Drivetrain Swap Guide

131 9809 Drivetrain Swap Guide Jeep Cj6 And Chevy Small Block Engine Swap

You'd think small-block Chevys came in Jeeps from the factory, but people swap with way more than just Jeeps and Chevys these days. Hardcore 'wheelers are concocting all-new ways to come up with the ultimate purpose-built rigs-there are more tasty parts, more custom-building talent, and more gnarly need than ever.

This issue's special drivetrain section proves it with tons of overkill: You'll see the latest gear splitters, crawler boxes, max-beef drivetrain parts, and even old Mopar musclecar axles for Toyotas. It's all boffo trick, opening up tons of powertrain possibilities. Multiply the number of today's available axles times the number of transfer cases, crawler boxes, trannies, adapters, and engines, and you can see that potential drivetrain combos are in the thousands. Get creative, and even a small-block Jeep swap becomes a one-off custom job.

And this story will give you the drivetrain-placement considerations required when dropping any drivetrain into any 4x4. The example? A small-block Jeep built by Joel Snyder and Joe Schaff at Stage West. It's a standard swap made complicated by a Scrambler/CJ-6 long wheelbase, a short pre-'72 front clip, an NV4500 trans, and a 4-to-1 Crawler box. By installing all these components at once, Stage West shows that you can gain the best performance by considering the engine/trans/'case combo as a whole. Sure, most swaps involve changing just one member of the drivetrain combo, like a new tranny onto an existing engine. Even so, look at the big picture-if the new trans is longer than the old one, do you move the transfer case rearward or bump the engine forward? Any swap is an opportunity to place the components to your advantage. Once we give you an overview of the parts Stage West used, we'll outline your drivetrain-placement concerns in five categories.

Front-axle clearance

Fore And Aft
Driveshaft length: On short-wheelbase vehicles, the problem is getting the transfer case far enough forward that the rear driveshaft is not too short. Generally, fullsize trucks with short trannies or tall lifts have the opposite problem: The front driveshaft is too short. In either case, you may be able to move the engine/trans/transfer case fore or aft to cure driveshaft-length problems.

Front-axle clearance: Unless you have a very tall lift, very stiff suspension, or IFS, it's likely that the front axlehousing will move upward far enough to hit the oil pan or possibly the vibration damper and pulley. Careful analysis of suspension action versus clearance to the engine is crucial; if the engine can't move rearward, can you move the axle forward?

radiator-to-fan clearance

Radiator-to-fan clearance: You want at least 1 inch from the fan blades to the radiator to prevent contact during frame flex. In our case, a short-style water pump helped gain about 1 inch of clearance versus the '69-and-later long style, as did trimming the stock radiator support from the military M38 A1 grille, cutting out the back of the headlight buckets, and spacing the lights forward so the radiator could be moved forward. If all else fails, electric fans can be the savior.

Distributor-to-firewall clearance

Distributor-to-firewall clearance: As you move the engine aft, a rear-mounted distributor is always the first obstacle. Firewall bashing is an option, but for Chevys, MSD's PN 8570 small-diameter distributor can help. It's 7/8 inch shorter and 3/8 inch smaller in diameter than conventional non-HEI distributors. Keep in mind that frame flex can push the firewall into the cap and crack it, so at least 1/2 inch clearance is best.

Shifter location: If the engine is far rearward and the tranny is long, or if you have an Advance Adapters Ranger Overdrive between the engine and trans, the shifter can get pushed too far rearward. Bending the stick is an easy answer, but even the base of the shifter may get close to the seat or console. With an automatic, an aftermarket cable shifter is the solution.

Clutch linkage: Some swappers wish to use the stock mechanical clutch linkage and position the engine so it will line up. We'd say that's a bad compromise considering the other issues with engine placement. If the mechanical linkage won't line up, use a hydraulic clutch-it's better for twisty trails, anyway.

Weight bias: This is rarely considered, but it can help in hillclimbs to put weight on the front end by moving the engine forward, especially with a light V-6. Conversely, mud trucks often want more rearward weight, and place the drivetrain farther back to load the rear wheels.

The Combo:

Engine: The small-block for this swap is a GM Performance Parts 300hp 350 crate engine, PN 12355345; it's available from any GM Performance Parts dealer, usually for less than $2,000. It comes as a long-block with the tin installed, and once you add the appropriate balancer, flywheel, intake, carb, and ignition (all available through the GM Performance Parts catalog), it makes 300 hp at 5,000 rpm and 369 lb-ft at 3,500 rpm. We've found this engine capable of reasonable low-rpm rock-chugging as well as top-end power for sand blasting.
Engine: The small-block for this swap is a GM Performance Parts 300hp 350 crate engine, PN
The 300hp 350 is an externally balanced engine, requiring a GM 6 3/4-inch (PN 6272221) or 8-inch (PN 1255197) balancer as well as a counterbalanced flywheel. Stage West used a 10 1/2-inch Centerforce clutch and a 153-tooth flywheel designed for the one-piece rear-main-seal engine.
The 300hp 350 is an externally balanced engine, requiring a GM 6 3/4-inch (PN 6272221) or
Transmission: The trans is the popular NV4500 manual five-speed Overdrive available through JB Conversions. Knowing the trans would be installed with a Dana 300 transfer case, John White at JB supplied a GM-style trans case with a Dodge tailshaft housing and output shaft that mates to the Dana 300 (or 300-type crawler box) without an adapter. The pre-'96 GM case also bolts to the bellhousing without an adapter, unlike the Dodge and post-'96 GM cases. Eliminating adapters makes the overall drivetrain shorter, and that's always a good thing. Additionally, the trans features the hard-to-find 6.34:1 First gear ratio; the more common 5.61:1 ratio trannies are usually about $500 cheaper.
Transmission: The trans is the popular NV4500 manual five-speed Overdrive available throug

Transfer case: The Dana 300 'case we used was a prized '80-early '81 model that has a shorter output than the later models by about an inch. Not much, but an inch can make the difference when trying to get driveshaft angles correct. According to JB Conversions, the early output shaft is also slightly stronger since the grooves for the speedo gear are not cut into the shaft but are sleeved onto it.
Transfer case: The Dana 300 'case we used was a prized '80-early '81 model that has a shor
Also lengthening the drivetrain is a 4-to-1 Crawler (arrow), an add-on gear-reduction unit that fits between the tranny and the transfer case without the need for adapters. It uses NP241-style planetary gears, and thanks to aftermarket gear availability you can choose a ratio of 2.72:1 (which is what we used), 3.50:1, or 4.0:1. With the NV4500 and 5.89 axles, the crawl ratio is 265:1. Overall length of the crawler box is 7 1/4 inches, negating its use with even a CJ-7 (94-inch wheelbase) unless you get really creative with a short trans and a V-6 moved far forward. The crawler-box shifter is cable-actuated so its linkage is no problem; however, the crawler moves the transfer case rearward, so fabricating longer linkage is required.
Also lengthening the drivetrain is a 4-to-1 Crawler (arrow), an add-on gear-reduction unit
A conventional small-block Chevy bellhousing cannot be used to bolt the NV4500 to the engine, so Stage West used one from Advance Adapters with the clutch fork on the driver side. Another option is the genuine GM bellhousing as used on '93-and-newer trucks with the MT8 trans and a gas engine. However, this GM bellhousing uses an integral clutch slave cylinder on the passenger side. It's ideal for vehicles with driver-side transfer case output, but lousy for passenger-side output since the driveshaft will hit the slave cylinder.
A conventional small-block Chevy bellhousing cannot be used to bolt the NV4500 to the engi