Upgrading A Street/Strip ’66 Nova With A Moser 12-Bolt

Back before Covid was all anyone could talk about, we had the opportunity to follow along as Top-Fuel drag racer, Larry Dixon, updated his ’66 Nova to be a true street and strip terror. The project started with the plan of installing a modern LT4 engine and a 4L75 automatic transmission. You can read all about the upgrades he incorporated by clicking here. The car was a raging success.

Like any true hot rodder, after the new LT4 was installed and race-ready, Larry understood the next issue he would need to overcome would be the somewhat-less-than-adequate 10-bolt rear under the Nova. Sure, the 8.5-inch rearend is a decent unit. That is until you start throwing serious horsepower at it. The modern, supercharged LT4 is definitely throwing more power to the 10-bolt than it can handle. For that reason, he immediately started planning an upgrade to a stronger rearend.

Moser 12-bolt

When you order a Muscle Pak rear, you get everything you need to stab it in place and drive. Since Larry added Wilwood brakes to his Muscle Pak, he decided to upgrade the fronts as well.

Well, the pandemic hit, and the car got put on the back burner for a while. That is until May 2021. That’s when planning for another iteration of the car was put into motion. His latest upgrade is by way of a new Chevrolet Performance Connect & Cruise LT5 engine. If you are interested in reading about the new mill, click here. The original rear was out of its depth with the LT4, and with the LT5 on the horizon, he was wise to contact the folks at Moser Engineering for a serious upgrade. Not only is Moser a trusted name in drag racing, but the rearend company is also located only a short drive from Larry’s shop.

Thought Process

Choosing a rearend to handle serious abuse is a decision many enthusiasts need to make. For Chevrolet fans, the 12-bolt is usually the rearend of choice. However, the 9-inch is a very stout unit as well. I know what you’re thinking, “a Ford rear does not belong in a Chevy.” To that I say, If Moser builds a completely new housing and fills it with aftermarket parts, is it really a Ford rear? I think not. However, to keep it civil, a 12-bolt was chosen for this upgrade.

Each Muscle Pak rear is assembled by one individual to ensure a quality product is delivered to the end-user.

Although the debate between using a GM 12-bolt versus a 9-inch can get heated, it’s impossible to argue the merits of both and not realize both are good options. GM fans can rejoice, however, as the 12-bolt is actually a more efficient rearend than the Ford. This is because of the 12-bolt design’s placement of the pinion gear relative to the ring gear centerline. The 12-bolt has a 1-1/2-inch distance while the 9-inch has a 2-1/4-inch distance. This delivers a three-percent horsepower advantage to the 12-bolt. The 9-inch is also nearly 30 pounds heavier than the 12-bolt.

Pakin’ Muscle

Once Larry had finally decided which rear he wanted, it was time to reach out to order his new Moser 12-bolt. Enter the Muscle Pak rearend. According to Moser, the all-new 12-bolt housings are designed and manufactured in the USA.

“Our Moser 12-bolt housings are completely new and manufactured from Moser-owned casting boxes,” says Jeff Anderson, Moser’s Marketing Director. “Moser only uses American-made steel, forged in U.S. plants, using Moser-designed dies and tooling. You feel the sense of devotion to the U.S. and patriotic pride when you talk to the people at Moser.”

Moser 12-bolt

Jeff Anderson at Moser recommended the use of a Wavetrac differential. The Wavetrac carries a lifetime warranty, even when used in racing.

Moser Engineering’s Muscle Pak gives the end-user OEM-located mounting provisions, axle tubes made from seamless steel tubing (3-inch O.D., 1/4-inch-thick wall), custom alloy 30- to 35- spline bolt-in axles, bearings, studs, seals, heavy-duty retainer plates, new housing ends, choice of differential, choice of U-joint size pinion yoke, gears, chrome rear cover, Timken bearings, brakes, and, emergency brake cables. Each custom order is fully assembled and there are a myriad of available options.

Make no mistake, this is a street car. However, Larry is hoping for his Nova to be a nine-second strip terror as well. For that reason, he did order a few options/upgrades for his Muscle Pak. While the factory drum brakes would technically work, adding a set of rear discs was something Larry planned to do in the future anyway, so why not order them now. Disc-brake options come in the form of economy units, vented-disc  Wilwood binders, or Moser-spec drag-race parts. If you wish to stick with drum brakes, that is also an option. You can even opt out of ordering brakes entirely. Since this will be a very quick street car, Wilwood units got the nod, because, well, stopping is a good thing.

Internally Tough

Inside the Moser 12-bolt, we find a pair of 35-spline axles, a Wavetrac differential, and 3.55 gears. With the build plan including a Chevrolet Performance Connect & Cruise supercharged LT5 and eight-speed automatic transmission, this should be one heck of a ride. “I chose the 3:55 gear ratio vs 3:73,” says Larry. “As I kept fine-tuning the previous LT4, I was trying to calm down my setup on the starting line. I chose the 3.55s just trying to take the edge off of the hookup.”

To say the Moser 12-bolt Muscle Pak is complete is an understatement. The delivered rearend even comes with the parts needed to connect the emergency brake.

One of the more confusing choices one will encounter when contemplating a rearend upgrade is differential selection. Nobody is content with a one-wheel-wonder when building a rear. A “posi” is the one requirement that every enthusiast expects with the upgrade. But there is more to it than just iterating the word. While the enthusiast-accepted general term, posi, refers to a clutch-biasing differential, various differentials get locked into the nomenclature.

Clutch Or No Clutch

A traditional clutch-type limited-slip (posi) was offered as original equipment in many GM performance cars. These units rely on clutches to transfer power to the wheels. During normal operation, the clutches slip just enough to allow for smooth cornering and then engage with more force as torque is applied. This torque loading drives both wheels equally. When used in a daily driver or hot rod, these units function well. However, these do rely on internal clutches, and as the miles add up or with aggressive driving or track use, the clutches and other internal components will become worn and severely degrade performance. Luckily, rebuild kits are widely available so that these units can be restored to like-new performance.

As you can imagine, Larry has a busy schedule, so he needed a little help. "I had Charlie Patterson of Patterson Driveshafts swap out the U-joint and Michael Lang of Fluid Transfer Products build brake lines for me."

However, instead of a clutch-type posi, Jeff recommended that Larry use the Wavetrac. The Wavetrac uses helical gears that exert friction on the differential container, which then distributes torque between the driven wheels. Because they require a lot of friction to function, owners should not add any friction modifiers. Because of its design, the Wavetrac can actually deliver power to the only tire with traction — even if the other wheel is completely off the ground — making it a great choice for those participating in autocross or road course racing.

Larry did tell us he is using a block on each spring perch to lower ride height. The look is spot on.

When Jeff Anderson of Moser spec’d the rear, he suggested the use of the Wavetrac, and we wondered why. “We used the Wavetrac simply because it offers a lifetime warranty, even if used in a motorsport environment. As long as you put the correct gear lube in it, they will honor the warranty. That’s hard to come by in today’s marketplace.”

Installing Durability

Although Larry’s Nova came with a non-performance-rated 10-bolt rear, Moser’s ordering process of the Muscle Pak allows any enthusiast to order the rear in the configuration needed. To that end, the Moser Muscle Pak dropped right into place after the 10-bolt was yanked out of the way.

“The Muscle Pak still continues to be a huge market mover for us because it is a bolt-in replacement for most applications,” says Anderson. “With today’s busy schedules, it can help the enthusiast get back on the road quickly. No digging for information on what brakes you need to go with certain applications, worrying about gearing and installing parts correctly along with painting or powder coating the rear so it looks good. We can save you time, and deliver it quickly, often leaving our facility within three to five business days from the time of order! It is honestly as close to plug-and-play as you can get with aftermarket rearend components.”

With the new Muscle Pak 12-bolt in place, Larry no longer needs to be concerned with rapid expulsion of the rearend’s inner parts,

With the new Moser 12-bolt rearend in place, we’re hopeful, Larry can get the new engine and transmission combo installed very soon so we can see if he is able to hit his nine-second quarter-mile goal. We think it’s doable, but the proof will be in the pudding as they say. Stay tuned as we bring you more updates as they happen.

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Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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