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.
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.