Old School - Jeep Engine Swaps

Most likely, it was some GI during World War II that first started modifying Jeeps to better suit his needs. While there were many modifications made to meet certain war-time criteria, not much was done to increase power output. However, I remember reading a short story in high school about a GI who put a Mercedes engine in his unit commander's Jeep during the war. Fiction, most likely, but it could have happened. With the sales of the civilian models after the war, the emphasis by Jeep was on farm accessories, not power. Some became huntin' Jeeps and a few became play toys. But it wasn't long before the recreationalist found the lowly flathead four-cylinder to be lacking.

A young engineer by the name of Vic Hickey made some modifications to his Jeep that included a custom-built aluminum cylinder head. He went on to develop such vehicles as the Baja Boot race vehicles, as well as numerous others and a line of off-road accessories. In the early '50s, Willys developed a new cylinder head that placed the intake valves in the head, but the exhaust valves remained in the block. This F-head, along with a new camshaft, raised power from a lowly 60 horsepower to a whopping 75. OK, maybe it didn't help that much, but it did help, even though the M-38 had grown to the larger and heavier M-38A1. To fit this engine in the CJ series, Jeep had to build a new body with larger dimensions. The CJ-5 was born, basically, a civilian copy of the M-38A1. But the old-style flatfender wasn't dead quite yet. By raising the cowl and the hood some 4 inches taller and with some other minor changes, the engine fit in the CJ-3A (dubbed the CJ-3B).

My first engine swap was an F-head in my MB. This was actually a pretty common swap. Some slight firewall modifications and a Holley carb off of a Ford Falcon six allowed the hood to close. Or you cut a hole in the hood and built some type of a raised box. But if you went that route you had to forget about folding down the windshield.

Get more than three people together and they had to race their Jeeps. When I graduated to a CJ-5, more power was needed, so a whole bunch of modifications were made to that engine that I covered in the March '06 article on engine performance modifications.

Even though my friends were going with Chevy V-8 conversions, I elected to go with a Buick V-6, which at the time was questioned by most of my peers. This was later to become a very popular swap. Why that instead of a V-8? Because I wanted to race in a particular class among other reasons. So popular was this swap that from '66 to '71, Jeep made the Buick V-6 an option and put the additional two more cylinders engine, the 350 Buick V-8, in the Wagoneers and pickups.

Cool thing about the V-6 is that it's basically a shortened version of the 350 Buick, yep, a virtual bolt-in, so this became a popular swap. By '69, however, I graduated to a 350 small-block Chevy with a Rochester fuel-injection system in front of all things, the original T-90 transmission. Yes, the trans broke a lot, but that's another story.

OK, I'm getting ahead of myself, so let's back up a bit and go back to the '50s and early '60s again. There were some flathead Ford V-8s swapped into Jeeps using homemade adapters and, later, manufactured adapters. These were the days when hot-rodding was getting started and flathead Fords were ubiquitous. Ford's 272s and 292s were sometimes seen and Studebaker's sixes and V-8s were fairly common. The flathead six used in the Jeep utility wagons was also used for swapping material. However, the six's longer length put the last two cylinders into the cab and required a heavily modified firewall. The main reason for using the last three engines was that they used the same transmissions as the CJs did, so no adapter was needed.

These engines still didn't offer the performance that people wanted, so more homemade adapters began appearing. The first modern V-8 swap I ever saw was in '60 - a 318 Mopar V-8 with an automatic no less, all stuffed into a CJ-2A. I am sure there were lots of the new small-block Chevy V-8 swaps being done at the same time and this engine was soon to become the engine of choice.

Clarence Shook of Rancho Jeep (later to become Rancho Suspension), perhaps, was the first to do some major engine swaps. At first, the engine adapters were flat steel plates about 31/44--inch thick, but the rear-mounted GM small-block distributor required either a modified firewall in the CJ-5s or a very modified firewall in the CJ-2A and 3A. One could move the transmission and transfer case forward, but this put the trans and transfer case shift levers up under the dash.