Mission Impossible: Part One

Rich Smiecinski's large frame and quiet demeanor cannot be easily interpreted as he sits at the counter of the general store. Some would consider his size and soft voice a metaphysical contradiction. But here a bond, a friendship, was created between this Vietnam veteran and the author, the result of exposing one's deepest convictions about God, country, and the American way. This somehow gave birth to the idea of building a carbureted 350 Corvette engine that would not play second fiddle to an LS1, matching the latest small-block's every move in terms of power, torque, fuel economy, and emissions. Corvette Fever will try to do what everyone said cannot be done. This is that story.

Something Old, Something New

The engine for our project belongs to Rich Smiecinski of Hackettstown, New Jersey. He purchased a rough-around-the-edges '81 for the sole purpose of performing a complete frame-off resto-modification. This car would end up being unique, so a standard-issue powertrain would be out of the question. Often, participants in this hobby become one-dimensional, considering only the power that an engine produces. But in the real world, power is only one aspect of a car. That's what makes the C5 so appealing; it's a near-perfect blend of ride, handling, acceleration, top speed, fuel efficiency, and braking, all this while offering the reliability of an anvil and a minimal impact on the environment. One need go no further than the LS1 to assign credit for a majority of these attributes. With a cleansheet-of-paper approach to the ubiquitous small-block Chevy, this will be the benchmark for our engine design. While retaining the '81 block, we hoped to design and build an engine that would pass an I/M 240 drive cycle emissions test for an '01 vehicle, be simple and inexpensive to build, deliver more than 20 mpg while burning pump gas, and make at least 350 hp and 350 lb-ft of torque. The kicker would be that it would have to use a carburetor, sacrificing the benefits of a high-tech electronic-fuel injection system. Individually, none of our requirements would be hard to meet, but collectively they would require an engineering tour de force. To accomplish this, all of the stops would have to be pulled out and an eclectic mix it old and new technologies would need to be married.

With this settled, the services of a machine shop and dyno facility would be required. Pro-Motion Engines L.L.C. of East Hanover, New jersey, stepped up to the plate. Owner Larry Lempecki has years of experience and is recognized by his peers as one of the country's top machinists. He runs a tight ship with a small crew of dedicated workers, which allows for a high level of quality control.

If we were successful, we knew there would be no shortage of naysayers claiming the machine shop fudged the test numbers, so using Pro-Motion's dyno would be out of the question. We needed a reliable, unbiased test center with extremely accurate equipment.

The University of Northwestern Ohio in Lima is one of the few colleges that offers a degreed motorsports program, and hence has a complete machine shop and dyno facility featuring Super-Flow 901 equipment with data acquisition. The faculty and students there are great and always welcome the opportunity to work with a cutting-edge engine, so we signed them on as our official test center.

An engine is a series of compromises, and through good engineering, this trade-off can be limited, but not totally eliminated. Balancing fuel economy, emissions, and power is not hard if the octane of the fuel is unlimited. An engine's thermal efficiency is linked directly to the compression ratio, and in turn impacts the brake specific fuel consumption (BSFC). But higher compression ratios induce abnormal combustion, better known as detonation, and require higher-octane fuel. An aside to this, the I/M 240 emissions test also examines a pollutant called oxides of nitrogen (NOx), which is produced in great numbers if detonation occurs. The cylinder head, piston design, and cooling system would then need to address these concerns.

Choosing The Right Parts

Picking the wrong mix of components is the most common cause for disappointing results when building an engine. A systems approach is required to create the necessary harmony. Building a magazine feature engine has manufacturers tripping over themselves wanting to donate parts and services in trade for ink. But here at Corvette Fever, we take a different approach. We choose the parts that would work best to meet our goals, and then contact the manufacturers for their input. This allows a project to progress without any political boundaries, letting form follow function.

When the dust settled, we decided on a 6-inch-long connecting-rod 355 with GM Vortec truck cast-iron cylinder heads, a roller hydraulic camshaft, a dual-plane intake manifold, hypereutectic pistons, and a Demon carburetor. ACCEL would supply the spark with a Billetech distributor, a 300+ digital ignition, and 8.8mm spiral core wires.

In addition, all of the engine parts were exposed to a cryogenic process by 300 Below Cryogenic Tempering Services Inc. in Decatur, Illinois. The pistons, cylinder heads, headers, and intake manifold were sent to Swain Tech Coatings in Scottsville, New York.

During cryogenic processing, the part is placed in a chest-style device that resembles a freezer. This computer-controlled unit then slowly brings the temperature in the processor down to minus 120 degrees F through normal refrigeration. Once the part cold-soaks and stabilizes at that temperature, nitrogen gas is introduced and the environment is chilled to -300°F and remains there for 36 hours. The computer-controlled process slowly warms the parts before they're removed and heat-cycled in an industrial bake oven from ambient temperature to 150°F and back numerous times.

The purpose of this procedure is to remove all residual stress from the metal. When any metal is drilled, machined, welded, cast, or formed, a stress is induced. If these stresses are left unchecked, the part either cracks, fails, or distorts over time.

Many benefits will be reaped through cryo-processing. By deep freezing and then slowly warming the component, the molecular structure is realigned, allowing for greater strength but, more important in this application, eliminating bore distortion and maintaining piston-ring seal.

Dan Swain is a ceramic engineer, and his company is a leader in coatings. The use of coatings in engine building has been slow to gain acceptance with the novice but is standard procedure for race teams, along with much of Detroit. The cylinder heads and piston crowns were treated with a ceramic thermal-barrier coating. This serves to increase power while reducing the fuel consumption. It's the result of using more of the heat from combustion to expand against the piston instead of being absorbed into the parts. In addition, the reflectiveness of the coating increases the rate of flame travel. Cylinder pressure then peaks in fewer rotational degrees of the crankshaft past top dead center while also limiting abnormal combustion. The coating was also applied to the quench region, valve face, and exhaust port. A coated exhaust port helps empty the cylinder during blow-down, which is defined as the moment the exhaust valve opens and the pressure in the cylinder is substantially higher than in the header or exhaust manifold.

Physics dictates that if heat is transferred from a gas in motion to another source, the gas will experience a decrease in velocity. The coated exhaust port limits thermal transfer into the cylinder head and water jacket, also allowing the cooling system to work more efficiently. It must he remembered that any exhaust gas not purged during blow-down needs to be pushed out by the piston on the exhaust stroke. The work performed by the piston is then considered a pumping loss. In any internal combustion engine, there are three areas that limit the power produced from the potential of the heat energy supplied by the fuel: thermal, pumping, and frictional losses. Our design approach was centered around minimizing losses in all three areas. To this end, a dry film coating was applied to the piston skirt for friction reduction, while the long connecting rod will decrease friction with reduced angularity.

Searching for every advantage, the cooling system was addressed. Evans Cooling Systems in Sharon, Connecticut, developed a unique package that includes its special coolant marketed under the name NPG, or non-aqueous propylene glycol. This product uses no water and has a boiling point of 369 degrees F at atmospheric pressure. Eliminating corrosion by the lack of water, the coolant creates lower metal temperatures in the combustion chamber, which in turn allows fora higher compression ratio with improved octane tolerance. It is offered as a pour-in product alone, but we decided on the complete kit for the most effectiveness. It included an Evans-designed aluminum radiator, a water pump, and a thermostat. The NPG coolant has not only different thermal and viscous characteristics from normal ethylene glycol antifreeze, but a lower dynes rating. This establishes the surface friction of a liquid. A decrease in the dynes/cm reading indicates a liquid that will release from the water jacket in the cylinder head more readily after undergoing a phase change called nucleate boiling. This phenomenon occurs with all coolants, thus the liquid's effectiveness as a cooling medium is in part established by its ability to release and re-condense, allowing fresh coolant to come in contact with the area.

The Method To Our Madness

With the preliminaries now covered, an in-depth explanation of the main engine components is in order.

Cylinder Heads

As mentioned previously, a delicate balance of compression ratio and octane tolerance would need to be established while promoting sufficient airflow to meet our power goals. The cylinder head is a key element, and the GM Vortec casting proved a worthy contender. It boasts a quick-burn combustion chamber with excellent swirl characteristics, relatively high squish-to-bore area relationship for the promotion of internal charge acceleration, and an idealized spark plug location. These design features allow fora high thermal efficiency while limiting abnormal combustion. In addition, they are inexpensive and readily available; we got ours from Jim Pace GM Performance Parts. The relatively small intake-runner volume was not designed to support large-cubic-inch engines and was the deciding factor in not stroking the small-block.

Even though the cylinder heads come assembled and are a direct bolt-on, Mike Tiedemann of Pro-Motion Engines did some work on ours. The stock GM valves were replaced with those from REV Inc. They are high-flow stainless-steel style and were 0.100 inch longer than stock. The additional length was to provide more freedom in valvespring selection with the camshaft grind that was being used. The cylinder head comes standard with 1.94/1.56-inch intake and exhaust valves, respectively; we retained the intake dimension but stepped up the exhaust side to 1.60 inch. In our experience, the Vortec heads do not respond to a larger intake valve unless the intake port is heavily modified. We chose not to sacrifice mixture motion for airflow. Octane tolerance is of the utmost importance on a street engine that must pass a NOx test. The bowls were blended into the seat and a five-angle valve job performed. Ford 3.8L V-6 valve-stem seals were used for their excellent oil control. The cylinder head and deck of the block were milled to achieve a static compression ratio of 10.72:1. It must be recognized that due to the cast iron's superior thermal retention, this would be equivalent to an aluminum-head engine with an 11.72:1 ratio. A good rule is that an aluminum head requires one complete point more compression to obtain the same thermal efficiency of a cast-iron design. To put this in the proper light, we are hoping to use 92-octane fuel with a compression ratio that would be nearly 12.0:1 if fitted with an aluminum head. The spark-plug orientation of the Vortec head has the electrode near the center of the bore while biased toward the exhaust valve. The ideal spark-ignition point is in the bore center since it's the most turbulent region, while the exhaust valve isthe hottest area. The spark-plug location impacts not only the octane tolerance, but also the cylinder pressure rise.

Pistons

It's accepted that all automotive and light-truck pistons are made from aluminum, but that alone is not descriptive enough. What we identify as aluminum is actually alumina blended with copper, magnesium, nickel, silicon, or any combination of these metals. These alloys are used to create a material that offers the properties required for both manufacturing and operation in an engine. Concerns are founded on machinability, corrosion resistance, weight, hardness, strength, expansion from heat, wear, and scuff resistance. The amount of silicon alloy is categorized three ways: eutectic, hypoeutectic, and hypereutectic. To understand this, we need to consider the term "saturated" and its meaning.

By definition, saturated describes when a material is fully impregnated. When pertaining to aluminum, the previously mentioned terms describe the amount of silicon. This concept can be understood by comparing aluminum to a glass of iced tea, with the silicon being the sugar. If sugar is added to the tea, at first it will become dissolved and be inseparable from the liquid, but if this is continued, the liquid will become saturated and will accept no more sugar. The excess sugar will not become part of the solution, but will fall to the bottom of the glass in crystal form. This is what makes the Keith Black (KB) piston unique: the amount of silicon used. The point of saturation for aluminum is identified as eutectic and occurs when the silicon level reaches 12 percent. Aluminum with levels below 12 percent are considered hypoeutectic. When the silicon accounts for more than 12 percent, the material is considered to be hypereutectic.

If you're paying attention, this should raise a question. Since we stated that 12 percent is the saturation point for aluminum, how can a hypereutectic piston exist? In the same manner that the sugar crystal falls to the bottom of the glass when the tea is saturated, the unabsorbed silicon precipitates out of the molten aluminum and forms hard particles. The secret of the KB piston is the controlled placement of the precipitated silicon in small, well-distributed particles, which is a byproduct of their unique foundry process and mold design. KB pistons have 16 to 18 percent silicon content, meaning that 4 to 6 percent of the piston's total silicon content is in particle form. This produces their unique performance, wear, and expansion properties, and is the reason we used them.

Connecting Rods

A production small-block Chevy uses a stroke of 3.480 inches with a connecting-rod length of 5.7 inches. This yields a rod-to-stroke ratio of approximately 1.638. By maintaining the same dimension for stroke and altering the length of the connecting rod, the ratio is impacted. The numerically higher the ratio, the less angularity the connecting rod experiences as the crankshaft swings during rotation. Less angularity relates to a reduction in friction. In addition, the rod-to-stroke ratio affects the length of time in crankshaft rotation degrees that the piston dwells at top dead center (TDC). Again, higher numerical ratios create longer dwell times at TDC. Our engine used a longer-than-stock 6.00-inch connecting rod that was manufactured by Power Detroit.

They are beautifully made in Trenton, Michigan, from 100 percent American steel and can support up to 750 hp. This is an important issue since many companies today are sourcing connecting rods of inferior quality from China. The longer Power Detroit rod yielded a rod-to-stroke ratio of 1.724, reducing rotating friction and increasing piston dwell at TDC.

As piston dwell time increases, the octane tolerance of the engine is increased along with the amount of low-speed torque. By keeping the combustion-chamber region smaller for longer in the crankshaft's arc of rotation, the cylinder pressure builds quicker while the small area does not readily allow for the creation of a rouge flame front. The downside of a high-numerical ratio is the instantaneous piston velocity is decreased, and since an engine is an air pump and this ability is keyed to piston speed, less through-put can be experienced.

Valvetrain

The camshaft chosen was an ACCEL hydraulic roller EFI grind, PN 74211. This profile has produced excellent results with a long runner TPI setup and would hopefully do the same with a carburetor. Known for its quick ramp and minimal overlap, cylinder pressure would be built quickly. Being ground on a lobe separation angle of 112 degrees, hydrocarbon emissions production would be kept in check. Mike Miskovitz of Pro-Motion Engines did all of the assembly and machine work and had to design a spacer plate to use a step-nose hydraulic roller cam in an old-style block. The lobe lift is ground at 0.350 inch, and when used in conjunction with the GM Performance Parts 1.6 full roller rockers, it netted a gross valve lift of 0.560 inch for both the intake and exhaust sides. The cam was installed 1.5 degrees retarded from the intake centerline to help engine breathing at higher rpm in the hopes of meeting our 400hp goal.

Induction

When it came to the intake manifold, the decision was easy: Edelbrock. The Vortec cylinder head has a unique port-entry angle and also has only four intake-manifold bolts per side instead of the usual eight. Edelbrock offers two styles of manifolds: Victor Jr. race-style and a dual-plane Performer. Since this is a street engine, the throttle response and low-speed torque characteristics of the Performer gave it our nod. The intake manifold required no port-matching, being a perfect fit to the cylinder head, but was treated to a thermal-barrier coating on the underside by Swain Tech. By limiting the heat transfer from the lifter valley into the charge air, power can be increased by 1 percent for every 10-degree-F temperature drop. The converse of this is also true—heating the air limits the oxygen content and reduces power the same amount for every 10-degree-F jump.

All new engines use electronic fuel injection, but we bucked that trend and went with the old standby, the carburetor. Wanting the most efficient fuel-and-air mixing device of this type on the market, our search ended with Barry Grant Inc. and its Demon carburetor line. Offered as four distinct models, we used the 650 Speed Demon with vacuum-secondary operation. The design and manufacturing process of the Demon line allow for greater airflow potential while atomizing the fuel better than traditional carburetors. The Speed Demon would have its work cut out for it with our goal of reduced BSFC and emissions. The fact that it is very tunable also weighed in our decision. In addition, Barry Grant Inc. provided a Super Speedway block-mounted fuel pump and a high-flow replaceable cartridge fuel filter.

Ignition

ACCEL is a leader in ignition, and its 300+ CD system offered all of the features we required. Do not be deceived by its small size; it packs the wallop of an arc welder. Featuring multi-strike capabilities below 3,500 rpm and one of the longest burn times in crankshaft rotation degrees, in theory it will not only help make power, but reduce emissions and improve fuel economy. The rate that spark advance is introduced will be critical to our success, so the ACCEL Billetech vacuum and mechanical advance distributor was chosen for its quality, accuracy, and tunability. Featuring both a vacuum and mechanical advance, the spark rate can quickly and easily be adjusted. ACCEL 8.8mm spiral-core wires carried the voltage to Autolite Platinum spark plugs.

After all this preparation, thought, and work, our engine was complete and ready to be tested. We head out to Lima, Ohio, with reservation. Will all the math and theory prove correct, or will we fail to meet our power and fuel efficiency goals? Even if we are successful now, will the emissions test do us in? Whatever happens, you'll learn about it in an upcoming issue.