1967 Chevrolet Corvette - Double Vision

It's Like Déjà Vu All Over Again With This Twin-Turbo Sting Ray

Steve Temple Jun 28, 2010 0 Comment(s)
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"We have deep depth."

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Why go to so much effort on forced induction, when a big-block might be way simpler? Well, just ask Gale Banks. He's no Yogi Berra (thankfully), but does have his own choice expressions about turbocharging. Here's his in-depth take on the subject:

"Putting it simply, in terms of performance, a good twin-turbo 350 V-8 will turn your engine inside out," Banks points out. "Bigger engines add power, but turbocharging bigger engines really gets the job done."

Is that deep or what? After all, Banks has long been known for a wide range of performance upgrades, everything from muscle cars to 220mph pickups fitted with diesel (yes, diesel) engines.

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"If I didn't wake up, I'd still be sleeping"

"With me, it's always about power," he adds. "We've been able to pick up 200 hp more with the turbos over a Roots-type blower." And it's streetable, durable power, since Banks insists on rigorous testing on all of his company's performance upgrades.

"For the twin-turbo program, we had one engine called 'the mule,'" notes a Banks engine technician. "That's because we kicked the livin' crap out of it." Since this setup is a whole 'nother animal from most Corvette mills, we decided to dig even deeper into the Banks approach.

For instance, hot rodders are fond of saying, "There's no replacement for displacement." True, but what sort of cubes are we talking about? Is it the cubic inches of the engine that count, or the cubic inches of air in the combustion chamber? As Banks points out, it's definitely the latter.

"The towels were so thick there, I could hardly close my suitcase."

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In other words, if the engine were stuffed with up to 15 psi of boost, it would effectively double in size. That means 14.5 psi of boost will make a 350ci performance engine seem like a 700ci performance engine. That's one tight suitcase!

Turbocharging does this for two reasons: first, the internal friction of the engine remains largely the same regardless of boost, so almost all of the extra power from the turbo(s) is available to power the vehicle. Second, the boost in the induction system actually helps push the pistons down on the intake stroke.

In contrast, on a normally aspirated engine, that intake stroke creates a pumping loss (that is, negative torque). Gearheads might counter by pointing out that turbochargers create exhaust backpressure, increasing the pumping loss on the exhaust stroke. But this is not the case if the system is carefully engineered with only a minor exhaust restriction for the dual turbos, so that boost pressure always exceeds exhaust-system backpressure.

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Mrs. Lindsay: "You certainly look cool."
Yogi Berra: "Thanks, you don't look so hot yourself."

Well, both are true in the case of Park's heavily customized Sting Ray. The body mods are really chilling, but the super-wide hoodscoop, front spoiler, fender flares, and recontoured tail were a one-off deal done by local guys, and the molds are long gone.


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