MODIFYING AN LT1 Corvette for improved performance can be a trying business. Aftermarket parts are scarce, the work itself is often maddeningly difficult, and even the most intrepid Corvette tuners may be inclined to treat you like an end-stage Ebola victim. Given these hurdles, we were pleasantly surprised to learn of Trick Flow Specialties' new Fast as Cast GenX LT1 top-end kit, which should be available by the time you read this.
Carrying PN TFS-K304-430-400, the package generates a claimed 430 horses and 400 lb-ft of torque when installed on a healthy, stock-displacement LT1 engine. If accurate, those figures would put a '92-'96 Vette's output on par with Bowling Green's latest, and restore much sorely needed performance credibility to the aging Gen II small-block. We'll be installing the full kit on our '96 C4 coupe in the weeks ahead, but for now, let's take a closer look at the package's specifics.
Heads TFS has offered GenX LT1 cylinder heads for a few years now, but the company's first effort employed largish 195cc intake ports and was intended for stroked or forced-induction engines. The new Fast as Cast version relies on a downsized, 185cc port that makes it ideally suited to naturally aspirated, stock-cube combinations. As the name implies, these heads are designed to offer superb flow right off the shelf, eliminating the need for costly and time-consuming port work. TFS' Al Noe explains the concept:
"Fast as Cast is a process where we optimize the port design and shape (just like a CNC-ported head) and then make port core tooling to be an exact duplicate. With current manufacturing processes, we can make a cylinder head with tight-tolerance cast ports. We also CNC the chamber, CNC bowl blend, and CNC the intake manifold port opening."
Another characteristic that separates these heads from everything else on the market is the orientation of the valves. Rather than using the standard SBC valve angle of 23 degrees, the Fast as Cast heads employ valves that are rotated to 21 degrees.
"We did this to allow us to make a very tight, small [54cc], efficient chamber to keep the stock compression ratio, and also to keep the valve seats from protruding into the deck surface of the head," says Noe. "We could make a [23-degree] small-chamber LT1 head, but two problems would occur: first, the valve-seat ring would protrude into the deck, which makes milling the head a nightmare. The second problem is the small, tight chamber with a 23-degree valve angle is not a great design. Rolling the valve angle two degrees allows us to have a small, torquey intake port with an excellent-performing chamber design attached to it."
Other notable features include 67cc exhaust runners, 2.02/1.60-inch valves, and heavy-duty valvesprings suitable for up to 0.600-inch lift. In addition to being the prime mover in the Fast as Cast LT1 top-end package, the heads are available separately, as well as in a bare version.
Camshaft Realizing that few Corvette enthusiasts are willing to trade driveability for a few extra high-rpm horsepower, TFS engineers designed the package's camshaft to embody an acceptable compromise between enhanced output and everyday civility. The specs-0.530/0.530-inch lift (with 1.6-ratio rockers), 219/227-degree duration, and a 113-degree lobe-separation angle-are not dissimilar to those of GM Performance Parts' highly regarded LT4 "Hot" cam, which is perhaps not surprising given the latter's reputation for superb all-around performance.
Like any internal engine modification, the cam does require post-install ECM tuning, preferably performed on a chassis dyno. Given the power increases involved, that seems like a small price to pay.