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Jeeps Kick Ass Engine - The History Of The 4.0L

Assembly Line
Tori Tellem | Writer
Posted April 1, 2006
Photographers: Courtesy of Jeep

The 4.0L Is History

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).

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