Understanding the 1.7L Kenne Bell Twin Screw Supercharger

The 1.7L Kenne Bell twin screw supercharger is a popular forced induction upgrade for small-block Ford and other applications, prized for its positive-displacement design that delivers instant boost and strong low-end torque. Unlike centrifugal superchargers, the twin screw architecture compresses air internally before feeding it into the engine, resulting in excellent throttle response and a broad powerband. However, like any high-performance mechanical system, this supercharger can encounter issues that affect performance, reliability, and drivability. This guide walks you through the most common problems—from boost pressure inconsistencies to overheating and abnormal noises—and provides actionable solutions. Proper diagnosis and maintenance are key to getting the most out of your Kenne Bell 1.7L setup.

Common Boost Pressure Issues

Low or Inconsistent Boost

One of the most frequent complaints is lower-than-expected boost or boost that fluctuates under load. Potential causes include:

  • Vacuum or boost leaks in the intake tract: Check all couplers, clamps, gaskets, and the supercharger-to-intake manifold seal. Even a small leak can reduce boost significantly.
  • Faulty boost control solenoid (if using a bypass or wastegate setup): A stuck or malfunctioning solenoid can bleed boost prematurely.
  • Worn or damaged supercharger rotors: Over time, debris or lack of lubrication can score the rotors, reducing compression efficiency.
  • Clogged air filter or intake restriction: A dirty filter or undersized intake pipe starves the supercharger of air.

To troubleshoot, perform a pressure test on the entire intake system. Use a smoke machine or a boost leak tester to pinpoint leaks. Inspect the bypass valve operation and verify that the supercharger oil is at the correct level (using Kenne Bell’s recommended fluid).

Over-Boost or Boost Spikes

Excessive boost can lead to detonation and engine damage. Common causes include a stuck bypass valve, incorrect pulley ratio, or faulty tuning. Ensure the bypass valve opens fully at idle and part-throttle. If you’ve changed pulleys, recalculate the boost potential and adjust the tune accordingly. A wideband air/fuel ratio gauge is essential for monitoring under boost.

Overheating and Cooling System Deficiencies

Forced induction increases heat load dramatically. The 1.7L Kenne Bell supercharger itself generates heat through compression, and without adequate cooling, intake air temperatures (IATs) can soar, leading to power loss and knock.

Insufficient Cooling System Capacity

If your engine coolant temperature climbs under prolonged boost, the radiator, fans, or water pump may be undersized for the added power. Upgrade to a high-flow radiator, electric fans with a programmable controller, and a higher-capacity water pump. Ensure the coolant mixture is appropriate for your climate.

Blocked or Inefficient Intercooler

Kenne Bell twin screw superchargers typically use an air-to-water intercooler core integrated into the intake manifold. If coolant flow is restricted or the heat exchanger is undersized, IATs rise. Flush the intercooler system annually, check for air pockets, and consider a larger heat exchanger with a dedicated coolant tank and pump.

Poor Airflow to the Supercharger

The supercharger inlet needs a clean, cool air source. Avoid hot air from the engine bay. Install a cold air intake with a heat shield. Also, ensure the supercharger’s own cooling fins (on the case) are free of debris for proper heat rejection.

Unusual Noises and Mechanical Wear

Kenne Bell superchargers are known for a characteristic whine, but any change in noise—especially grinding, rattling, or high-pitched squealing—should be investigated promptly.

Worn Bearings

The rotor bearings inside the supercharger can wear after many miles or due to low oil level. Low oil level is a common cause of bearing failure. Kenne Bell specifies a high-quality synthetic gear oil (e.g., KB #P-7000). Change it every 20,000 miles or per the manufacturer’s recommendation. If you hear a deep rumble or growl, especially at idle, suspect bearing wear—rebuild or replace the unit.

Loose Mounting Hardware or Misalignment

Check all mounting bolts and brackets. Vibration can loosen fasteners over time, causing clunking or rattling. Also inspect the supercharger pulley for wobble, which indicates misalignment or a worn pulley bearing. Use a laser alignment tool to align the supercharger pulley with the crank pulley.

Damaged Rotors (Contact or Debris)

If the rotors are contacting each other or the housing (due to bearing failure or debris ingestion), you’ll hear metallic rattling or scraping. Stop operation immediately. Disassemble and inspect the rotors. Minor scuffs may be polishable, but deep scoring requires rotor replacement. Always use a screen on the inlet to prevent foreign object damage.

Fuel Delivery Problems Under Boost

A 1.7L supercharger often doubles or more the horsepower output, demanding significantly more fuel. Without adequate fuel delivery, the engine runs lean, risking detonation and destruction.

Clogged Fuel Filters

A restrictive fuel filter starves the injectors at high flow. Replace the filter every 10,000 miles or whenever fuel pressure drops under boost. Use a high-flow fuel filter rated for your pump’s flow rate.

Insufficient Fuel Pump Capacity

Stock fuel pumps are rarely sufficient for forced induction. Symptoms include fuel pressure dropping as boost rises (voltage-sensitive pump). Upgrade to a high-flow in-tank pump (e.g., Walbro 450 LPH) or a dual-pump hat for serious power. Verify fuel pressure with a gauge at the rail; it should rise 1:1 with boost (i.e., 43 psi base + boost pressure).

Incorrect Fuel Pressure Regulator Setup

Use a boost-referenced fuel pressure regulator to maintain consistent differential pressure across the injectors. If the regulator is not connected to manifold vacuum/boost or is faulty, fuel pressure may not rise correctly, causing lean conditions. Test with a vacuum pump and ensure the regulator holds pressure.

Injector Upgrade and Duty Cycle

Stock injectors may run excessive duty cycle (beyond 80%). Calculate your fuel flow requirement using horsepower estimates. Injectors should be sized to keep duty cycle under 90% at max boost. Kenne Bell often provides injector recommendations for each kit. Use a high-impedance injector matched to your tuning platform.

Common Installation Errors and Their Consequences

Improper installation is a leading cause of poor performance and mechanical failure. Even a small mistake can cascade into major issues.

Misaligned Components (Pulleys, Brackets, Belt)

If the supercharger pulley is not perfectly aligned with the crankshaft pulley, belt wear accelerates and may even throw the belt under load. Use a straightedge or laser to check alignment. Adjust by shimming the supercharger bracket. Also ensure the belt tension is within specs—too loose slips, too tight loads bearings.

Incorrect Tuning or Base Settings

After installation, the engine management system must be calibrated for the increased air flow and fuel delivery. Many Kenne Bell kits include a pre-tuned ECU flash, but if you change pulley, injectors, or other components, custom tuning is essential. Driving without proper tune can cause severe detonation. Use a wideband oxygen sensor and check air/fuel ratio targets (typically 11.5–12.0:1 under boost).

Hoses and Fittings Not Secured Properly

Boost leaks often originate at loosely clamped silicone hoses, especially on the intercooler-to-throttle body connection. Use T-bolt clamps instead of worm-gear clamps for high-pressure sections. Double-check all vacuum lines for cracks or disconnects that could affect bypass valve operation.

Ignition Timing and Heat Range

Forced induction requires retarded timing and colder spark plugs (e.g., one range colder than stock). Install heat range appropriate plugs and gap them slightly tighter (0.030–0.035 inches) to prevent blowout under boost. Check that the knock sensor is functioning. If detonation persists, reduce timing through tuning.

Bypass Valve and Belt Slippage

Bypass Valve Not Opening or Closing Properly

The bypass valve (often called a blow-off valve in some setups, though Kenne Bell uses a recirculating bypass) is critical for driveability. If it sticks closed, part-throttle boost spikes and surge can occur. If it sticks open, you lose boost. Clean and inspect the valve, replace the diaphragm if torn, and ensure the vacuum line is routed correctly.

Belt Slippage Under High Load

High boost and rapid acceleration can overcome belt grip. Symptoms include a squeal at throttle tip-in and fluctuating boost. Upgrade to a wider belt (if the system allows) or use a serpentine belt with better grip material. Also check the belt tensioner—a worn tensioner won’t maintain proper tension. Use a belt dressing sparingly; better to fix the underlying tension issue.

Noise Diagnosis: Separating Normal from Abnormal

All Kenne Bell superchargers produce a distinct whine, especially at high rpm. But not all noises are normal. Here’s a quick reference:

  • Normal whine that rises with engine speed: air being compressed. Fine.
  • High-pitched squeal at idle or idle-up: Often a belt slip or vacuum leak. Check belts and bypass valve.
  • Rattling or clicking that speeds up with engine rpm: Could be a loose heat shield, bracket, or even a spark plug wire arcing. Inspect physically.
  • Deep rumble or grinding at idle: Bearing wear imminent. Stop using and inspect oil level and condition.
  • Metallic scraping or chirping: Rotor-to-housing contact. Stop engine. Rebuild required.

Use a mechanic’s stethoscope or a long screwdriver against the ear to localize sounds on the supercharger case versus the engine.

Lubrication and Maintenance Best Practices

Proper lubrication is the single most important factor for longevity. Kenne Bell superchargers have a sealed oil system. Use only the recommended synthetic oil (KB #P-7000 or equivalent Mobil 1 synthetic gear oil 75W-90 is sometimes used, but verify). Change oil every 20,000 miles or annually for severe use. Check level through the sight glass—oil should be at the center of the window when the engine is warm and off. Overfilling causes heat buildup; underfilling causes bearing failure.

Inspect all hoses, clamps, belts, and pulleys at each oil change. Clean the intercooler heat exchanger fins with a low-pressure water spray. Keep the air filter clean. If you track the car, consider an oil cooler for the supercharger (aftermarket plate-style cooler kits exist).

Tuning Considerations for the 1.7L Kenne Bell

Beyond the base tune, fine-tuning can unlock more power and improve safety. Use a quality tuning suite compatible with your vehicle’s ECU (e.g., SCT, HP Tuners, or DiabloSport). Key parameters:

  • Fuel tables: Enrich under boost to 11.5–12.0:1 for gasoline. For E85, target 9.0–10.0:1.
  • Ignition timing: Pull timing about 1.5–2 degrees per pound of boost from the normally aspirated baseline. Use conservative timing and monitor knock.
  • Boost control: If using a boost controller, ensure the wastegate or bypass valve reacts quickly to avoid spikes.
  • IAT and coolant temp correction: Program timing and fuel corrections for high IATs to prevent knock.

Data logging is your best tool. Log boost, fuel pressure, wideband AFR, intake air temp, coolant temp, and knock sensor output. If you see knock counts above 2–3 consistently, reduce timing or add fuel.

For further reading and OEM documentation, visit the Kenne Bell official website for installation manuals and technical bulletins. The Modular Fords supercharger forum has a wealth of owner experiences and troubleshooting threads. For intercooler optimization, refer to Air Flow Research's cooling guides.

Conclusion: Building a Reliable Supercharged Setup

Owning a 1.7L Kenne Bell twin screw supercharger rewards you with exhilarating performance, but it demands attention to detail. The most common issues—boost leaks, overheating, unusual noises, fuel delivery inadequacies, and installation errors—are all preventable with thorough workmanship and routine maintenance. Regularly inspect the supercharger oil, the condition of the rotors, and the integrity of the entire intake and intercooler system. Invest in proper tuning and data logging. By addressing problems early and following best practices, you can keep your Kenne Bell supercharger running strong for tens of thousands of miles, delivering that signature instant boost and broad power that makes it a benchmark in forced induction.