Few cars in modern automotive history are as much of a total package as the modern GTO. With an incredibly stiff chassis, great handling characteristics, and seamless LS power, it is a true match made in GM heaven. Getting behind the wheel only proves this point further, as the GTO is always in full control, no matter how hard that go-pedal is stomped. The GTO can easily handle 500- or even 600-horsepower or more and still be as controlled and easy to drive as it was when it was bone stock.
So, wanting to test the limits for ourselves, we set out on a horsepower pursuit to eternal dragstrip happiness by adding more power to Head Poncho, our resident 2005 GTO. While there were many ways to go about it, we decided to keep things simple-almost scientifically simple-so we left the car naturally aspirated to avoid any more weight gain to our already heavyweight hitter. Going the all-motor route would also reduce the amount of down time required as we wouldn't have to spend days tuning it if it had a forced-induction setup. So, the hunt was on for a free-breathing top half to complement our 6-liter pony eater.
Heading Out
With our goals laid out, we looked for a top half that would offer the perfect balance between power, reliability, torque and oh yea, power. (You can see our priorities, can't you?) To get these results, the centerpiece to our horsepower recipe was going to rely heavily on our cylinder head choice so we didn't bother playing any games and went straight to the awesome TFS GenX pieces. These heads have 13.5-degree valve angles and come fully assembled with 7-degree titanium retainers for immediate installation and no hassles (however, they are also available bare should you want to use your own valvetrain.)
Currently, TFS offers three versions of its fully assembled, CNC-ported GenX aluminum cylinder head, with each easily identified by their intake runner volume. The 215cc, 225cc, and 235cc versions denote their ideal applications as each one of these has a correlating valve size to match a particular engine's breathing needs. For instance, its 215cc units are ideal for the 5.7-liter LS1 as the 2.040/1.575 valves clear the smaller bores perfectly. With our LS2's larger 4.0-inch bore we were able to take advantage of TFS' larger 225cc castings with their upsized 2.055/1.575 valves. The even-larger 235cc versions are best suited for stroked or force-fed applications, which we rightfully admitted to ourselves as being a bit more than we really needed. So, with the 225cc units added to our shopping cart (PN TFS-3060T001-C02, $2,395) we then grabbed a pair of new GM head gaskets and ARP head bolts (PN 134-3610, $113). With our head selection finished, it was time to move ahead with our camshaft choice.
For our moderately aggressive 225cc heads, we went with TFS' Track Max camshaft (PN 306-02003, $339). It checks in at a healthy 228 degrees of duration at .050 lift on the intake and 230 degrees on the exhaust. Lift is pretty stout at .585 on both sides and keeps the valvesprings happy by staying below their .600-lift limit. In addition, the cam is designed to provide maximum power and torque without any valve-to-piston interference, especially at the upper reaches of the tachometer. With our head and cam package selected, it was time to move ahead to the supporting valvetrain components and an intake manifold upgrade.
Our GTO attacks the quarter...
Our GTO attacks the quarter mile with newfound ferociousness. With our new top half in place, our LS2 Goat has picked up nearly one whole second and nine mph, for a new best of 11.33 at 119 mph. For a full weight street car on 17-inch drag radials, that handles on par with Europe's best, we consider it phenomenal.
The centerpiece (or more correctly,...
The centerpiece (or more correctly, centerpieces) to our horsepower gain are a pair of TFS GenX 225cc cylinder heads. Known within LS circles as the head to buy, they provide incredible mid- and high-lift flow for that perfect balance of midrange torque and high-winding horsepower. With CNC-massaged 65cc chambers and runners, the smooth airflow that these heads provide also ensures great throttle response. Additionally, the valvetrain is ready for the high-lift cam of your choice with its .600-lift springs and titanium retainers.
To complete our head swap,...
To complete our head swap, we needed a few more bits of hardware, namely a camshaft and some valvetrain components. For the cam, we went with TFS' most aggressive Track Max hydraulic roller for the LS that offers 228/230 duration at .050 valve lift and .585 lift on both sides at the seat. To make it work with the Harland Sharp 1.7 ratio roller rockers, we used 5.7-inch TFS pushrods. Rounding out the necessary parts for our new top half, we looked to Summit Racing for a set of 42-lb. injectors and ARP for a set of head bolts to replace the factory torque-to-yield units. Although not necessary, a new timing chain is ideal. On an LS2, you'll need one that has provisions for the camshaft position sensor.
To match the new airflow potential...
To match the new airflow potential of our LS2, we decided to ditch the factory intake in favor of FAST's LSX 90mm intake manifold. A perennial favorite amongst the GTO crowd, this composite two-piece intake manifold can keep up with just about anything an LS racer can throw at it and installation is incredibly easy. However, due to its lightweight construction, a ported cast aluminum unit may be better suited should you add a nitrous system later on. Nevertheless, this is one great piece that has recently been updated to a 92mm inlet size.
To start things off, Nick...
To start things off, Nick Stevko removes the coil packs, rocker arm covers, the factory LS2's intake manifold bolts, and disconnects the fuel line.
With the harness removed,...
With the harness removed, the intake manifold is pulled off and quickly chucked into the dumpster with other useless items like modular Ford engines.