Trick Flow Specialties LS3 Head/Cam Kit Install

No Compromises

Jay Heath Dec 2, 2013 0 Comment(s)
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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.

Details, Details

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.

Package Goods

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.

Genx 255 Intake 2/20

1. At 255cc in volume, the GenX 255’s intake runner is actually a hair smaller than the LS3 stocker’s. But thanks to its “competition” CNC porting and modified design, it flows around 15 percent more air.

Exhaust Port 3/20

2. The exhaust port, meanwhile, is slightly larger than stock (87cc, as opposed to 86), and fairly wallops it in terms of flow numbers (252 cfm vs. 189). Exhaust flow is arguably the factory LS3 head’s weakest feature.

69cc Combustion 4/20

3. The heads’ 69cc combustion chambers also receive the CNC treatment, while the 2.165/1.600-inch valves are oriented at 12—rather than the stock 15—degrees. The latter change increases piston to-valve clearance, promotes airflow, and boosts combustion efficiency, according to engineer Downs.

Tfs Dual Valve 5/20

4. This being Trick Flow Specialties (TFS), the heads come fully assembled with dual valvesprings, steel locks, and a choice of steel or (optional) titanium retainers.

Tfs Complete Top End Kit 6/20

5. Opt for the complete top-end kit, and you’ll also receive a full complement of fresh head bolts, longer-than-stock pushrods (7.75 in vs. 7.40), and much more.

2011 Chevy Corvette Cyber Gray Grand 7/20

6. Our test subject was an ’11 Cyber Gray Grand Sport showing just 4,000 miles on the clock. The six-speed manual car was in pristine shape and featured an internally stock engine.

American Racing 8/20

7. The car’s owner did decide to add a set of American Racing Headers’ long-tubes and high-flow cats prior to the head/cam install, the better to make use of all that extra airflow. These exhaust mods alone tacked on nearly 26 hp and 12 lb-ft to the GS’s stock rear-wheel tallies.

Intake Ports Stock 9/20

8. This comparison of the intake ports on the stock (right) and TFS heads reveals only minor differences in external size and configuration. Internally, the TFS runners have been heavily “massaged” for increased flow with no loss of velocity.

Tfs Head Structural 10/20

9. Things are much the same on the exhaust side, where the two heads use an externally similar D-shaped port configuration. This view does provide some evidence of the TFS head’s structural fortifications, which provide a solid foundation for higher-hp combinations.

New Tfs 11/20

10. With the timing cover and related hardware removed from the front of the engine, Lovell slides the new TFS camshaft into place. Designed specifically for use with the GenX 255 heads, this hydraulic roller grind specs out at 0.625/0.625-inch lift and 0.230/0.238-degree duration.

Cometic Multilayer Steel Head 12/20

11. The TFS kit includes a fresh pair of Cometic multilayer steel (MLS) head gaskets, shown here laid in place on the engine block.

Cylinder Heads Clean 13/20

12. It’s always a good idea to treat new cylinder heads or other engine components to a spritz of brake cleaner and compressed air before installing them. This will remove any metallic residue left over from the casting and machining processes.

Tfs Pushrods 14/20

13. The driver side takes its place atop the engine. Note the new TFS pushrods have already been installed.

Genx 255 Head 15/20

14. Each GenX 255 head comes with its own billet TFS rocker-arm stand. “There are some potential issues with the factory rocker geometry that have been corrected with this stand,” says Mike Downs.

Ls3 Engine Button 16/20

15. With the internal work complete, it’s time to button up the rest of the engine, add the necessary fluids, and see how the new combo performs.

Corvette Pcm Basic Tune 17/20

16. Before we can strap down the car for follow-up dyno testing, Lovell uploads what he describes as a “safe, basic tune” to the Vette’s PCM. Afterwards, turning over the modified mill for the first time unleashes a horripilation-inducing sonic apocalypse from the factory quad tailpipes. (Translation: This is one mean-sounding Corvette.)

2011 Chevy Corvette 18/20

17. Then, it’s back to the Dynojet, where the Grand Sport promptly pumps 478.28 hp and 439.99 lb-ft to the rollers. Those numbers represent improvements of roughly 73 hp and 40 lb-ft, respectively, over our previous headers-only pull. A few days later, the car’s owner will call Lovell to enthuse, “This car feels faster than my old C6 Z06!”

Dyno 19/20

18. A look at the dyno sheet (which shows the results of our baseline blue, headers-only red, and headers/heads/cam green pulls) reveals why. Unlike some parts combos that boost high-rpm performance and the expense of low-end response, the TFS kit posts sizable hp and torque gains at every point on the graph. With this kind of output and driveability available from 376 cubes, who needs an LS7?


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.

Vette Tech Center 20/20

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