Hidden Horsepower! 10 Stealth Secrets for Building a Covert Powerplant

For some performance fans, especially in the realm of vintage muscle cars, overt displays of power-enhancing changes are distinctly frowned upon. To resto “numbers” 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 “nonstock” appearance is unacceptable, and efforts to recreate the vehicle in its original glory are carried out to the point of fanaticism. This usually dictates a totally stock build. Others want to build to a similar theme, but more power is a welcome possibility, within the confines of a relatively stock appearance. Does this approach 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, often without giving away a clue.

A stock-appearing engine certainly can benefit from the application of 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 they can involve the substitution of production internals in favor of performance-bred replacements. The possibilities are nearly boundless, 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.

Crankshaft Capacity

The fast track to more power and torque is pumping up the displacement, a goal most effectively accomplished via an aftermarket stroker crank. This is perhaps the most flagrant violation of originality, however, it also offers one of the greatest opportunities for outright gain. Increasing the crankshaft stroke will increase the cubic-inch capacity of the engine in a way that is anything but trivial. Aftermarket stroker crankshafts are readily available for all engine types that will increase the displacement. For instance, a 350 small-block can be readily stroked to 383 ci or more, and those added cubes offer a pure increase in torque production. It is something to be seriously considered at the time of an engine rebuild, and though the street competition will never be the wiser, you certainly will be whenever the throttle is stood on end.

Employing a stroker will require a complete reworking of the engine’s rotating assembly, as well as modifications to the block’s crankcase to allow clearance for the long-armed crank. However, the popularity of this mod in the performance world has made the procedures relatively routine for most specialty engine shops. Stroker assemblies are readily available for virtually all popular engine families, often featuring the full rotating assembly including rods and pistons. On the street, displacement rules, and with a stroker combination, virtually any engine can benefit from a sizable boost in size.

Winding Down Windage

Whether we concern ourselves with it or not, we are all familiar with aerodynamics. An object moving through a fluid medium, in this case air, is subjected to the drag imposed by that fluid, in the form of resistance to motion. Now consider how this may apply to the inside of an engine. Here we have the internal components at a high rate of motion, particularly the spinning crankshaft. While we are 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.

Numerous steps can be taken to reduce the amount of oil snared by the moving crank and to make the crankshaft slice more effectively through whatever oil is there. High-performance crankshafts are profiled on their protruding counterweights to very effectively improve the crank’s ability to cut through the oil and direct it away from the projecting rod journals and in toward the static main cap area. Quality aftermarket cranks can be found 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 to 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 drain-back in the center of the block by using standpipes, which allow for crankcase ventilation, but direct drain-back to the front and rear extremes of the block, away from the spinning crankshaft. Reducing windage adds horsepower, and best of all, the tricks involved in getting it done are all hidden within the assembled engine.

Ring in the Power

Piston ring technology has improved dramatically since the early days of V8 muscle, and not taking advantage of these gains to some degree is nothing short of ludicrous. Improvements here are in materials, dimensions, and 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. Today, aftermarket high-performance rings made of ductile iron or specialty steel are readily available. Ductile iron or steel rings are much more durable in demanding conditions and will take the punishment where a brittle plain iron ring will break. Most of the high-performance ductile iron rings are moly coated, which greatly reduces bore friction and wear and also aids ring sealing. Modern nitrided steel rings are strong enough to provide excellent durability, even at greatly reduced thickness.

In the old days, standard production engine compression rings measured 5/64 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 1/16 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 1⁄16-inch ring suitable for production, and now this ring width and even thinner sections are commonplace, even in OEM engines. In rebuilding a vintage engine, a 1/16-inch ductile iron moly ring pack should be considered the standard for increased power and engine life, while even thinner sections such as the popular 1.2mm and 1.5mm rings are worthy of consideration.

Reduced friction and better materials are only some of the improvements that can be taken advantage of. The ring end gap presents a path for internal engine pressure leakage, and custom engine builders can order slightly oversized rings and custom file-fit each ring into its respective bore to minimize this leakage and improve power. Taking that concept one step further are special “gapless” rings, such as those manufactured by Total Seal. The gapless design uses a specially machined two-piece ring assembly that allows the end gaps to be overlapped, effectively closing off any potential leakage through the end gaps. Second compression rings with a profiled Napier face improve performance by reducing friction. Oil rings also come into play, with reduced sections such as the popular 3mm assembly adding to power by reducing drag. A good modern piston and ring combo will free substantial power in an engine assembly and offers no external cue to its presence.

Dyno It

Once an engine is assembled and running in the car, almost nothing can compare with a good dyno session for making the most of the power waiting to be unleashed. Optimizing a combination is very difficult to achieve by any other means, and a well-instrumented dyno with 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, the car will be run under various loads and conditions, and the mixture will be recorded. Careful changes to the air/fuel ratio will optimize power and economy. The gains can be very substantial even on a completely original engine, while dialing in a custom-built or new engine is the best way to be assured that the powerplant is delivering what it is capable of.

Part of the dyno tune should include finding the optimal ignition timing for peak power and then massaging the timing curve for the best balance of economy and power while avoiding detonation. We have routinely had vehicles dyno-tuned and found that power gains of 10 to 25 hp are not uncommon. A well-equipped dyno shop should have the tuning parts to make the necessary modifications. 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.

Camshaft Considerations

Nothing determines the character of an engine in quite the same way as the camshaft, and at the same time, few parts have such a dramatic effect on output. Technology in camshafts has seen a constant progression 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 there’s a wide range of aftermarket cams, and 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 action, 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 to a modern hydraulic roller design. Hydraulic roller cams are standard equipment in all modern engines, and the major aftermarket cam suppliers such as Competition Cams or Crane can provide kits to retrofit this technology into 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 profiles. Whether the decision is to go with a flat-tappet or a modern hydraulic roller, there is a 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 add measurably to performance in a completely inconspicuous way. The aftermarket camshaft manufacturers can help you select a camshaft that matches your power and driveability goals.

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 in airflow, and the aftermarket is flush with high-flow cylinder heads to do the job. Even the best of the older OEM heads are hugely disadvantaged compared with modern aftermarket offerings in terms of airflow capacity. That gap can be narrowed substantially with custom head porting. Increased head flow produces power gains without compromise; the engine will idle and drive as nicely as a stocker, but with a huge gain in output that will keep pulling as the tach rises.

Porting is a job entirely dependent on the individual artist working the metal, but gains of 25 percent to 30 percent or more in airflow are not uncommon from factory heads ported by experts. On the other hand, incompetent work here can 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 airflow of the stock intake manifold, 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.

Consider Coatings

A technology that has enjoyed enormous growth in the last few years is performance engine coatings. Coatings can provide for an increase in output and durability without altering the external aesthetic 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 in producing 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 that are prone to high levels of friction, reducing parasitic loss while adding insurance against engine failure. Piston skirts, oil pumps, and bearings 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 the connecting rods. The area of coatings is something that was virtually untapped at the time classic muscle cars were built, but that’s no reason not to take advantage of what’s available today. Even the OEMs are beginning to employ coatings for their benefits in durability and power in engines such as GM’s LS-series.

The Squeeze

Compression ratio equates to power and efficiency and has no drawback. However, there is a ceiling on how much compression can be exploited, and that is the detonation limit of the engine. 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 if trying to push the limits.

For engines built in the after the early ’70s, there is quite a margin for improvement, since the compression ratio of these engines 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 it directs, as well as the combustion characteristics of the engine. 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.

Consumables: Engine Oil, Spark Plugs, Air Filters, and More

Squeaking 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 engine oil, spark plugs, the air filters. Attention to detail on items such as these will benefit output in a very unobtrusive way

Standard paper 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 such as the offerings from AMSOIL, 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 the synthetics. Spark plugs can also show a small gain in output, and 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 taking the required correction steps in machining to set these measurements to the desired specifications. A few examples would be helpful here. Imagine that there is a variation in 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, to set the critical squish/quench clearance, this inaccuracy will make it impossible to set this important clearance accurately. Now imagine that there is 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 the specs of the individual components and then building the engine with a high degree of accuracy to exact specifications. Those specifications will be at the builder’s discretion to optimize the performance of the engine. Going back to an example, consider our scenario of out-of-spec individual rod length. The builder may target a piston-to-head clearance of 0.035 inch clearance for a razor sharp maximum quench/squish effect in combustion. The variation will not allow this to be accomplished. Typically, lower-grade engines are built to conservative targets to absorb the inaccuracies of the nonblueprinted components and clearances. Blueprinting allows the builder to optimize the engine for its full performance potential.

This story was originally published March 18, 2008. Photos by Steve Dulcich.

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