1991 GMC Syclone - SYCO

A Syclone that goes 8.40s in defiance of sanity, common sense, and many doubters

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"Grow up and get an 8-cylinder." This phrase has been uttered on more than one occasion and it left an indelible impression on Vinny Di Prima. But clearly, the 44-year-old owner of 1991 Syclone #1373 isn't inclined to do what he is told. "I wanted to prove everyone wrong. I wanted to be the fastest out there, and I said it can be done." But that is certainly easier said than done. "I had a lot of problems over the years. I tried different combinations, different engine builders, nobody could get it to live." But eventually the Massapequa, New York, native got it right through perseverance and a stubborn belief in the 90-degree V-6.

The process of becoming the swiftest Syclone to grace the 1320 began in 1999. Vinny purchased Syclone #1373 from the legendary Jerry McCoy of McCoy Motorsports, who had already converted it to rear wheel drive and was one of the first to run 9s. But now it had been stripped to a bare shell, and Vinny would be starting from scratch. About the only thing that would remain from its previous incarnation was the roll cage. The frame itself was taken apart from the body, and modified extensively. Using components from Competition Engineering, Hell Bent Race Cars beefed up the frame and added ladder bars to the rear suspension. Using ladder bars to transfer weight to a Moser 12-bolt with Mickey Thompson 315/60/15 drag radials bolted up to the 35-spline axles, Vinny would have no issues with traction—eliminating any fancy electronics.

1305 1991 Gmc Syclone Side 2/9

By all means, do not get the impression that this Syclone is low-tech, but perhaps just a little more straightforward and simple than you might think. Starting with the powerplant, a Chevrolet Performance Bowtie V-6 block is kept at the stock 4.3-liters using a forged rotating assembly from Diamond Racing, Carrillo, and a little-known company—Crank Specialty. The same tried and true Brodix 23-degree heads that have powered the fastest Syclones to date find themselves atop this 9.5:1 engine as well, except these are nearly straight out of the box. Extreme Race Engine cleaned up the ports a little and matched them to a GM intake manifold, Wilson elbow, and 105mm throttle body. Vinny drilled, tapped, and welded the intake to house six massive (160 lb/hr) injectors that are fed 52 psi of C16 by a Weldon pump.

The wet-sump motor was finished off with an LSM solid roller cam with custom specs that are surprisingly mild and seemingly suitable for a street driven vehicle. "A bigger cam would mean more cylinder pressure." No O-rings are needed, Vinny said he's never blown a head gasket, but Inconel valves and Beryllium valve seats were a must. The ample seat pressure caused issue with stainless steel valves, which was one of several hard lessons learned during the build. Another was the uneven cylinder temperature in the V-6 block. "Even from the factory they had this issue. The #6 cylinder gets hot." Excessive cylinder wall scuffing was the telltale sign that the clearances needed to be opened up on this cylinder. After discovering this secret, Extreme Race Engine was able to put together a durable motor that would live.

Aside from the engine build, Vinny did most of the work himself on the Syclone including fitting the motor into the chassis with a TCI Powerglide, Turbo Action Cheetah shifter, and Pat's 3200-stall converter. He also wired up the FAST XFI engine management and set up the ignition system using an MSD Digital 7 Plus, billet distributor, high-output coil, 8mm wires, and #10 plugs. A set of Strange drag brakes and Centerline wheels put the Syclone back on the pavement and ready to ship over to Kooks Custom Headers for the hot-side piping. Kooks built a beautiful set of headers out of 17⁄8-inch stainless steel tubing, which neck down to 2.5-inches before merging at a Precision 88mm turbo mounted in the bed. A 5-inch downpipe vents the turbine and a TiAL 60mm wastegate protects it from overspinning. Charged air has a short commute to the PT2000 air-to-water intercooler mounted by its side, before routing back up to the engine bay with 4-inch tubing where a TiAL blow-off valve is the last defense before 32 psi of boost is smashed into the little V-6.




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