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.
Air Flow Research
AFR has released an all new 375 cc Magnum Series BBC head, the largest and highest flowing BBC product in its line-up with flow numbers that are closer to 18 degree Pro-stock style heads. If you’ve got the displacement AFR’s head can feed it with an intake port that flirts with 440 CFM at a usable lift-point, and enough complimenting exhaust flow to still maintain over 75% of that number at .800? lift (335 CFMs at .800? lift). While this runner is more aimed at 572 – 632 cid applications, in a light car it could still be considered in 555-565 cid aggressive builds that are built to reliably turn 7,800 – 8,500 rpms (Ti valves are recommended over 8,000 rpms). The company explains this head will be best utilized with camshafts in the .780? – .850? range to take full advantage of its higher lift airflow. But this head also provides low and mid-lift flow as well (400+ CFM at .600? lift). This head comes with a .750? thick head deck, reinforced rocker stud bosses, and is equipped with 2.350? intake/1.880? tulip exhaust valves.
RHS Cylinder Heads
RHS’s Kevin Feeney echoes what other experts have said about selecting BBC cylinder heads – the first step is to determine what your customer is trying to accomplish with the engine: torque/hp or the best combination of the two. This and the size of the engine are vital to choosing the proper runner volume for your application. In too many instances, says Feeney, racers tend to purchase cylinder heads based on high lift flow numbers that are easily achieved with large ports and valves but do not necessarily provide them with the performance they are looking for.
In most street strip applications, you are dealing with a heavier vehicle and in most cases an automatic transmission, which would benefit from a smaller runner with cross section that maintains port velocity to provide a strong torque curve to get the vehicle off the line and good high lift airflow for horsepower. When using a conventional BBC head the combustion chamber size is fairly standard and the head can be milled to achieve the compression ration desired, he says.
The RHS BBC Pro Action and Pro Elite BBC heads utilize stock rocker arms, intake and exhaust manifolds. The only special requirement is 4 longer head bolts or studs on the exhaust side of the head to accommodate the raised exhaust port required to overcome the restriction inherit in the OE design. “ Our as cast and CNC heads are ready to use right out of the box and are available assembled in a variety of valve spring and retainer options,” says Feeney. “Port matching of the intake manifold is always recommended to ensure a smooth transition from the manifold to the head and eliminate the airflow being disrupted before it enters the cylinder. Ideally you want the manifold to be slightly smaller than the head.
RHS’s most popular head is one that is ready to assemble or install without additional machine work required, according to Feeney. “We are finding a trend towards the purchase of assembled cylinder heads and believe this has a lot do to with us providing a head utilizing Comp Cam brand components that can be tailored to their camshaft requirements verses buying a one size fits all part with generic components.”
Feeney says the heads are designed to use a 14mm .750? reach gasketed plug which provides the engine builder with a variety of heat range options. He recommends a conservative approach, starting with a little colder plug to begin with and then move to a hotter plug if your combination and tune requires it.
Feeney also recommends using an adjustable checking pushrod to determine the length that provides the best valve train geometry during assembly. “Our complete package can be an excellent option for some, versus just bolting on a set of new heads. We find that when engine builders work with one of our techs to put together a cylinder head and camshaft package that fits the vehicle and application instead simply buying a cylinder head that has the highest flow numbers, they have the better chance of meeting their customer’s expectations.”
The all-new MERLIN X Aluminum BBC Heads from World Products combine flow characteristics common to expensive race-only heads with exotic splayed valve setups designed to accept up to 2.350? and 1.880? valves, as well as “standard” Mark IV intake systems. This has been accomplished through “rolling” the head to a 16° valve angle, designing highly efficient intake and exhaust ports and using a special 90cc combustion chamber. According to World, you’ll probably need to get a set of pistons that take advantage of the chamber design, but other than that you can use most of everything from a standard big block Chevy, so when you add up the performance potential versus total cash outlay, it can make sense to your Sportsman racer customers.
The RPM Xtreme for big-block Chevy is an all new design that is CNC ported to achieve optimal air-flow for maximum horsepower and torque in high performance street and light duty racing applications. The casting and port design are all new and engineered to be as close to perfect as possible. To ensure consistency from port to port, the RPM Xtreme has a CNC ported combustion chamber, and then CNC ported in the bowl area (above the valve) for a smooth transition into the valve seats.
The intake runner entries and exhaust runner exits are partially CNC ported for improved air-flow. RPM Xtreme big-block Chevy heads have a 24.5° x 4.4° intake valve angle, 15.5° x 4.2° exhaust valve angle, stock exhaust port locations, and the spark plug angles have been modified to produce a smooth flame front for increased fuel efficiency and maximum power. Two port designs are offered, a 300cc Oval and 325cc Rectangle. Both options are equipped with high-quality valve springs for valve lifts of up to .700?.
Edelbrock’s Big Victor Spread-Port 18° CNC cylinder head is intended for high output, large cubic inch BBC racing engines with 4.84? bore spacing, this new head is an improvement over existing 18° designs. The casting is made from A-356 aluminum and is Hot Isostatic Pressing processed (HIP) for superior strength and durability, dimensional stability, and exceptional finish quality.
These heads feature CNC ported spread intake ports and raised exhaust runner design for improve flow efficiency. The chambers are also fully CNC ported and Edelbrock includes extra material in the deck to allow fine tuning of the combustion chamber design if desired.
Patriot’s Freedom Series heads meet the demands of the BBC world, while keeping the quality high and the price reasonable. Patriot’s BBC heads come as cast with a 320cc intake runner, US made bronze guides, and a 5 angle valve job. Chevy High Performance used these to build their 675 hp 496. These heads come standard with a 119cc chamber, assembled in Patriot’s own facility with 21-4N stainless 2.250?/1.880? valves, .600? hydraulic roller springs, steel retainers, 7/16? studs, guide plates, and Viton seals.
Trick Flow’s Al Noe says you do not want to use a 360cc intake port on a 396 cid street engine or a 280cc oval port on a 632 cid drag race engine. Valve size will increase appropriately with port size. Trick Flow makes a 280cc oval port, and 320cc or 360cc rectangle port cylinder heads specifically so that engine builders can pick the right cylinder head for their application. You also want make sure that the spring and retainer package is matched appropriately to what the customers needs are. Noe says Trick Flow offers numerous spring and retainer packages for a number of applications, and can also custom tailor a spring/retainer package to suit a customer’s particular needs.
Another key thing to look at are the components a manufacturer will use. Noe says they use only American made A356 castings. “They are machined in-house at our facility, with the best components available to produce an extremely durable, high quality product. While there certainly are less expensive ‘generic’ heads available, they’re typically cast from ‘mystery metal’ using inexpensive components. Even though a customer may save a few hundred dollars, if the engine drops a valve because of cheap component breakage, in the long run the few hundred they save ends up costing them thousands. We build an excellent performing product at a fair price, and we’re proud to provide excellent customer service before, during, and after the sale.”
Noe says TFS heads come with a 3 angle valve job done on a Serdi. Both intake and exhaust are CNC bowl blended, and the intake ports are CNC port matched. Assembled heads are most popular, says Noe, because you can take them out of the box and bolt them on. With the numerous spring packages and retainer options, customers can bolt them on and go with no need for spring changes, retainer swaps, etc. TFS also has three spring packages from 1.530 diameter for flat tappet cams to 1.640 diameter for solid roller camshafts.
Big block TFS heads have a rectangular port intake manifold with dominator flange set up for drag racing. “Our sales-tech department can custom select parts for your application,” says Noe. “And we have literally hundreds of different combinations we have tested over the years, which will help in selecting the right parts for our customers. Having two Superflow engine dynos in house makes us do the work rather than the customer when it comes to proper parts selection.
Noe says Trick Flow dyno tests every product it sells. “In developing our Big Block Chevy cylinder head line, we wanted to focus on areas which would deliver great value to our customers-CNC port matched intake ports, CNC bowl blends, American Made castings, and the best possible components available. Our heads deliver great bang for the buck! Since we develop and test all of our own products in house, we also have a very good understanding of what will and what will not work, and are happy to help our customers build an excellent combination which will make great power while being low maintenance.”