Читать книгу Mopar Small-Blocks - Larry Shepard - Страница 8
ОглавлениеCRANKSHAFTS AND CONNECTING RODS
A crankshaft’s main function is to change the pistons’ up-and-down motion into rotational motion, which can be measured as torque and horsepower. Each small-block crank has five main bearings and four journals with two rods per journal.
The crankshaft is another engine part that you should take to a machine shop for inspection. A machine shop can repair almost any crankshaft if it is still in one piece. The most common problem is that small pieces of dirt pass through the engine over time and the dirt scratches the journals. The machine shop or crank grinder can typically repair this damage by carefully grinding the crank journals undersize. A common amount for this operation is .020 inch. The crank is then referred to as a 20-20 crank meaning the mains and rod journals are both .020-inch undersized. You use .020-inch undersize bearings with it.
The stroke measurement is often used to categorize small-block cranks. Mopar A and Magnum cranks fall into one of two groups. The 3.31-inch stroke for the 273, 318, 340, and 5.2L is one group; the 3.58-inch stroke for the 360 and 5.9L is the other.
Only a few production crankshafts are offered for the Magnum and A-engine. This cast 3.31-stroke crank has a casting number on the second counterweight on the left. All street and street/strip packages use the 3.31 stroke crank, and it can typically support 500 to 600 hp. But chances are if you plan on building this much power, you would want at least a 3.58-inch stroke.
The 3.31-inch-stroke crank weighs about 54 pounds; the 3.58-inch-stroke crank weighs about 58 pounds. Cast cranks are generally lighter than forged cranks. The long-stroke 360 crank also has larger diameter mains by .310 inch. The radiused, sealing surface on the end of the number-5 main is smaller on the large-main 360 oil pan.
Small-block cranks become complicated in relation to external balancing. All 360/5.9L cranks are externally balanced, but the 5.9L uses less weight than the 360. The 318 is not externally balanced in either A-engine or Magnum versions. The forged-crank 340 (1968–1971) is not externally balanced, but the cast-crank 340 (1972–1973) is externally balanced.
When building an engine, consider your performance targets. Production crankshafts are suitable for up to about 600 hp for a high-performance street build. If you’re planning to build a race engine, start with a race block and use a performance crank (typically forged or billet).
Both forged and cast crankshafts are internally balanced and have been installed in 318 production engines. When a crankshaft is externally balanced, non-symmetrical weights have been added to the vibration dampener and the flywheel/torque converter/flexplate. The A-engine generally added weight to the torque converter face; the Magnum family adds the weight to the flexplate. In manual transmission cases, the weight is removed by drilling holes in the engine side of the flywheel.
An Eagle forged crankshaft is ideal for performance applications. This 3.31-inch-stroke crank should be good for any street or street/strip package. Customers that want the high-RPM, high-output model probably would want a longer stroke, at least 3.58 inches. The key for cranks, after the stroke, is if the journals are full radiused. Production cranks are under-cut and performance cranks often are fully radiused, and the full radius requires the bearings to be clearanced on the sides, offered by Sealed Power.
It is very difficult to differentiate between a forged crank and a cast crank. If you have a cast crank and it has a casting number on one of the counterweights, you are in good shape. Forged cranks generally do not have 5-, 6-, or 7-digit numbers on the counterweight that can be used for identification. The basic forging process tends to wipe away any number, so they are very rounded and difficult to read. Cast cranks tend to have sharp edges, whereas forged cranks do not.
External Balancing
Vibration and unwanted harmonics are the enemy of any engine, and if left unresolved, they lead to catastrophic engine failure. Thus, any engine, particularly high-performance engines, must be properly balanced. For a max-performance or race engine, I recommend internal balancing performed by a machine shop.
My main reason for recommending internal balance for max-performance engines is that flywheels and converters are often swapped or replaced for performance reasons. Therefore, each time, it must be externally re-balanced. With Magnum engines, external weight is added to balance the flexplate, so converters can be swapped (tested) easily without adding weights to each converter.
With many max-performance applications, SFI dampeners are required. There are SFI externally balanced dampeners, but the choice tends to be limited. Most of these racing applications need lighter-weight dampeners and the external weight limits this approach.
Max-performance engines equipped with manual transmissions present another challenge. These often use a clutch with an aluminum flywheel; it’s very difficult to use aluminum flywheels with any external-balance setups. The drilled holes in the flywheels are used to create the proper amount of external weight, but it assumes that the hole is drilled in steel or cast iron. Because aluminum is so much lighter than cast iron or steel, the balance holes need to be very large.
Solutions are possible, but they are expensive. One solution is to add steel weights to the engine side of the flywheel, but they must be machined into a relief so they do not hit the block. They are then screwed into the flywheel, which makes it expensive.
To explain why some small-blocks are externally balanced and some are not, you have to look at the engines in more detail. The size of the production counterweights on the crankshaft is designed for the production piston, rod, and stock stroke of 3.31 inches in standard forged steel.
Cast iron is slightly lighter than forged steel. When the Chrysler 340 switched from forged steel to cast iron in 1972–1973, the counterweight lost weight and the balance was lost. A small amount of weight was added externally to put the engine assembly back in balance. With a longer stroke, the counterweight has to become larger (heavier).
Space inside the crankcase is also a limiting factor. The long-stroke 360 needed a lot of weight, so it was added externally. When the Magnum 5.9L was introduced, it had much lighter pistons; therefore, the amount of external weight was reduced.
The number-5 main journal is the widest journal on the crank, and therefore it is the least loaded on a load-per-area basis. It is also where the rear seal is located. It is to the left of the bearing surface. The bearing surface is smooth, while the rear seal surface has oiling slots cut at an angle, at approximately 45 degrees. The rear seal groove is the trapezoid-shaped area cut into the block below the seal surface. It is wider at the top and narrower at the bottom. The rear seal sits in this area. If the new crank has these oiling slots cut too deeply or the edges are left too sharp, the neoprene (rubber) seal will leak. This requires a rope seal, which fits in the same groove.
The crank journal oiling holes are in every journal, several per journal in most cases. The crank gets oil from the main oil galley down to the main journals. From there the crank gets the oil out to the rod journals. There are typically two holes per journal, one for each rod. Each one of those holes comes from one of the mains. The production cranks basically let the machining enter the journal and then add a small radius. The aftermarket cranks take this a step further and taper the entrance in the rotation directions (left and right as shown). This helps get oil into the bearings.
These are the top half of the main bearing shells. The top shells get the oiling hole and the groove that helps spread the oil around the bearing. Grooving the crank weakens the crank. Most of the bearing loads are on the bottom shell because the pistons are trying to push the crank out the bottom, so the top shell, the one in the block, is loaded lightly, relatively speaking. This means that the groove doesn’t really weaken the bearing and is very important to getting oil around the bearing. Sealed Power and Clevite are two good choices.
To tell a 360 crank from the 3.31-stroke group, measuring the main bearing diameter and looking for 2.81 inches is probably easier than measuring the 3.58-inch stroke.
High-Performance Street Cranks
An aftermarket performance crank’s most important attribute is that it often has more stroke, so you can create a stroker package and thus add more cubic inches in the engine. Another advantage is having a version that is not otherwise available, such as a 360 crank (3.58-inch stroke) with small mains (318/340 size).
Most production cranks are cast, but forged cranks are stronger and take more abuse. Cast iron is lighter than steel if all specifications are the same. Performance cast cranks from manufacturers such as Scat and Eagle weighs about 54 to 56 pounds. Forged cranks with these same strokes from Scat, Eagle, K1, and Callies weigh about 58 to 60 pounds.
The problem is that all of these crank manufacturers offer lightweight and super lightweight forged crank options; however, they do not list weight specifications for these options. The weight is removed from the crank by machining. If you plan on running a high-RPM engine (more than 7,000), you should consider a lighter forged crank.
Actual race cranks for the small-block come in all sizes and styles. Although most race cranks tend to be forged or billet, the aftermarket does make cast crank versions because they are much less expensive to build.
Early in small-block racing, race cranks were made with an eight-bolt crank flange, similar to the Hemi racing block. This adds complexity to the customers’ overall engine package, so in later years, six-bolt cranks were also used in max-performance applications.
Flywheels and flexplates are available for either flange. Most max-performance or racing cranks use a special stroke to achieve a certain displacement. The 2.96-inch stroke was designed to give the 340 engine a displacement of 305 ci, which was required by the Trans-Am sanctioning body. This is what the 1970 305 Trans-Am racing engine used.
The second race crank consideration is inertia, or rotating weight. The forged race crank can be made at less weight and less inertia.
The cast crank is slightly lighter because of the material but not as strong as the forged crank. In general, the amount of stroke is more important than the amount of horsepower. With the 3.58-inch stroke, more than 600 hp might mean a forged crank, but you probably have selected the forged crank earlier because it is lighter. Be sure to balance any new and lighter crank.
Every rod must have an oiling hole and that hole must be connected to a main journal. These holes are drilled at an angle that has to be calculated by the manufacturer to start and end up in the correct places.
Production forged cranks made from 1050 or 1053 heavy-duty alloy of mild steel are strong and easy to machine in very large quantities. The aftermarket developed a special alloy forging steel and it offered a 65-percent increase in strength over mild steel. When racing RPM and output went up, strength needed to increase.
To fill this need a special alloy steel called 5140 was introduced for cranks that offered a 6.5-percent gain in strength over the 1050 steel baseline. Then the aftermarket moved on to 4340 material that offered around a 75-percent gain over the 1050 baseline. These high-carbon steels (5140 and 4340) offer more strength but are more difficult to machine and they wear out tools fast, which makes them suited to low-volume performance/racing applications.
Note that on the rod journal that is just below the pan rail, with only one rod and rod cap on it, next to the main cap, the journal does not have a groove (undercut) next to the side of the crank . It transitions from the rod journal to the side of the crank in a smooth radius, which is called a full-radius crank. This style of crank is made for racing and generally very popular in the aftermarket because it is stronger than using the undercut. With full-radius cranks, you have to radius the bearing shells.
Most engine builders have opted for 4130 (125,000 psi) or 4340 (145,000 psi) forged cranks because of their toughness and longevity. The 4340 crankshafts have supported up to 1,500 hp, so unless you need a billet crank, a 4340 forged crankshaft is suitable for extreme and racing builds. Strength numbers are based on SAE tensile-strength data.
Billet Cranks
A billet crank starts out as a large round log of steel (an ingot) and then a CNC mill fully machines it into the desired dimensions. This process makes it very easy to change the stroke; therefore, you can produce a special one-off crankshaft that has the exact dimensions you need.
With a forged crank, small adjustments can be made, but these changes are very limited by the forging. If you are looking for a special stroke length, such as 2.88 or 4.25 inches, you might be looking at a billet crank.
Measuring the width of the rod journal on the crank with a dial vernier is quite easy and the width will come in handy to estimate rod side clearance. It is difficult to measure rod side clearance directly until the engine is being final assembled, which might be too late to fix any potential problem.
A billet crank can be used for a high-horsepower street/strip engine, but these are expensive cranks used for their high strength in race engines. Weight considerations must be taken into account if a lighter crank is desired in a race engine. Moldex is one of the premier billet crank manufacturers but has a limited website; Winberg, Callies, K1, and Scat have more information posted on their websites. They can make almost any variation of the Mopar small-block crank.
For example, the Trans-Am engine used a 4.04-inch bore (stock 340) and a 2.96-inch stroke. Assume that you want to build a 295-ci engine out of the basic Trans-Am package; the stroke has to be 2.88 inches and that length is not readily available. If you want to duplicate it, you must purchase a billet crank. Longer stokes than offered by readily available forgings are more likely, such as 4.050 inches or longer.
Opinions differ about whether or not a billet crankshaft is stronger than a forged crank. One thing is certain, billet crankshafts are stronger than cast and, in most cases, support up to 1,500 hp. But it can cost up to $3,000 to build a billet crankshaft. Unless you need to construct a billet crankshaft for a special application, you are probably better off with a forged crankshaft. The biggest advantage of a billet crank is being able to build an engine with a unique stroke.
Notes:
• The 340 block has thin cylinder walls and it cannot be overbored more than .030 inch. Sonic-test before boring to be sure proper thickness is available.
• The .030-inch oversize is a common aftermarket piston and ring size for these engines.
• The 3.79-inch stock was a common performance crank/stroke in the 1980s and 1990s before the 4.00-inch cranks were readily available.
• Race blocks allow bigger bores than 4.07 inch.
• Most cranks that increase the amount of stroke over the engine’s standard stroke are generally called stroker cranks. Stroker cranks are an easy way to increase the engine’s displacement for increased torque and horsepower. A stroker crank must be used with other parts that work together as a team. The easy one is a stroker crank and a special piston that adjusts for the extra stroke length by moving the pin up in the piston and using the stock rods. In some cases both the rods and pistons are changed.
Crankshafts for Your Application
In an effort to tie all engine hardware together into performance packages, I created five packages that vary from 350 hp to over 700 hp, and all are intended for street/strip applications.
| Package | Best Crank | Rod |
| No. 1 | Stock, cast or forged | Stock with good bolts |
| No. 2 | Stock, cast or forged | Stock with good bolts |
| No. 3 | Aftermarket cast or forged | Above or HP I-beam |
| No. 4 | Forged | HP I-beam or H-beam |
| No. 5 | Forged | HP I-beam or H-beam |
Note: Any one of these packages could use a lightweight forged crank. But neither a lightweight forged crank nor a billet crank is required.
Almost all race cranks use full-radius journals on the cranks; all production cranks, both cast and forged, use undercut journals. The full-radius journal makes the crank much stronger. Undercut-radius cranks make it easier to assemble the engine, which is very important when you are building 50 engines per hour or 1,500 engines per day. The bearings must take a full radius into account either by radiusing the bearing individually or by obtaining bearing manufacturer information for full-radius journals.
When you buy a new crankshaft, you don’t have much prep work before you install it, but you should carefully inspect it for nicks, scratches, and any damage. You also need to verify a few measurements. I recommend doing a quick check on the crank’s end play by installing the number-1, -5, and -3 thrust bearings and lowering the crank into place, torqueing the three main caps, and checking the end play with a dial indicator.
In most cases, a new crank comes polished. In some cases, a used crank can be polished to remove very light scratches and normal wear; then reinstalled.
Repair
If the wear is high and/or there are scratches that are too deep to polish out, the crank is typically sent out for repair, which means to grind it undersize. This might be .020 inch. It is common to grind the crank .020/.020-inch undersize and then use matching undersize bearings.
A technician uses a special machine to balance your crank, rods, pistons, and dampener and flexplate/flywheel. You need to balance the assembly and you can’t change pieces after the balance numbers are set. Sometimes the dampener (at far right) and flexplate/flywheel (about in the center) are optional. If you can provide all of the weights needed, the manufacturer can balance the crank. With a used crank, if the rods are staying the same, and the pistons are made to service weight, then balancing may be optional. However, many performance pistons are lighter and you might want to rebalance for the lighter hardware.
A machine shop might put the crank in V-blocks to measure the stroke. However, if you want to measure it yourself, it is most easily done in the engine. With one piston-and-rod assembly installed (rings optional), rotate the piston to BDC (bottom dead center) and use a dial vernier to measure from the top of the block to the top of the piston. Use a straight edge at the top of the block to help keep the vernier straight. Rotate the piston up to TDC and measure from the top of the piston to the top of the block (piston’s deck height). Subtract the two numbers for the stroke. (Photo Courtesy R. Koffel)
If the crank needs more serious repair and the amount of undersize grinding is .040 or .060 inch, you should consider having the crank re-heat-treated by a process called nitrating. Grinding the crank more than .020 or .030 inch grinds much of the crank’s surface hardness away. The nitrating process can add hardness.
A qualified local machine shop should check the balance of your new crankshaft (in this case, it’s an Eagle forged crank). Most cranks are ground to an assumed common package, but most engines are somewhat different, so there can be problems that your local shop will find because they have the actual hardware. If extra-light pistons were assumed and only light pistons are being used, the crank’s counterweight may have a lightening hole that is not needed. The shop will press in a cast iron/steel plug, cut to size, and then weld it in (the dark spot at the top left of the first counterweight). Aftermarket manufacturers usually use the stamped numbers on the front face on forged cranks for identification purposes.
Lubrication Grooves
The rear main seal surface, just before the crank flange, contains small grooves cut at an angle to the centerline of the crank. Almost all production cranks have these grooves. Aftermarket cranks may or may not have these grooves. Chrysler replaced the original rope seal in the late 1960s, and the newer rubber (neoprene) seal with the lip design that must point at the center of the engine does not require these grooves. If you find a new crank that has the grooves and they have sharp edges, the grooves should be polished to help protect the rear seal from damage.
On a new crank, if the grooves are cut too deep or the edges of the grooves are too sharp, the rubber rear main seal may not seal and the engine leaks oil. The solution is to use a rope seal, but they are difficult to find. It has been so long since rope seals were used that most manufacturers just put the rubber seal in the various gasket kits. You can obtain a new rope seal from Best Gaskets, among other suppliers.
Crank Mods
Crank manufacturers offer special modifications. Some modifications offer advantages in windage and rotating inertia, but they can be very expensive. When it comes to making the crank lighter, I prefer to cut down the counterweights’ diameter because it gets the most weight off.
Once the block and crank are prepped, you should check the crank’s endplay at the final assembly to make sure it’s within spec. The crank is rotated so that one of the flat counterweights is up and access is available. Set up the dial indicator with the pointer parallel to the crank centerline and the pointer on the flat surface of the counterweight. Use a large screwdriver between the counterweight and the bulkhead and lever the crank rearward. Zero the indicator and then lever the crank forward. The reading on the indicator is the crank endplay.
The main cap just to the right of center has the special cap screws used with the windage tray. If a windage tray is going to be used, these special headed bolts are required. If you are planning on using a stroker (long-stroke crank) then you may have to clearance the rotating assembly to the windage tray. This holds true for special aftermarket scrapers and windage trays by companies such as Milodon.
Knife-edging also makes a crank lighter. For this approach to be helpful, you have to include high RPM in the equation. For most people, knife edging isn’t worth the expense, but a lighter crank at a competitive price is worth it!
Only two bearing sizes are offered for the small-block: the standard 273-318-340 and the large main 360. Bearings have been made of tri-metal, aluminum, or babbit, but tri-metal is the most popular today. Clevite, Sealed Power, Mahle, King, and Dura-Bond make bearings for the Mopar small-block.
Most make a version of a tri-metal bearing (copper-lead mix typical), but several manufacturers offer an aluminum mix. Mahle offers a moly-graphite coating, which may provide a wear benefit.
Some bearing companies offer bearings that have been radiused for use with full-radius cranks. Most bearing companies offer various under-size bearings for the repaired cranks (.020-inch undersize is common).
The basic dampener design has a steel/cast iron outer ring that is mounted to the hub by a rubber isolator (thin strip). As the engine vibrates, the outer ring absorbs these vibrations and basically cancels them out. You should always select a vibration dampener suited for the specific engine, in this case a Mopar A or Magnum. Although not required, SFI dampeners are best; these include versions from ATI, TCI, or BHJ.
I recommend staying away from aluminum dampeners (solid) or any one-piece dampeners. If an SFI dampener is not available for your engine, stick with the production dampener for street use. A street engine or street/strip engine must have a dampener, and many options are available. Any street/strip manual transmission should have an SFI dampener, and any engine using 7,000 rpm or higher should have an SFI dampener. The leading manufacturers are ATI, TCI, BHJ, Pro/Race, and Fluidampr. Each unit is unique.
Race engines need lightweight dampeners, but street or street/strip engines do not require a low-mass dampener. The TCI Rattler weighs just over 8 pounds and features a unique construction.
The Pro/Race offerings are more traditional with a steel outer ring construction and a production-type weight of more than 11 pounds.
The BHJ dampener is also built with the outer-ring-style construction (similar to production) and weighs just under 8 pounds with a combo option at just over 6 pounds.
ATI has the most models that feature two or three discs/rings mounted inside of a shell. The shell can be made of steel (8.75 pounds) or aluminum (6.25 pounds). Both are three-ring versions plus there are two-ring versions at 7 and 5.45 pounds, respectively. I do not recommend the two-ring versions for street use.
The Fluidampr is distinctly different from others and is around the production weight.
Dampeners need to be tuned for specific engine hardware: stroke, engine RPM, etc. I feel the Fluidampr is best for non-standard engine hardware, unique stroke length, or unique cubic inches, etc. Several dampener manufacturers solve the external balance issues of the 360 and 5.9L engines (they are not the same) by adding small weights in the hub area.
The non-symmetrical 360 dampener is basically round but has an offset weight. The weight is placed in the wide flange on the front of the dampener, which only extends for about 200 to 250 degrees, or in a trough cast into the front face of the outer ring for less than 180 degrees.
These non-symmetrical dampeners are also somewhat thicker than the standard 318/340 dampener. The original 5.9L Magnum used a dampener similar to that of the 5.2L. Newer versions used a large, one-piece dampener and front pulley.
The 318 dampener (on the right) is symmetrical; basically a round disc. There is the timing mark on the outer ring and the six bolts that allow the front pulley to be attached. The 273 and 340 forged crank dampeners are basically the same as the 318. The original Magnum 5.2L engines used a similar dampener but newer versions went to a one-piece dampener and front pulley assembly, which is very heavy and difficult to work with. The 360 external balance dampener is on the left with the weight added toward the top of the dampener.
The 360/5.9 external balance dampener can have the external weight removed from the opposite-side weight (see page 33). The trough in the face of the dampener from about one o’clock to about seven o’clock removes weight that balances the engine just like adding weight to the dampener at four o’clock.
The connecting rods are a critical part of the rotating assembly. The rod’s weight (in grams), material (steel, titanium or aluminum), alloy (forged steel or high-carbon steel for the steel versions), style (I- or H-beam), and pin retention (pressed or floating) are all important.
Production Versions
There is not much to pick from in the production small-block connecting rod area because they are all made of forged steel and are 6.123 inches long. The tricks come with the 318 rod being lighter and the 340 rod having a bushing in the small end to accept a floating pin. All production rods use 3/8-inch bolts and nuts to attach the cap to the rod’s beam.
All race dampeners are SFI-approved and these dampeners can be used on externally balanced engines. Race dampeners were made much lighter, but lighter weight tends to place more stress on bearings. In some very popular engine packages, the manufacturers actually develop (or tune) the dampener to the specific engine package and RPM range that the engine is currently using.
For high-performance applications, use ARP bolts in place of the stock rod bolts in any production rod. With good bolts, the stock rod is fine. High RPM will cause problems for pressed pins, but stock rods typically hold up well.
Aftermarket High-Performance Rods
Selecting the correct connecting rod is one of the most important decisions you make when building your engine. Mopar connecting rods are offered in I- and H-beam design and in forged or billet constructions. Cast rods (not used in Mopar small-blocks) are adequate for base high-performance street engines up to 500 hp, but beyond that you need to consider a forged connecting rod. Billet rods are typically used for 800-hp race builds. Aluminum rods are also forged and are used on supercharged engines but not required in the street/strip versions. They are limited to race engines. Another player is titanium, but these are also race-only parts.
Connecting rods are detailed parts. Because all production rods have the same length (6.123 inches) you can use the forging number for identification or you can weigh the assembly and compare weights.
For engines built to rev more than 7,500 rpm, I recommend a high-performance rod from Eagle, Scat, K1, Carrillo, or Manley. You must not mix and match rods; they need to be installed as sets. My first choice is the 585-g Scat I-beam with 7/16-inch bolts and cap screws; it provides adequate strength for any street/strip build package. All production rods use 3/8-inch bolts, except K1 rods, which use 7/16-inch bolts for greater strength. However, these bolts add weight to the rod assembly.
In some cases, the I-beam rod is slightly lighter than the race-designed H-beam style. The Eagle I-beam rod weighs 605 grams; the H-beam version weighs 680 grams. The standard Manley I-beam rod weighs 555 grams but is limited to 550 hp; the “Pro” I-beam rod (a heavier forging) weighs 670 grams and is rated at 700 hp.
Note: Only the 340 used floating pins. Connecting rod weights: big end, 500 grams; small end, 226 grams.
When mounted to the connecting rod, the piston must have clearance between the two-piston pin towers (one on each side). This production-based piston has 1/4 inch on each side. With performance or racing pistons, this clearance tends to get much smaller and, in some cases, may have to be checked. This is not really required for production or service packages. Note the round hole in each pin tower for pin oiling. Each manufacturer uses a different method to oil the pins.
The big end of the rod holds the rod bearing shells and bolts hold the cap on to the beam, which in turn holds the rod to the crank. The key to all of that happening correctly is the rod bolt and nut (toward left). Production-based rods use the rod bolt and nut attachment method. Note the forging number on the beam (at right). It has eight digits so it is probably a Magnum rod. The A-engine used seven-digit forging numbers.
The 340 forging is the only A-engine connecting rod that has a bushing for use with a floating pin. It is difficult to see the bushing after it is installed but you can see the small step in the machining at the pin bore, which is just the end of the bushing. This bushing cannot be added to the standard forging used in 273/318 engines because there is not enough material around the small end to support the bushing machining.
The H is actually a heavy-duty rod designed for extreme performance and racing. Keep in mind that Scat and Carrillo do not publish weights for their H-beam rods. The K1 H-beam rods weigh 656 grams with 7/16-inch bolts. However, I don’t think 7/16-inch bolts are required for these street applications, but they are a nice plus if they don’t add weight as does the lightweight Scat design.
Dyers and other billet rod manufacturers offer H-beam rods in four categories: light (585 grams), ultra light (575 grams), super light (540 grams), and heavy (600 grams). Billet rods are best suited to special-application engines, such as race 305 engines with 2.96-inch stroke.
