The fact that nostalgia is big business has not been lost on the marketing team at Chevrolet. One need only look at their most recent ZL1, ZR1 and (the focus of this story) LS7 to see that they are not above playing off the success of performance past to sell future fast. Unlike the two supercharged applications, the all-motor LS7 was much more in tune with its namesake. We applaud the fact that Chevy saw fit to make the modern versions follow this tradition of performance.
In the case of the new LS7, Chevy knew that enthusiasts wouldn't accept the moniker applied as a sticker package to some pedestrian-pushing poser. After all, the original LS7 was a high-compression, solid lifter 454 originally slated for use in the '70 Corvette (essentially a 454 cube version of the L88 of 1967-'69). Prior to production, the wild LS7 combination was cancelled, but was later offered as a successful crate motor through Chevy dealers. Though the LS7 never saw use in a production vehicle, its popularity as a performance swap engine more than justifies its legendary status.
The modern LS7 certainly carries the torch, offering performance the old fashion way, through cubes and compression. Though not quite as high as the original, the 11.0:1 compression offered by the modern LS7 is right up there with the best of the factory muscle car motors. Down on displacement slightly to the original 454, it is important to remember that the 427.5 ci offered today comes in a small-block package. Not just physically smaller, the modern LS7 also offers all-aluminum construction, a composite intake and electronic fuel injection.
The modern LS7 delivers not just more power than its big-block brethren, but does so while delivering four times the fuel mileage and far fewer harmful exhaust emissions. Time and technology have indeed marched on, but it is nice to know that the current configuration is true to the performance of the original.
As impressive as a modern LS7 is, there are always ways to make it even better. The key to performance on any engine is airflow. Increase the airflow through the motor and you will be rewarded with more power. Notice we said airflow through the motor and not just to the motor. Unfortunately, the internal combustion engine doesn't recognize potential airflow. The mere fact that a larger throttle body, intake manifold or even cylinder heads flow more air doesn't necessarily translate to increased power.
The entire LS family of small-blocks was treated to high-flow cylinder heads, but none more than the LS7. With enough flow from the stock head to easily feed the 505hp 427, adding ported heads to an otherwise stock motor will yield predictable results. Having 600hp heads on a 500hp motor means adding a set of 650-700hp heads might not offer much in the way of additional power, since the combination already has enough head flow to support the current power level. That is why our test of the new Brodix STS BR 7 273 heads was run on something capable of utilizing the extra airflow.
The new STS BR7 273 heads from Brodix offer a unique combination that all but guaranteed success. It is true that airflow equates to power, but there is more to the equation than big numbers. Getting big flow from big ports is easy, but doing so with reasonably sized ports is the key to a successful head design. Factory LS7 heads offer plenty of flow (exceeding 335 cfm), but do so with sizable intake port volumes (270-plus cc). Getting even more flow from a production casting means making the port even bigger. As long as the flow rate goes up in proportion to the increase in port volume, power production is assured.
The problem is that there are diminishing returns when it comes to improving flow. What Brodix did with its STS BR7 273 head was start with a smaller, more efficient port than the factory LS7 head. By doing so, it was able to come up with an LS7 head that offered not only over 400 cfm at 0.700 lift, but did so without resorting to excessive port volume. In fact, according to its literature, the new STS BR7 273 heads flow 416 cfm at 0.700 lift through an intake port that measured just 273cc (roughly equivalent to a stock LS7). What this means is that even a stock LS7 can take advantage of the extra airflow offered without concern for lazy, oversized ports that might hurt drivability and low-speed performance.
The Brodix STS BR7 273 heads offered a number of desirable features, including oversized valves, a 12-degree valve angle and full LS7 compatibility. The Brodix LS7 heads combined full CNC porting with a 2.25/1.614-inch valve package and 71cc combustion chambers to maximize head flow through the 273-cc intake port. With a peak advertised intake flow of 416 cfm at 0.700 lift (240 cfm for exhaust), these Brodix heads offered big-block flow through significantly smaller ports. This is important when running these heads on (relatively) small-displacement motors.
Part of the credit for the impressive flow numbers goes to the 50-degree valve job on the intake (45-degree on exhaust). This represented an increase of roughly 80 cfm over the stock LS7 heads. Additional beneficial features included a standard LS7 exhaust pattern, valve centerline and intake flange. Naturally the Brodix heads also accepted the factory (or aftermarket) 1.8-ratio rockers. The Brodix LS7-based heads were recommended for LS applications sporting a minimum bore size of 4.125-inches. The valve size, placement and chamber size necessitate the large bore diameter.
The Brodix heads looked good on paper, but just how would all the specifications translate into power? To properly test the big Bros, we needed a suitable test motor that offered a minimum bore size of 4.125 inches. What we had was something even bigger, capable of utilizing every last cfm offered by the STS BR7 273 heads.
The big-inch stroker small block started out life with a new aluminum block from RHS. Looking to maximize displacement, we stepped up to tall-deck block, which offered the capability to swallow a massive 4.5-inch stroke with plenty of deck height to spare for acceptable rod ratios. The A357-TR RHS aluminum block was a serious piece of hardware and offered an impressive list of features including Clean-Cast technology, priority main oiling system and billet main caps with ARP studs. Filling the stroker-friendly RHS block were equally stout components from Lunati, Wiseco and K1. Lunati supplied a massive 4.5-inch billet stroker crank, which was combined with a set of 6.30-inch forged K1 rods and 4.185-inch Wiseco forged, flat-top pistons. The bore and stroke combined to produce a displacement of 495 ci, easily surpassing the '70 454 LS7 big-block.
The cubes combined with flat-top pistons and 71cc combustion chambers to produce a static compression ratio of 13.5:1. Sealing the big beast was a set of Cometic MLS head gaskets secured by ARP heads studs. Additional components employed on the RHS stroker included a Moroso pan, pick up and windage tray, an adjustable timing chain designed specifically for the tall-deck block (1 extra link per side) and a custom hydraulic roller cam from Crane Cams. Big for a hydraulic roller LS application, the powerful Crane cam featured 0.661 lift, a 260/276-degree duration split and a 114-degree lobe separation angle.
The 0.661 lift came courtesy of the 1.8 rockers employed on the LS7 heads. Were this cam run in an LS1 or LS3, the lift would reduce to 0.624 thanks to the smaller 1.7-ratio rockers. Crane Cams also supplied a set of link-bar hydraulic roller lifters and hardened pushrods for the test.
Feeding the beast was a Mast Motorsports (high rise) single-plane intake designed to accept the Holley 1050 Ultra Dominator carb. Ensuring adequate fuel to the stroker was a complete Aeromotive fuel system, including an A1000 fuel pump, regulator and filter.
To properly test the Brodix heads, we first needed to establish a baseline with the LS7 stroker with stock style heads. Test number 1 involved the installation of a set of as-cast LS7 LSX (ports cast to duplicate production LS7 CNC heads) heads. The heads were upgraded with a suitable valve package from Brian Tooley Racing to accept the rpm capability and 0.661-lift cam. Both heads were run with the same 1 7/8-inch headers, though given the displacement and power potential, this stroker combination would likely respond to a set of 2.0-inch (or larger) headers. After jetting and timing, the 495 stroker produced peak numbers of 744 hp at 6,300 rpm and 682 lb-ft of torque at 4,700 rpm.
After swapping over to the Brodix STS BR7 273 heads, the peak numbers jumped to 799 hp at 6,500 rpm and 714 lb-ft at 5,300 rpm. The Brodix heads never lost out to the stock LS7 heads, offering significantly more power and torque from 4,000 rpm past 6,500 rpm. Torque production with the Brodix heads exceeded 700 lb-ft from 4,400rpm to 5,800 rpm. Obviously the big flow and small port volume worked well on this big-inch application.