TT Performance Parts & 4L65E Transmission

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.