For many enthusiasts the 1991 Syclone has been a wet dream-literally: since its inception, boasting incredible 0 to 60 numbers that even put 90s-era Ferraris to shame-especially in the rain. Its all-wheel-drive system was the precursor to the many AWD sports sedans we now see on the road. But often the limited-edition truck is shamed by its critics, who claim it is too hard to work on, and that the factory 4.3L V-6 simply isn't a very good motor. Whether or not you share these beliefs, the thought of trading the iron-headed V-6 for a Gen III/IV V-8, some of the most potent factory GM engines ever made, should interest you. In fact, it has been one of the most talked-about swaps on the Sy/Ty message boards for years. And though it's been talked about and maybe even tried, it has never been done...until now.
When 64-year-old business owner Doug Aber took his Syclone to Vengeance Racing in Cumming, Georgia with only the dream of owning something truly unique, an LS2 swap seemed the natural choice for the Gen III/IV specialists. The only question was: how? Since keeping the AWD system was an essential part of the build, it was decided that keeping the transfer case in the factory location would be the best course of action to keep things simple and avoid potential problems. As a result, selecting the right transmission to mate to the LS2 and transfer case was going to be an issue. The initial plan of using an AWD version of the 4L60E from a late-model truck proved insufficient because of its extended dimensions (that would have pushed the motor and transfer case forward). After more thought, trial and error, and consultation with RPM Transmissions, Vengeance decided to use the factory 700R4 case stuffed with Level V 4L60E internals to withstand quite a bit of punishment, and take commands from an LS1 F-body PCM. The transfer case and prop shaft have also been beefed up for the additional brunt of the LS2. A TCI flexplate, B&M trans cooler, and Vigilante 3200-stall converter give further support.
Once the position of the motor was established via the trans and transfer case location, Vengeance fabricated a set of motor mounts and modified a truck oil pan to accommodate it. Along the firewall, the heater box had to be remolded to clear the motor; meanwhile the rear coil packs would also need to be slightly relocated on the valve covers. Using a stock LS2 shortblock (recently pulled out of another customer's car), Total Engine Airflow Stage 3 ported LS6 heads, and a Vengeance VRX3 226/228-duration cam, the Sy's potent new powerplant was firmly defined. It needed only a set of 1.75-inch long tube headers fabricated by Vengeance as well as a 3-inch dual exhaust with an X-pipe and Magnaflow mufflers to give it a rich V-8 tone and low 11-second potential. The top end was treated to a ported FAST LSX intake, 90mm throttle body, 36lb/hr injectors, MAF from an 2002 Camaro, and K&N cold air intake for an 2006 Trailblazer SS to make the transformation complete.
The 17x9.5 wheels are one-offs purchased from GMMG that were created for use on a prototype, special edition F-body. Spacers were used for proper fitment on the Sy. BFG KDW rubber, 3.73 rear gear, Koni shocks and C5 Z06 front brakes make the truck a blast to drive on the street. --->
One of the other challenges to this build, according to Vengeance proprietor Mike Carnahan, was integrating the LS1 wiring harness, PCM, and fuel system with the Syclone's wiring and gauge cluster. After some head-scratching and soldering, an in-tank Walbro 255lph fuel pump was supplying 55psi of fuel pressure, a conversion box purchased on the internet had the tachometer functional, and since the rest of the gauge cluster ran off a 5-volt signal it wasn't too difficult (Mike said) getting it operational as well. Once a set of high-flow electric fans from Spal were wired in, Mike dialed in the tune using EFI Live. Finally, Aber took his truck back to Port Charlotte, FL and has since enjoyed the tremendous torque from the larger-cube motor and its hard street launches. At the track this translated to an impressive 11.37 at 117mph. Doug's next goal is to have Vengeance install a nitrous kit that will get him into the 10s. The swap may have taken more time than Doug or Vengeance care to remember, but that is a dream worth waiting for.
 The interior is purposefully...  The interior is purposefully kept as factory appearing as possible. Vengeance went to great lengths to keep the gauge cluster operational even with the new motor and PCM. Only the Aeroforce Interceptor and Autometer fuel pressure gauge deviate from stock. |  For a fairly radical swap,...  For a fairly radical swap, Vengeance did a terrific job of keeping it very seamless. Fabricated motor mounts and headers, a remolded heater box, and a modified LS1 truck oil pan were just a few of the custom parts required to swap the factory turbo 4.3L V-6 for an LS2. The TEA-ported LS6 heads, VRX3 cam, and ported FAST intake used in this build typically make 450-475 rear wheel horsepower on GTOs, according to Vengeance. The best track time so far is an 11.37 at 117mph. |  Doug Aber of Port Charlotte,...  Doug Aber of Port Charlotte, FL purchased his 1991 Syclone new, and in addition to spending a great length of time at Vengeance Racing, it has had a complete frame-off restoration and repaint from Collision Custom Services, which is also located in Cumming, GA. |