The main concerns for LT swaps are fitting the oil pan, accessory drive, power steering, and fuel system. Another issue is the exhaust (mainly headers or manifolds) because the head design for LT engines is different from the LS series, and there are simply not very many options for swaps, so you need to get a little creative.
The first thing that needs to be done in a swap is physically fitting the engine into the chassis. This may require several attempts, so make sure to have a quality engine hoist, heavy chains (or better yet an adjustable load leveler), and a helper. It is much easier and safer to do this work with help. Make sure to have a level, measuring tape, and notepad for taking measurements and notes on the fitment into the chassis. If the original engine is still in the chassis, take photos and measurements for reference.
Installing an LT engine begins with engine mounts because this is the key to everything else. There are many ways to get this done, depending on the vehicle. A bolt-on adapter is the most common and by far the simplest solution.
Much like the LS platform, the LT-series engines use a four-bolt engine mount that is just forward of the block centerline where the rear two bolts split the center cylinders. A small-block Chevy (SBC) has mounting bosses on the block that sit roughly between the two front cylinders. This pushes the LT forward of where the typical SBC sits. Adapting the LT to fit where an SBC or LS rested is not much of an issue; retrofitting an LT to a platform other than that is a little more challenging, but even that is pretty simple.
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Dimensionally, the LT is about the same size as the SBC, although the back of the block is shorter than the SBC because there is no ledge for the bellhousing. Additionally, the mechanical fuel pump is at the back of the block, requiring extra clearance. Most swappers simply adapt the LT-block mounts to the commonly available SBC mounts and then go from there. With so many options for placement, it can get a bit sticky trying to figure out exactly what is needed.
The factory motor mounts are a wild departure from the standard SBC style. There is a large damper on a large three-bolt flange. Shown here is a 2014 L83 engine with truck motor mounts.
The factory LT engine mounts are wildly different from SBC-style mounts. These mounts use a large polymer bushing to dampen the engine vibrations. The bushing is bolted to the frame, as opposed to a clamshell that is secured with a single through-bolt. In some instances, the factory mounts can be used, but they are very large and require substantial fabrication to get the alignment right. Using SBC mount adapters offers more options, and they are generally easier to fabricate frame stands for.
Typical installations need the engine in the factory SBC location, which references the bell-housing mounting plane. This is 1¹∕₈ inches rearward from the factory LT mounting point, so these are known as 1¹∕₈-inch rearward adapters. This position works well in most GM vehicles but not all. The 1987 Camaro project featured in this book required setting the engine, an L83 5.3L truck LT-series engine, just 5/8 inch rearward to gain the necessary clearance for the firewall. We used adapters from Trans-Dapt, which also makes the 1¹∕₈-inch rearward adapters and 5/8-inch forward pieces for vehicles that need even more clearance.
Adapting an LT to a factory GM SBC frame stand is a balancing act. There is the firewall clearance to deal with as well as the front of the engine. The oil pan and accessories can get in the way, especially when using factory components. In most cases, the factory truck-only vacuum pump will not clear any GM muscle car frame, but it will clear on most truck chassis. Additionally, the factory AC compressor location is on the passenger’s side, down low, tight to the block. Many aftermarket adapter mounts simply will not clear the factory compressor, and the compressor does not clear the frame or crossmember in most vehicles, so you have to sort that out.
Most swappers elect to use adapter plates because they are simple and allow the use of readily available (and inexpensive) SBC mounts. There are many options for adapters from single-position adapters, which are the most common and simple, to multi-position and even sliding mounts. We have used all three types, and they have their benefits and drawbacks. The biggest issue with single-position adapters is that they are just that: one position. If you run into a clearance issue, purchase a different set that works with your project.
There are substantially fewer companies making Gen V adapters compared to LS adapters, which means fewer are available to choose from. This isn’t really a big problem, however, because those that are available are quite versatile. Brands including Trans-Dapt, ICT Billet, and Dirty Dingo have the parts needed. For those swapping LTs in the place of LS-series engines, ICT Billet even makes Gen V LT-to-LS chassis adapters.
If basic adapters are needed, these are the ones you want. They are built from laser-cut steel and painted black, and they work. They come in three flavors: 1¹∕₈ inch rearward, 5/8 inch rearward, and 5/8 inch forward (with or without rubber or polyurethane engine mounts). We used these in the 1987 Camaro featured here. They fit well, clear all of the components, and do precisely what they are supposed to, all for less than $80 (plates and hardware only, no mounts).
The measurements reference the relative position of the engine to the factory LT position, not the mounts themselves. So, 5/8 inch rearward means the engine itself sits 5/8 inch from the LT-series mount, which is half the difference between the SBC and LT positions.
Let’s say you have a custom chassis or something that is not already fitted with GM SBC frame stands. In this case, custom mounts are needed. Trans-Dapt has you covered with the 4604 and 4605 biscuit-style mounts. Similar to the early SBC front mounts, these adapters are universal for frame rails that are 27 to 33 inches (4604) and 24 to 30 inches (4605) apart, so the tabs can be bolted or welded to the chassis, and then the LT can be simply dropped in place. This greatly simplifies the process of swapping an LT into non-GM vehicles. Just about any non-GM application can make use of these mounts for around $115.
This block adapter can use any of the three main GM motor mounts types: tall/narrow, short/wide, or the 1973–1998 clamshell style. This mount sets the engine rearward 5/8 inch, which is half the distance between an SBC bellhousing plane location and the LT plane location. The Camaro featured in this book used this measurement because the SBC position is too close to the firewall.
Say that you need an LT because you already swapped an LS into your car but you want the latest and greatest in powertrain technology, or maybe your factory LS-powered car is just not up to the task anymore. Well, my friends, the geniuses at ICT Billet have the part you need: billet aluminum LS-to-LT swap adapters. These adapters relocate the LT engine to the LS position in fine style. They clear all the important components and come with the hardware to mount them.
ICT Billet also has multiposition mounts for LT swaps. This means there are three unique position options with a single adapter. All positions move the engine 0.72 inch up in the chassis, which may not work for those using the very tall truck intake, but this provides clearance for the crankshaft-to-front crossmember clearance, which is a problem in some vehicles. The three positions are set at the stock SBC position (1.125 inches back), 1.625 inches forward, and 2.25 inches forward. This measurement refers to the actual engine position.
These billet aluminum adapters from ICT Billet are drilled for multiple positions from the stock SBC position to 2.25 inches forward.
ICT Billet states that its adapters will allow the use of the factory AC compressor and vacuum pump in the 1.625-inch position with the plates trimmed to remove the factory SBC position mounting holes. Although, this may cause a clearance issue between the oil pan and steering linkage or front crossmember.
Another option is to purchase mounts from Dirty Dingo, which has two styles: static multiposition and sliding mounts. We used the sliding mounts on a 1971 Buick GS, and they worked very well. They allow the position of the engine to be adjusted to fit the original Buick 350 frame stands, which is something that no other mount will do.
Like the other multiposition mounts, these start with the factory SBC position, which refers to the bellhousing mounting plane. This is the most rearward position for the engine using these mounts. From there, the mounts move 11/16 inch forward, 1¹¹∕₁₆ inch forward, and 2¼-inch forward from the stock SBC position. These mounts do not clear the factory AC or vacuum pump. They use multiple positions drilled and tapped into a single mount, so the position of the engine can be adjusted as needed without buying new mounts.
The frame stands determine which style of motor mount is needed. This one is on the 1971 Buick GS, and it is not compatible with any of these adapters because it is a Buick frame stand. Oldsmobile and Pontiac each have their own versions, so you need to convert to Chevy stands.
For unique circumstances, the sliding mounts may be the best bet. These mounts allow the engine to be positioned in the stock SBC location, up to 2 inches forward, and anywhere in between. This means that minor adjustments can be made for specific applications, while static mounts can’t be adjusted. These mounts are quite long and a little complicated to secure, but they are worth it if you are working with nonstandard frame stands, such as Buick, Olds, and Pontiac. They do not clear the vacuum pump or AC compressor using the factory accessory drive.
These Dirty Dingo mounts were the first commercially available LT swap mounts, and they provide some options that you don’t get with other adapters. Instead of a single position or several fixed points, the adapter bolts the block, while the motor mount bolts to a second piece that slides on the block adapter. This allows you to put the engine wherever you need it. These are very large though, so they do interfere with the factory AC compressor mount.
GM TRUCK MOUNTS
Standard adapter plates work for GM two-wheel-drive (2WD) trucks with SBC frame stands, but four-wheel-drive (4WD) trucks are a much different story. The crossmember is in the way, which keeps the standard mounts from working. Dirty Dingo offers 1973–1999 Chevy truck 4×4 mounts that are adjustable from the standard SBC position up to 2.5 inches forward and an additional 1/2 inch rearward. These are made from laser-cut steel and are powder-coated black. They do not clear low-mount AC but will clear the vacuum pump.
Most adapter mounts are designed to work with the standard SBC three-bolt engine mount. For GM-chassis vehicles, there are three different versions of motor mount: tall/narrow (early style), short/wide, and clamshell. The first generation of SBC mount was a biscuit mount used on 1955–1957 GM chassis. In most cases, these chassis need to be converted to a later-style engine stand.
The clamshell type is more common on later GM vehicles, but they can be found on some converted 1964–1972s. The clamshell’s design uses 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 common SBC-style mounts that most LT-swap adapters use. There are two versions of these mounts. The most common is the tall/narrow (left), which are used in most GM applications. On the right is the short/wide mount, which are used on GM 307 SBC applications. Determining which one is needed depends on the available frame stands.
These are most common in Chevrolet muscle cars. However, the tall/narrow distinction is confusing because the frame pad is called short/narrow. The tall/narrow refers to the engine-mounted component. These are the SBC mounts used for 350/396/454 engines in Chevrolet vehicles. The center of the engine mounts measure 2³∕₈ inches between the mounting ears and 2³∕₂₆ inches tall (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). GM part numbers for these frame stands are 3980711 for left hand and 3980712 for the right hand. These frame stands are readily available in the aftermarket as reproductions.
For the Chevy 307-ci engine, General Motors used a different set of frame stands. The frame stands are taller than the 350 version by 1/2 inch. The width of the pad (where the two mounts come together) is also different; the 307 mounts are wider, measuring 2⁵∕₈ inches on both the frame stand and the engine block mount. The block mount is shorter than the 350 version, measuring 1³∕₄ inches tall. These are the most commonly sold mounts at the parts store, so it pays to know the difference.
One of the biggest issues with LT1 swaps is the water-to-oil cooler. In most applications, this simply does not clear the frame. Most GM trucks have enough clearance, but car frames do not.
The type of mount needed depends on the vehicle, the accessory drive, and the oil pan. That being said, the best solution is to use the 350 version. These mounts raise the engine a little higher than the 307, which provides better clearance for the oil pan and steering linkage. In most cases, the engine will still need to be raised a little more to clear the steering linkage. About 1/2 inch usually works, depending on the oil pan and the angle of the engine/transmission.
If working with a non-SBC-powered GM chassis (such as a Buick, Olds, Pontiac, or Cadillac), then convert to the SBC version of frame stands. In most of these applications after 1964, the same-year SBC frame stand should fit. On pre-1964 vehicles, General Motors had not fully switched to universal frame designs, so a Buick B-Body frame is not the same as a Chevrolet B-Body. This requires modifying the chassis to either accept the SBC frame stands or building a custom stand to mount to the engine.
Written by Jefferson Bryant and republished with permission of CarTech Inc
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