When most people think about performance the first thing that usually comes to mind is more power. Improving the performance, control, and driveability of first-generation Mustangs is much more than increasing horsepower and torque.
This Tech Tip is From the Full Book, FORD MUSTANG 1964 1/2 – 1973: HOW TO BUILD & MODIFY. For a comprehensive guide on this entire subject you can visit this link:
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In this book, I cover what you can do to not only make more power, but also to improve the driveability, reliability, and durability of your engine. I only discuss engines originally offered in first-generation Mustangs and focus this coverage on the Windsor small-blocks and some of the Lima and FE big-blocks. I do not cover common passenger car 6-cylinder engines or rare engines such as the Boss 302, 351, or 429.
In other chapters I also get into engine swaps, crate engines, and the logic for them. For now I assume you’re going to modify your existing engine or use a similar short-block. I discuss parts that go on the engine (such as a water pump) as well as the related vehicle components (radiator, fan, etc.). I can’t get specific about each possible engine/component so I keep the discussion generic. I explain various modifications, the types of options available for each, and when they should be used. My general guidelines should help you narrow down your choices to a certain type of part or modification. You still have to do your own research to choose the specific part and manufacturer that’s best for you.
With regard to the short-block and its associated components (crankshaft, rods, pistons, etc.) I assume that nothing will be changed for your daily driver unless repairs are needed. Your existing shortblock is either in good shape, rebuilt/ blueprinted, or replaced with a crate short-block.
Installing a crate engine is often the best option. High-quality machine shop services don’t come at a cut-rate price. In many cases a ready-made crate short-block is less expensive than performing all the machine shop procedures, buying parts, and assembling an engine. In addition, the crate engine will suit your specific performance goals and your budget. You don’t have to wait as long for a crate, plus you benefit from a proven and properly matched combination of components. Manufacturing processes have been validated over hundreds or thousands of prior products.
If you still decide to do a rebuild because you have a numbers matching engine or want to control the process more closely, make sure you find a reputable machine shop that has positive references from people you trust. (Mike Mavrigian’s Modern Engine Blueprinting Techniques explains the proper steps for blueprinting and balancing. It will help you understand your options at the machine shop so you can make better decisions.)
For high-performance street applications, a crate engine that produces about 500 hp with 6,500 or less RPM is commonly available. Most stock Windsor/small-blocks and FE 390-ci or larger big-blocks can generate this amount of power and are affordable. When you buy a crate short-block from a reputable source, such as Dart Machinery, Coast High-performance, or Ford Racing, etc., you can be assured of this, whereas a given machine shop may not have the proper knowledge and/or equipment.
Of course, some stock blocks are better rebuild candidates than others. In fact, many builders use the later 5-liter small-blocks rather than the older 289/302 blocks because parts are more plentiful and affordable. These engines also have better materials and machining, plus hydraulic roller cams. A reputable crate-engine or short-block supplier uses the best block because they don’t want any returns or warranty claims. They generally rate their products for a maximum output. They have produced hundreds, if not thousands, of each combination for virtually any use, so they have a huge database of information.
A typical short-block for a high-performance street car uses a stock-type iron block and forged I-beam connecting rods. These rods are sufficient for mildly to moderately modified engines up to 500 hp when upgraded with stronger (ARP or similar) rod bolts. With power levels of 550 or more a stronger, forged H-beam rod with precision-ground alignment sleeves and larger, stronger ARP cap screws suffice. This design is far superior to using the shoulders of the rod bolts for locating the connecting rod caps. Solid dowel pins are stronger but aren’t usually needed in this situation. You should usually use a full-floating piston pin with a bronze bushing at the small end of the rod with a small and properly located oiling hole for the pin.
Many other variables, such as the materials used, as well as the specific manufacturing methods and processes chosen also must be addressed. Select a crate engine that matches your needs and budget to have these correctly decided for you. Carbureted and EFI engines are offered with a variety of camshaft, cylinder head, induction, and internal part options to match your requirements. If you decide to build a short-block you need to research such factors and discuss them with the machine shop to determine what’s best for you.
The bottom line regarding connecting rods is that a simple I-beam rod with upgraded/ARP bolts generally suffices for a 450-hp small-block (550 hp for big-blocks) with proper balancing, blueprinting, and assembly into a good block. If you’re making 600 hp (800 hp for big-blocks) and/or going to higher RPM, you should upgrade to the H-beam rods/ cap screws.
For a streetable track-day vehicle with even more power (up to 800 hp with aftermarket small-blocks, 950 hp for big-blocks) you’ll likely go right to a solid-doweled H-beam rod. However, if you’ll be experiencing much higher RPM a specially machined and doweled lightweight I-beam rod may be best. It should be made from a superior alloy (4340 or 300M) steel and upgraded to use stronger cap screws. This setup can be stronger than an H-beam rod yet significantly lighter to perform better at the higher RPM. These rods can often withstand more than 1,000 hp.
If maximum RPM in a smallblock with an output of 500 hp or less is expected they can be further machined and lightened. This would likely only be the case where a very light steel rod was needed instead of an aluminum rod. The latter aren’t advisable for street or other longterm use due to their tendency to fatigue and stretch with time. Stick with the H-beam for most street and road race uses.
Piston selection can be complicated. In addition to choosing pistons that fit and are strong enough, you also have to consider compression ratio and compression height. For a daily driver you’ll likely use a cast, stock-replacement piston although there are advantages to upgrading to a hypereutectic piston. The latter are lighter and stronger so they hold up better. They’re more dimensionally stable, thus providing a better seal, improved performance, reduced oil consumption, longer life, lower noise (particularly on cold starts), and lower emissions.
Hypereutectic pistons cost a bit more than regular castings but less than forgings. For a moderately modified engine of 400 hp or less they can be a good choice if you don’t significantly increase engine output. With significantly more power, you’ll likely want to use forged pistons.
The options for forged pistons are numerous, so here are a few of the things to consider when choosing one. Piston material, ring choices, and coatings need to be researched independently because there are so many options available for many engine packages. The correct diameter and compression ratio are most critical, and you need to correctly determine bore size, stroke, and combustion chamber volume. The compression height (where the top of the piston is relative to the top of the bore) and the top shape are piston-specific factors. In general, you want the piston to travel as far up in the bore as possible without creating clearance problems with the valves or the head. The thickness of the head gasket can influence this but it’s usually best to have the top edge of the piston at or very slightly below the top edge of the bore.
Piston dome shape largely affects compression ratio (CR). Your options are dished, flat-top, or domed. Dished types keep the compression ratio lower and provide the least restriction to mixture flow. If you can get the CR you want with a dished piston it’s often the lightest and best choice for in-cylinder motion/mixing. This helps increase the burn rate for better combustion efficiency. With aluminum heads and 93-octane pump gas, a CR of 10:1 to 10.5:1 is generally feasible for street use without the need for octane boosters. This can often be achieved with a mildly dished piston. This CR is about optimal for a street-performance car though generally not possible for a daily driver with stock replacement parts (about 9.5:1 max).
For a streetable track-day car, engines are built with a higher CR for increased output and to prevent preignition/detonation. The CR is really only limited by rules for a particular event or series. Unless you’re willing to always use special fuels, octane boosters, etc., the highest CR you should consider for a street car with aluminum heads is about 11.5:1 because the quality of pump gasoline can vary.
To achieve a higher CR you likely need a flat-top or (more likely) a domed piston. Flat-top pistons often need to be “fly cut” to provide extra clearance for the valves, especially when high-lift cams and/or largediameter valves are used.
Combustion chamber shape and valve location are also factors. Some cylinder heads, such as the Trick Flow Specialties Twisted Wedge heads, rotate the combustion chambers and slightly change the angle of the valves to unshroud them for better flow. Special pistons are thus needed to properly match the new valve locations.
Pins and Rings
You need to consider piston pin height, especially for a stroker engine. The same bore and stroke can be achieved with a variety of rod length and pin height combinations. Piston speed, rod angles, thrust pressure, and many other parameters must be considered, especially with higher power levels. You also need to decide whether or not the pin will extend into the oil ring groove, which is usually to compensate for an increased stroke. This can result in an additional leak path for oil and combustion pressure.
Oil ring technology has improved greatly to make these leaks less of an issue but it’s best to avoid them, particularly for a street-driven and/or road race vehicle. Doing so provides better ring sealing, combustion efficiency, and performance.
With regard to other pistonrelated items, it’s usually good to have a small oil hole under each piston pin boss for extra oiling. In very high-output, high-RPM engines it may even be necessary to install oil jets, which squirt additional oil under each piston to help cool them. In general, a street-driven vehicle should use a production-style ring pack with standard-tension rings. Low-tension rings can be fine for a race car where maximum power is desired and the increase in oil consumption is not a concern. Likewise, neither very thin rings nor reducing the number of rings is a good idea for a street car. Gapless rings can provide a better seal as long as they are properly fitted and installed.
If you use a crate short-block/ engine these choices will be made for you. Otherwise you should check with piston and ring manufacturers, the shop you’re using, and others for recommendations. In any case, make sure the ring gaps are sized correctly to each individual cylinder and they are properly staggered away from each other on each piston.
Piston pin choices are to use a 1018 steel (or similar) stock replacement pin for a daily driver or a mild street performance car. Move up to a stronger and lighter 8620 steel tapered-wall pin for most street performance applications. For very high-output street performance cars and streetable track-day cars a 52100 bearing steel pin has the lowest weight and highest strength, for about twice the cost of 8620 pins.
Using piston coatings is another aspect to consider because it offers anti-friction coating on the piston skirts. This OEM technology allows a reduced piston-to-bore clearance to improve combustion efficiency, especially when the engine is cold. It also reduces noise on initial startup and improves piston stability under virtually all conditions. This coating is generally not very expensive and is particularly appropriate for forged pistons where a larger bore clearance is required because forgings tend to change shape more than cast or hypereutectic pistons. An antifriction coating can allow you to have the added strength and (sometimes) lighter weight of a forging while not sacrificing too much piston-to-wall clearance and sealing.
Other coatings, such as heat barriers on the piston crown and/ or harder coatings for the piston pins, are generally not needed for the engines in this book. Similarly, hard anodized top ring grooves, exotic/ultra lightweight skirt designs, special pin locks, gas ports, etc., are also neither advisable nor needed for street cars. Leave them to racers.
The rotating assembly is a crucial part of the engine package. For a daily driver you only need to use what you already have, or its equivalent, if it needs to be rebuilt or replaced. A cast crankshaft along with OEM main caps and balancer do just fine for a near-stock power level. If you’re doing a rebuild, some minor cleanup in terms of chamfering the oil holes on the crank and making sure the fillet radii are revised can reduce the potential for stress concentration. If there’s no other damage all you really need to do is a balancing job if you intend to keep the engine and further upgrade it.
The stock bearing caps and bolts are fine as long as they’re not worn or damaged. You should, however, upgrade to a better bearing set for the mains, rods, and cam just to get the benefit of greater durability.
The cost difference between a “performance” bearing set and a direct-replacement set is minimal but the performance bearings generally have a stronger backing material with added clearance for the crank journal edges as well as thinner/ stronger, yet superior, facing materials. Some silicon-based facings can actually help to micro-polish the crank journals over time to improve performance and longevity.
Additionally, performance bearings generally have longer oil grooves (where applicable) to enhance lubrication while still providing enough bearing surface area to handle the higher loads of high-performance use. They also tend to be more resistant to corrosion and embedding of debris, which should improve durability in long-term use. Full competition/race bearings should be avoided because of their much higher cost and their tendency to trade durability for load capacity
If you want even more power for a high-performance street car or a streetable track-day car, you almost surely need an aftermarket block for the Windsor small-blocks (except for possibly a 351-based engine with not much more than 650 hp). Aftermarket blocks, such as the SHP blocks from Dart Machinery, are capable of handling far more power (more than 600 hp) due to many design changes they incorporate relative to even the best stock blocks.
The Dart SHP small-block (8.2- or 9.5-inch deck heights), for example, is an all-new precision-machined casting with much closer tolerances than the comparable OEM block yet it also retains the ability to bolt on the original (or comparable aftermarket/upgraded) components. Other design changes include thicker decks, cylinder walls, and other surfaces for strength and improved sealing as well as revised/scalloped coolant passages. All of these increase total coolant flow and equalize the flow at each cylinder. This prevents hot spots and/or insufficient coolant flow, which can reduce power and increase detonation.
The oiling system has also been upgraded to a “priority” design, which directs oil to the main bearings first for greater dependability, especially under higher accelerations and turning. A really neat feature is that the head bolt holes are all blind, tapped holes that don’t open up into the coolant passages. This not only stops potential leaks but it also ensures more accurate torque readings because you don’t need any sealant on the head bolts (or studs). Stronger, splayed, fourbolt steel (versus iron) main caps are used on the three center main bearing bulkheads to greatly increase strength and stability without the need for a main bearing girdle. The crankshaft is held much more solidly and securely, thus reducing flexure and the potential for bearing damage and/or failure.
The Dart SHP blocks also allow for the use of later-model OEM-style roller hydraulic camshafts because the bosses for the “spider” retaining plate as well as provisions for the “dog bones” and roller lifters are present. Roller hydraulic camshafts can generally provide significantly better performance without the driveability and other tradeoffs of a flat-tappet cam. They also last much longer and are not as noisy, nor should they require periodic adjustment.
Aftermarket blocks, such as Dart’s SHP small-block, retain the stock motor mounts and you can still bolt on just about any OEM and aftermarket component, plus you have much, much higher strength, durability, and performance potential compared to stock components. Such a block certainly sets you back a few more pennies than a stock block, but it’s the only way to go once you get beyond a certain power and/ or RPM level. Dart also offers even stronger versions (Iron Eagle, etc.) of the small-block Windsor, which are intended for even more extreme and/ or competition use. A lightweight aluminum version is also available (see Chapter 6).
You can stay with a stock block for a big-block engine up to 800 hp or so as long as you’re not revving it too high and you upgrade the rotating assembly. However, it’s usually best to go with a stroked 351-based crate engine instead of a big-block, even if the latter is what you already have. It’s often much harder to find upgraded parts, including crankshafts, for bigblock engines (except for the 460). You can make big power with a bigblock and it is even easy to do. At higher power levels, costs rise and parts availability drops. A big-block rarely achieves the overall refinement possible with a stroked Windsor.
For a high-performance street vehicle, you can still use a cast crankshaft if you’re using a stock block and the power level is 600 hp or less (800 hp for a big-block). You want to upgrade to a better crank, however, at the higher end of that range. A crank cast from high-carbon steel is a relatively inexpensive upgrade from a stock cast crank yet it is all you need with a stock block. A stock block will likely fail before the crank, especially if lighter rotating parts (pistons, rods, etc.) are used. For the main caps you can still use the stock caps although you may want to go with stronger studs and nuts from ARP rather than reusing the stock bolts. ARP studs are made from a much stronger material and they distribute the load better within the block while also ensuring a more accurate torque reading. Using premium fasteners, such as those from ARP, protects against damage and failure. Buying a complete engine set from ARP provides these benefits and ensures you have the correct fastener types, sizes, and lengths.
For even more bottom-end strength with a stock small-block you can use a main bearing girdle. This steel brace ties the main caps together to spread the loads that each one encounters. The effect is to reinforce each individual cap. It can really stabilize a stock-block engine with two-bolt main caps; highly recommended if you’re near 600 hp. Big-blocks are a deep-skirt design, which inherently performs a similar bracing function.
Once you’ve decided on an aftermarket small-block such as the Dart SHP or a big-block to make up to about 600 (small-block) or 800 hp (big-block), you need to think about the type of crankshaft you need. At these power levels a cast crank no longer gets the job done; it’s time to step up to a forging. Forgings made from 5140 or 4130 steel are generally good up to about 700 hp, depending on the specific type of use (drag racing versus road racing, etc.).
For higher outputs up to 1,000 hp or so a heat-treated 4340 alloy forging is probably the best way to go. At these high power and/or RPM levels the material used is critical but so are the manufacturing processes and design elements. First make sure you have the right alloy for your situation and then narrow down your options by comparing the type of heat treatment used, the type of hardening (nitriding versus induction, for example), the surface finish and polishing specs of the finished crankshaft, and design features such as the rolling of the fillets and the shape of the counterweights, etc.
As your short-block is being assembled be sure to use an appropriate assembly lube, such as those from Joe Gibbs Driven, Royal Purple, or Red Line. All the bearings (main, rod, cam) should be coated with lubricant to ensure there’s no damage on initial engine startup. Engine assemble lube stays put and offers superior protection against wear until the oil pressure rises enough to take over. This lube also blends into the oil and does not clog filters or oil passages.
A final component to consider here is that of the harmonic balancer. Production engines are usually externally balanced, which means the balancer and the flywheel/flexplate must be matched to properly dampen the torsional vibration pulses of the crankshaft and prevent destructive resonances. Internally balanced engines are referred to as having zero or neutral balance; they don’t require any imbalance on the balancer or flywheel/flexplate. Ford used mostly 28- and 50-ounce balancing specifications, which relate to the counterweights attached to (or integrated into the design of) the balancer and flywheel/flexplate. Later 5.0L engines, for example, are 50-ounce balance engines while most of the early small-blocks had a 28-ounce balance spec.
Many aftermarket crate engines and short-blocks are neutrally internally balanced so there’s no external counterweighting. This requires more precise internal blueprinting and balancing but it is worth it because the engine is able to be balanced to a finer specification with less total weight, particularly in terms of rotational inertia. This helps improve engine responsiveness and also eliminates the potential for a counterweight to fall off and cause extreme imbalance and vibration, which could result in engine failure. Bottom line? Know the balance spec of your engine and use the appropriate components. They all must match.
For a daily driver an OEM direct-replacement balancer is usually more than sufficient for its mild level of modification. These can be purchased fairly inexpensively at most major parts stores and are a good thing to replace even if you don’t need to rebuild or replace your engine. The reason for this is that virtually all stock/OEM balancers consist of two metal pieces with a rubber layer between them. Over time the rubber can deteriorate to the point where the metal parts shift relative to each other, thus creating an imbalance and the resultant vibration. Because the timing marks for the ignition are also on the outer metal ring such a shift also causes an error in setting the ignition timing. If there are any signs of the rubber layer having cracks or the metal parts having shifted (such as the outer ring being cockeyed so that it appears to wobble while the engine is running), the balancer should be replaced.
The high-performance engines require an upgraded balancer to match any changes made to the short-block and to better handle the higher forces and RPM. In most cases, an upgraded aftermarket balancer of the same basic design as the OEM part suffices. The Professional Products balancer, for example, is an excellent choice because it has a removable balance weight. The materials and tolerances have been improved to handle higher stresses and speeds plus there are additional timing marks for more accuracy. This particular part complies with SFI specification 18.1, as is required by many sanctioning bodies before a vehicle can participate in their events.
For more serious competition vehicles there are other balancers that use silicon gel, rotating weights, and other proprietary design approaches, which do an even better job of canceling torsional vibrations, making more power, and reducing bearing wear. They are really only necessary with very high power levels and at very high RPM. Their cost is significantly higher and they are usually not designed for long-term/street use and/or harsh climates.
Stock rubber motor mounts tend to fail over time by developing cracks, which allow increasing amounts of unwanted engine movement. In extreme cases a mount can fail completely, thus allowing the engine to move to the point of preventing proper function of the clutch (especially with the stock clutch linkage) or even causing a stuck throttle.
On a daily driver with few modifications a new set of stock-type mounts normally do just fine.
For a high-performance street car you want to upgrade to polyurethane mounts, which further reduce unwanted movement. Those made by Energy Suspension also have an internal metal interlock feature to provide additional safety should the polyurethane material fail; these tabs still restrain the engine to a limited range of motion until repairs can be made. In some cases it may be necessary to add a supplementary torque strap or chain to further restrain engine movement under very high torque conditions. This also helps prevent damage to the polyurethane and serves as a redundant safety feature.
Adjustable mounts can be used to change the location of the engine slightly by lowering it a bit and/or moving it slightly front to back. This can help with handling by locating the engine mass in a more favorable position plus it can also help resolve clearance and packaging issues.
For maximum flexibility, strength, and safety fabricated solid mounts or an engine plate can be used. These are very hard to live with on the street due to the extra noise and vibration they transfer to the rest of the car. The engine plate can also make servicing spark plugs, etc., much more difficult. Realistically, these should only be considered for the streetable track-day car or for true race vehicles.
Adjustable mounts that have some polyurethane cushioning in them are a much better choice for regular street use.
Written by Frank Bohanan and Posted with Permission of CarTechBooks