This CNC-ported LS1 head shares...
This CNC-ported LS1 head shares all the attributes that make the GenX the new heavyweight contender in the LS-engine ring. Among them are improved casting rigidity and raised valve-cover rails, making the use of aftermarket roller rockers a breeze.
Early adopters of the C5 in 1997 will remember. Those of you who drove your shiny new coupe off the dealer lot and directly into the staging lanes at the local dragstrip no doubt recall the novelty that was the all-new LS1 engine. Mid-to-low-13-second elapsed times were plenty quick back in the day, and the old-school guys certainly took notice. Do any of these backhanded compliments and gems of enlightened opinion ring a bell?
"Yeah, cool, but those engines won't last."
"Sure, it's quick. For what it is."
"That's as fast as they'll ever go."
"I'd rather push my big-block than drive one of those. " (OK, I made the last one up, but you just know some ignoramus somewhere said something to the effect.)
Trick Flow's line of GenX...
Trick Flow's line of GenX cylinder heads offers an appropriate model for nearly every member of the LS engine family. Shown here is the company's LSX CNC-ported head.
We all know now that those first LS1s were just the tip of the iceberg. In less than two years, those mighty little 346s were commonly turning mid-11s at nearly 120 mph, with little more than some rudimentary head porting, a cam swap, and some headers. Hit 'em with a shot of nitrous and bang! You were in the 10s. Not bad for what was dismissed as a novelty engine just several months before.
As the LS1 pioneers continued to identify and work around each successive performance bottleneck (remember the excitement around the LS6 manifold?), a subtle shift in attitude began. Slowly but surely, mainstream performance enthusiasts begin to take notice of the LS-series engines. No longer was the LS1 the engine of choice only for Corvette and F-body guys. It began showing up in high-end street rods and even some boutiquey muscle-car restifications.
The intake port on an LS1...
The intake port on an LS1 CNC-ported head has only slightly more volume than the as-ported version. This maximizes port velocity for improved throttle response.
Now, 12 years on, there are LS-series powered cars running in the 7s. There are nearly a dozen choices in aftermarket cylinder heads. There are even a small number of aftermarket aluminum and cast-iron blocks. Want a turbo or supercharger to strap on that mill? No problem; there are oodles of choices. Arguably, no family of engines before or since has enjoyed such spirited development from the aftermarket.
Among those throwing their hat in the ring is none other than Trick Flow Specialties (TFS). Long known for its small-block-Ford cylinder heads, which were at the forefront of the 5-liter-Mustang revolution of the 1990s, TFS has broadened its offerings with cylinder heads for big- and small-block Chevys and, notably, the LS-series engines.
The combustion chamber of...
The combustion chamber of the LS1 CNC-ported head is shaped to induce swirl, maximizing combustion efficiency. Stainless-steel valves rest in hardened valve seats.
TFS' GenX series of cylinder heads represents the Ohio company's first foray into the LS-series arena. Offered in five versions, there's a GenX head to fit just about any conceivable application. Each version is available fully assembled with stainless-steel valves, 1.300-inch dual valve springs rated at 0.650-inch of maximum lift, 7-degree titanium spring retainers with machine-steel locks, Viton valve seals, and hardened valve springs. The heads are also available as bare castings with just seals and guides. Best of all, TFS heads are made in the USA.
For stock or moderately modified LS1 and LS2 engines being built with one eye on the budget, TFS offers its GenX as-cast heads. Though less costly, the as-cast heads benefit from all the same features as the high-end CNC-ported units. Trick Flow's first order of business was to design and cast an ultra-rigid structure that minimizes flex for improved head-gasket sealing, even when subjected to the extraordinarily high cylinder pressures often seen with boost or nitrous.
The exhaust runner of the...
The exhaust runner of the LS1 CNC-ported head is kept relatively small as well. The remaining roughness seen in many of the ports is common to all CNC'd heads, regardless of manufacturer. These are simply low spots in the casting that fall just outside the tool path of the machine.
TFS' big dog is the CNC-ported...
TFS' big dog is the CNC-ported LSX. Here's a look at the intake port.
Combustion-chamber volume has been opened up on the LSX CNC-ported head. This is done to unshroud the larger valves and take maximum advantage of cylinder bores 4.125 inches and larger.
LSX CNC-ported heads also...
LSX CNC-ported heads also benefit from extra head-bolt holes to provide maximum head-gasket clamping. Here's a look at one of the CNC-ported exhaust runners.
Next, TFS revised the valve angles to 13.5 degrees, which decreases valve shrouding and improves airflow at all lift levels. Speaking of valves, the LS1 version features 2.040-inch intake and 1.575-inch exhaust valves. The LS2 heads benefit from an intake-valve upgrade to 2.055 inches. The spark plugs have been relocated to improve flame travel, thereby increasing combustion efficiency and, in turn, power production. Knowing that the use of aftermarket roller rockers often causes interference with stock valve covers, TFS raised the valve-cover rails to improve rocker clearance. Yes, you can hide your fancy aftermarket rockers under the stock valve covers with no need for spacers.
Even though TFS offers heads for both the 3.900-inch-bore LS1 and slightly larger 4.000-inch-bore LS2, the heads perform nearly identically on the flowbench. Max flow is 305 cfm at 0.600-inches of valve lift on the intake side, and 233 cfm at the same lift on the exhaust. As you'd expect, the combustion chamber is slightly larger on the LS2 version--65cc versus 64cc for the LS1. Intake-port volume for the as-cast LS1 head is 215cc, while the LS2 version is listed at 225cc. Both versions share a common exhaust-port volume of 80cc.
Vengeance Racing was asked...
Vengeance Racing was asked to assemble a test engine utilizing the LSX CNC-ported heads and a host of top-shelf parts in a relatively mild-mannered combination. On a chassis dyno with pump gas, the stout 440ci mill knocked out 682 hp (see graph, below). Turn up the wick, and these heads will get you north of 750 without breaking a sweat.
As cast, Trick Flow's GenX heads will outflow and outperform many of the CNC-ported cylinder heads on the market (see tables 1 and 2). But if better isn't good enough for you, or you're building a maximum-effort race engine, you'll want to take a hard look at TFS' CNC-ported GenX heads. With all the same features as the base heads, the CNC versions further benefit from highly refined intake- and exhaust-port shapes provided by the porting process.
The LS1 and LS2 versions pick up approximately 5 percent of additional flow potential over the as-cast versions (see tables 3 and 4). While that's a handsome gain, the big jump comes when you pull the trigger on TFS' LSX head. Though based on the same casting as the LS1 and LS2 models, the CNC-ported LSX head is opened up significantly to maximize the airflow in and out of a big-bore engine measuring 4.125-inches or larger.
The intake-runner volume has grown to 235 cc's, prompting the use of a 2.080-inch intake valve. A larger combustion chamber of 70 cc's allows for unrestricted flow past the larger valves and enhanced swirl characteristics. The exhaust valve measures 1.600-inches and opens to an 80cc exhaust runner. Lastly, the heads are drilled for six head bolts, to take advantage of the extra clamping ability provided by GM Performance Parts' LSX block.
So it all sounds pretty good, doesn't it? But the informed reader knows there's more to a pair of cylinder heads than just flow-bench numbers. TFS knows this, too, so it built a test engine to show just what its wares are capable of. Using the previously mentioned GM Performance Parts LSX block as a foundation, TFS filled it with a Lunati 4.125-inch-stroke crank, a set of Lunati 6.125-inch I-beam connecting rods, an octet of Diamond Racing forged pistons, and a relatively mild (0.629-inch lift) Lunati hydraulic roller cam. On pump gas, the 440-inch mill thumped out in excess of 680 hp at the crank. With more compression, more cam, and race gas, this combination would be easily capable of more than 750 horses!
That oughta be enough to get (and keep) the attention of those big-block guys.