Bolting the adapters to the engine is simple: four socket head bolts and you are done. Make sure you use some anti-seize compound to prevent galling of the different metals.
Numerous companies make adapter plates to convert the LS mount to accept a Chevy small-block three-bolt mount. With so many adapters (hundreds of different brands are available), deciding which to use is the tough part.
When compared to the Chevy Gen I/II small-block, the stock LS engine motor mounts are located farther back toward the bellhousing. If a motor mount is bolted to the frame using these holes, in most vehicles the engine sits too far forward. This increases the nose weight of the car, causing instability.
Some adapter mounts are for specific applications, such as the Holley mounts for GM A-Body cars. In addition, universal adapters are available with offset mount locations, such as 1.25 inch forward and .5 inch up, to better facilitate engine placement for chassis and body clearance. Dirty Dingo offers adjustable adapter plates, so you can get the positioning just right for your application.
Simple adapter plates are a common solution for many LS swaps’ engine mounts. These plates from Hooker are made of billet aluminum. They bolt to the Gen III/IV four-bolt engine mount pad and allow a three-bolt GM motor mount to bolt on.
Not all adapters are the same. This kit from ATS flips the Chevy small-block mounts upside down to set the engine lower in the chassis. These are designed to fit the first-generation Camaro and the GM A-Body.
Simply bolting the adapter plate to the engine block provides mounting provisions for the old-style Chevy small-block three-bolt engine mount. This allows the LS-series engine to essentially drop right into the chassis without much effort.
For yet another alternative, American Touring Specialties (ATS) offers a set of LS adapter plates that feature an early-style motor mount in an upside-down configuration. ATS offers this arrangement so the engine can sit lower in the car and farther back toward the firewall, for better stability and a lower center of gravity. With these ATS mounts, an LS engine can be swapped into most any GM A-Body.
Depending on the motor mount, certain interference issues may occur, most commonly, oil pan to crossmember and ground clearance, passenger-side valvecover to air conditioning compressor, and transmission bellhousing to transmission tunnel clearance.
Some adapters, such as these Trans-Dapt mounts, require a lock nut on the back side of the plate. The external webbing makes it a bit of a pain to install the lock nuts, but these nuts are recommended to add extra security.
Opinions vary as to which adapter style is the best fit for 1964–1972 A-Body platforms. The reality is that it depends on your engine, transmission, and component combination. This time frame in GM’s history was the beginning of using corporate parts throughout the GM brands.
Before 1964, GM nameplates Cadillac, Chevy, Buick, and Oldsmobile manufactured and installed parts unique to their respective models; as a result, only a few components were shared across brands. In most cases, the chassis platform shared the frame or unibody structure, but very little else. In 1964 this changed, and suddenly GM brands were using “corporate” parts that interchanged between platforms, starting with suspension components and transmissions.
Engines, however, were still brand-specific. Although this does create a bit of a headache, the nice thing for 1968–1972 A-Body builders is that all the frames are drilled for every engine stand. You can easily bolt a Chevelle engine stand into a Buick, Oldsmobile, or Pontiac frame.
Once the locking nut is on the back-side, you tighten the bolt in the plate (which is also threaded) and then tighten the lock nut. If your adapter plates require nuts, you can use a box wrench with a tap on one side to hold the nut in place while you install it.
Converting a 1968–1972 BOP (Buick, Olds, Pontiac) to work with the standard LS conversion mounts is handled one of two ways: convert to Chevy small-block frame stands or use LS-specific frame stands.
The early 1964–1967 A-Body cars are more difficult because these were not designed to accept all engine makes. A Buick used Buick mounts, a GTO/LeMans used Pontiac mounts, and so forth. A couple of aftermarket solutions do not require welding: Hooker (Holley) and BRP Hot Rods adapter mounts. They use existing holes in the frame to adapt the chassis to accept an LS engine mount. The Hooker mounts use the fourth-gen Camaro LS motor mounts, and the BRP mounts use a proprietary polyurethane mount. Conversion mounts that adapt non-Chevrolet A-Body frames to accept a Chevy small-block mount are readily available through companies such as Original Parts Group.
When adapter manufacturers talk about “stock location,” it is important to recognize that this refers to the original engine-to-transmission mating surface plane. LS engines are 1 inch shorter than a traditional Chevy small-block. Therefore, they do not have offset cylinders, and this means that the rear of the block is shorter than the Gen I block. Adapters that position an LS in the “stock location” place the transmission mating surface in the same location it would be if a Gen I Chevy small-block were installed in the vehicle.
Chevy Adapter Mounts for the A-Body
Most adapter mounts are designed to work with the standard Chevy small-block three-bolt engine mount. For the A-Body, three different versions of motor mounts are offered: clamshell tall/narrow (early style), and short/wide.
Clamshell Mounts
The clamshell type is more common on later GM vehicles, but can be found on 1964–1972s. These use a stamped steel pod that bolts to the engine with a steel and rubber mount that bolts to the frame. These can be used with most adapter mounts.
Tall/narrow, short/wide, and clamshell are the three main types of motor mount that have been used for the typical Chevy small-block frame stands. The clamshells are completely different from the other types. The tall/narrow mounts (left) are used for 350s and big-blocks. The short/wide mounts (right) are used on 307 cars. They both bolt to the engine, but wreak havoc on your engine position and install.
Tall/Narrow Mounts
These are the most common in Chevrolet A-Bodies. The tall/narrow distinction is confusing, however, as the frame pad is called short/narrow. Tall/narrow refers to the engine-mounted component. These Chevy small-block mounts from a small-block 350 were adapted to the big-block 396/454 engines in Chevrolet A-Body cars.
There is about a 1/4-inch difference in overall height between the tall/narrow (left) and the short/wide (right) versions, but it’s not enough to allow some other components to fit. In addition, the narrow mounts don’t sit down on wide 307 frame stands.
The center of the engine mounts measures 2⅜ inches between the mounting ears and 2