Читать книгу Swap LS Engines into Chevelles & GM A-Bodies - Jefferson Bryant - Страница 8
ОглавлениеThe 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.)
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 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 2⅜ inches wide and 1⅝ 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.
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 2⅝ inches on both the frame stand and the engine block mount. However, the block mount measures 1¾ 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.
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.
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.
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.
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 floor-pan 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.
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.
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.
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.
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.
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.
With the stands in place, set the new LT1 in the chassis, allowing you to check the fit for the oil pan and components.
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.
The LT1 wet-sump pan does not fit the stock chassis. The only option at the time was to modify the chassis. Right before press time, a new aftermarket oil pan was introduced by BRP Hot Rods; Dirty Dingo is developing one as well.
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.
Some late-model transmissions are larger than classic transmissions. They sometimes do not fit the transmission tunnel or do not fit in the stock location. But there are solutions for achieving enough clearance. The automatics have removable bellhousings and these often take up more room due to the bolt flanges. This is the reason sliding the engine forward 2 inches is a good idea. With the engine forward, most late-model 4-speed autos fit without any mods, as do T56 6-speed manuals.
A-Body transmission crossmembers vary only by frame style. This tubular mount is used in most coupes, four-doors, and wagons. The crossmember has been hacked on and needs to be replaced, but it worked out for fitment in the 1969 Chevelle.
The Hooker LS swap crossmember works for all transmission types and is very clean and lightweight. This unit was used in the Chevelle for the 5.3/Muncie swap shown in this book.
GM A-Body frames have multiple mounting points built in. All you might need to do is slide the factory crossmember into another set of holes. Remember, an early transmission sits about 2 inches farther back from the LS engine, depending on the engine mounts. The LS has a flush casting in the back, and unlike the Gen I Chevy small-block, there is no extra material on the back of the block. This convertible/performance chassis is boxed from the factory for strength. The crossmember bolts to the top of the chassis in contrast to the lower channel with open frames.
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 transmount 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 floorpan 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.
The key to correct transmission angles is to position the tailshaft at an angle between 2 and 5 degrees, and it should match the rear pinion upward angle. Too little or too much causes vibrations and premature joint failure. An angle finder should be used to set the transmission at the proper angle. The U-joints must be “working” to last; if the joints are positioned at 0 degrees, they will burn up.
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.
For an LT1 swap, the factory crossmember sits way too high, keeping the tailshaft from sitting at the correct angle. You could modify the crossmember or replace it with an aftermarket version. Lowering the factory crossmember requires dropping the center section because the exhaust doesn’t clear if the entire unit is lowered. The transmission needs to drop about 3 inches.
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.
For the Buick, I opted for a G Force Performance Products crossmember because it’s the only one available for boxed frames. To mount it, you drill out the stock bolt holes to 1/2 inch.
The G Force crossmember has a dropped-center mounting plate, so the transmission sits lower in the chassis for tunnel clearance, about 3 inches. You can always adjust the transmission mount with the provided mount spacers. I used one spacer on this install.
Placing the nuts into the chassis can be difficult; this trick helps you install them: Roll half a thread onto a long bolt and then thread the nuts onto the upper bolts. These nylock nuts are a little easier to work with than other nuts.
The beefy crossmember has large hoops for exhaust clearance and fits the chassis quite well. It’s very strong and provides excellent support and strength, which helps maintain chassis strength. It is a little heavy.
I also installed the G Force sliding transmission mount so I had 2 inches of travel to mount the transmission to the crossmember. When sliding motor mounts have been installed, a sliding transmission gives you extra flexibility so you can correctly position the engine, transmission, and driveshaft for the best performance possible. A sliding transmission mount is especially helpful with sliding motor mounts because you can quickly exceed the reach of the factory slots in the crossmember.
I installed the mount and then slid the crossmember in place. You may need to remove the sliding section of the mount and roll the bolts into the crossmember slots because the bolts are actually studs and are made long for installs that need spacers.
Performance Project: Choosing a Driveline
When performing an engine swap, the driveshaft often needs to be replaced because it isn’t compatible with powertrain and chassis requirements. Most often simply shortening the stock driveshaft is not a suitable solution. Your LS engine swap requires a significant investment that includes preparation, fabrication, time, money, and effort. Why use the same old driveshaft that will never work like a properly designed custom unit?
This Dana cast slip yoke is strong enough and withstands up to about 800 hp, depending on the application. If it had been used, it would have saved the entire driveline. Unfortunately, the stock yoke broke, causing the shaft to become wadded up under the car. Once engine output approaches the 800-hp mark, you need to consider using a billet slip yoke because this is probably the strongest option available.
In most cases, dropping in an LS engine increases the torque and horsepower output. Any time you increase the power output to the stock driveline, you must consider the impact on the stock driveshaft. Most factory driveshafts are balanced for a range of 3,000 to 3,500 rpm. Increasing shaft speed higher than 3,500 rpm can induce a parasitic effect. Steve Raymond of Dynotech Engineering said, “I have had several NASCAR teams tell us that our driveshaft saves them 3 to 7 hp on their chassis rolls dynamometers. That’s why balance is important and why we manufacture shafts for about 85 to 90 percent of the NASCAR teams.” The stock balance on the stock driveshaft is not good enough for anything but a stock engine.
Dynotech Engineering uses Balance Engineering’s driveshaft balancers because they are considered the best in balance accuracy. Dynotech suggests balancing a performance driveshaft at a minimum of 5,000 rpm, and as high as 7,500 rpm. This ensures a properly tuned driveshaft that reduces parasitic loss.
Both slip and pinion yokes are critical driveline components that physically connect the transmission, driveshaft, and differential. Break one of these and you often experience expensive car damage and loss of control. That said, a cast yoke often withstands up to 800 hp for most applications. But you can exceed 800 hp for certain cars such as lightweight hot rods with street tires because they put less strain on the driveline than a 4,000-pound Chevelle with slicks and 500 hp. You need to carefully consider this, however, and often it’s better to upgrade.
The chances of breaking the pinion yoke are slight. The compact design places more material in important places, yielding a strong component. That is not to say a cast yoke is bulletproof, but a billet steel yoke such as this one from Mark Williams is pretty close. New yokes usually come with better joint caps, instead of lighter-weight stock-style U-bolts, which are prone to distorting the U-joint bearing caps.
Another option when using a cast pinion yoke is to use U-joint caps instead of the weaker stock-style U-bolt retainers. This increases the clamping force and eliminates the possibility of distorting the caps. New billet yokes typically come with the proper retaining caps.
Choosing your driveline shop is important. Dynotech Engineering uses CNC-operated welders to ensure a perfect weld every time.
Along with balance, the length and diameter of the driveshaft directly affect the performance of the unit. Determining the required length for the driveshaft necessitates looking at several factors. The distance from the rear yoke to the transmission seal is the most important measurement because it determines the overall length of the driveshaft. Measure this length with the pinion yoke installed and the car at ride height. The pinion yoke influences the measurement, and changing from a cast-steel yoke to a billet pinion yoke can alter the length by as much as 3/4 inch.
Provide these measurements to the driveshaft shop and they can create the complete shaft with the required slip yoke and predetermined run-out for the slip yoke. For most applications, a run-out of 1 inch is more than enough to provide the play needed for suspension travel, so do not let a shop convince you to accept more run-out than that. Some transmission shops insist on running out 1-1/2 inches, but this could be disastrous and lead to driveshaft failure. With that much of the slip yoke hanging out of the transmission, there could be less than 3 inches of splined yoke in the transmission, thus creating a wobble in the yoke that would cause a heavy vibration at various RPM. Stick with the 1-inch rule.
Always measure the driveshaft length at drive height. If the vehicle is too low to crawl under it on the ground, jack up both ends and use jack stands under the rear end and front suspension; be careful to make sure all the stands are at the same height. The slightest variation in the suspension can throw off the measurement, resulting in a driveshaft that does not fit.
Once welded, the driveshaft must be balanced. This Balance Engineering balancer spins the shaft to 5,000 rpm, ensuring a proper balance for high-performance applications. This machine has the capability of revving to 7,500 rpm.
This is a fully welded aluminum shaft and yoke. Note the clean, CNC-welded joint.
The function of “critical speed” (CS) factors into the length versus diameter rule. Critical speed is the RPM at which the driveshaft becomes unstable and begins to bend in the middle. This is also known as “jump roping.” The longer and smaller (diameter) a driveshaft is, the slower its critical speed. Critical speed is felt as excessive vibration, and if run at CS too long, the unit will fail. To calculate the critical speed, you must know the length, diameter, wall thickness, and material module of elasticity. Then, using the critical speed calculation formula, you can plug in the numbers to calculate the driveshaft’s critical speed.
The formula for balancing the driveshaft is shown here. The red dot in the center is the actual rotational center and the yellow dot shows the center of mass. This represents an unbalanced shaft. The distance between the rotational center and the center mass determines the amount of weight needed to shift the center mass to the rotational mass.
A driveshaft that is too small in diameter for its length can exhibit serious parasitic effects on the drivetrain. The first type of bend is referred to as first-order bending. Once this starts, the shaft often starts to flex up and down, and this is referred to as “jump roping.” As a result the driver feels a significant vibration and the shaft and U-joints eventually fatigue.
Driveshaft material is just as important as its length and diameter. Original equipment manufacturing (OEM) steel driveshafts are for just that, OEM power. An OEM shaft is rated for no more than 350 ft-lbs, or 350 to 400 hp. For high-performance use, drawn over mandrel (DOM) seamless tubing and chrome-moly steel are the two materials used. DOM steel is better than OEM steel, handling much more torque, up to 1,300 ft-lbs and 1,000 to 1,300 hp. DOM steel can be spun faster, as well, with its higher RPM rating, making it suitable for any stock LS application. This is a good choice for any car that does not need a lightweight unit.
The step up from a steel shaft is chrome-moly, which is the strongest material available. It’s used in 3,000-hp Pro Stock cars. Chrome-moly steel tubing can be heat treated as well, raising the torsional strength 22 percent and increasing the critical speed 19 percent. Steel is heavy, which increases the load on the engine bandit so that it takes the engine longer to get to speed.
Reducing driveline weight is important, so lighter materials are sometimes a better choice. Aluminum is the most common performance driveshaft material. A lightweight aluminum shaft reduces rotational mass by freeing up horsepower from the engine and reducing parasitic loss. Aluminum driveshafts are strong but cannot hold as much torque as steel. Therefore, some custom driveshaft shops do not have “twist” guarantees on aluminum driveshafts. An aluminum driveshaft supports up to 900 ft-lbs, or 900 to 1,000 hp, making it a great lightweight choice for most muscle cars.
Carbon fiber, also an option, is the most efficient in terms of parasitic loss, but it is also the most expensive; it is not needed for high-performance street use, but often is used for high power figures, up to 1,200 ft-lbs, or 900 to 1,500 hp. Carbon-fiber driveshafts are strong and have a surprisingly high torsional strength, resisting twisting and reducing the shock factor on the rear end. Carbon fiber also has the highest critical speed module of elasticity, meaning the shaft doesn’t flex at slower speeds, unlike other material components. Coupled with the highest critical speed factors and the light weight, a carbon-fiber driveshaft can free up as much as 5 hp over a stock steel driveshaft. When winning is everything, 5 hp might make the difference.
Reaching critical speed causes first-order bending. This complex formula is used to calculate the critical speed for a driveshaft. All driveshafts have a critical speed depending on their length and diameter. The module of elasticity of the shaft material is an important part of the equation. Learning these numbers can be a little tricky because most shops keep the specific numbers close to the vest. For steel, the basic modulus of elasticity (MOE) is 30, aluminum is 10, and carbon fiber depends on the manufacturing processes used, so no numbers are available.
The type of U-joint used is more important than most people think. The “lubed for life” Spicer U-joint (left) is stronger than its same-sized greaseable counterpart (right).
Once the driveshaft is measured and ready to build, there are a few other issues to consider. Phasing the U-joints with the weld-in yokes is an important part of the equation. With every rotation of a U-joint at any degree other than zero, a fourth-order vibration is generated. This shows up as a torsional pulse, which is felt as a significant vibration. By phasing the weld-in yokes to minimize the combined degrees of rotation, the fourth-order vibration is drastically reduced. The weld-in yokes need to be installed on the same plane; they can’t be rotated off axis of one another.
This diagram shows the difference between the two types of joints. The greaseable joint (top) has less material in the center of the joint, reducing its strength and, therefore, torque level. A solid U-joint (bottom) does not require maintenance and is much stronger.
The quality of U-joints makes a difference, and not just the brand, so you need to consider the design of the U-joint as well as the load capacity. The typical choice for most cars is 1310-series U-joints; for performance applications, however, the rugged 1350-series joints are the better choice. The larger the series number, the larger the trunnion.
Trunnions are the protruding shafts that the caps ride over. Larger trunnions equate to more torsional strength. Torsional forces are exerted in a twisting motion. Changing to a larger series U-joint is not a simple task; you can’t just buy bigger joints. All yokes (slip, bolt-on, and weld-in) must match the desired joint size. You can opt for crossover U-joints, but they tend to not be as strong and they don’t last as long. This allows you to mate a larger (or smaller) U-joint to the yoke.
For example, you buy a new driveshaft that comes with 1350 weld-in yokes, but your car has 1310 yokes for the transmission and rear differential. A 1350-to-1310 joint has a 1350 on one side and a 1310 on the other, allowing you to install the driveshaft until you replace the slip and bolt-on yokes. Although it can be done, using crossover U-joints is not suggested as a long-term solution. The smaller size basically becomes a fuse and breaks eventually.
The type of joint, solid-body versus greaseable, is important as well. The Spicer-style solid-body U-joints come “lubed for life,” and do not have grease zerk fittings. This makes them a little stronger because they do not have the stress risers created by the opening for the zerk fitting in a greaseable U-joint.
Building the right driveshaft for the application is critical; every high-performance vehicle should have a driveshaft professionally built by a shop that specializes in high-performance drivelines. Have your facts straight if you are going to have a local shop build your driveshaft. The shop or builder needs to stand behind its driveshaft 100 percent. Tell the shop it is for a high-performance application, which is very different from a stock driveshaft and needs to be held to a higher standard.
Ordering a driveshaft over the Internet from a reputable high-performance builder requires accurate measurements and clear instructions of what you have and what you need. In the end, you will receive a driveline that will be perfect for your swap.
From left to right, 1350, 1330, and 1310 are the three most common sizes of U-joints. The 1310, the most common U-joint, is found in most cars. Performance yokes are made of the 1350 series U-joint, though larger and smaller units can be found. Make sure you use the same-series joint throughout the entire driveline. A drivetrain is only as strong as its weakest link.
