For some applications, overt displays of power-enhancing changes are distinctly frowned upon. We're not just talking about the traditional "sleeper." For instance, many vintage musclecar enthusiasts go out of their way to keep their engine's appearance relatively "stock." In the realm of resto purists, parts such as custom manifolds, modern carburetors, or tube headers fly in the face of the goal of recreating the historically correct appearance. In these circles, anything giving away a "non-stock" appearance is unacceptable, and efforts to recreate the vehicle in its original glory are sometimes carried out to the point of fanaticism. Others might stray from total originality as long as the components resemble the factory equipment. Does a stock look necessarily count out the potential for performance augmentation? We would have to answer that with an emphatic "no." Buried deep within the engine's internals are opportunities for substantial power gains without giving away a clue.
A stock-appearing engine certainly can benefit from modern technology and advancements for very substantial power gains. The levels of this deception can be as subtle as the modification of selected original parts, or it can involve the substitution of production internals in favor of performance-bred replacements. The possibilities are nearly endless, and the prospects for power gains are truly enormous. We will detail some of our favorite little tricks, all of which are proven to substantially encourage output without offering a visual clue.
1) Crankshaft Capacity
This is perhaps the most flagrant violation of originality, yet it is totally discreet and offers one of the greatest opportunities for outright gain. Of course, we're referring to a stroker crankshaft. Increasing the crankshaft stroke will increase the engine's cubic-inch capacity in a way that's anything but trivial.
Aftermarket stroker crankshafts are readily available for most popular engine types. For instance, a 350 small-block can be readily stroked to 383 cubic inches, and those added cubes offer a pure increase in torque production. It's something to seriously consider at the time of an engine rebuild, and though no one will be the wiser, you certainly will be whenever the throttle is stood on end.
Employing a stroker will require a complete replacement of the engine's rotating assembly and often requires modifications to the block's crankcase to allow clearance. However, the popularity of this mod in the performance world has made stroker kits readily available, and the procedures are routine for most specialty engine shops. On the street, displacement rules, and with a stroker combination virtually any engine can benefit from a boost in size.
2) Winding Down Windage
While we're familiar with the resistance of air, one can only imagine the magnitude of resistance imposed as the crank struggles against the oil in the crankcase. In a running engine, a portion of the oil drains back upon the crankshaft, where it can become entangled in the crank's rotation, costing power. Further oil can be pulled up from the sump below, most significantly under the forces of braking, acceleration, and cornering as the oil sloshes around in the pan.
There are numerous steps that can be taken to both reduce the amount of oil snared by the moving crank and make the crankshaft slice more effectively through whatever oil is there. High-performance crankshafts are profiled on their protruding counterweights to improve their ability to cut through oil, directing oil away from the projecting rod journals and in toward the static main cap area. Quality aftermarket cranks can be had with nicely profiled counterweights, and even an original crankshaft can be modified in a similar way to reduce windage losses. Power gains on the order of 10-15 hp can be achieved at high rpm.
Other mods seek to separate the oil from the spinning crankshaft. Here we can employ windage trays, which separate and form a barrier between the crankshaft and the oil reserve in the sump. Baffling in the pan can also be added for similar benefits, helping with oil control under driving forces. Other tricks include using a crank scraper, a closely fitted sheetmetal projection mounted to the internal oil pan rail, which will "scrape" excess oil as the crank spins by. Further improvements can be had by controlling drainback in the center of the block by using standpipes, which allow for crankcase ventilation but direct drainback to the block's front and rear extremes.
3) Rings In The Power
Piston ring technology has improved dramatically since the old days. Neglecting these advancements is nothing short of ludicrous. Improvements can be found in materials, dimensions, and ring configuration. Considering materials, old-fashioned plain cast-iron rings wear the cylinder bore at a high rate, are high in friction, and are marginal in strength. Aftermarket high-performance rings made of ductile iron are a better choice. Ductile iron rings are more durable in demanding conditions and will take the punishment, whereas a brittle plain iron ring will break. Most of these high-performance rings are moly-coated, which greatly reduces bore friction and wear and aids ring sealing. No serious engine should be built with a lesser ring.
In the old days, standard-production engine compression rings measured 5U64-inch thick, which put a substantial amount of surface area in contact with the bores. The weak, plain cast-iron material relied on the high cross-section for strength. High-performance and racing engines would typically use a thinner cross-section of 1U16 inch, reducing friction and improving the ring seal at high rpm by virtue of a lighter and more reactive ring. Better ring materials made the 1U16-inch ring suitable for production, and now this ring width and even thinner sections are commonplace in OEM engines. In rebuilding a vintage engine, a 1U16-inch ductile iron moly ring pack should be considered the standard for increased power and engine life. In recent years, high-tech steel rings have grown in popularity, as have narrower 1.5 or 1.2mm or 0.043-inch widths, which are worth considering depending upon the application.
4) Dyno It
Once an engine is assembled and ready to run, almost nothing can compare with a good dyno session to make the most of the power waiting to be unleashed. Optimizing a combination is very difficult to accomplish by any other means, and a well-instrumented dyno and an experienced operator can help get the most of what you have. Dyno-tuning will typically aim at optimizing the fuel system and ignition. A well-equipped dyno shop will have equipment to monitor the air/fuel ratio, and the engine can be run under various loads and conditions as the mixture is recorded. Careful changes to the air/fuel ratio will optimize power and economy. The gains can be very substantial even on a completely stock engine, while dialing in a custom-built high-performance engine is the best way to be assured that the powerplant is delivering what it's capable of.
Part of the dyno tune should include finding the optimal ignition timing for peak power and massaging the timing curve for the best balance of economy and power while avoiding detonation. There is quite a range of expertise from shop to shop, so consider carefully and ask around to find the most competent facility in your area.
5) Camshaft Considerations
Nothing determines an engine's character in quite the same way as the camshaft, and few parts have such a dramatic effect on output. Camshaft technology has constantly progressed over the years, and the opportunity is wide open for improvements to output. Many enthusiasts are under the impression that an aftermarket camshaft equates to a raspy, nasty race-car idle and poor street manners. The fact is many of today's designs can offer much more power than the older stock sticks without the associated ill temperament. Older camshaft designs were comparatively slow in terms of lobe acceleration and velocity, necessitating long duration to achieve high-performance levels. Long duration rapidly deteriorates idle quality and vacuum, as well as low-rpm performance. A modern cam grind can offer substantially more power through higher lift and area under the lift curve without sacrificing driveability.
Even more improvement can be had by going with a modern hydraulic roller design. Hydraulic roller cams are standard equipment in most modern engines, and the major aftermarket cam suppliers can provide kits to retrofit this technology into popular older engines. Hydraulic rollers have proven durable in OEM applications, and can provide a broader power curve in an older engine. The advantage is in the higher velocity that can be built into a hydraulic roller cam's profile. Whether the decision is to go with an original-style flat tappet or a modern hydraulic roller, there is huge potential for increased power available here. Along the same lines, upgrading valvetrain components with quality aftermarket pieces like stiffer pushrods or roller rockers can measurably add to performance in a completely inconspicuous way. Aftermarket camshaft manufacturers can help you select a camshaft that matches your power and driveability goals.
6) Porting For Power
Looking for a seriously healthy boost in output but want to retain a totally stock appearance? Consider having the heads custom-ported. It's no secret that the fast track to big power is airflow, and the aftermarket is flush with high-flow cylinder heads to do the job. Even the best of the older factory heads are hugely disadvantaged compared to the modern offerings in terms of airflow capacity. That gap can be narrowed with custom head porting. Increased head flow produces power gains without compromise; the engine will idle and drive as nicely as with the stock heads, but it will keep pulling as the tach rises.
Porting is a job entirely dependent on the individual artist working the metal, but the experts can achieve airflow gains of 25 to 30 percent. On the other hand, incompetent work here can actually ruin a cylinder head. Select your cylinder head man based on proven results and reputation, not price.
Porting isn't limited to the cylinder head. Experts can also dramatically improve the stock intake manifold's airflow, and even the stock cast-iron exhaust. Other options on manifold work include the Extrude Hone process, an automated abrasive process that can be applied to the intake or exhaust manifolds. With no visual clues to give away the game, custom porting is a must-have for huge output in a stealthy package.
7) Consider Coatings
A technology that has enjoyed enormous growth in the last few years is performance engine coatings. Coatings can provide an increase in output and durability without altering one external detail of a stock-appearing engine. The three basic categories of coatings are thermal, friction, and oil shedding. Thermal coatings present a shield to heat transfer, slowing the movement of heat through treated engine components. Experienced engine builders can use this property to their advantage to produce power. Common applications of thermal barrier coatings include piston crowns and combustion chambers. This helps to retain the heat of combustion in the cylinder, where it can add power rather than being absorbed as inefficient heat loss. Thermal barriers are often applied to the valves, helping control the heat transferred to the incoming mixture and reducing the tendency toward detonation in the process. Even the internal surfaces of the cylinder head and manifold's ports can be coated, altering the thermal characteristics for greater power production.
Antifriction coatings can be applied to a variety of engine parts, reducing parasitic loss while adding insurance against engine failure. Piston skirts, oil pumps, and crank journals are just some of the components that can benefit from friction coatings. The oil-shedding coatings work to reduce windage by minimizing the amount of oil that will "stick" to a component such as a rotating crank or connecting rod. Even the OEMs are beginning to employ coatings for the benefits in durability and power in engines such as the Z06's LS7.
8) The Squeeze
The compression ratio equates to power and efficiency and has no drawback to driveability until the point where increased pressure triggers detonation. There is a ceiling on how much compression can be exploited, and that is the engine's detonation limit. Any steps that will allow more ratio to be used will pay dividends in power, but detonation must be avoided at all costs. Employing coatings can allow for greater compression, and that combination can add substantially to output. A carefully designed engine can tolerate an efficient high-compression ratio while living nicely on pump gas. This is an area where the engine builder's knowledge and experience is put to the test, especially when trying to push the limits.
For a great number of engines built after 1970, there's quite a margin for improvement in compression ratio since the factory ratio was very low. When considering increasing the ratio, many factors must be balanced. Key among these factors are cylinder pressure as it relates to the camshaft, or more specifically, the valve events the cam directs, as well as the engine's combustion characteristics. The combination can be skillfully planned, taking advantage of good squish and quench characteristics through piston selection and block machining. This improves detonation tolerance and allows for a practical increase in compression ratio. Cooler running also helps in this regard. Adding ratio will add power without conspicuous external engine changes, but it must be approached with the needed level of execution to the rest of the engine package to avoid dreaded detonation.
9) The Consumables
All the power an engine can develop isn't limited to the internal hardware. Upgrading some of the common maintenance items to those designed for high performance is an easy way to reap power gains. Some items that make the cut here are the engine oil, the spark plugs, and the air filter. Attention to detail on items such as these will benefit output in a very unobtrusive way.
Standard paper-element air filter elements can present a restriction to flow that will cost power. An easy upgrade here is an oiled cotton/gauze element such as the type available from K&N, ACCEL, or Holley. These filters are designed for high flow, and unlike paper elements, they maintain that high flow with use. These filters can be had in OEM replacement specs, fitting the stock filter housing just as the original. In enclosed housing filter cases, the mod is totally invisible.
In the area of engine oil, modern synthetics almost always show a power gain through decreased friction. The benefit here is twofold, since besides providing a measurable power gain, these lubricants significantly reduce engine wear and cut down on internal engine deposits. We strongly recommend synthetics. Spark plugs can also show a small gain in output. It's the small details that add up to a sharper-running powerplant.
One of the most overused and least understood terms in the realm of engines is "blueprinting." Essentially, it means the engine is built with a high degree of precision, making careful measurements of critical clearances and performing corrective steps in machining to set these measurements to the desired specifications. A few examples would be helpful here. Imagine if there's a variation in a connecting rod length of several thousandths of an inch. If the engine is being built to an exact blueprinted spec for piston-to-head clearance, this inaccuracy will make it impossible to set the critical squish/quench clearance. Now imagine there's a variation in combustion chamber volume-not an unusual situation. The compression ratio will vary from cylinder to cylinder, making it impossible to target an exact desired ratio. Now imagine that the block's deck surface is out of parallel with the crank. The cylinders along that bank will vary in both compression ratio and piston-to-head clearance, throwing off both. The examples can go on and on, but the bottom line is that variations in specifications of individual components limit the ability to target accurate and desirable specifications when building the engine.
Blueprinting means measuring and correcting specs in the individual components; then the engine is built with a high degree of accuracy to exact specifications. Those specifications will be at the builder's discretion to optimize the engine's performance. Typically, lower-grade engines are built to conservative targets to absorb the inaccuracies of the nonblueprinted components and clearances. Obviously, if the pistons are about 0.050 inch in the hole, a few thousandths here or there in the rods or decks won't matter. Blueprinting allows the builder to optimize the engine to its full performance potential.