Our product line of boosted engines uses turbos, twin screw and centrifugal superchargers to compress intake air (see pictures below). Many of our street performance customers are uncertain which power adder is best for them. There is no universal best choice. Their optimum solution depends on factors including: intended application, ease and cost of installation, longevity, personal preferences and space limitations to name a few considerations. We are often asked to explain the differences, pros and cons.  The internal features of twin screws (bypass & intercooler) and their effects are often not well understood and will therefore be the primary focus here now.

Power Adder Types

Both turbos and centrifugal superchargers spin compressor wheels whereas twin screw superchargers act as positive displacement pumps. Turbos are powered by exhaust gas, whereas superchargers are powered by the crankshaft. All three power adders are widely used on 1,000 hp plus pump gas builds.  It is important to recognize that the stated horsepower is a peak number at a specific RPM and horsepower is a number calculated from torque and rpm (HP = (Torque x RPM) / 5,252). How each gets to their peak horsepower is different, as can be seen overlaying the dyno charts of three essentially identical LS engines with different power adders.

While all three converge at high RPM, the twin screw delivers much more power at low RPM. The turbo’s power curve is the least predictable as it is spooling up while the centrifugal supercharger’s is perfectly linear. These differences are immediately manifest in throttle response. All else being equal, the twin screw are unsurpassed for shredding tires at low RPM.

Twin Screw Internal Bypass

Most of our twin screw builds use Whipple Superchargers so we will use them as our template here.

These units come with both a vacuum actuated internal bypass and liquid-to-air intercooler. Under light throttle pressure, the bypass is open directly to the intake manifold. When the bypass is fully open, the engine is running naturally aspirated.  The screws continue to rotate, but with negligible power loss as they experience no resistance. Increasing throttle pressure will cause the bypass to close. Nailing the gas pedal will slap the bypass shut sending the engine from NA mode to full boost in an instant. If you want explosive power, this is undoubtedly your ticket. If you control your right foot, you will also get great gas mileage and range.

Internal View of 3.0L Whipple Supercharger showing intercooler and bypass

Be careful what you pray for.  You may get it.  There are trade-offs.

Our 427ci Whipple supercharged LS engines are max effort.  This requires us to use aftermarket blocks and forged rotating assemblies, among other design changes, to handle the shock of the bypass slapping shut.  The same supercharger could be slowed downed using a different pulley combination and used safely with an OE block, but with far lower horsepower.

Moving past the engine, the extreme torque (>1,000 lb-ft) of our Whipple LS builds are a challenge for the entire vehicle.  We pair them with custom transmissions (4L80e and T-56). The rest of the drivetrain and chassis must also be up to the task.  Aftermarket axles and 9” rear ends are pretty standard as are complete aftermarket frames.  These same issues must be considered with both turbos and centrifugal superchargers. They come on softer and are therefore more forgiving. 

No Limit Engineering custom frame with 9" rear

Twin Screw Intercoolers

Compressing air raises its temperature and that heat must be removed from the inlet air. Failure to do so costs a lot of power and makes the engine susceptible to knock. You can lower intake air temperature in different ways such with intercoolers, alcohol fuels and water-methanol injection.

Intercoolers are generically either air-to-air or water-to-air types. Air-to-air intercoolers are widely used with boosted engines, but they require fabrication and a lot of space. Whipple superchargers have internal liquid-to-air intercoolers underneath the screws. This makes them compact and easier to install and that is the takeaway here. A lot more can be said about intercooling, but we will leave that for another day.

Conclusions

The internal bypass and intercooler influences:

• Vehicle design considerations,
• Ease and cost of installation,
• Throttle response / driveability,
• Gas mileage / range       

Twin screw superchargers such as Whipples are favored in street performance, marine and off-road end-uses running pump gas. Their internal features allow each of these motorsport genres to benefit from their instantaneous power on demand and compact configuration.

Turbos and centrifugal superchargers become more dominant in racing as horsepower requirements increase and fuels are switched from gasoline to alcohol.  Oxygenated fuels’ evaporative cooling eliminates the need for intercooling in whole or in part.  The internal bypass of a twin screw can become a liability when precise throttle control is required. A work-around is to pin the bypass closed. An example is Icelandic Formula Off-Road which requires both low-end torque and precise throttle control.

Overall, a lot of thought and information is required for choosing the best power adder for any given application. If you are at this point, please call us at 815-725-2727.  We will work through all the details to get you the package that best fits your specific needs.

CENTRIFUGAL SUPERCHARGERS (ProChargers)

Belt Driven, Liquid-to Air (displayed at SEMA 2024 - Maxima Racing Oil)

Direct Gear Drive, No Intercooler, Dedicated E85

TURBOCHARGERS

Single Turbo, Liquid-to-Air

Twin Turbo, Air-to-Air

Exploded View FAST Liquid-to-Air Intercooler