A wastegate is an item typically associated with turbo systems, but Detroit-tuner Joe Borschke has found great success by weaving them into supercharged engine systems to boost torque. In fact, on a pair of '10 Camaros fitted with identical bolt-on ProCharger centrifugal blower systems, he coaxed more than 60 lb-ft out of the wastegate-equipped car over the comparable, non-wastegate car. At some points on the dyno chart, there was more than a 70-lb-ft advantage. No matter how you slice it, that's a significant increase and the path to delivering it is relatively simple-if you're handy at welding and tuning. And it was a solution that Borschke says fits the bill for optimizing blower performance across a broader RPM range.
"The fit, finish and general performance of the ProCharger systems for new Camaros is impressive, but they don't seem to make as much torque as they do horsepower," says Borschke. "That's primarily a function of the boost curve of the centrifugal design."
As you may already know, centrifugal superchargers use an impeller, similar to a turbocharger compressor wheel, with strategically engineered vanes to spin and compress incoming air-hurling it out the outlet and eventually into the engine. And of course this impeller is connected to a gear system and a pulley. Much like those in a transmission or rear end, those gears multiply the revolutions that the pulley makes via the serpentine belt and engine speed. As RPM increases, the airflow from the supercharger will increase at a faster rate. Because of that, maximum boost is not achieved until the engine's red line, or maximum RPM level. So the centrifugal "rolls" into its boost and is generally easier to launch, with a stronger feel through the upper RPM levels. However, on the street more torque and mid to low RPM power would be more beneficial. Enter the wastegate theory.
"We've installed, tuned and dyno-test a bunch of ProCharger systems upgraded to the D-1SC compressor and you can pretty much bank on them making 550 horsepower and 500 lb-ft of torque at the wheels, with about 8 pounds of boost," says Borschke. "We wanted to get more torque out of them to make the cars feel stronger and more fun on the street. We turned to the wastegate, then started experimenting with smaller-diameter blower pulleys to push more torque higher in the RPM band. With the wastegate, we can spin the blower faster to produce greater boost and bleed off the extra pressure that's not necessary," says Borschke. "This allows the boost to come on much sooner, gaining midrange power- especially torque-that you can really feel on the street. But more importantly, helps maintain the right boost for the engine to prevent detonation in a stock engine."
Of course, there's a fine line to balance with the size of the wastegate. Borschke uses a 44mm unit on the LS3 Camaros, which he reports is plenty large enough. With stock motors, the 8-pound spring is used in combination with a 4-inch pulley (instead of the usual 4.75-inch pulley). D-1SC-equipped combinations with the 44mm wastegate make about 7.5 pounds of boost by 4,900 rpm, compared to the 8 pounds generated at the top of the tachometer on "standard" systems. "It's right in the sweet spot of making power where you're going to use it on the street," he says. "We've seen upwards of 590 rear-wheel torque with some vehicles." In case you are wondering, pulleying down even further is not reccomended as anything smaller than 4 inches generates too much heat for the intercooler. The folks at ProCharger will also warn against over-spinning the blower, and as the result aren't big fans of using wastegates. However, it is hard to argue with the benefits.
In many ways, this combination delivers the best of the turbo and blower worlds. The boost level remains constant at higher RPM, like a turbo engine, but delivers the unmistakable torque characteristic of blowers. Borschke admits a bit of torque is sacrificed at the top end, but that's not a concern in a car used primarily on the street. "You'll never miss it on the street," he says. "It's a small price to pay for the greater feeling of power in the mid-range. Heck, the right cam change would help alleviate that high-RPM deficiency, too."
Check out the accompanying dyno chart and graphs and you'll see the dramatic differences of the test vehicles with and without the wastegate. As Borschke mentioned earlier, the standard kit delivered the expected 550 rwhp/500 rwtq numbers, while the wastegate-equipped car's best numbers were 579 horsepower and 568 lb-ft of torque to the tires. That's about 6 percent greater horsepower and 14 percent more torque.
A closer look at the numbers is more revealing: the wastegate-equipped car crossed the 500-rwtq threshold by 3,700 rpm. That was 1,000 rpm sooner than the other car and it held above the 500 mark through 5,900 rpm. The non-wastegate car flirted with 500 lb-ft only between 5,200 and 5,400 rpm.
It's a similar story with the rear-wheel horsepower, where the non-wastegate Camaro peaked, of course, at the 6,100-rpm limit. The Camaro with the wastegate hit is peak a few hundred RPM earlier; and it bested the other car's peak prior to 5,400 rpm.
Of course, we had to ask about the bottom line on this modification.
"Generally, it's about $600 for the cost of the wastegate and installing it," says Borschke. "There are tuning implications, too, so it's better to do it with installation of the kit. It would cost more to retro-fit a wastegate on a car that already had the blower system installed and tuned."
So, on a blower system that costs approximately $7,000 to purchase and have it professionally installed, the wastegate upgrade represents less than a 10-percent premium. In bang-for-the-buck terms, that seems like a deal to us.
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