J.R. Granatelli’s 700-Plus-HP Trailblazer SS

Even some of the most die-hard car enthusiasts have never heard of the GMC Syclone or Typhoon. These trucks broke new ground when they hit the dealer showrooms. They showed the world that if you were looking to go fast, you didn’t have to settle for a two-seater sports car. Joe Granatelli, owner of Granatelli Motorsports, is one of those who did notice them. “I’ve always been an SUV kind of guy, had a Cyclone, had a Typhoon, and I like the fact the Trailblazer had the Corvette engine. From the day I bought it, I wanted to build a modern day Typhoon.” J.R., as he is known around his shop, is doing just that. Check out some of the features and upgrades that his team has done to the car so far.

These cars come from the factory with 400 horsepower at the back of the engine and optional four-wheel drive. That might be good for some, but J.R. was looking for more right away. So, with only 300 miles on the truck, the engine was yanked from the frame rails and the build began.

The short block in these trucks is already a stellar piece. The LS2 engine was refined to 420 cubic inches (6.8 L) by way of a .30 over bore and a 4.25 stroke on the crankshaft. Two Trick Flow TFS-LS2 heads were used on the top half, but the real eye candy, the Magnuson 122 Supercharger, is sitting directly on top of the engine. “We run the blower at 10 psi and it still only has a hint of whine at wide open throttle,” J.R. says. “I always liked a more quiet sounding vehicle.”

Don’t take it the wrong way, this truck has some grunt to it. Under the hood, Kooks 1 7/8 headers lead to a Granatelli Header Back 3-Inch Exhaust.

To handle the tuning on the engine, J.R. started with Granatelli’s own Mass Airflow Sensor. J.R. claims that this MAS increases air flow up to 60% and adds up to 25 RWHP. From there, the stock ECU was tuned using EFI Live Software to get the truck to perform well.

All of the machine work and assembly was done in-house at Granatelli Motorsports. Then the engine was towed over to Duttweiler Performance to be strapped onto an engine dyno and tested for power. The results were very exciting: 725 hp and 775 ft/lb. That almost doubles this engine’s already respectable performance from the factory.

TCI got involved for the transmission. The 4L70E was beefed up to handle the power with some new clutches and gears. For the torque converter, the experts at TCI recommended the Street Fire Converter with a 2500 stall. On a truck like this, that is only part of the drivetrain. J.R. has left the transfer case stock for now, claiming that experts have told him that it is good up to 750 hp without any modification.

Suspension components come from the Granatelli catalog. This truck uses the new GMS lower control arm package that works well with the stock air bags in the rear of these trucks. There’s also an upgraded panhard bar in the back.

SSBC brakes provide the stopping power. The front brakes measure thirteen inches, and the rear are eleven. He mounted a set of IForged wheels that are 8×20 in the front and 9×20 in the rear.

But before you think that this truck has lost its truck qualities, think again. “This truck is still 100% able to drive on the street with ease,” says J.R.. “My wife drives it to the store with no problem. In the summer, I pull my 24-foot boat with this thing, no problem.” That is the true test. You don’t see very many 700+ horsepower trucks that still have what it takes in the tune and durability of the engine to stand up to the demands of towing.

You thinking that this truck might not be able to perform then? You’d be wrong. In fact, the truck blasted down the quarter mile in 12.20 @123 mph in the rain of central California. Later, when the sky let up, the truck was back at the track once again where it went a best of 11.71 @129 mph with a 1.55 second 60’. Great numbers for a 5-ton truck!

Future plans for this truck are even bigger than the ones outlined in this article. J.R. plans on pulling the engine once again, in the quest for more power. He is planning on sticking a TVS-style blower on top of the engine and having it sit a little more forward than the current blower. That way, it can be driven on a solo belt and the boost can be turned up. “We are thinking somewhere in the ballpark of 15 psi should give the truck enough power so it can see 10.90’s,” J.R. explained. Getting there will take more than just a bigger blower. He also plans to install a water/menthol injection kit and fill it up with 100 octane fuel.

For now, though, he will just have to settle for the 725 hp that the engine currently makes, which is more than enough for most people. But if your last name is Granatelli, you are always searching for more power no matter how fast it can go.

About the author

Tom Bobolts

Tom started working for Power Automedia in early 2008 at the young age of 20. Starting off as an intern spinning wrenches in the PowerTV garage, Tom cut his teeth helping us build the very project cars we feature. Since moving inside the office, most of his time is spent writing and shooting installs - but he still finds time to get out in the shop. Outside of work, Tom enjoys a variety of different motorsports from Street Bikes, Muscle Cars and just about anything that demands high amounts of horsepower.
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