The venerable Jeep Six: a...
The venerable Jeep Six: a thing of beauty is a joy forever.
Make Mine Inline
Why an inline? For starters, they're inherently smoother runners than V-motors due to their design. Granted, improvements in balance-shaft technology over the years have made the V-motors run much more smoothly than they used to, but the I-6 is still inherently smoother-running in design and, for all intents and purposes, does not require balancing as you're using only a one-piece casting with a single cylinder bank. And yes, this means you can build out a straight-six without much excessive vibration. Also, one-piece inline engines have been less costly for the OEs to produce in large numbers, which means no shortage of older I-6s in junkyards. Looking for a venerable 232/258 Jeep motor from the '70s to scavenge parts from? Not a problem. Want a lightweight Buick V-8 of the same vintage? Happy hunting.
The big reason why you want an I-6, though, is low-end power, aka, torque. Inline engines, by their longish design, pose a fitment problem in a lot of newer vehicles (though they run just fine mounted transversely), so the traditional solution has been to keep their lengths as short as possible via long strokes and tall block heights. This undersquare design results in increased crank throw and piston speed that inhibits the engine's ability to turn high revs but maximizes its ability to produce peak power at lower rpm levels. And that in turn translates into an engine that'll make its maximum power at the kinds of slow speeds we like to run on rocky, rutted trails.
Finally, think about all the most legendary 4x4s of yore-the CJs and Scouts and early Broncos, the FJ-40s and Series 1 Landys. What did they all have in common? They all came standard with inline engines, most of 'em for many years. Jeep offered inline engines in every bobtail they ever built for nearly 60 years! So, for smoothness, availability, torque-per-liter, and simplicity of design (and in most cases, mileage, too), an inline-six has a V-block beat hands-down every time. If they're good enough for Unimogs, bygawd, they're good enough for us Real Wheelers.
The V-8 engine is superior...
The V-8 engine is superior to the six-cylinder engine in so many ways. When was the last time you heard someone say "I should've skipped the V-8 and got the 6-cylinder?"
Gee, I Could Have Had A V-8
We hear it all the time. Wheelers verbally wishing they could have a V-8 between the framerails of their Wrangler instead of the 4.0L I-6. Sure, the I-6 is a legendary engine that produces a fair amount of power and decent torque, and it's adequate for a stock Wrangler. But when you start bolting in the heavy mandatory trail must-haves, it becomes crystal clear that the I-6 isn't so adequate anymore.
Can you build up an I-6? Sure, and it can be made to be a real screamer. But here's the thing: You can pour stacks of money and untold hours into the I-6, but at the end of the day all you have is an engine that merely matches the baseline performance of a modern fuel-injected small-block V-8. The reality is that for most wheeling disciplines, the V-8 is the perfect engine. Think only the I-6 can make decent torque? Whether a small-block or big-block, a V-8 can offer equal servings of horsepower and torque when built correctly. You'll end up with ample horsepower for those high-speed mud pits and fire-road romps and deep torque for those rocky hillclimbs. The V-8 may not make the torque at low rpm like the I-6, but gearing can solve that in short order. And the aftermarket support for the V-8 is extensive.
Realistically, the V-8 vs. I-6 debate can be expanded to include the V-6 that is found in the new Wrangler JK. Many of the same folks who lamented the I-6's power shortfalls have shifted their attention to the V-6, and they're one of the catalysts for the booming Hemi V-8 conversion business. It didn't take long for companies like Burnsville Off Road to see that vast numbers of wheelers wanted more power. Now Burnsville has a stand-alone Hemi-to-JK conversion shop. Clearly, the people have spoken.
If you're like most wheelers, you have to drive your rig every day and naturally you need to get the most miles per gallon. Some will argue that the six-bangers get far better mileage. Not so fast there, Skippy. Once again, when folks see the small real-world mpg difference between the six-cylinder and the small-block V-8 they end up wishing they had the eight-banger. The reality is that the V-8 is a versatile performer that can do everything the six-cylinder can, only better.
-Ken Brubaker