Over the past couple of issues (Part I, Part II) we’ve taken an overall look at the why LS engines are so good – with a focus on cylinder heads. If you recall, we used a good set of aftermarket heads (Brodix BR7 jobs) as examples. In the first pair of articles, we looked at both the intake and exhaust ports on those cylinder heads. Both flow prodigious quantities of air through relatively small ports. It’s no secret that makes for a pretty darned good head. But there’s a wee bit more to the equation – great heads need an equally great combustion chamber. They also need a solid valve train layout. And that’s the basis for this final chapter in our series.
First, let’s look at the combustion chamber: Traditional Chevy small block cylinder heads have a valve inclination angle of 23-degrees. Stock style big blocks are splayed, but the intake valve angle is actually “worse” at 26-degrees. Admittedly, it’s canted 4-degrees, while the exhaust valve angle is 17-degrees with a similar 4-degree cant. In either case, if the valve angle is flattened (for example, small blocks to 18-degrees, big block intakes to 24-degrees), airflow is improved, and so is the combustion process because the “straightening” helps to unshroud the valves. Where the Chevy LS motor really differs is the valve angle. In the case of the Brodix BR 7 series of cylinder head, the valve angle is 12-degrees. Essentially, that straightens the valve up, unshrouds the sides of the valves within the combustion chamber and provides the basis for a small, efficient chamber. That translates into a situation where you can move air at a faster pace (increase velocity), and that’s really good news when it comes to cylinder heads.
In case you’re wondering, the first generation LS motor with a cathedral style port had the valves inclined at 15-degrees. Ditto with later LS3 and L92 style heads. The LS7 Corvette motor was the first with 12-degree heads (although the C5R race head, which preceded it is actually an 11-degree valve inclination affair). Essentially, Brodix took the basic valve layout of the Chevy LS7 head and enhanced it. In the case of the Brodix heads, the bowls on the basic BR 7 have been blended. On the STS BR 7, the chambers are completely machined (see the photos for a closer look). Ditto with the take-no-prisoners STS BR 7 273. In terms of head bolts, the BR 7 series accepts five or six head bolts per cylinder (standard LS7 or LSX). They take a readily available gasket from Fel Pro (1185-041) or GM (12582179), which is a stock Chevy LS7 head gasket. Spark plugs are conventional 14-mm jobs with ¾-inch reach (gasketed). More gasket specifications along with spark plug recommendations are shown in the accompanying technical specifications sidebar.
In terms of chamber volume, the Brodix BR 7’s are pretty much the same as all other LS7 style heads – they measure 71-cc’s. They can be milled to reduce chamber size, but given the already reasonably small chamber, it’s probably sufficiently sized for 99% of all applications. One thing you should be aware of is the fact these heads must be used on engines with bore sizes no smaller than 4.125-inches. Otherwise, you’ll end up with a valve kissing a cylinder wall.
Topside, the Brodix BR 7 heads are designed to use all stock components. That means conventional Chevy LS7 valve train hardware, or aftermarket hardware for the LS7 can be used. When you specify assembled heads, springs, retainers and locks can be custom tailored to your application. For example, the heads in the photos are fitted with titanium retainers and springs with 430 pounds open pressure (185 pounds on the seat). They’re good for a 0.700-inch lift mechanical roller camshaft. Brodix has recently upped the ante with a “Big Spring” version of this head. It accepts springs up to .650-inch in diameter.
The heads can be setup with conventional LS7 rocker pedestals to accept the offset intake rocker used on the LS7, but they can also mill the pedestal bosses flat. This allows you to use an aftermarket shaft rocker arrangement (Jesel, Crower and T&D all offer rockers for this arrangement).
What about accessories? All of the BR 7 heads have their ends milled and drilled to accept all common LS-motor accessories. That means any of the common accessory drive brackets bolt right on. Up top, the valve cover rail is in the stock location. Brodix also copied the stock valve cover pattern. That means stock Chevy (or aftermarket pieces for a stock Chevy) bolt right up.
Whew. As you might have guessed from going over this article along with the pair of earlier ones, the new aftermarket LS heads are pretty much over-the-top in terms of features and performance capability. Not only do they provide considerable performance potential, the overall packaging of the heads allows direct fits to many different race applications (production line and custom). But the bare bones reality (for me too) is that technology has finally caught up and has surpassed the well-established Chevy performance benchmarks. The LS engine is definitely where it’s at in terms of performance, and Brodix’s BR 7 series of heads are an excellent example of what is available today. Today’s technology really is in the fast lane.
BR 7 Technical Specifications
- Intake Valves – BR 7, STS BR 7: 2.204 x 5.200-inch o.a.l. x 8mm Stem, Bead Lock – BR 70204
- Intake Valves – STS BR 7 273: 2.250 x 5.200-inch o.a.l. x 8mm Stem, Bead Lock – BR 70204
- Exhaust Valves: 1.614 x 5.230-inch o.a.l. x 8 mm Stem, Bead Lock – BR 70614
- Valve Springs: 1.295-inch od Hydraulic Roller Spring – MA 221436,
155 lb Closed, 405 lb Open,
1.810-inch Installed Height,
0.600-inch Maximum Lift
Note: Brodix offers varied springs for varied applications
- Retainers: 1.290-inch 7° Steel – MA 23621
- Valve Locks: 7° Machined Bead Lock – MA 13098
- Valve Seals: 8 mm – CC 500
- Torque Heads: 11 mm Studs – 85 ft-lb With Oil; 8 mm Studs – 26 ft-lb With Oil
- Torque Rocker Studs: 22 ft-lb
- Intake Gaskets BR 7, STS BR 7: GM 19172113, FEL-PRO 1208-3 (.060)
- Intake Gaskets STS BR 7 273: GM 19172113 Trim to Fit, FEL-PRO 1208-3 Trim to Fit
- Head Gaskets: GM 12582179, FEL-PRO 1185-041 (4.175 Bore)
- Exhaust Gaskets: FEL-PRO 1440
- Head Studs: ARP 234-4317
- Accessory Bolt Holes Are Drilled
- Spark Plug (Baseline) Pump Gas: 14mm 3/4 Reach Seals With Washer NGK R5671A-7
- Spark Plug (Baseline) Race Gas: NGK R5671A-8
- Spring Pockets: May Not Be Cut Any Larger or Deeper Than 1.350
- Valve Angle: 12°
- Angle Milling: 0.060 in PER cc
- Dowel Shift: Standard
- Pushrod Slots: Standard
- Pistons: Standard
- Rocker Arms: Standard LS7
- Lifters: Standard
- Pushrods: Standard