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Old School - Jeep Engine Swaps

Posted in How To: Engine on May 1, 2006 Comment (0)
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This Jeep, powered by a 406 Ford, was a strong contender in the sand hillclimbs at Glamis Sand Dunes, California, in 1964. Note the bobbed front fenders back then.

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.

How about this 426 Chrysler with a dual four-barrel crossram manifold stuffed in a CJ-5 in 1963 at Pismo Beach, California?

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.

Fuel-injected Chevy V-8s were popular back in 1963, as they are today.

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.

The overhead cam Tornado six in Brian Chuchua's drag racing CJ-6. Yep, those are three Webbers on the intake.

Harry Buschert, who had a farm machine shop in Hemet, California, may have been the innovator of using the longer six-cylinder Jeep pickup input shaft in the CJ's transmission. His adapter, made up of two thick steel plates sandwiching a welded-in spacer, was my choice in '64. That same year at the Pismo Dunes, I remember seeing a 426 Chrysler engine along with its long ram intake for the twin four-barrel carbs in a CJ-5. I have no idea what he was using for a transmission; guess I was too wowed by the engine.

Soon to follow making adapters was Hoosier Machine in the Pacific Northwest. Other guys like Johnny Dias built some for friends and "Mr. Jeep," Brian Chuchua, by '63 was offering adapters for just about any engine, as well as performing engine swaps in his Fullerton, California, location. Jim Hicks of Hicks Muffler shop (later to be Hicks Jeep Shop) and Harvey's Jeep Shop were also pioneers on engine swaps. Soon, two major businesses were built for supplying adapters. Lloyd Novak's Novak Adapters started up in the early '70s and chose to stay with only adapting Jeep components and so still does the business acquired from him. John Partridge at Advance Adapters (originally named Advance Tooling and Engineering in '69) followed suit with their own versions, as well as adapters and such for other vehicles.

With a small-block Chevy, especially in a flatfender, distributor clearance is always an issue. This is a really crude example of how one person achieved this.

Motor mounts were pretty much a homemade choice. However, Chuchua was supplying motor mounts along with Con-Ferr and companies such as Western Truck Sales in Phoenix, Arizona. Chevrolet cars and trucks weren't using the side-block mounts of today, but the mounts came off the front of the engine. Patterns floated around throughout the various Jeep clubs of a yoke to be torch cut from a steel plate that bolted behind the crank pulley and extended to each side of the frame. The ends of the yoke were then mounted to the four-cylinder Jeep motor mounts now bolted to the top of the frame.

Chevys became the engine of choice, most likely, due to their availability as well as adaptability. The rear-mounted distributor was, however, no end of trouble and the firewall had to be modified. On a CJ-5 this could be accomplished with a big hammer, but on the flatfenders it usually meant a cut into the firewall. Now the distributor set back in under the cowl, and it was difficult to remove the cap and impossible to remove the distributor itself with the engine in place.

The 1949-53 Ford flathead V-8s were once popular engines due to their availability and compact size. Note that this one sports an alternator conversion. The smallish air filter leaves a lot to be desired in filtration ability. In case you're wondering, the large can on the right rear of the engine is an oil filter.

The 215 aluminum-block Buick and Oldsmobile engines were popular, as well as the Buick V-6, especially in the flatfender Jeeps because their compact size, front-mounted distributor, and light weight made for easy fitment. Other than replacing the L-head four with an F-head four in my military MB, the V-6 Buick swap was the first engine swap I did in a Jeep back in '64. There were also a few of the old Y-block Fords used and even some of the big-block FE series of engines. When Ford came out with its lightweight 221/260-cubic inch V-8s in '62, these also became a big hit once they were available in salvage yards. These engines weigh in at 475 pounds, not all that much heavier than the four-cylinder that they replaced and some 55 to 60 pounds lighter than the Chevy V-8. Oil filter clearance was a problem on the Fords and, at first, some sort of a remote filter was used. Later, it was found that the four-cylinder Ford tractor filter was a lot smaller and a direct fit.

The 153-cubic inch Chevy II four-cylinder became popular because it was considerably lighter than the F-head Jeep engine, and being four inches shorter it fit nicely in a flatfender. Also, lots of the Chevy V-8 parts were interchangeable with it.

A Ford Falcon six at 170 cubic inches made a pretty easy swap but, naturally, you had about a 3-inch firewall recess to make. The factory Ford clutch disk has the proper spline, but you had to make up a bushing for the throwout bearing. The upper bolts of the bellhousing matched up, and there was enough room to drill new lower holes.

The two-liter Pinto engine made for a good swap. Note all the clearance available and the fact that the hood will close. Capable of sustaining high rpm, it could spin 5.38 gears at freeway speeds without a problem.

The ubiquitousT-90 transmission was really the weak link in the power chain, and those that were after a bit more power without sacrificing dependability picked the 2,000cc Pinto four-cylinder engine. Rated at 100 horsepower and 120lb-ft of torque, the motor was happy to rev to 6,000 rpm and didn't mind the high rpm highway speeds that the 5.38 gears produced.

Cooling was always an issue because you couldn't buy ready-built aluminum radiators from your mail-order suppliers. The stock radiators, being overbuilt from the factory, were marginal but sufficient to cool the smaller cubic-inch swaps but not up to the task of a 283 Chevy. For WWII in the Burma theater, some military trucks had some heavy-duty, four-core radiators. With some slight modifications they worked great in Jeeps. These were in high demand, but still you were working with a radiator that was now 20 years old and never meant for a V-8. Lots of time was spent in wrecking yards with a tape measure trying to determine what radiator would fit with the minimum amount of modifications. One usually ended up cutting part of the headlight cans to gain more radiator width which was done when using a Ford Galaxy radiator.

Another trick was to cut out the front crossmember and weld in an inverted "U" channel that set lower between the framerails and allowed a taller radiator to be used by putting the bottom of the radiator into the channel. I even knew a guy that mounted one radiator in the normal location and then a second one in the bed of his Jeep trying to keep his high-horsepower Chevy cool. Heavy-duty truck fans that pulled a lot of air (and were also quite noisy) had their blades trimmed for clearance, not always producing a good balance.

These engine swaps added weight to the front of the Jeeps, so the solution wasn't a custom-built set of leaf springs but to just add more spring leaves. Front driveshaft clearance was often a problem as it is now, and it wasn't uncommon to severely limit right-side front suspension travel to prevent the shaft from hitting the bellhousing or starter. Some of the adapters cocked the engine so that the right side was slightly higher for additional clearance in this area. We would also move the engine over so it was offset to the passenger side for clearance around the steering box. This made for some unusual driveshaft angles. Not only did you have a shaft that was on an up and down angle, but now not in line with the rear end. You could move the steering box to the outside of the frame, but that also meant moving the pedal assembly over.

Routing the exhaust was pretty simple on a Chevy swap with the ram-horn style cast iron exhaust manifolds, even though there was a pretty tight bend for the header pipe to clear the frame. On some engines, like the Buicks, you could obtain a right-side manifold and put it on the left side. Other swaps required custom-built headers. It seemed that the only place for mufflers was under the body just outside of the frame. Not the most practical as they got pretty bashed up here. Plus, they were right next to your ear. If you could get a muffler shop to spend some time and work with you, it was possible to snake a set of glass packs inside the framerails and out the rear.

As I mentioned earlier, the T-90 transmission did a great job for what Jeep intended. But as great as it was, it was not up to 350-cubic inch motors. The later T-86, T-14s, and T-15s weren't much better, so transmission swaps came into play. Naturally, we will go into that in a future issue.

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