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.
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.
Whenever you install a new camshaft into an LS engine, you will need to upgrade the rest of the valvetrain as well to match the new powerband that will typically be higher than before. Since the TFS heads already come with high-quality springs and retainers, we concentrated our efforts on a set of high-quality roller rockers and pushrods. For the rocker arms, we went with a set of trick Harland Sharp 1.7 ratio arms (PN SLS17, $399) in their signature gold-anodized finish. As many LS racers know, the stock rockers have proven to work very well in competition, but for the utmost in reliability and valvetrain stability, going to the semi-shaft design of the Harland Sharp units really locks things down considering that the factory 8mm bolts are all that are used to secure everything to the head. To finish the installation, we then went with a set of 7.5-inch TFS hardened pushrods. The original factory roller lifters and lifter retainers were re-used as they've proven to handle plenty of RPM without any problems.
As LS engines go, the LS2 intake manifold is one of the least-flowing designs out there. Being on par with an LS1 intake in power potential, this left us wondering just how straddled our new engine combination would be with a rather "sucky" intake. So, a step up to a higher-flowing intake manifold was planned, but we had to examine our options first. The few intakes on the market fall into two main categories-those that are cast in aluminum and those that are molded from composite material. While the cast aluminum units on the market certainly have a durability advantage and can be ported safely for boosted or nitrous-injected applications, it's their price that makes them so attractive. They are priced quite reasonably but the weight penalty can be as much as 15 pounds, placed right over the nose of your ride.
Since we prioritized lighter weight and knew that our engine would live a simple naturally aspirated life, we went with the composite LSX 90mm intake manifold from FAST (which has been recently superseded by a 92mm version, which was unavailable at the time of print). Because all LS2s already have a 90mm throttle body from the factory, we didn't have to fork over as many greenbacks as our F-body friends would in order to have a complete 90/90 FAST setup (the FAST 90mm throttle body retails for almost $450 alone.) Another added expense was the FAST LS2 fuel rail installation kit (PN 54026, $76 from Summit Racing), which comes with fuel injector adapters and other miscellaneous hardware. In addition, keep in mind that the FAST intake manifold has its MAP sensor mount located at the rear so on an LS2 car (like ours) remember to pick up a MAP sensor relocation wiring kit. In total, adding the FAST LSX intake to your LS2 will cost you about $950 even if you re-use your factory DBW (Drive By Wire) throttle body.
Although the LSX intake is a proven performer and is a nice luxury, it is not entirely necessary for a street/strip machine, but we did it for the sake of matching our engine combo. If you are a nitrous user and abuser and don't mind the extra weight, going with one of the aluminum intake manifolds may be a great choice and can save you enough dough to use towards a good 150-horsepower nitrous system.
The last part of the engine upgrade was fuel delivery. Since the stock fuel pump in GTOs are proven up to 475 rwhp, we decided to leave ours alone. The injectors, however, tap out much sooner, so we swapped out the stock 33 lb/hr units for a set of 42 lb/hr units from Summit Racing. Like most aftermarket units, the Summit injectors are of the Rochester design with an EV1 connector. However, the factory LS2 injector harness uses an EV6 connector, which is the later, more compact style and cannot be plugged directly into the Summit Racing injectors. But not all was lost as we were able to source up a set of injector wiring adapters from Summit under PN TFS-89201, $7.50 each.
So with a stack of boxes jammed into our GTO's miniscale trunk, we headed over to our friends at TT Performance Parts in their new facility in Little Falls, New Jersey for the installation and required tune. Proprietor Matt Sorian and the lead experts on this project, shop manager Nick Stevko and technician Jake Soja, spent a full day swapping out our top half and making the dyno sing. Once installation was complete, we topped off all the fluids, let the car run for a while to check for leaks or any other issues, and then strapped the car onto the DynoJet chassis dyno.
Previously, our Head Poncho cranked out 350.1 rwhp and 336.7 foot-pounds and blitzed to a 12.28 at 110.8 mph with just bolt-ons including a full Stainless Works exhaust that was expertly installed by TTP's own Rob Flores. But this time around, we were eager to see how our new engine package would perform as we listened to it settle into a nice, choppy idle. With our engine up to operating temperature, Sorian dialed in a good baseline tune and put the car at full throttle and we watched the rollers spin as our LS2 screamed to redline. Anticipation was high but we were quickly let down as Sorian looked at the chart in disbelief and asked us to come over and take a look for ourselves. With our mouths open, we stared at the graph that showed no gain whatsoever. Shocked by what was before us, we looked at the screen one more time to see what was going on and noticed that our power was actually going down as our engine speeds increased and the tachometer was hovering around redline during acceleration.
We quickly realized that all our newfound power was simply slipping away and that the stock transmission was more than likely the culprit. After a quick cooldown, we pulled out the transmission's dipstick and quickly smelled burned fluid, indicating that the 4L65E was pretty much toast. It was a true shame that with only 20,000 miles on the clock, our factory-original slushbox was unable to handle our new setup. Saddened, but not deterred, Sorian tuned our car the best that he could and we headed back home, slowly but safely.
A couple of days later, we found a used transmission on the Internet. Because of deadlines, we thrashed all night to install it at our home office and the next day, headed out to our favorite proving grounds, Raceway Park in Old Bridge, New Jersey. If we weren't going to be able to get dyno numbers by our deadline, we were sure going to do our darn best to get good track numbers. So with the Nitto drag radials lowered to 17 psi, we headed over to the burnout box and gave our shoes a serious heat cycle. Staged and ready to go, we stalled the converter up to 1,500 and once the last yellow lit, stomped the gas pedal and let the converter flash to an indicated 4,000 rpm (which is about 400 rpm more than we used to see.) Our short times were still terrific, with a 1.65, and by half track, we already knew we were in for a new best. Sure enough, the Goat cranked off an 11.334 at 119.22 mph-and we were politely asked to leave the premises due to the lack of safety equipment. Driving home, we were astounded at the numbers as we picked up nearly a full second and nine miles per hour!
Few cars offer the perfect combination of power, ET, handling and comfort-even in modified form-as well as the GTO. As we've demonstrated with our Head Poncho, the right combination of parts and state of mind with any GTO will result in a true turn-key weapon that can annihilate any car next to you, even from a standstill. So wait no longer, go pick up one of these cars, build it the way you want it, and realize how the latest GTO redefines its own legend.