When it comes to First World quandaries, determining how best to squeeze more straight-line scoot out of a base 2008-2013 Corvette ranks well toward the safe end of the defensibility spectrum. After all, it’s not as if we’re talking about a choice based purely in ostentation or pretension, like, say, deciding which sommelier app to download to your new gold-colored iPhone 5S. No, a quicker, more responsive Vette pays tangible dividends every time you poke the loud pedal, and anyone who doesn’t twig that logic probably drives a Kia.
Fortunately for us non-Kia drivers, the engineers at Trick Flow Specialties (TFS) have recently applied their encyclopedic knowledge of engine-airflow management to the task of enlivening GM’s already vigorous LS3 engine. The result is the GenX 255 cylinder head, which promises to deliver the same type of performance increase we’ve seen from previous TFS heads for the LS1 and LS2, LT1, and traditional small-block Chevy. Let’s take a closer look at the GenX 255 to see how it manages that not inconsiderable trick.
Is Bigger Really Better?
Time was when improving head design involved simply employing larger ports and valves, the thinking being that more airflow meant more power. While the fundamental logic behind this approach is sound, there are many more factors to consider when designing a head for a car that’s destined for use on both the street and the track.
Take, for example, the highly tuned SBC engines used in NASCAR, which use cavernous ports and manhole-sized valves to flow a tremendous amount of air and deliver more than 850 hp. That’s an impressive figure for a powerplant displacing only 358 cubic inches, and it might leave the uninitiated wondering why Team Corvette was “only” able to pull 430-436 horses out of the 376-cube LS3.
Simply put, those NASCAR engines—which guzzle fuel, function optimally in a tiny rpm window well north of 9,000 rpm, and are subjected to full overhauls on a regular basis—are about as well suited to a street car as roller skates are to a rhino. The LS3, meanwhile, is paragon of smooth reliability, with a broad power band, exemplary emissions and fuel-efficiency numbers, and enough thrust to push a standard C6 through the atmosphere at more than 190 mph.
Still, that doesn’t mean it can’t be improved, and that’s where TFS comes in.
As good as the LS3 head is, it bears mention that its laudable output numbers are attributable in part to the use of intake and exhaust ports measuring a largish 257 and 86cc, respectively. A 10.7:1 compression ratio and that aforementioned 376ci displacement ensure good low-end thrust, but as anyone who’s flogged a later C6 will attest, the real horsepower magic resides on the higher end of the rev range.
It should come as no surprise, then, that the GenX 255—whose name reflects its intake-port volume—relies on subtle refinements, rather than indiscriminate upsizing, to improve flow, velocity, combustion efficiency, and, ultimately, power.
Most noticeable is the “competition” CNC porting TFS applies to each runner. That, along with moderate adjustments to the shapes of the runners themselves, helps yield flow numbers of 363 cfm on the intake side and 252 cfm on the exhaust—significant boosts over the factory head’s 316/189 ratings. What’s especially impressive is that the GenX 255s manage those numbers using what are essentially stock-size ports and valves, preserving velocity for good low-rpm response.
“We don’t feel there’s any real benefit to increasing the port volume, based on the existing valve sizes,” says TFS engineer Mike Downs. “This design is flow-bench and dyno validated.”
As is typical of TFS offerings, the heads come well kitted up from the factory. Dual valvesprings are standard on all GenX 255s, while titanium retainers and a six-bolt-per-cylinder mounting pattern (for use with Chevy Performance Parts LSX heads) are available optionally.
While the GenX 255s are sure to make big numbers by themselves, TFS also offers them in package form, complete with a custom camshaft and a full complement of installation hardware (PN TFS-K326-580-520, $3199.97). As we’ve enjoyed excellent results from the company’s top-end kits in the past, we didn’t hesitate to go this route once again when the opportunity arose.
Our test car was a low-mileage ’11 Grand Sport featuring a six-speed manual trans, NPP Dual Mode Exhaust, and zero aftermarket modifications, at least initially. Given that one of the chief advantages conferred by the GenX 255s is a tremendous increase in exhaust flow over stock, the car’s owner decided to have a set of American Racing Headers’ long-tube headers and high-flow catalytic converters installed before the top-end package went on. After all, it didn’t make sense to cork up all that extra air with a set of stock manifolds and cats.
The results of this simple modification were impressive, as the car’s rear-wheel output swelled from 379.62 hp and 377.50 lb-ft of torque to 405.21 hp and 399.10 lb-ft, respectively, on our in-house Dynojet chassis dynamometer. It’s worth noting that these improvements were achieved without follow-up PCM tuning, as we wanted to save that step until after the top-end parts had been installed.
With the car now suitably “unencumbered,” Greg Lovell and Kyle Miller from AntiVenom in Seffner, Florida, began tearing down the engine in preparation for the TFS parts. If you’re considering having this package installed on your own Vette, we strongly recommend using a shop whose technicians have extensive experience in modifying GM LS-series engines. As good as the TFS parts are, they can’t compensate for inexpertly executed mechanical work.
Fortunately for us, Lovell and Miller perform jobs of this sort on a regular basis, and they had our GS tester up and running again the same day. You’ll have to read on for our results, but suffice it to say that if uncompromised LS3 performance is your goal, the GenX 255 package is the solution to your quandary.
To hear our test car idling, revving, and making a pull on the dyno, click "Play" below and don't forget to check out the video section for more.