The key to any swap is getting the engine into the chassis. This can be easy or it can take weeks to figure out, it all depends on the car. The 1968– 1972 A-Body vehicles are easily converted to Chevy small-block frame mounts, but the earlier 1964–1967 A-Body cars are not as simple. General Motors certainly helped swappers by using the same motor mount design for all Gen III/IV engines, except the LS4, which is a front-wheel-drive platform. The LS-series engines share a footprint similar to the classic Chevy small-block engine’s, so they fit in virtually any chassis that can house a Chevy small-block. That’s a significant advantage to the swapper, as the conversion from a Chevy small-block to an LS can be as simple as adapter motor mounts.
The LS motor mount uses a four-bolt mount that bolts to the side of the engine block. This is not directly compatible with the standard three-bolt Chevy small-block mount. The most common solution for this change is converting the LS engine to the more usual early-style three-bolt engine mounts.
The original Chevy Gen I small-block from 1955 featured the three-bolt motor mount configuration, and the same motor mount pattern continued in production through the second-generation small-block, the LT1 and LT4. However, these engines are not to be confused with the new-generation 2014–up LT1 Gen V series. (Yes, General Motors reuses its nomenclature and it can be very confusing.)
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.
This tech tip is from the full book, SWAP LS ENGINES INTO CHEVELLES & GM A- BODIES: 1964-1972.
For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE
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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.
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.
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 valve cover to air conditioning compressor, and transmission bellhousing to transmission tunnel clearance.
Some adapters, such as these TransDapt 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.
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.
Once the locking nut is on the backside, 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.
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. The center of the engine mounts measures 23 ⁄8 inches between the mounting ears and 23 ⁄26 inches from the center of the mounting bolt to the top of the engine mount pad. On the frame stand, the mounting pad measurements are 23 ⁄8 inches wide and 15 ⁄8 inches tall (crossmember to pad). The GM part numbers for these frame stands are 3980711 for left-hands, and 3980712 for right-hands. These frame stands are readily available in the aftermarket as reproductions.
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.
Most LS engine adapters position the engine closer to the radiator, which is fine, because most of them do not run mechanical fans.
Short/Wide Mounts
Chevrolet used a different set of frame stands for the 307 than the 350 engine when installed in A-Body cars. The 307 frame stands are 1/2 inch taller than frame stands for the 350 engine. The width of the pad (where the two mounts come together) is also different. The 307 mounts are wider and measure 25 ⁄8 inches on both the frame stand and the engine block mount. However, the block mount measures 13 ⁄4 inch tall and therefore is shorter than the 350 version.
These are the most commonly sold mounts at the parts store, so it pays to know the difference.
The type of mount you need depends on your vehicle and the accessory drive and oil pan you use. That being said, the best solution is to use the 350 version. These raise the engine a little higher than the 307, which provides better clearance for the oil pan and steering linkage. In most cases, you still need to raise the engine a little more to clear the steering linkage. About 1/2 inch usually works, depending on your oil pan and the angle of the engine/ transmission. Most adapter plates require the 350 version.
Most A-Body cars have an interference issue with the inner tie-rod ends. The Mast oil pan for A-Body swaps has the best clearance, but you may need to raise the engine to get adequate clearance. The Hooker kit (shown) and similar kits have complementary parts that work as a complete system, and include mounts, pan, and headers.
Even with the right parts, some inner tie-rods are simply larger than others, which could result in light scrubbing, such as this on the bottom of the pan. This occurs at the extreme end of the turn radius
This tech tip is from the full book, SWAP LS ENGINES INTO CHEVELLES & GM A- BODIES: 1964-1972.
For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE
SHARE THIS ARTICLE: Please feel free to share this post on Facebook Groups or Forums/Blogs you read. You can copy and paste this link to share: https://www.lsenginediy.com/choosing-the-best-motor-mounts-for-a-chevelle-ls-swap
With the mounts on the block, the engine can be lowered into the car for a test fit. It is a good idea to test fit your engine before finalizing the details.
Energy Suspension’s correct tall/narrow mounts provide adequate clearance using the Trans-dapt adapters and Mast oil pan. The inner tie-rods just barely touch at full lock.
Hooker offers another LS swap solution for A-Body vehicles, particularly for non-Chevrolet brands that don’t have factory Chevy small-block frame stands. Instead of searching for Chevy small-block stands, you can use these pieces along with a fourth-generation Camaro LS motor mount to place the engine in the correct position. These are available in both “stock” position and in the 2-inch-forward position.
For the 1969 Chevelle project featured in this book, the 350 mounts were used with a set of Energy Suspension 31117G motor mounts and a Mast oil pan. The driver-side inner tie-rod cleared, but the passenger’s side hit the pan. I raised the engine with an additional spacer block between the engine and the mount, which allowed everything to clear. The Energy Suspension mounts come with one spacer; I used two.
LS Frame Stands
Using an aftermarket stand is an alternative to sourcing original Chevy small-block frame stands. Several versions are available with the most common being the Hooker (Holley Performance) mounts. These fabricated steel mounts bolt to the 1968– 1972 frames in the factory-drilled forward Chevy small-block position. The stands are designed to fit Gen-IV F-Body (1998–2002 Camaro) block mounts. The two versions of this mount are stock engine position and forward position.
Under the hood of the 1971 Buick GS lies this 400-hp Buick 350. Although the engine is in great shape, it is time for something new. The latest generation of GM horsepower, the LT1, will do nicely.
Even though the Buick shares most of the chassis components with the rest of the A-Body platform, the frame stands are not compatible. Only Chevy small-block mounts work for LS swap adapters, so the Chevy small-block mounts need to be installed. The Buick mounts shown here are set back way too far and too wide.
Accessing the bolts is tricky; you need a combination of wrenches and sockets to get to each of the nuts and bolts through access holes in the frame. The bolts pass through from the backside of the frame member.
Position A, or the forward position, is designed to reduce floorpan modifications for T56 6-speed transmissions and allows bolt-in installation of Turbo-Hydramatic 350, Turbo-Hydramatic 400, 2004R, 700R4, and 4L60/70 automatic transmissions. Position B, or stock engine position for a Gen I Chevy small-block, allows a TH350, TH400, or 2004R to mount to the engine using the stock crossmember without floor modifications. These mounts require extension floorpan mods with late-model transmissions and a custom transmission crossmember.
BRP offers a replacement mount that uses its proprietary Muscle Rods engine block mounts. This complete system includes a transmission crossmember and is designed to fit with Hedman Muscle Rod LS swap headers as well.
Chevelle small-block 350 stands replaced the Buick stands and, indeed, it makes a difference. The Chevy 307 stands are different from the big-block stands. For the install, I bolted them in place using the forward holes in the frame. All 1968– 1972 A-Body frames are drilled for all types of frame stands. I also used new Grade-8 bolts.
Earlier A-Body cars use a variety of adapters. Chevrolet models are easy, as Chevy small-block adapters are the standard. If you are swapping into a BOP A-Body car, you need to swap out the original mount for the Chevy small-block-type mounts. Although the non-Chevrolet mounts look as if they are the same or similar, they have different dimensions that are not compatible for completing a swap.
Another issue is that BOP frame stands are often in a different position than Chevrolet versions, similar to the later 1968–1972 frames. The most common solution is to use the 1964–1967 Chevelle 350 mounts for these early A-Body swaps.
Unlike the 1968–1972 models, the 1967-and-earlier frames use a single bolt pattern for all GM makes, three bolts in a triangular pattern. The frame stands themselves are different. This means that you must install Chevy small-block engine stands into the frame. Some swappers weld the engine stands to the frame, which demands a serious commitment to the placement of the engine. You must be 100-percent sure that the location is correct.
These Dirty Dingo mounts allow up to 2 inches of lateral movement. Adjustable motor mounts give you latitude to adjust the position of the engine and, therefore, flexibility to fit the exhaust, steering, air conditioning system, brake booster, and other underhood components. They are very popular because they offer more options for engine placement than other designs.
Adjustable motor mounts, with their many components, are more complicated to install, however. The slider (black piece) must be removed before the adapters are placed onto the block.
A spacer plate comes with the adapters to locate the mounts for the proper height in the chassis. Leave these out and you will not be able to install the bolts into the frame stands.
If your block is aluminum, you need to use anti-seize on the supplied Grade-8 bolts to prevent the threads from galling.
You mount sliding plates back onto the adapters using the installed studs. The final torqueing of the nuts and bolts is done after the position of the engine is set.
Here you can see the bare adapter. The “P” with an arrow dictates the side and front of the engine.
The bolts have hex heads; be careful not to strip the hex head when torqueing the bolts.
With the stands in place, set the new LT1 in the chassis, allowing you to check the fit for the oil pan and components.
Fortunately, this is not necessary. The 1964–1967 Chevy small-block frame stands are readily available as reproductions.
Hooker frame stands provide an alternative to converting to the Chevy small-block mounts. The stock location in 1964–1967 cars presents a major component fitment problem similar to the issue in the later A-Body. Often there is not enough clearance between inner tie-rods and the oil pan, but also the transmission and A/C compressor fitment are an issue with the stock setback. Hooker 1964–1967 frame stands provide a viable solution because you can position the engine 1 inch forward from its stock location. When used in the complete Hooker LS swap system, all component clearance and fitment issues are alleviated.
BRP also makes kits for the 1964– 1967 GM A-Body cars. Similar to kits for later vehicles, these bolt to the chassis and use either the Gen IV Camaro (Holley) or proprietary (BRP) motor mounts on the engine.
The 2014–up Gen V LT-series engines are similar to Gen III/IV blocks, but not enough to make them a simple drop-in replacement. At the current time, the aftermarket does not provide a full selection of motor mounts for the new generation of LT-series engines. There are a few options, however. The engine mounting location is the same, but the Gen V has a different bolt pattern. Dirty Dingo has sliding mounts for LT A-Body swaps that use the Chevy small-block frame stand and engine mount. The slider allows you to position the engine 2 inches forward, or aft, of its mounting position.
Written by Jefferson Bryant and republished with permission of CarTech Inc
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