Say you have a CJ with a healthy Jeep V-8 for playing in the sand dunes or doing the rocks. Can there be any improvement to such a potent combination? Yes. Such was the case with Dave Zelinka's bright-yellow '79 CJ-7. The Jeep's mildly modified AMC 304 had reliably served the CJ, but Dave was ready for something with a bit more performance. It was time to revamp the powerplant and provide the Jeep with some Bow Tie power.
After the decision was made to go with a small-block Chevy transplant, the rest was easy. The engine would be stroked and modified as needed, and a multipoint fuel-injection system would ride atop the lifter valley. Chevy V-8 engines are relatively simple to work on, reliable, and provide numerous fuel-injection options.
The goals were to install an engine setup that would provide smooth operation from idle up to about 4,500 rpm. Low-end torque for slow-speed crawling was more important than all-out high-end horsepower. The mid-band power, however, had to remain plenty strong for sustained street and dune driving. Reliability and decent fuel mileage were also important.
The engine of choice was a Chevy 383, basically a small-block 350 using a Chevy 400 crankshaft to stroke the engine, increasing the overall displacement. The 383 provides the improved torque characteristics of a Chevy 400 without the cooling problems of the larger-bore, siamesed cylinders of the 400. While this article will mention some of the parts used for the engine build, it won't show all the details involved in building such an engine. The major purpose of this story is to illustrate many of the considerations toward swapping most any small-block Chevy engine into a Jeep CJ.
The engine for this application was built upon a '78 four-bolt main 350ci block and a GM 400ci cast-iron crank with the main bearing journals turned down to match the block. Rods are stock pieces, and the pistons are Keith Black hypereutectic 9.5:1 compression units. A Summit TPI Hydraulic flat-tappet cam opens and closes the valves using 1.5:1 rocker arms, and the aluminum cylinder heads are Edelbrock Performance items. A GM L98 tuned port injection is used along with a speed density GM 7730 ECM (computer). The factory GM system offers reliability, self-diagnostic features, good parts availability, and a limp-home feature in the event of sensor failure.
The stock Chevy fuel injectors are rated at 22 lb/hr. With the increase in displacement and added flow upgrades, the stock injectors were replaced with 24lb/hr units. In addition, the factory base manifold and plenum were ported for improved intake flow. A factory harmonic balancer and automatic transmission flexplate from a 400 ci Chevy were used, and the complete assembly was externally balanced.
There are quite a few different transmissions and transfers cases that can be used behind a small-block Chevy, and there are numerous aftermarket adapters available to make the job easier. For this swap, an Advanced Adapters steel adapter ring was bolted to the back of the Chevy engine block to mate the engine to the original AMC version T400 auto transmission. The adapter ring laterally rotates the transmission mounting location 10 degrees, so the transmission mount must be shimmed on the passenger side of its mount. An adapter piece is also pressed into the end of the Chevy crankshaft. This piece receives the snout of the torque converter and is necessary because the adapter thickness moves the crankshaft away from the tranny. Steel spacers are also used between the flexplate and the torque converter.
New weld-in motor mounts using polyurethane donuts were used. For '76-'79 CJs with the Quadra-Trac transfer case, the engine and tranny are actually offset to the driver side to provide front driveshaft clearance near the Turbo 400 transmission. With the new motor mounts bolted to the block, and the engine located at its final position, the frame perches were positioned on the frame and welded into place.
Tubular steel manifolds from an '88 Corvette were used to keep the exhaust routed inside the framerails. The factory headers were Jet-Hot ceramic-coated to retain a clean appearance and prevent metal corrosion. The rest of the exhaust had to be modified and uses dual mufflers and dual catalytic converters to be emission-compliant in all 50 states.
The tuned port injection requires a GM computer (ECM) for complete engine control. The ECM was mounted as high as possible under the dash on the passenger side for protection from rain and water. The heater box was temporarily removed from the interior to provide easy installation. Additionally, a TPI-style accelerator cable was required, and the opening in the firewall had to be modified to accept the new cable. A vehicle speed sensor (VSS) was added inline to the speedometer cable where it connects to the transfer case to provide speed information to the ECM.
To supply the needed 45-psi fuel pressure for the new motor, a Holley inline electric fuel pump was mounted on the framerail next to the fuel tank and connected through a steel pre-filter. The output of the pump was connected to the fuel-injection system using the existing hard fuel line plus some stainless-braided lines and AN fittings. A fuel return line was also needed for the system. Steel-braided hose was used to connect to the existing hardline on the Jeep that had previously been used as the connection between the tank vent and the evaporative canister.
Follow the detailed photos as we show some of the pertinent changes and mods that were required for the swap from the AMC V-8 to Chevy V-8.