Car Craft
Click here to find out more!

Turbo Pontiac 400 Build - Ludicrous Pontiac Power

Ken Crocie Built A 489ci Stroker Pontiac Pressurized With A Single Turbo And A Q-Jet That Is A Recipe For Ludicrous Power

By , Photography by

The Crucible
As it turned out, assembling the parts and building the engine was the easy part. Once Crocie bolted the 489 to Westech's dyno, all sorts of weird things began to occur. With the first pull on the dyno, Crocie knew something wasn't right. "We could hear a whoosh-type noise as soon as the turbo spooled up," Crocie says. That's when he realized the wastegate was too small, so the motor came off the dyno until he found a larger valve.

With the larger wastegate installed and venting, the engine would sometimes make lots of boost and power, and then other times, the power would just drop off. "We kept looking for the rag in the manifold," Crocie jokes. He and Westech's Steve Brule must have checked to ensure the secondaries were opening a dozen times. Everyone was bagging on the Q-jet, so they tried a Holley and the power instantly came up. For anyone else, that would have been the end of the story. But Crocie wasn't willing to give up on the Q-jet so easily, especially because decades earlier the Rochester carb had worked flawlessly. He was determined to find the problem.

After several abortive attempts, he decided to start measuring everything that moved, including boost pressure in the manifold and the hat. That's when he discovered he had 19 pounds of pressure in the hat and only 6.5 psi in the manifold. Clearly something was amiss, and everything pointed to the Q-jet's unique secondary throttle linkage arrangement. When the choke is on, a small lever engages a lock on the secondary throttle linkage that prevents the secondary blades from opening. The secondary shaft employs a spring that wraps up and allows the primaries and the linkage to fully open. From the outside, this appears to be wide-open throttle (WOT). The reality is that the spring merely wraps up, while the secondary blades remain closed. When Crocie applied 19 psi of boost pressure through the top of the carburetor, the pressure on the large secondary blade surface area was enough to prevent the linkage from opening the blades. The fix was to use a large set screw to create a direct connection to the throttle blades.

Getting the secondaries to open merely created the opportunity for more problems. Crocie knew the Q-jet was limited to a single fuel inlet, so he had previously modified the needle and seat to increase the area by roughly 100 percent from the stock 0.110-inch diameter to 0.150 inch and raised the fuel pressure to 9 psi-but the air/fuel ratio vagaries persisted. He then tried an Edelbrock Q-jet that solved the problem, which then led him on a quest to discover why his original carburetor failed. He discovered a photo in a now-out-of-print book, Rochester Carburetors by Doug Roe, in which Roe illustrates a secondary main well restriction and how to remedy the issue. The critical photo is on page 252 if you have a copy of the book. Crocie modified his carburetor and then had to dramatically lean the air/fuel ratio with Q-jet metering rods that finally delivered the air/fuel ratio to a slightly rich 12:1. These last few changes required at least half a dozen trips to the dyno-all in the name of making the right power for this package. But once he got it all sorted out, the Pontiac really made some steam.

Once Crocie cleared the fuel metering hurdle, this Pontiac made some thumpin' torque. The final question arose when they discovered the Pontiac's torque peak was somewhere on the south side of 3,500 rpm-and the 489 was making well over 700 lb-ft even at that rpm. Crocie felt the factory block may not be able to take the abuse, so all testing began at 3,400 rpm with peak torque somewhere below this starting point. Ultimately, the engine made an astonishing 744 lb-ft and a respectable 537 hp. The horsepower numbers obviously could be far greater with a better intake, carb, and exhaust, but given this Pontiac's heritage, these are killer numbers. The biggest problem will be finding a pair of rear tires that can handle the torque.

Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
Car Craft