Texans have a saying "All hat and no cattle," which is a great euphemism for someone who talks a big game but has little to back him up. This could also relate to somebody with a big head, which leads us to where we are really going with this—a new big-block Chevy cylinder head from Brodix with big aspirations. The difference is this head can deliver the horsepower to back up its big-hat claims. Let's take a look at the new SR20 head and what it could deliver for your next big-block adventure.
Let's start by making something very clear. This is not your typical big-block Chevy street head. With a 440cc intake port, these heads are clearly intended for big-inch, big-power race applications. In order to appreciate what Brodix has done, let's first revisit a stock big-block Chevy. Early in the Rat motor's development, Chevy engineers tilted the valve angles, which gave the big-block its early porcupine nickname. They finalized this with diverging angles of 26 degree for the intake and 17 degrees for the exhaust. Not only that, but each was also tilted with a second, lateral angle of 4 degrees. This additional, compound angle was intended to move each valve away from the cylinder wall with increasing valve lift, which drastically improves the flow.
The SR20's name immediately tells us that Brodix has chosen to stand the intake valve up an additional 6 degrees in search of more flow. To help the exhaust side, it too has moved from its stock 17 to a steeper 13 degrees. This change is immediately evident with a glance at the valvetrain because the exhaust valvesprings are as close to the valve cover gasket rail as possible. While the valve angles have changed, Brodix retained the original 4 degree compound angle. This was all part of a plan to build a cylinder head with amazing flow potential combined with a huge intake valve. The complete version of the SR20 comes with monstrous 2.40-inch intake valves while shrinking the typical 1.88-inch exhaust diameter to a smaller 1.800. These valves are then stuffed in a 95cc chamber, which offers excellent compression opportunities while minimizing dome volume. As mentioned, the intake port is an equally large 440 cc's intended to feed large-displacement engines. This is reinforced by the fact that the minimum bore size for these heads is a 4.600-inch diameter. When combined with a minimum stroke of 4.250, that produces 565 cubic inches. More than likely, these heads will find their way onto Rat motors displacing closer to 600 inches.
There are several other features that will require specific required components. To start, the intake ports have been raised 0.500-inch, which means these heads will demand a specific Brodix intake manifold. Because both valves have been rolled to their new angles, this means the heads will require a shaft rocker system. Brodix has worked with both T&D and Jesel on this head and both companies offer a dedicated shaft system that will accommodate the new angles. Because the exhaust valve is moved so close to the valve cover rail, a different valve cover and head studs are also required, which Brodix also supplies. Of course, the new valve angles will also require custom piston valve reliefs to match the new valve angles for adequate valve-to-piston clearance, so you will need to add that to your list of requirements should you be considering a switch to these new heads.
So how good are these heads? Short deadlines didn't give us time for independent verification, but looking at the accompanying flow numbers from Brodix, if you can push the valve lift up to 0.900-inch lift, these heads will deliver 500-plus cfm. There are plans afoot to use these heads on an upcoming CHP big-inch big-block buildup, but for now in terms of potential, we can share that Shafiroff Racing Engines currently offers a 582ci naturally aspirated Rat crate engine that the company says makes 1,105 hp at 7,200 rpm with 860 lb-ft of torque at 5,900. That's a sick 1.9:1 horsepower per cubic inch. Granted, this is a full race motor with 14.5:1 compression and a full T&D shaft rocker system. So this just shows what these heads are capable of delivering. Big ports – big flow – big power. It's all there for the taking.
Test performed by Brodix at 28 inches of water test depression
Minimum 4.600 inch bore
|Valve Lift||Intake Flow||Exhaust Flow||Exhaust-to-Intake|
|Brodix SR20 head, assembled||2208100||Summit Racing||$3,072.97 ea.|
|Brodix SR20 head, bare||2208000||Summit Racing||2,259.97 ea.|
|Brodix intake manifold, std. deck||BM2020||Summit Racing||569.97|
|Brodix intake manifold, raised deck||BM2021||Summit Racing||527.97|
|Brodix SR20 valve covers||BRSR20VC||Summit Racing||498.97|
|Head ARP studs for iron block||235-4323||Summit Racing||242.22|
01. The new Brodix SR20 heads are just the ticket for a near 600ci drag race big-block. With 440cc intake ports and 507-cfm flow capacity, these heads are destined to deliver big power.
02. The SR20 head uses raised intake ports that are 0.500-inch taller than the OE orientation. Beside the huge size, the intake valve angle is pushed to 20 degrees versus 26 with the exhaust at 13 as opposed to 17 degrees stock.
03. The CNC version intake port opening measures 2.580 inches tall by 1.815 inches wide and measures a healthy 440 cc in volume.
04. The exhaust port is also raised closer to 0.625 inch relative to a stock big-block exhaust port and has also been pushed outboard, making the port longer. The port exit measures 1.790 inches tall by 2.065 inches wide. Note that the CNC work has moved one side of the port is as far out as it can go, having protruded into a head bolthole.
05. The fully CNC’d chamber measures a scant 95 cc but manages to accommodate massive 2.400-inch intake and 1.80-inch exhaust valves.
06. The intake and exhaust seats are an Ampco 45 copper alloy that works well with the 50-degree intake seat and 55-degree exhaust seat angles. This alloy is softer than a typical cast iron seat.
07. You can readily see the change in the exhaust valve angle as the valvespring now crowds the valve cover rail. As a result, Brodix had to cast a unique valve cover for the SR20 head that kicks outward on the exhaust side to clear the exhaust valve retainers.
08. This is a slightly distorted top view of a standard big-block cylinder head. The SR20 valve angles are closer to vertical yet employ the same 4 degree compound angle.
09. Because the intake port has been raised, this necessitated a matching, taller, single-plane Dominator flange intake from Brodix. There are two versions, one each for standard and tall-deck engines.
10. This plenum view offers a near straight shot from the base of the carburetor into the ports.
11. The valve covers may look like a typical cast big-block piece, but the outboard wall has been kicked out to clear the relocated exhaust valves. A normal tall big-block cover will not clear unless it has been modified.