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

Back before Covid was everyone’s talk, we had the opportunity to follow suit as Top-Fuel drag racer Larry Dixon updated his ’66 Nova into true street and strip terror. The project began with plans to install a modern LT4 engine and a 4L75 automatic transmission. You can read all about the upgrades he’s bundled in by clicking here. The car was a huge success.

Like any true hot rodder, once the new LT4 was installed and ready to race, Larry understood the next issue he needed to address was the insufficient 10 bolt rear under the Nova. Sure, the 8.5-inch rear is a decent unit. That is until you start throwing some serious horsepower at it. The modern, supercharged LT4 definitely puts more power into the 10-bolt than it can handle. For that reason, he immediately began planning an upgrade to a more powerful rear.

When you order the back of the Muscle Pak, you get everything you need to stick it in place and drive. Since Larry added Wilwood brakes to his Muscle Pak, he’s decided to upgrade the front as well.

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

Thinking Process

Choosing a rear camera to deal with serious abuse is a decision many fans have had to make. For Chevrolet fans, bolt 12 is usually the rear choice. However, the 9-inch is a very sturdy unit too. I know what you’re thinking, “the back of a Ford doesn’t belong in a Chevy.” To that I say, If Moser builds a completely new housing and fills it with aftermarket parts, is it really behind Ford? I do not think so. However, to keep it civil, a 12-bolt was chosen for this upgrade.

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

While the debate between using a 12-bolt versus 9-inch GM can get heated, it’s impossible to argue over the merits of the two and not realize that both are good choices. However, GM fans can rejoice, because the 12-bolt is actually a more efficient rear end than the Ford. This is due to the 12-bolt design placement of the pinion gear relative to the ring gear centerline. 12-inch bolts are 1-1/2 inches apart while 9-inch bolts are 2-1/4 inches apart. This gives a three percent horsepower advantage to the 12.9-inch bolt and is also nearly 30 pounds heavier than the 12-bolt.

Pakin muscles

After Larry finally decided which rear he wanted, it was time to order his new 12-bolt Moser bolt. Enter the back of Mr. Muscle. According to Moser, the all-new 12-bolt housing is designed and manufactured in the US.

“Our 12-bolt Moser housing is brand new and manufactured from Moser’s proprietary casting box,” said Jeff Anderson, Moser’s Director of Marketing. “Moser uses only American-made steel, forged in US factories, using Moser-designed dies and tools. You feel a sense of devotion to the United States and patriotic pride when you talk to the people at Moser.”

Moser 12-bolt

Jeff Anderson at Moser recommends using the Wavetrac differential. Wavetrac carries a lifetime warranty, even when used in racing.

Muscle Pak from Moser Engineering provides end-user OEM-located installation requirements, axle tubes made of seamless steel tubing (3 inch OD, 1/4 inch thick walls), special alloy bolt shaft 30 to 35 splines, bearings, studs, seals , heavy duty retaining plates, new housing ends, differential options, U-link size pinion yoke options, gears, chrome rear cover, Timken bearings, brakes and, emergency brake cables. Every custom order is fully assembled and there are a myriad of options available.

Make no mistake, this is a street car. However, Larry expects his Nova to be a nine-second strip terror as well. For that reason, he ordered several options/upgrades for his Muscle Mr. While factory drum brakes would technically work, adding a rear disc set is something Larry plans in the future, so why not order one now. Disc brake options come in the form of economy units, ventilated disc Wilwood straps, or Moser-spec drag-race parts. If you want to stick with drum brakes, that’s also an option. You can even choose not to order the brakes completely. Since it’s going to be an insanely fast street car, the Wilwood unit gets the nod, because, well, stopping is a good thing.

Tough internally

Inside the 12-bolt Moser, we find a pair of 35-spline axles, a Wavetrac differential and 3.55 gears. With build plans including a supercharged Chevrolet Performance Connect & Cruise LT5 and an eight-speed automatic transmission, it’s been an extraordinary ride. “I chose a 3:55 vs 3:73 gear ratio,” says Larry. “As I continued to perfect the previous LT4, I tried to calm my setup at the starting line. I picked 3.55 just trying to take advantage of the hookup.”

To say that Moser’s 12-bolt muscle pack is complete is an understatement. The shipped rear even comes with the necessary spare parts for connecting the emergency brakes.

One of the more confusing options one will encounter when thinking about rear upgrades is the differential selection. No one settles for the magic of one wheel when building the rear. A “pos” is the only requirement that every fan with an upgrade hopes for. But there’s more to it than just repeating words. While the enthusiastically accepted general term, pos, refers to coupling bias differentials, various differentials are locked into the nomenclature.

Clutch Or Without Clutch

A traditional clutch type limited slip (posi) is offered as original equipment on many GM performance cars. These units rely on a clutch to transfer power to the wheels. During normal operation, the clutch slips just enough to allow for a smooth bend and then works with more force when torque is applied. The loading of this torque drives the two wheels in a balanced way. When used in daily drivers or hot rods, this unit performs well. However, this does rely on the internal clutch, and as distance increases or with aggressive driving or track use, the clutch and other internal components will wear out and seriously degrade performance. Fortunately, rebuild kits are widely available so that these units can be returned to their like-new performance.

As you can imagine, Larry has a busy schedule, so he needs a little help. “I asked Charlie Patterson of Patterson Driveshafts to swap the U-joints and Michael Lang of Fluid Transfer Products had brake lines for me.”

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

Larry did tell us that he uses the blocks on each spring perch to lower ride height. The display is just right.

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

Installing Durability

Although the Larry’s Nova came with a non-performance-rated 10-bolt rear, the Mr. Moser Muscle ordering process allowed any enthusiast to order the rear in the required configuration. To that end, Mr Muscle Moser fell right into place after the 10-bolt was pulled out of the way.

“Pak Muscle still continues to be a big market mover for us as it is a bolt-in replacement for most applications,” says Anderson. “With today’s hectic schedule, it can help enthusiasts get back on the road quickly. There’s no need to dig up information about what brakes you need for a particular application, worry about gears and getting parts right along with painting or powder coating the back to make it look good. We can save you time, and ship them quickly, often leaving our facility within three to five business days of ordering! It’s honestly as close as plug-and-play you can get with aftermarket rear parts.”

With the new 12-bolt Muscle Pak in place, Larry no longer has to worry about quick ejection of the rear inside,

With Moser’s new 12-bolt refit, we’re hoping Larry will be able to install a new engine and transmission combo soon so we can see if he can hit his nine-second quarter-mile target. We thought it could be done, but the proof would be in the pudding as they say. Stay tuned as we bring you more updates as they happen.

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