 4.0L cylinder head and Mopar fuel injection (which it invented) combo to get 200 horses. Another way to get more power is to run a Hesco aluminum head, which can help the engine crank out up to 300hp. Additionally, Clifford's Performance makes a carbureted intake manifold. A popular fix for the leaky, stock carb has been to switch to a two-barrel Holley or Weber.
* Chad Golen of Golen Engine Service says the 4.0L's computer is pretty flexible. You can add a larger camshaft and modify the cylinder heads without having to do much to the base computer. Also, Golen makes a 4.6L stroker long-block from the 4.0L (covered in Jp's August '05 story "The Insane Inline, Part 1").

Related Articles

Comments

Connect With Us

Newsletter Sign Up

Subscribe to the Magazine

Sponsored Content