Is A 427 Cubic-Inch Small-Block Viable For The Street

As the old adage goes, “There’s no replacement for displacement.” Today, more than ever, that maxim rings true with many auto enthusiasts wanting a stroker engine and every engine builder seemingly offering one. Why stick with 305-, 350-, or even 400-cubes when you can have a 427 cubic-inch small-block Chevy mill resting between the frame rails. All it takes is merely swapping in a larger-than-factory-stroke crankshaft?

While contemplating the idea of a stroker crank, keep in mind that one change will set into action a series of cascading dominoes which could lead to components physically interfering with one another within the block. Some (or all) of the engine components may need to be modified or upgraded to meet a desired performance level. Suddenly, the modest monetary investment could mushroom into an endless money pit if proper planning is not established and followed.

Meet the Panel

To see what is required for a stroker build, and to ensure money would not be wasted, we contacted Evan Perkins with JE Pistons, Mike McLaughlin of Lunati Power, and Tom Lieb with SCAT Crankshafts to see what parts they recommend for a street driven, 600 horsepower, gen-I-based 427ci small block. When we say street driven, we mean a real street engine, not a race engine that can occasionally hit the street. We need an engine that will start without difficulty, idle relatively smooth, cruise comfortably, and provide excellent performance without undue maintenance requirements.

At this point, this engine build will be strictly on paper, and this constitutes the planning phase of an engine build. The knowledge and advice from our experts will provide a solid short-block, and with their experience, the components for the top-end of the engine will be determined based upon achieving our goal of 600 hp.

Stock or Aftermarket Block 

Our first concern was whether a build like this could survive while using a stock block. A factory casting seems like a good choice, but there are some drawbacks. When we posed the idea to our panel, the answer by all three was ,“yes, a stock block could be used, but why would you?”

“A factory, gen-I block can withstand the desired horsepower, as 600 hp out of a 427ci engine is a cakewalk in today’s day and age,” Perkins stated. “But, an aftermarket block is far more up to the task in terms of durability, especially if there will be competition involved. It is also inadvisable to put a 4-inch stroke crankshaft [the bare minimum required to achieve 427ci] in a stock block for street use. The deck height, cam-to-rod clearance, and the oil pan rails are very tight. Can it be done? Yes, but the rod-to-stroke ratio and overall longevity are highly compromised.”

McLaughlin chimed in, “A stock block with a 4.125-inch or greater bore will have the head-bolt holes too close to the cylinder, which will lead to cracking. Additionally, the connecting rods will be extremely close to hitting the camshaft, so a small base-circle-ground cam will be required. What is essentially needed is a raised-cam block – an aftermarket block.”

Lieb added, “The horsepower should not be an issue, the biggest obstacle will be machining the block without hitting a water jacket. To avoid the issue with possibly hitting a water jacket, I would recommend a Dart SHP block at a minimum, and the best block would be the Dart Iron Eagle. It is clearanced for the 4-inch stroke.”

Rotating Assembly

Perkins said, “A forged rotating assembly would be essential in this application. A 4032-alloy piston material would be sufficient, but if boost or nitrous will be used, 2618 alloy is a must. The rods would need to be a strong forging with a suitably strong fastener. I would recommend a JE Pistons’ flat-top-style forged piston for this application and a compression ratio of roughly 11.0:1. With aluminum cylinder heads and an electronic ignition system, operating that compression ratio on pump gas is entirely doable. As for piston rings, a carbon-steel ring would be more than up to the task of sealing combustion.”

Lieb stated, “A SCAT Excalibur 4340-alloy lightweight 4-inch crankshaft will work for normally aspirated applications. The Excalibur features straight-shot oiling, lightening holes in all rod journals, and bull nose counterweights for improved windage. The Excalibur is rough balanced to 1800 grams plus or minus 2-percent. If power adders are used, a SCAT 4340 Pro Series crankshaft is recommended. The Pro Series features knife-edge counterweights making it a perfect crank for increased RPM and power.”

Lieb shared, “We recommend using SCAT stroker-clearanced, 6-inch Pro Series I-Beam connecting rods with 7/16-inch ARP bolts. These rods feature polished beams with a reinforced big end for normally aspirated applications. For power adders, SCAT’s Pro Sport H-Beam connecting rods are suggested. We recommend a 4032-alloy forged piston and plasmamoly rings. The compression will depend on the fuel and heads being used, but a naturally aspirated application with an aluminum head, 10.5:1 should be fine with premium fuel.”

Although very tempting, it is best to stay away from the ultra-low viscosity engine oils for the street. While great at the track where every last horsepower must be extracted from the engine, on the street the rotating assembly must operate from extended idle to WOT. That’s why a quality multi-grade oil, such as 5W-30, is a must even though it sacrifices a few ponies. While a dry sump would benefit our 600-hp quest, a larger capacity wet-sump oiling system will have to suffice on the street. Because of ground-clearance concerns, a 7- to 8-quart low-profile pan with kickouts is highly recommended.

Cylinder Heads

To achieve 600 horsepower, we’ll need a cylinder head that will flow approximately 300 cfm at .600-inch lift. A pair of Trick Flow Super 23 230 cylinder heads feature a heart-shaped combustion chamber with 2.08-inch intake valves, 1.60-inch exhaust valves, dual valve springs with a maximum valve lift of .680-inches, and a stock 23-degree valve angle will accomplish our goal. The 70cc combustion chambers will help raise the compression ratio into the 10 to 11.0:1 range (depending upon the valve reliefs of the flat-top pistons and the head gasket thickness). The heads are shipped with 230cc intake runners and 78cc exhaust runners.

These cylinder heads include angled spark plugs, thick decks and walls for additional porting as needed, and raised valve-cover rails. Trick Flow designed the 230 heads to use all standard small-block valvetrain components. There is no need for a more expensive valvetrain with offset rockers and relocated rocker studs. The heads come with titanium retainers and 10-degree locks, and include screw-in rocker studs and guide plates. The Trick Flow heads do require the use of head gaskets with a 4.155-inch-bore diameter.

Camshaft Selection

To work with the Trick Flow heads, McLaughlin suggested a custom-ground Lunati hydraulic-roller camshaft kit. This camshaft has a duration of 255/265 degrees at 0.050-inch lift, and a gross lift of .624/.624-inch with 1.6:1 rocker arms. This camshaft has a 108-lobe separation angle (LSA), a 4/7-cylinder swap, and a .900-inch base circle for additional connecting-rod-to-camshaft clearance.

The camshaft will work best with a 10.0:1 compression ratio or greater, and if the drivetrain relies on an automatic transmission, the converter needs a stall-speed of approximately 3,000 to 3,500 rpm. The rear gears will need to be 3.73 or higher. The camshaft should make excellent power and torque above 3,000 rpm.

We had some concerns with the narrow LSA, which would result in more overlap, a tight RPM powerband, and likely, a harsher idle quality than we prefer. However, the additional cubic inches may smooth the radical idle to a more acceptable lumpy idle. The torque with this cam will peak earlier in the RPM band as the power comes on quickly, but it will tend to fall off just as swiftly. The tighter LSA will provide a peakier power curve that tends to resemble the shape of a triangle rather than a broad torque curve found with a wider LSA.

Induction and Exhaust

While we considered using a dual-plane intake manifold, we feel a single-plane will more easily achieve 600 hp. For that reason, we will sacrifice a little down low in the power curve to gain at the top. Edelbrock’s Super Victor single plane manifold will work well with the Trick Flow heads and Lunati camshaft. It is designed to work with heads utilizing a standard-port location. The carburetor pad height is 5 1/2 inches from the end seals, and the runners have a 2.80 square-inch cross section.

According to Edelbrock’s website, both engine dynamometer and in-car tests have shown additional torque is available by adding a 1-inch-high open (not four-hole) carburetor spacer. Other than some minor gasket matching of the manifold ports, the Super Victor appeared to be tailor-made for our small block without any runner modifications.

To handle the fueling chores, we like the 850 cfm Xtreme Performance Holley Ultra XP carburetor. The new Ultra XP carburetor is a mechanical-secondary 4150 model, designed for use in high-horsepower engines. The carb has contoured venturi inlets, which offer a smoother, better-balanced airflow for increased horsepower. The Ultra XP carburetors are lighter than a Holley race carburetor, yet have a 20-percent increase in fuel capacity.

With the exhaust ports in the stock location, a pair of off-the-shelf headers with a 1 7/8-inch primaries dumping into a 3-inch collector will be a decent starting point.

Lighting It Off 

An MSD 7AL-2 ignition-control box will work to light off the air/fuel. The 7AL-2 includes a built-in two-step rev controller, a diagnostic-troubleshooting LED and external terminal strips for convenient wire hookup. An MSD coil and Pro-Billet distributor will work with MSD’s 7-series ignition. A good quality set of helical-wound spark plug wires such as MSD Heli-Core wires, (properly routed) are required to get the maximum performance from the ignition.

Rounding Out the Pieces

To keep the crankshaft and camshaft in sequence, a Lunati Cams fully rollerized timing chain with a 9-slot keyway and Torrington bearing will provide adjustability of the installed camshaft centerline. A Weiand Team G aluminum water pump will keep the coolant flowing. A reputable manufacturer’s harmonic balancer and flexplate will be bolted onto each end of the crankshaft.

Wrapping It Up

To meet our needs, the engine would be outfitted with hi-po parts to provide longevity, reliability, and drivability, while meeting the desired performance level of a streetable 427 capable of pushing a 3,000-pound Chevy into the high-9-second range, yet rumble through town without difficulty. Think a small-block 427 is for you? Develop a plan and determine the cost effectiveness of the build compared to your budget.