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Bob Walla Racing
Bob Walla of Bob Walla Racing (BWR) developed aluminum heads for 348/409 engines because of pent up market demand. He came out of the box with two styles of 409 heads. One is based on the 690 version, which is one of the best production heads Chevrolet made, while the other is a raised-port version of the same head. Chevrolet never made such a head and it’s a product of Walla’s own history running 409s and racing with others who praised the engine design. BWR released both styles of heads in 2007 and it doesn’t take a lot of searching to see the letters “BWR” on the heads of fellow 348/409 racers and hot rods.
Bob Walla aluminum heads show very little metal between the two valve seats for the use of bigger valves. On the intake side of the head, note the intake port almost spans the width of the head. On the top of the head, note the strong bases for the screw-in studs.
CNC-machined from 356 T6 aluminum, both of the BWR heads take advantage of the capacity for bigger valves, using 2.19-inch intake and slightly bigger, 1.750-inch exhaust valves. The bigger valves have a bigger shaft diameter of 11/32 inch versus the production size of 3/8 inch. Walla says the intake size can even go a little bit bigger and run a 2.25-inch valve, and that’s about the maximum that can fit in the BWR heads. To facilitate making the ports and the geometry of the valves, pushrods, lifters, and rockers work more effectively, the total length of the valves has been increased to 5.250 inches.
BWR raised port heads have been reworked on both the exhaust and intake sides. On the outside, the two center exhaust ports have been raised to increase flow and also line up with the two outside exhaust ports. Along with the better flow, this makes header building a little easier as the exhaust flange ports can now run in parallel series. On the inside, BWR raised-port heads offer intake ports that are all raised by 3/4 inch. Although that makes them actually shorter in length, they are now better positioned for much straighter and faster flow from the intake to the valves. Typically, these heads offer an 18 to 20 cfm faster flow.
Bob Walla racing aluminum Chevy 409 shows some very large intake and exhaust valve ports.
Edelbrock RPM Performer
Industry giant Edelbrock created the latest W engine heads, which have received a healthy share of attention in the aftermarket world. The Performer RPM 409 heads are cast from high-quality T356 aluminum and weigh 31.5-pounds each—half that of a Chevrolet W iron head. Sold completely bare or assembled, they’re based on the 425-hp version of the 409 head and include numerous improvements not seen on the original Chevrolet heads.
RPM Performer 409 heads offer swirl polished, stainless-steel valve sizes of 2.19 on the intake and 1.72 inches on the exhaust. By comparison, a stock 348 uses valves that measure 1.94/1.65 inches so the upgrade is substantial. Edelbrock uses hardened valve seats for use with unleaded fuel so street use of these heads is very much possible.
The intake ports of the Edelbrock head in detail. No surprise, the Edelbrock head far outperforms the stock iron head. It features CNC port-matched 220-cc intake and 115-cc exhaust ports. If you’re going to build a high-performance street or a race engine, you should start with an aftermarket block that can handle more than 600 hp and then go with a suitable set of high-flow heads, such as the RPM Performers.
The RPM Performer’s 7/16-inch screw-in rocker arm studs keeps the rocker arms securely anchored to the heads, which is an upgrade from the stock Chevy with 348’s pressed-in studs and the pinned 409. Chevrolet also set the studs at different angles with the intakes at 8 degrees and exhausts at 12. Edelbrock made its own design and set them both to 10 degrees. The result is consistency and a simpler pushrod guide plate to work with the larger pushrod holes in the heads.
The RPM Performer heads flow at 285/222-cfm at .700-inch lift literally right out of the box. The wall thickness of the ports on these heads is liberal enough for engine builders wanting more flow or to be able to tune that flow. Those ports are vastly improved over OEM units by one simple operation. The original ports use a harder angle as they turn toward the valvestems. Edelbrock used a smoother approach that increases flow to the cylinders. As CNC machines machine almost all of the aftermarket heads these days, those machines were used to step cut the ports for a good basic flow that easily exceeds the OEM pieces.
The Edelbrock head from the top side shows screw-in studs, push rod guide plates and valvesprings in deep pockets, and of course, this design supports the production of horsepower. The stock heads came with pinned-in rocker studs and didn’t have guide plates. Today, most of these features are standard equipment on aftermarket heads.
Although Chevrolet started with twin valvesprings when it brought out the 348, today’s spring technology has allowed Edelbrock to use modern 1.55-inch diameter, single valvesprings on their assembled versions. That spring rate is good for most applications up to 6,500 rpm with flat-tappet cams with up to .600 lift or most hydraulic cams. Big-block Chevy rocker arms fit Edelbrock’s W heads.
Other features include the use of steel threaded inserts, exhaust header bolt holes and rocker studs. All the holes in the block are drilled and tapped (when needed) as part of the precise CNC work on the block. And speaking of bolts, Edelbrock also offers its own head bolt kit that consists of high-grade bolts and hardened washers. Pipe sealant is needed because the bolts often go into the water jackets of the block.
Edelbrock also created its matching RPM Performer dual-quad intake manifold and that is detailed in the induction chapter. Keeping for a family of W parts, Edelbrock also made two versions of cast-aluminum, finned valve covers. They come in a black powder coat or polished finish. Neither use PCV nor oil fill openings, so an intake manifold with an oil tube is needed. The valve covers fit OEM 348/409 heads except for Z11 versions.
This aluminum head has been taken off a race engine to replace a few valves. Note the carbon deposits and how they do not appear in the lower part of the head. This indicates more of the fuel burning takes place close to the spark plug and on the top and center of the piston face. In the case of W engines, the top of the cylinder has a slight oval shape.
Written by John Carollo and posted with permission of CarTech Books
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