Back in the last episode, we gained 50 rwhp by swapping to high-flow ported heads (Jose Motor Sports) and a hydraulic roller cam (Comp Cams). Our power gains were quite impressive considering there was roughly a 3 psi loss of boost. Apparently the 58mm Precision turbo we installed in Part 3 was a great upgrade for the stock cam and heads at the time, but could not support enough air volume for the latest higher-airflow combination. This proved it necessary for a move up to a larger turbo in order to restore boost and find out what the real gains would be at the same boost (20 psi). We called the tech line at Precision Turbo with the specs of our new combination and explained the boost loss. They recommended we use the new 6262B (62mm) unit that would restore boost and even give us the option to crank it up further. To maintain a stock-like underhood appearance, we ordered a stock intercooler with a fatter Duttweiler neck-end from G Body Parts. These two bolt-ons would bring back boost while moving more air rapidly to team up with the high-flow heads and roller cam from Part 6.
During the winter GN owner Tim Cairone found a local deal on an ‘87 3.8L short-block. He couldn't pass it up. It was a complete balanced assembly with forged JE pistons and H-beam Eagle rods. Downtime during the cold winter months was a perfect time at Tim's shop (Shore Wheels, Tuckerton, NJ) to swap out the short-blocks. Sure, the balanced, lighter/stronger, rotating/reciprocating parts will add a few horsepower to our test results, but will also be more durable for future dyno and track duties. Once the V-6 was running with the new 62mm Precision turbo and Duttweiler necked, stock intercooler, it was broken-in for roughly 300 miles with 18 psi boost.
Once again we visited our friends at Tune Time Performance for dyno testing and to tune for a safe AFR (air/fuel mixture ratio) before turning up the boost. Our buddy Matt Hauffe (Tune Time's owner and tuning expert) would be at the wheel of Tim's GN handling dyno duties. On the first pull we were pleased to find gains in power (19 hp, 24 lb-ft) at 18 psi boost (lowest boost from 62mm turbo) compared to the smaller 58mm turbo (17.5 psi, most boost from 58mm turbo). By following Precision's recommendations we benefited with the right size turbo to match the airflow volume needed for our combo. Follow along the captions and check the charts and graphs to see the big-time gains realized by sorting out a well matched combination. In our next episode we'll be back to track-test Tim's efficient street cruiser.