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1992 GMC Typhoon LS1 Engine Upgrade - Conversion Immersion

Trading The Typhoon's 4.3L V-6 For A Turbo LS1 And 10-Second Timeslips

John Ryan Feb 1, 2010

If you've been into performance for a long time, it's very possible that the following applies to you as well. Like many performance addicts, Dan Marks of Wonder Lake, Illinois, caught the bug in his teens and he's never been able to shake it. He's owned some quick cars over the years including a 1995 Cobra he turned into a tire-melting 1,100-rear-wheel-horsepower animal. While most folks resign themselves to having fast cars that sleep most of the week and commute in a boring daily driver, the longtime Senior Technician at Speed Inc. simply couldn't have that.

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At the Shcaumburg, Illinois shop Dan was no stranger to making gobs of power with LS technology and turbos. Additionally, he is a longtime fan of GMC Typhoons, and has lusted after them from the first day he laid eyes on one back in the early '90s. However, the high collectability of these vehicles has kept their prices strong and as a result, this was an unfulfilled dream until last year. Dan was browsing on, and noticed an ad for an 89,000-mile, mostly stock 1992 Typhoon. Dan haggled over the price and a deal was struck. Modified with only a cold-air intake and chip, the truck was a fun high 13-second ride. Dan did actually put a few hundred miles on the truck before tearing it down, but his goal to combine his longtime admiration of these trucks with a modern LS driveline finally won out and so the truck went under the knife.

Having had years of experience designing and fabricating custom LS-based builds, Dan made a list of goals that included extreme performance, retaining all-wheel-drive, and last but not least, keeping air conditioning for his lengthy commute. Dan started his build by yanking out the factory engine, turbo system, and exhaust. He wisely left the stock transmission and transfer case in place for his initial engine mockup. A junk engine block was used to see what modifications would be needed to shoehorn an LS-based mill in place of the original V-6. While whipping up custom motor mounts was anticipated, Dan also discovered that the factory heater box needed to be clearanced or the engine would not fit. With regards to the LS swap, this was one of the few major modifications needed, other than building a custom transmission crossmember.

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Next, Dan turned his attention to the rest of the driveline. With plans to make somewhere in the neighborhood of 700-rear-wheel horsepower, Marks knew that the factory 700-R4 transmission and wimpy 7.5-inch 10-bolt rearend would last about 10 seconds into his first testdrive. After some research, Finish Line Transmission of Bensenville, Illinois, got the nod to build him a Level V 4L80E transmission, which is rated to handle over 1,000 horsepower. Dan went with another trusted company, Yank, to supply him with a 3,200-stall converter that would have lock-up and handle 800 lb-ft of abusive torque. Custom length chrome-moly driveshafts were ordered from Suburban Driveline, and a '67 Chevelle 12-bolt was narrowed and modified to bolt up to his factory suspension.

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Having sorted out the drivetrain, Dan turned his attention topside to the engine and turbo setup. A used 6.0L iron block stroker, sporting 402 cubic inches, was acquired and then freshened by Advanced Automotive in Roselle, Illinois. They also installed a custom camshaft, which was specified by longtime friend and coworker Jim Moran. A pair of ET Performance 245cc cylinders heads made their way atop the engine along with a GM Performance Parts carb-style intake manifold. A set of Speed Inc. fuel rails, an MSD 90mm throttle body, and a set of 80 lb/hr injectors top off the long-block. Faced with either buying a custom oil pan or making his own, Marks purchased a wallet-friendly 2007 Escalade oil pan, which he cut and modified to fit. Eschewing a rowdy external fuel pump setup, twin Walbro 255 in-tank fuel pumps were installed in the factory gas tank.

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Speartech was selected to provide a custom engine control harness, which uses a factory PCM. A 3-bar MAP sensor was used so that the truck can utilize a speed density operating system capable of keeping up with the boost, which eliminates the MAF, though it maintains use of the 02 sensors for closed loop correction. A 1992 Chilton's manual gave him the necessary info to mate up the new harness to the factory analog gauges. A lone Auto Meter boost gauge is the only clue in the interior that this truck might be packing some extra ponies.

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Last but not least, Dan fabricated a custom twin-turbo setup using 16-gauge mild steel for the custom headers and hot side; aluminum was used for the cold side. Twin 61mm, Garrett GT35R turbos sit up top, and the downpipes are partially routed through the truck's inner fenderwells. The three-inch downpipes merge into a four-inch single exhaust that runs to the rear bumper. Dan initially only used a four-inch MagnaFlow muffler, but a persistent drone drove him to experiment by adding an additional muffler, made by Vibrant, just before the tailpipe. Twin TiAL 44mm wastegates and 50mm blow-off valves help manage boost. To keep this 9.5:1-compression 402 pump gas-friendly, he elected to use a Precision Turbo air-to-water intercooler core, for which he fabricated the endtanks. A five-gallon fuel cell serves as the water tank, and he plumbed in a marine application pump that flows 1,200 gallons per hour. Lastly an 18-inch fan from a Volvo manages to keep the truck cool in traffic.

After only a few delays, which were mostly waiting for parts and a detour to fix the oil pan that got crunched during the install, Dan and Jim dropped the front prop shaft, and put the Typhoon on Speed Inc's Dynojet dynamometer. All of the hard work paid off when, with only 10.5 psi of boost, the truck cranked out 780-rear-wheel horsepower on straight 93-octane pump gas.

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Though extremely swamped at work and busy at home raising his young son, Dan managed to get out to Great Lakes Dragway in late June of this year. Rolling on Cooper Zeon street tires, Dan was rewarded with an initial 10.8 at 132-mph pass. Since the PCM short-shifted the One-Two shift, Dan knew the truck would go a little quicker with a perfect pass. Dan and onlookers were thrilled when he cranked off an impressive 10.5 at 135 mph, achieving a 1.7 short time on street tires. "I had to pedal the throttle in First gear on that pass and two other passes, so I think that the truck will run even quicker with some more traction." Since Dan's 4,200-pound family hauler did not have all of the required safety gear for his e.t. and mph, he got the boot from track officials. A return trip with Mickey Thompson 255/50/16 drag radials at all four corners helped him click off a 10.18 at 135 mph with a 1.50 short time. The scary part is that we think Dan is still barely scratching surface of his truck's potential. I wouldn't be surprised to hear of a 9-second pass in a few months. In the meantime he'll be prowling the streets in the northern Chicago suburbs, so proceed with caution if you happen to roll up on a green/gray Typhoon with a slightly lopey cam-it's kinda fast.


Speed Inc.
Schaumburg, IL 60193



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