Back in 1991, the dogs days of the sad, slow, so-called economy efficient sports cars were starting to come to an end. The days of the poorly performing 350-cu.-in. Tuned-Port Injection (TPI) engine setups that General Motors was using for their unimpressive performing sports cars were about to be replaced by a much more stout performing LT1 350-cu.-in. engine.
But before the switch would be made, the GMC truck division of General Motors made an interesting move to get involved in some of the performance making hype that GM was encouraging at the time. GMC made a move and signed a contract with a company called Production Automotive Systems (PAS) which in-turn would create the fastest production trucks of its time: the '91 GMC Syclone pickup truck and '92-'93 GMC Typhoon SUV.
The Pass Company was no stranger to this type of work as Pontiac called upon them to help them build the very famous 1989 Turbo Trans Am 20th Anniversary Edition.
PAS engineered a 4.3-liter Vortec engine that came equipped with a turbocharger and an intercooler to fit in both the Syclone and the Typhoon. To efficiently transfer engine power, both models would receive the four-speed 700R4 automatic transmission, the same trans that the Corvette was using at the time.
What made the Syclone and the Typhoon so unique to other trucks is that they used a very performance efficient all-wheel drive system. That technology helped these trucks that had an underrated, unofficial horsepower rating of 280 get down the quarter-mile with times that could stop the clocks somewhere in the high-13-second range. And since these trucks were so well-liked, there were a lot of upgrades promoting even faster quarter-mile times, in fact, some that were darn right amazing (10 and 9 second passes).
With great gas mileage, great performance and the fact that they were limited production, the GMC Syclone and Typhoon were and are still great car collector items for all car enthusiast alike. With a limited production of only 2,998 '91 Syclone's, 2,500 '92 Typhoons and 2,200 '93 Typhoons built, the price tags on these rare trucks still stay up in the $15,000 to $25,000 range for the ones that are still in good condition.
Unfortunately, the PAS company based in Troy, Mi., that was responsible for the GMC Syclone and Typhoons engineering and design would go out of business after GM decided not to go forward with any more specialized GMC vehicles at the time. This decision was mostly due to the progression of the Corvettes, Camaros, Trans Ams and the need to focus on the new technology of eclectic vehicles.
Disp.: 262 C.I. (4.3L)
Horsepower: 280 BHP @ 4400 (Syclone) 285 BHP @4400 (Typhoon)
Torque: 350 lb-ft @ 3600 (Syclone) 350 lb-ft @ 3600 (Typhoon)
Comp. Ratio: 8.35:1
Firing Order: 1-6-5-4-3-2
Oil Pres. (Min) 6 psi@ 1000 RPM, 18 psi@ 2000 RPM, 24 psi@ 4000 RPM
Round: .001 (production) .002 (service)
PISTON RING: Compression: Groove Clearance: .0012-.0032 Gap: .010-.020 (top) .010-.025 (2nd) Oil: GC: .002-.007 Gap: .015-.055 PISTON PIN: Diam: .9270-.9273 Piston Clearance: .0002-.0007 Rod Fit: .0008-.0016 Interference
MAIN JOURNAL: Diam: #1 2.4484-2.4493
#2 #3 2.4481-2.4490
Taper: .001 max
Out of Round: .001 max
MAIN BRG. CLEARANCE: #1 .0010-.0015 #2#3 .0010-.0025 #4 .0025-.0035
CRANK END PLAY: .002-.006
CRANKPIN: Diam: 2.2487-2.2497
Taper: .001 max
OOR: .001 max
ROD CLEARANCE: .0013-0030
SIDE CLEARANCE: .006-.014
LIFT +- .002 Intake .357 Exhaust .390 Journal Diam: 1.8682-1.8692 End Play .004 -.012
Lifter Hydraulic Rocker ratio 1.5:1
Lash Adj. One turn down from zero Face Angle 45 deg.
Seat Angle 46 deg.
Runout .002 max
Seat Width 1/16 to 1/32 Stem clearance .0010-.0028 Spring length 2.03 Valve Spring Pres. 76-84 lbs @ 1.70 in Closed 194-206 lbs @ 1.25 in
Open Installed height 1 23/32"
Valve Spring Damper: Free Length 1.86 # coils 4