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1970 Chevelle SS LS6 & Drivetrain - Modern Muscle, Part 2

Part 2: Making the "new" LS6 Fit

Barry Kluczyk Sep 1, 2003
Sucp_0309_01_z 1970_chevelle_ss_ls6_drivetrain Engine_removal 2/19

Clean, good-running 402 and Turbo 400 transmission were yanked in preparation for the LS6 swap.

In our last issue, we introduced the '70 LS6 Chevelle SS built by GM's Performance Division. What makes this particular LS6 Chevelle so interesting is that the engine is a new LS6 (PN 12562190)-the very powerplant that moves the Corvette Z06 with such gusto.

The folks at the Performance Division started with a genuine Chevelle SS 396. Besides dropping in the modern engine, GM's new 4L65E transmission (PN 24221888) was bolted in, too. With a higher torque capacity than the 4L60E transmissions found in countless Z28s, the 4L65E promises to hold up to the 405 horses and 400 ft-lbs of torque of the LS6.

For 2003, GM offers two crate versions of the LS6: one is the complete engine (minus electronics) listed above, while the other (PN 12498399) is a long-block assembly, but it comes with a Camaro-style oil pan. (The Corvette pan has "wings," making it harder to swap into most vehicles.)

The 4L65E was originally developed for use with the V-8-powered cars of GM's Holden subsidiary in Australia, but it's now available in the USA as an over-the-counter part available through GM dealerships' parts department.

Sucp_0309_02_z 1970_chevelle_ss_ls6_drivetrain Test_fit 3/19

Test-fitting the LS6 engine included the use of plywood to mock the position of the motor mounts.

The remainder of the powertrain includes a custom aluminum driveshaft (shortened to fit the new transmission) and the Chevelle's stock (but refurbished) 12-bolt Posi-equipped rear axle. It's fitted with a '70-correct 3.31-ratio ring and pinion.

As for the rest of the car, it was in pretty good shape when purchased by GM, but required a thorough going-through to restore a like-new appearance. There are some neat details inside the car, too, including an Abbott Enterprises Cable X converter, which allows the use of the stock speedometer with the new, electronic transmission. The news trans was also complemented with a console shifter "PRNDL" cover from Year One that has a readout indicating the overdrive position of the transmission.

We covered the cosmetic restoration of the Rally Red Chevelle, including bodywork, chassis detailing and interior work, in the last issue of SUPER CHEVY. With this issue, we delve into the LS6/4L65E combo's installation.

Although the Chevelle's basic restoration was mostly cosmetic, it was a completely different story when it came to swapping the old iron big-block and Hydramatic for the aluminum LS6 and electronically controlled 4L65E.

"We started with the stock locating point of the engine and transmission," says Keith Benson, project manager. "From there, we mocked up where the engine and transmission would mount."

Sucp_0309_04_z 1970_chevelle_ss_ls6_drivetrain Installation 4/19

Installation of the engine was made infinitely easier with the removal of the Chevelle's front "dog house." (Full-frame cars are a breeze to work on this way.)

Besides providing a logical starting point for the powertrain's placement, maintaining the original engine/transmission mating point allowed the shift linkage to be bolted up, albeit with a few necessary modifications. But knowing what other parts would be necessary for the swap wasn't so apparent. For that information, the technicians performing the swap consulting an excellent guidebook produced by General Motors: "LS1 Engine Kit Installation Guide" (GM PN 88959384).

"The book is a must for anybody who wants to build a car like this," says Mark McPhail, GM's powertrain manager for special vehicles. "The book lists all the available parts and part numbers, and recommends what should be used when swapping in an LS1-based engine."

We were impressed by the thoroughness of the book, which includes side-by-side comparisons of Corvette, Camaro and GM Truck LS1 varieties, including oil pans and front accessories. There are even recommendations for cooling fans. We suggest buying the book before you buy an engine, or start hacking up your car's chassis.

Close Quarters
Even with the LS1 installation guide, snugging the LS6 into place took some planning and ingenuity. Here's what Benson and his crew did to make it fit:

Sucp_0309_08_z 1970_chevelle_ss_ls6_drivetrain Electric_fan 8/19

As is specified in GM's "LS1 Engine Kit Installation Guide" (GM PN 88959384), an electric fan setup from a GM U-van (Venture, Montana, etc.) was mounted to a stock-type radiator.

* The engine is an '03 LS6, but the oil pan is from a Camaro. Over-the-counter LS1 engine kits come with Camaro-style pans, although Corvette and truck pans are available, too. (A truck pan was tested for this swap first, but was determined to be too deep.)
* The cast-aluminum Camaro oil pan was trimmed in the front to clear the Chevelle's crossmember. (Any competent welding shop can perform this modification on similar projects, says Benson.)
* Windage tray was modified slightly to work with the modified oil pan.
* Scratch-built engine mounts.
* Corvette accessories were replaced with '02 Camaro accessories.
* JBA Camaro headers flow into '00 Camaro catalytic converters.
* Standard Chevelle radiator fitted with GM U-van (Venture/Montana, etc.) electric fans and controller.
* Custom motor mounts and frame notched slightly on driver and passenger sides for clearance.
* Custom air intake utilizes '96 Impala SS air box.

Sucp_0309_09_z 1970_chevelle_ss_ls6_drivetrain Alternator 9/19

Despite the A-body's abundant underhood room, there were still some tight fits during the engine swap. Here, the LS6's low-mounted alternator is precariously close to the later-model, tighter-ratio Monte Carlo SS steering box that was used instead of the stock unit. It was an equally close fit between the driver side valve cover and the brake booster. The car is not equipped with air conditioning.

The Chevelle's firewall was left untouched during the swap, although the proximity of the driver side valve cover to the brake booster is very close. "This car doesn't have air conditioning and that made the job infinitely easier," says Benson. "I think an A/C system would have caused us fits in the long run."

Minding the LS6's operation is an off-the-shelf GM computer that is part of a GM swap kit for '99-and-later engines. The controller uses an S-truck mounting bracket, mounted to the driver side inner fender. A base Corvette calibration keeps the engine turning.

Benson points to a few other neat details that give this post-modern musclecar additional underhood character: "To mimic the fuel line routing of the original big-block, we flipped the LS6's fuel rail 180 degrees, so the fuel line flows down the passenger side of the engine," he says. "Also, we used 1970-style hose clamps for the radiator and heater hoses."

Because the LS6 uses a returnless fuel system, a return line from the engine to the fuel tank was unnecessary. However, fuel requirements mandated the use of a high-pressure, in-tank fuel pump. Rather than modify the stock tank, a new tank was crafted with all the necessary inner baffles by Rock Valley Antiques of Stillman Valley, Illinois. As it is painted Restoration Black, like the rest of the chassis, the tank is a hidden deviation from the car's stock appearance.

Sucp_0309_10_z 1970_chevelle_ss_ls6_drivetrain Transmission 10/19

Here, the 4L65E transmission is bolted up. Installing it without resorting to cutting the trans tunnel required the use of 1/4-inch shims placed in the body-mount locations. Raising the car this way avoided the need to bang on the tunnel to fit the transmission. Note, too, the Camaro catalytic converters... This Rally Red Chevelle has a "green" streak.

Along with the tank and high-pressure pump, the fuel system required the use of a C5 Corvette's integral fuel filter/pressure regulator. Although it looks like a standard fuel filter, the device also incorporates the fuel system's pressure regulator, maintaining 58 psi. The filter/regulator has a return line to the tank, but only one high-pressure line to the engine. It's a must for this swap.

Shim Sham
The most challenging part of the swap, according to Benson, was the installation of the 4L65E transmission. Although not much bigger than the Turbo 400, the 4L65E is bulkier in exactly the wrong places to fit the A-body trans tunnel. The solution was a series of 1/4-inch shim, or, as Benson calls them, "pucks." The shims were added to the body mount locations and provided the necessary clearance for the new transmission.

"Without the pucks, we would have needed to hack the trans tunnel," says Benson. "Lifting the body a 1/4-inch is imperceptible to the eye, but it saved all kinds of time and trouble when it came to fitting the transmission."

Also, the tail length of the 4L65E is longer than the Turbo 400's, which required a shorter driveshaft. A 3-inch-diameter aluminum shaft was custom-made for the Chevelle by Sterling Performance Products, of Roseville, Michigan, and was capped with heavy-duty 1350 U-joints. The stock 12-bolt Posi and its 3.31 gears are still in place, although like the rest of the chassis components, the entire rear axle assembly was reconditioned.

Sucp_0309_14_z 1970_chevelle_ss_ls6_drivetrain Airbox 14/19

The air box is from a '96 Impala SS. The placement of the airbox behind the driver side headlamps (seen here) proved to be an airflow restriction (see sidebar story).

Locating the Chevelle's axle is a catalog's worth of Hotchkis A-body suspension goodies. Control arms, springs, sway name it. All-new urethane bushings were used throughout, too, including the front suspension. And, like the rear axle, Chevy threw whatever Hotchkis parts would stick to the Chevelle's front suspension. "It's great stuff," says Mark McPhail. "The Hotchkis parts make the car drive like it weighs 500 pounds less than it really does."

Interestingly, the Chevelle rides on 16-inch wheels originally found on an S-10 with the ZQ8 suspension package. These great looking five-spoke aluminum wheels have been released by GM as an over-the-counter package (PN 12498299), which includes four rims, the center caps, etc. "The offset of the wheels looks right in the fenders of GM rear-drive cars of the '70s and '80s," says McPhail. "The ZQ8 wheels look modern and fit right; I think it's a great option for anyone with a GM car looking for new wheels."

Sucp_0309_15_z 1970_chevelle_ss_ls6_drivetrain Rear_axle 15/19

The 12-bolt Posi rear axle was rebuilt, painted and re-installed with the stock 3.31 gears. Check out the custom driveshaft and Flowmaster exhaust system, too.

With its modern powertrain and tightened suspension, this "new" LS6 Chevelle performs on the street with daily-driver ease. And though it's an easy cruiser, don't think this Chevelle's performance is tepid. There is, after all, a Z06 engine under the cowl induction hood. (After our photos were completed, the Chevelle was returned to the garage to make the cowl induction system functional for the engine.)

The LS6 gives the Chevelle a 400-horse punch (see sidebar story) and with the aluminum engine's considerable weight advantage over an iron big-block, the power-to-weight ratio is remarkably favorable. "We did this project to prove that, with a little ingenuity, any enthusiast can perform a similar swap into his own early GM car," says McPhail. "Almost everything you need to do it can be ordered from a GM dealer's parts department."

That doesn't make the job necessarily easy, but it takes much of the trial and error out of the equation. And with the results we've seen in this Chevelle, it seems very much like a worthwhile project.

Sucp_0309_16_z 1970_chevelle_ss_ls6_drivetrain Fuel_tank 16/19

A custom, baffled fuel tank was created by Rock Valley Antiques for the Chevelle, because of the high-pressure requirements of LS6's fuel system. The LS6 has a returnless fuel system, which means there's no return line from the engine to the tank, but the fuel system needs the C5 Vette's integrated, inline fuel filter/pressure regulator. It feeds the engine with a single high-pressure line, but has its own return line to the tank. Fuel pressure for the LS6 is 58 psi.

Not surprisingly, after GM's "new" LS6 Chevelle was completed, GM's Mark McPhail wanted to see "what she would do." After finishing up our last photos of the car's assembly, we called Greg Banish at Detroit Speedworks. His Warren, Michigan, dyno and tuning shop happened to be only a couple of miles from the facility where the Chevelle was built. Banish juggled his schedule to make some room on his Mustang chassis dyno for the Chevelle.

With the car strapped down, Banish started turning the Mustang's big rollers with the LS6-powered A-body. The first couple of pulls were OK-consistently putting down more than 300 horses to the rear tires. But the pulls revealed the engine seemed to lack for air at higher rpm.

We all stared under the hood of the Chevelle with a collective, unspoken, "Hmm..." McPhail started fiddling with the air box, which was from a '96 Impala SS. It was located in the corner of the engine compartment behind the driver side headlamps. "This might not be the best spot for the air box," he pondered.

He was right. After inverting it so that the air filter was exposed, Banish got back behind the wheel and made another pull on the dyno. The Chevelle instantly picked up nearly 10 hp and the engine's improved breathing was confirmed by the dyno's computer printout.

When the session was over, the Chevelle put down 319.5 horses to the rear wheels, or 400 horses at the flywheel-just about even with Chevy's 405-horse rating for the LS6 engine.

Better still, the Chevelle left breathing a lot better than when it arrived.


Detroit Speedworks
Warren, MI 48092



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