Overhead-valve pushrod engines are supposed to be dead. At least, that’s the proclamation all the major in-market car magazines made on the eve of the LS1’s debut in 1996. The cam-in-block, two-valve-per-cylinder V8 was an anachronism with one foot in the grave, soon to be replaced by all manner of innovation—internal combustion and otherwise. And while many of those rapidly developing technologies have come to pass—direct injection, diesel, hybrid, electric, and variable displacement to name a few—we still have major breakthroughs in “knuckle-dragging” V8s every few years.
These advances have often been combined with pushrod V8s to raise the bar of mechanical efficiency—a term that’s associated with fuel economy, but is really a proxy for horsepower. Try as its detractors might, the mighty pushrod V8 in the guise of the small-block Chevy has yet to be dethroned 22 years later. Just when we think we know everything there is to know about the mechanics of internal combustion, another technology gives “two valves per cylinder” a new lease on life.
So why have the smartest guys in the room predicted the end of two-valve combustion engines for so long? The genesis of that answer is in a somewhat obscure concept known as the ratio between the valve curtain area and swept cylinder volume. Historically, a traditional pushrod engine hits an airflow limit before it hits the mechanical limit of its rotating assembly and valvetrain; at some point, the pumping losses to draw air through a small opening can’t be overcome. To combat this, hot rodders use performance camshafts to increase valve lift and duration, boosting the airflow into the combustion chamber, but at a significant cost.
More event duration causes a drop in dynamic compression ratio. The upper limit for cylinder pressure and thus horsepower is ultimately controlled by the amount of air and fuel trapped in the combustion chamber, so closing the intake valve later and later means less air and fuel trapped. Sure, you get back some of that with pressure wave tuning and scavenging, but there are limits. Sooner or later, you pay the piper with poor idle, dirty emissions, a peaky power curve, and low vacuum. For years, it was thought the panacea was adding more valves, and that’s exactly what Chevy did with the first iteration of the LT5 in 1989 and what Ford did with the four-valve InTech Mod motor a few years later. Doubling the intake and exhaust valve curtain area (the valve circumference times the valve lift) for the same displacement means having your cake and eating it. It’s just harder to run out of flow before the mechanical limits of the engine are reached, which manifests as more power at a higher engine speed (witness Ford’s Voodoo V8 with 526 hp at 7,500 rpm from a mere 5.2L).
Dual-overhead-cam V8s proved more powerful, all things being equal, but all things aren’t equal (namely, the complexity, cost, and serviceability). During the 2000s, other incremental improvements were being made that took some of the wind out of the DOHC’s sail, primarily the dizzying progress of computational fluid dynamics. Breakthroughs in CFD meant that the discharge coefficient of OHV intake ports started going way up, most notably with the rectangle-port LS3 and the Chrysler Apache Hemi heads—something DOHC proponents never bargained for.
It’s in this milieu that Hammerhead Performance Engines owner Greg Brown found himself in several years ago. Brown, who at the time worked for famed Ford engine guru Jon Kaase, well knew the benefits of Ford’s 385-series Boss 429 Hemi. Brown had a front-row seat to the development of Kaase’s inspired Boss Nine cylinder heads and lamented that the small-block Ford guys had been left behind. That passion consumed him to the point that he struck off on his own to start Hammerhead.
His first job was to create the hemi-based cylinder heads you see this month, taking full advantage of the latest developments in flow, mating them to the inherent advantages of a hemi combustion chamber. But wait, these are Ford Windsor cylinder heads on an LS3-based engine. What gives?! The mind of the true engineer isn’t Ford-centric or Chevy-centric, it’s airflow-centric, and the ports Brown had developed for his Windsor hemi had incredible flow. As luck would have it, the bore centers for the Windsor and the LS3 were close enough that minor tweaks to the machining of the bolt holes and piston crowns would allow fitment on an LS3. With just 416 ci and a laughably small hydraulic roller cam, Brown’s LS hemi puts down 636 hp at a loafing 6,500 rpm and pulls enough vacuum to suck Lake Michigan dry. It fits under a flat hood and runs on 91 octane, too. Yeah, we’d say pushrod two-valve V8s are a long way from dead!
[ Hemi heads aren’t new, but the Hammerhead LS cylinder head piles the newest advances in CFD on top of the Hemi’s already significant airflow advantages. The result: airflow of such a high quantity and quality that it obviates the need for a giant...