This 427 small-block uses the same twin-turbo thinking we’ve refined for decades: manage air temperature, reduce restriction, and control boost cleanly. The big mistake is feeding a turbo from underhood air with the hood shut. That gives the compressor hot, low-density air right when the engine needs mass. We want cold air from the nose of the vehicle. From there, the system is built to keep pressure loss down and response under control. The 4500-pattern inlet and large butterflies cut restriction at wide-open throttle. The twin 60-1 center-inlet turbos provide the airflow to support serious horsepower, while the high-temp castings package the turbocharger, wastegate, and heat shielding in a way that protects nearby components. On the back side, the shuttle-valve dump system is there for one reason: when the throttle closes, boost has to get out now. A large, fast dump path keeps the plenum under control during throttle lift. That’s what makes a twin-turbo street engine act civilized instead of temperamental.
Gale Banks introduces a 427 small-block Chevy being mocked up as the Hot Rod 60th anniversary engine, with the goal of delivering it to Hot Rod by Christmas 2015. He notes that a separate program will cover the long-block build itself, while this installment focuses on the turbo system and air-management hardware. The engine is intended as a practical street combination rather than an all-out race build, despite its substantial power capability.
Banks also frames the project as a collaboration rooted in hot-rodding history. He says many legendary companies and longtime friends contributed to the build, reflecting the era of enthusiasts old enough to remember the debut of the 1955 Chevy. That historical context sets up the engine as both a technical exercise and a tribute piece.
Banks explains that he has been developing twin-turbo small-block Chevy systems for more than 40 years, with roots going back to the late 1960s. Early versions used pressurized carburetors and a pair of Rajay turbochargers. With iron heads and a relatively straightforward setup, those engines made about 700 horsepower.
He recalls taking one of his 350 marine long-blocks from the Banks marine program, adapting it for street use, and fitting it with twin turbos. That engine powered what he describes as the first magazine-featured street car clocked at more than 200 mph, appearing on the cover of Car and Driver in June 1984 in one of the Banks Firebird tuner cars.
About 20 years before this video, the program moved into fuel injection and Garrett-based turbochargers, which Banks describes as the modern era of the package. Even then, the system still used TO4-based units, but with large 60-1 compressors. On pump fuel, that combination produced roughly 1,115 horsepower from a 375 cubic-inch engine that he characterizes as not especially serious or exotic. For the current project, however, he chose to build a 427 simply because he likes the number 427.
The visible hardware on the sides of the engine is an updated version of Banks' high-temperature casting for turbo mounting. This casting supports the turbocharger and the wastegate while allowing flexible outlet positioning. Because the wastegate connection is V-banded, the wastegate outlet can be vectored in whatever direction the installation requires.
Banks points out several practical details in the packaging. Heat shields are used to protect nearby components, including the valve cover, valve cover gaskets, the alternator, and, on the opposite side, the air-conditioning compressor. The front accessory drive is from Vintage Air, using what he describes as their latest and very slick-looking front-end system. The overall arrangement is meant to package a serious twin-turbo system cleanly on a street-driven small-block Chevy.
Banks emphasizes his preference for wastegates with a large diaphragm diameter relative to valve diameter. The units shown were built to Banks' specifications by Turbosmart, and he describes them as a good product. The large diaphragm area is part of his approach to stable and effective boost control.
The system uses two wastegate-controlled, center-inlet turbochargers. He then places the turbochargers onto the mock-up to show the intended arrangement. The pair are 60-1 units, and Banks says that this compressor sizing provides enough air mass and air density to support just under 1,200 horsepower. Even with that capability, he reiterates that the engine is meant to be an everyday driver.
As for the eventual vehicle, he mentions several possibilities: his 1990 Chevy short-bed pickup, originally a 454 SS, or his wife Vicky's 1970 1/2 Firebird Formula 400, which he describes as a particularly romantic piece of machinery.
A major part of Banks' air-management philosophy is feeding the turbochargers with cold air from the nose of the vehicle. He strongly opposes mounting air cleaners directly on the compressor inlets and then closing the hood, because that causes the system to ingest underhood air in the 180 to 200 degree range. In his view, that approach is fundamentally flawed because the resulting air density is too low.
Instead, he wants outside air taken from the front of the vehicle and routed into the compressors. From the compressor outlets, the system can either send the charge through charge-air cooling and then into the intake plenum, or use water-alcohol injection. For this particular engine, the plan is to use water-alcohol injection into the risers of the Bill Mitchell Products intake manifold.
Once the boosted air reaches the plenum, the induction system departs from Banks' earlier blow-through carburetor work. He notes that blowing through a carburetor involves a great deal of trickery and still does not produce a refined fuel curve, especially when altitude changes are involved. Although he understands carburetors, he says he has not carbureted anything in decades.
For this engine, the manifold has been converted to a 4500 flange pattern in place of the older 4160-style arrangement. The throttle butterflies are now 2 1/4 inches in diameter, effectively Dominator-sized. The purpose is to minimize restriction, and Banks says the pressure drop through the throttle area at wide-open throttle is almost nil. The result is a much more suitable inlet arrangement for a high-airflow, boosted EFI street engine.
At the rear of the plenum is Banks' shuttle-valve air-dump system, a design he says he developed more than 40 years ago and never changed because it works so well. The visible dump port has a matching outlet on the opposite side. Inside the dump port is the shuttle piston.
Under load, the piston blocks the outlet. When the throttle is closed, a spring-loaded mechanism moves the piston so the port opens immediately. Banks identifies the spring guide and piston stop at one end of the assembly, and explains that a -10 AN line runs from this system to a point below the butterflies on the manifold chimney. The moment the throttle starts to close, the valve goes fully open. A cap seals the piston-stop end of the assembly.
Banks describes this as the quickest and largest-port dump valve on the market, saying he does not know of anything faster or larger. In practical terms, it is the system's rapid-response pressure-relief device for throttle-lift events, integrated directly into the plenum design.
With the shuttle-valve system in place, the plenum is essentially complete except for the top cover, which Banks sets in place to show the finished appearance. The mock-up demonstrates the overall architecture of the twin-turbo small-block: side-mounted turbo hardware, protected accessories, a large-flow plenum and throttle entry, and an unusually large and fast dump-valve arrangement.
Banks closes by saying more updates will follow and will be posted on bankspower.com. He also points viewers to additional historical material on the company's twin-turbo development, including videos and written background available through the twin-turbo section of the site. The emphasis throughout this installment is not on promotion, but on showing how decades of Banks twin-turbo development informed the layout and hardware choices on this 427 small-block Chevy.