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:
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Mounting an LS engine between the frame rails is only one part of the job; you also need to support the rear of the transmission. Although the LS bellhousing has an extra bolt at the top, its bellhousing pattern is the same as the Chevy small-block’s. This allows just about any traditional Chevy bolt-pattern bellhousing to bolt to an LS engine. Adapting the transmission mount to each vehicle is usually a combination of stock components modified with new mounts.
For most A-Body applications, the stock crossmember can be modified to fit late-model transmissions, including the T56 manual transmission and the 4L60E automatic. With the engine mounted to the frame, the transmission must be supported in front of the transmission mount for access. The transmission bolts to the stock mount if it is properly aligned with the engine.
You need to consider firewall clearance when adapting an older GM transmission to an LS engine and installing it in an A-Body. The Gen I small-block was designed with offset cylinder heads that leave about 2 inches of space between the bellhousing mounting pad and the back of the cylinder heads. Consider this spacing issue when deciding whether to use the stock transmission.
Gen III/IV engines do not have offset cylinder heads and, therefore, the cylinder heads are flush with back of the block. When it comes to planning your swap, you need to adjust for this lack of space between the bellhousing and the cylinder heads. The cylinder heads are not necessarily longer, but the back of the block is shorter. Adapter plates for the stock location provide a space of about 2 inches between the back of the engine and the stock transmission in the stock location. In turn, it’s often necessary to relocate the transmission mount and/or move the transmission crossmember to bring the two components together, depending on the position of the motor mounts.
For stock-position adapter plates, the engine should match the same position for most GM automatic transmissions to fit in the stock location as well.
When choosing the transmission for your swap, carefully consider its location and how it will mount to the chassis. In the stock position, older GM transmissions such as Muncie 4-speeds, TH350/400s, and 2004Rs mount to their original location in the vehicle. For 1968–1972 cars, the stock crossmember fits and bolts into the correct location along the original nine-bolt pattern.
However, 1967-and-earlier cars have a four-bolt transmission crossmember pattern on the frame, limiting the options for the stock crossmember. Your engine position and transmission choice may require a modification to the factory crossmember or replacement with an aftermarket unit.
Another solution is the sliding transmission mount from G Force Performance. This special trans-mount bolts to the transmission and allows for up to 2 inches of travel fore and aft to reach the crossmember. These are particularly handy for swaps using sliding motor mounts; fewer mounting bolts means fewer options for mounting positions.
The late-model transmissions, including the manual Tremec T56 and GM 4L- and 6L-series automatics, are different. The T56 is a very long transmission, so fitting this into any A-Body with the stock setback requires fabricating a new transmission tunnel. The stock crossmember can be used in 1968–1972 A-Body cars with the stock setback adapters. Many owners, however, are not comfortable with or do not possess the skill set to fabricate a custom transmission tunnel. Cutting and welding in new sheet metal and chopping up the floor pan is a major undertaking, and many swappers are not interested in hacking up their car. The alternative is to use a forward-mount adapter with an aftermarket crossmember. This allows the T56 to fit with minimal tunnel modifications.
For late-model automatics, you need to carefully consider the same factors. Here, the main issue is that they have bolt-on bellhousings, and that creates a clearance problem in the front of the transmission tunnel. The stock setback pushes the transmission back enough so that the bolt flange hits the tunnel. Serious modification is required to rectify the issue. Moving the engine forward 1 inch solves the problem, and the factory crossmember can be used as well.
When installing an LS engine, getting the driveline angle correct is critical in terms of strength and reliability. The transmission must be angled between 1 and 5 degrees downward on the yoke. For performance applications, 2 degrees is optimal. An angle finder (available at most hardware stores) can determine this angle. You place it against the tailshaft and let the needle rest until it points to the drive angle. If the stock crossmember bolts to the engine and the drive angle is between 1 and 5 degrees, it will work.
If the drive angle is not between 1 and 5 degrees, the crossmember must be modified so the driveshaft has an adequate angle. Several methods can solve this problem, but it depends on the crossmember you are using. Two versions of crossmembers for A-Body cars are available: a tubular unit for open-frame cars and a formed steel unit for boxed-frame cars (all convertibles, El Caminos, most GTOs and Stage 1 Buicks, and some Oldsmobiles).
With late-model transmissions, the most common issue is the tailshaft sitting too high in the car. Because the crossmember sits on top of the frame, it cannot be lowered easily. You can cut and weld the ends to lower the entire crossmember or you can drop the center; either one achieves the same end. The crossmember, however, also has raised sections for the exhaust, so lowering the center is the better option.
If that’s not possible, a new crossmember is required. Numerous aftermarket crossmembers are available for open-channel frames. Some motor mount adapter brands, such as Hooker (Holley) and BRP Hot Rods, are complete systems, designed to work with the same brand’s transmission crossmember. If you have a boxed frame, the open-frame transmission crossmembers don’t work and you need a special crossmember. G Force Performance makes a heavy-duty crossmember that fits the A-Body boxed frame quite well and is perfect for LS swaps. BRP Hot Rods makes a boxed frame crossmember designed to work with its swap kit.
The keys here are driveline angles and keeping the tailshaft square between the frame rails. When fabricating crossmembers to support the transmission, use materials that are strong enough to hold the weight and torque of the transmission. Tubing (round or square) is a good material to use because it provides structural stability with less overall material thickness and weight. Flat-plate steel requires thicker material to achieve the same structural integrity. Angle steel is another excellent material for custom transmission crossmembers.
Written by Jefferson Bryant and republished with permission of CarTech Inc
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