Turbo Tech - The Great Wastegate Debate

A little turbo technology can give centrifugally blown engines a significant torque boost

Barry Kluczyk Oct 4, 2011 0 Comment(s)
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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.

Dyno Chart
RPM LB-FT (With Wastegate) LB-FT (No Wastegate) HP (With Wastegate) HP (No Wastegate)
3100 243 168 143 99
3200 411 243 248 148
3300 460 335 287 210
3400 482 400 310 258
3500 489 421 324 280
3600 497 430 339 294
3700 508 439 357 308
3800 516 447 372 323
3900 522 456 387 337
4000 528 461 401 350
4100 537 458 418 357
4200 543 466 433 371
4300 549 472 448 385
4400 555 479 463 400
4500 561 488 479 417
4600 564 493 492 430
4700 566 491 505 438
4800 568 493 518 450
4900 567 493 527 459
5000 568 493 539 468
5100 562 498 544 483
5200 534 500 528 494
5300 542 501 546 504
5400 549 500 563 513
5500 550 499 575 521
5600 544 495 578 527
5700 534 492 579 533
5800 523 488 576 538
5900 512 487 574 546
6000 499 481 569 549
6100 484 475 562 550

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