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Choosing Aftermarket BBC Cylinder Heads for Street/Strip Applications
Choosing the right heads comes down to knowing what the vehicle will be used for and trying to match the best combination of heads, cam and intake to achieve optimum performance for your customers.
By Brendan Baker
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In 1958, Chevrolet released the first big block for use in its trucks and heavier passenger cars. It was called the “W” engine and it came in three engine displacements until 1965: 348 cid, 409 cid and 427 cid. After Chevy introduced its “mystery engine” to NASCAR in 1962 with a combustion chamber and canted valves, the Mark IV production engine became affectionately known as The Rat, taking a cue from the small block Chevy motor’s moniker of The Mouse.
By 1965 Chevy’s new Big Block 396 cid was put in its flagship Corvette model. Later, 427 cid and 454 cid versions followed. Horsepower for these engines was estimated to have reached a peak output of 650 hp at the height of the muscle car era. And big block racing applications had horsepower rated even beyond that.
Later the 454 Big Block was given fuel-injection in 1996 in order to meet OBDII requirements and was dubbed as the 7400 Vortec. In 2001 GM introduced a stroked version of its 454, with displacement up to 494 cid (8.1L).
While the bigger is better fad is still in vogue, using stock ported heads to extract more power is starting to fade. One reason it has been fading is there are a plethora of aftermarket cylinder heads on the market that are designed with flow and velocity in mind for performance big block engines. As the aftermarket continues to push larger displacement combinations, even 555 cid BBCs are becoming more and more common with 600+ cid engines more plentiful than ever before.
Choosing the right heads comes down to knowing what the vehicle will be used for and trying to match the best combination of heads, cam and intake to achieve optimum performance for your customers. If your customer says he wants a street/strip engine, you need to find out how often it will hit the track and what he expects out of it when it does. What kind of performer is he looking for? If he says he wants to take it out on Friday nights and cruise around town and occasionally take it to the track for fun, then you’ve got a different story and different set of expectations to meet.
Here’s what leading players in the cylinder head arena told us about working with Big Block Chevys.
Dart’s Jack McInnis says the single most important thing when choosing your cylinder heads is to be realistic about how the car will be set up and used. “The size of the engine, rpm range, camshaft, type of fuel, weight and gearing all factor in,” says McInnis. “Whether the car will be street driven 99% of the time, or if it will be primarily raced and driven on the street only occasionally will make a big difference in the choice as well.”
McInnis says most OE components are compatible with Dart heads so your customer can keep many of the stock ancillary parts. He says their heads are designed to perform right out of the box and do not require any additional finish work before installation. Port matching the intake manifold can be helpful where maximum power output is desired. It is always wise to check the fit and match of all ancillary components before final assembly.
Dart’s Iron Eagle and PRO 1 cylinder heads for big-block Chevy are the direct descendants of Dart’s Pro Stock engine program, incorporating sophisticated wet-flow technology and improved combustion efficiency. All Dart heads are cast and machined in Dart’s own Detroit area facility.
Dart’s Iron Eagle cast iron big-block heads are designed for street performance, bracket racing, oval track competition, tractor pulling, and high-performance marine applications. The Iron Eagle is available with either a high-velocity 308cc intake runner that produces incredible torque or a 345cc version that’s perfect for big-inch, high-rpm Rat motors.
The valve angles are rolled 2 degrees and the exhaust port is raised .300˝ to improve airflow while maintaining bolt-on compatibility. The 308cc head is fitted with 2.25˝ intake and 1.88” exhaust valves, and the 345cc heads uses 2.30˝ intake and 1.88˝ exhaust. Both have a compact 121cc chamber which promotes combustion efficiency. Iron Eagle cylinder heads are a tremendous performance value where weight is not a primary concern.
Dart’s PRO 1 aluminum heads have been completely redesigned inside and out. A new highly efficient chamber with improved fuel distribution, spark plugs located as high and and as close to the center of the chamber as possible and five-angle intake seats to shear the liquid fuel and air as it enters the chamber are the product of wet-flow research.
Additional features which include a new exhaust port design, new exhaust face and fully machined end pads. Inspired by Dart’s championship-winning Pro Stock designs, the PRO 1’s features include rolled valve angles, extra-long intake valves and raised exhaust ports yet the PRO 1 can be used with off-the-shelf pistons, valve train components, and intake manifolds. Dart uses virgin 355-T61 alloy for extra strength.
Dart’s PRO 1 CNC heads are their competition cylinder heads. Every intake port, every exhaust runner, every valve bowl and every combustion chamber is 100% CNC machined on special dedicated PRO 1 castings. A choice of 335cc and 355cc intake ports is available so you can match the runner volume to your engine’s displacement and rpm range. The high-velocity raised exhaust ports are modeled on Dart’s Pro Stock heads using airflow concepts that dramatically improve cylinder scavenging and the engine’s ability to accelerate quickly.
Multi-angle intake valve seats direct the air-fuel mixture into the chamber like an airfoil, reducing turbulence and preventing fuel separation. Fully radiused exhaust seats provide the smoothest possible transition into the ports for hot exhaust gases. Improved cylinder scavenging allows more fuel and air to be burned on the next power stroke.
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