Twin FTW: Power Adders Part 1

Words And Photos: Richard Holdener

There are many ways to improve the power output of your typical internal combustion engine. Given its status as a glorified air pump, the basic mechanics are such that anything that improves the airflow through the motor will improve the power out of the motor. For our needs, the most common improvements generally fall into one of three categories, bolt-ons, displacement and (of course) power adders. The bolt-ons include things like carbs, cams and cylinder heads, while a hike in displacement follows the bigger is better theme. Both of these routes offer plenty of potential, but they pale in comparison to the gains offered by power adders and no discussion on power adders would be complete with mentioning turbocharging!

Turbochargers are simultaneously simplistic and sensational. A turbocharger consists of a pair of impeller wheels connected by a common shaft. Exhaust energy is used to spin the turbine wheel which in turn spins the compressor wheel. The spinning compressor wheel draws air in, compresses it and then force feeds it to the unsuspecting (in our case) small block Chevy. There is, of course, more to the equation than bolting on just any old turbo, but know that with the proper turbo system, power gains exceeding 50% are commonplace and we have seen gains reach as high as 300%. Simplistic in operation, the turbo (or in our case turbos) must be sized properly for the intended application. The turbo must also receive a steady supply of clean oil and, it is always a good idea to run the boosted air through some sort of intercooler to both improve power and reduce the chance of harmful detonation. Check out how we dealt with each of those necessities on our twin-turbo small block.

The small block in question originated from the local wrecking yard. After being pulled from a ¾-ton truck, the 350 was first upgraded for dyno use with an Edelbrock RPM Air gap intake and 750 Holley carb. Run in this configuration, the junkyard small block produced 310 hp but the bolt-ons continued with a COMP XR282HR cam and RHS aluminum heads. The Xtreme Energy cam offered a .510/.520 lift split, a 230/236-degree duration split and 110-degree lsa. The stock Vortec heads were replaced by a new set of RHS aluminum heads. After installation of the new heads and cam, the power output of the 350 jumped from 310 hp to 405 hp (and 392 lb-ft). Satisfied with our baseline, it was time for the power adders. In preparation for the turbos, we removed the oil pan and drilled and welded drain fittings in place. We also replaced the Holley 750 carburetor with a dedicated blow-through carb from Carb Solutions Unlimited (CSU). In addition to the usual jetting, the CSU carb featured adjustable, boost-referenced power valves to dial in the air/fuel mixture under boost. Though the stock short block featured powdered-metal rods and cast pistons, proper tuning ensured the necessary safety margin during testing.

Not technically a kit, our twin-turbo system was a conglomeration of low-buck components we threw together for dyno use, in much the same way enthusiasts might do so to fit their chassis. Starting with a pair of shorty headers, we welded a v-band flange to connect the remainder of our exhaust. The shorty headers were installed upside down and the exhaust was fed to a pair of tubes that contained the necessary T4 turbo and wastegate flanges. These flanges were filled with a pair of 76mm, T4 turbos from CX Racing controlled by dual, 45mm Hypergate wastegates from Turbo Smart. Since the turbos were capable of supporting 700 hp each, having a pair bordered on excessive for our mild small block. In truth, boost response would be improved by switching to just one but we liked how twin-turbo small block rolled off the tongue. Because heat is an unwanted byproduct of pressure, boost from the pair of turbos was fed through an air-to-water intercooler to the carb bonnet and CSU carburetor.

After running the mildly modified small block in normally aspirated trim, we eagerly installed our power adders. Nothing wakes up a motor like boost, just take care not to get too greedy, since additional power is as easy as dialing up the boost. Configured to produce a peak of 8.9 psi, the twin-turbo system improved the power output of the 350 from 405 hp and 392 lb-ft of torque to 597 hp and 569 lb-ft of torque. The boost curve rose slightly, from 6.4 psi at 3,600 rpm to a peak of 8.9 psi at 6,100 rpm. Since man does not live by peak numbers alone, know that torque production exceeded 550 lb-ft from 4,300 rpm to 5,600 rpm. Before calling it a day, we couldn’t resist turning up the boost slightly to a peak of 10.2 psi. The small increase in boost had a positive effect on power, as the peak numbers jumped to 640 hp and 606 lb-ft of torque. This represented an increase of 235 hp (58%) over our normally aspirated motor and we smiled knowing our power adder had plenty left in reserve!

Huge gains are what power adders are all about, and this twin-turbo small was a perfect example of what happens when you add even low boost to a typical V8. After upgrading the heads, cam and intake on the wrecking yard motor, the normally aspirated 350 produced 405 hp and 392 lb-ft of torque. The power numbers jumped substantially after installation of the twin turbo set up. How much are power adders worth? How does an extra 192 hp and 178 lb-ft of torque at 8.9 psi sound? Equipped with the turbos pumping our just under 9 psi, the twin-turbo 350 produced 597 hp and 569 lb-ft of torque.

One of the great things about power adders in general and turbos specifically is their ability to easily dial in more power. With turbos, more power is a simple matter of increasing the boost pressure. Of course, this assumes the turbos will support the extra power, but we had more than enough flow in reserve on our twin system. Stepping up from a peak of 8.9 psi to 10.2 psi brought a sizable jump in power. The increased boost pressure pushed the power peak from 597 hp and 569 lb-ft of torque to 640 hp and 606 lb-ft of torque. There was obviously more power to be had from the system but we were satisfied for now with our 640-hp small block.

To read Power Adders Part 2, click HERE! We put a nitrous kit on this same small block.

https://youtu.be/199fiJsYwSU

Sources

COMP Cams
compcams.com

CSU
csucarbs.com

CXRacing
cxracing.com

Daytona Sensors
daytona-sensors.com

Edelbrock
edelbrock.com

Holley/Hooker/Weiand
holley.com

RHS Cylinder Heads
racingheadservice.com

Turbo Smart
turbosmartusa.com

About the author

PPN Editor

Power & Performance News is the source for news, tech and products that help you get more performance from your vehicle. If powertrain performance projects and hardcore technical content are your interest, Power & Performance News is the publication designed for you. Our acclaimed editorial staff covers all aspects of engine and driveline upgrades with a mission of presenting information that is both interesting and achievable for the “average car guy”.
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