Understanding Your Tial TS-Double Compound Turbo System

The Tial TS-double compound turbo system represents an advanced forced-induction architecture that pairs a small, quick-spooling turbocharger with a larger high-flow unit in series. This design delivers exceptional power across the entire rev range, combining low-end throttle response with top-end horsepower. However, the complexity of this system means that problems can arise from interactions between the two turbos, the wastegate strategy, oil supply, and heat management. This guide covers the five most frequent issues owners encounter, with step-by-step diagnostic and repair procedures to keep your setup performing at its peak. For official specifications and diagrams, refer to the Tial Sport product pages and the TS-double installation manual.

1. Boost Leaks – The Silent Performance Killer

Boost leaks are the most common issue in any turbocharged system, but in a compound setup they can be especially deceptive. Because the pressure differential between the primary and secondary turbo changes with RPM, a small leak at one point may only manifest under certain load conditions. A loss of boost pressure not only reduces power output but also forces the turbos to work harder, increasing heat and risking damage to the wastegate and turbine.

Symptoms of Boost Leaks

  • Loss of peak power: The engine feels flat at high RPM, especially after the secondary turbo comes fully online.
  • Unstable boost levels: The boost gauge needle fluctuates or fails to hold a steady pressure under sustained throttle.
  • Hissing or whistling sounds: A distinct air leak noise during acceleration, particularly when the system is under load.
  • Higher than normal turbo spool time: The turbos take longer to reach target boost because the escaping air must be compensated for.

Diagnosing Boost Leaks

Begin with a visual inspection of all charge air piping, silicone couplers, T-bolt clamps, and intercooler connections. Look for cracks, splits, or signs of soot around joints. The most reliable method is a pressurized boost leak test. Rig a test cap on the turbo inlet or throttle body, apply shop air (15–30 psi, never exceed the system’s maximum rated boost), and listen for hissing. Use a soapy water spray on every connection—bubbles reveal the leak location. For compound systems, pay extra attention to the crossover pipe between the two turbos and the wastegate plumbing.

How to Fix Boost Leaks

  • Repair or replace damaged hoses: Heat, oil contamination, and age can cause silicone hoses to soften or crack. Replace any that show splitting or deformation. Use only high-quality, reinforced silicone rated for turbo temperatures.
  • Tighten or replace clamps: T-bolt clamps can loosen over time. Retorque to manufacturer specifications. If a clamp has stripped threads, replace it immediately.
  • Seal flange connections: Gaskets at the turbo outlet, intercooler, and throttle body should be in good condition. Apply a thin layer of high-temp RTV silicone where required.
  • Inspect the wastegate gasket: A leaking wastegate seat can mimic a boost leak. Remove the wastegate and check the sealing surface for imperfections. Tial recommends using a new gasket each time the wastegate is removed.

2. Wastegate Malfunction – Overboost vs. Underboost

In a TS-double system, the wastegate controls boost pressure by diverting exhaust gas away from the larger secondary turbine. A malfunction can cause either overboost (dangerously high pressure) or underboost (lack of power). Common root causes include a stuck valve, a damaged diaphragm, incorrect spring preload, or a blocked reference line.

Symptoms of Wastegate Issues

  • Overboost: Boost gauge spikes well above the target, often triggering fuel cut or boost cut in the ECU. Engine may knock or ping under load.
  • Underboost: The system fails to reach target boost, especially in the mid-to-high RPM range where the secondary turbo should be active.
  • Inconsistent boost control: Boost rises slowly or oscillates, with the wastegate chattering or failing to open at the correct pressure.
  • Excessive exhaust noise: A hissing or fluttering sound from the wastegate area suggests the valve is not seating properly.

How to Diagnose Wastegate Problems

Start by checking the wastegate actuator for smooth operation. With the engine off, disconnect the boost reference line and apply regulated air to the actuator port using a hand pump. The actuator rod should move smoothly and the pin should rotate freely. Compare the spring cracking pressure to the Tial specification for your spring color (e.g., a blue spring typically cracks at 14.5 psi). If the actuator does not hold pressure or sticks, the diaphragm may be torn. Also inspect the valve seat inside the wastegate housing; carbon buildup can prevent full closure. Finally, verify that the wastegate reference line is not kinked, blocked, or disconnected.

How to Fix Wastegate Malfunctions

  • Replace the actuator diaphragm: Tial sells rebuild kits for all their wastegates. Follow the exploded view in the Tial wastegate rebuild guide.
  • Install the correct spring: Ensure the spring matches your desired boost level and the combined flow of both turbos. For compound systems, spring selection is critical; a spring that is too weak will cause overboost, while too strong leads to underboost. Tial offers springs from 0.4 bar to 2.0 bar.
  • Clean the valve seat: Remove the wastegate from the manifold and gently scrub the valve and seat with a brass brush and solvent. Do not use steel wool or abrasive pads that could damage the sealing surface.
  • Check the boost reference source: The wastegate must see clean, consistent pressure. Tap into the intake manifold or a dedicated port on the primary turbo discharge. Avoid using a port after the intercooler if there is a significant pressure drop.

3. Turbo Lag – Spooling the Compound System Properly

Compound turbo systems are designed to reduce lag compared to a single large turbo, but issues like mismatched turbo sizing, restrictive exhaust flow, or poor tuning can reintroduce hesitation. The primary (smaller) turbo should spool quickly and hand off to the secondary around 3,000–4,000 RPM. If the secondary takes too long to come online, lag can feel worse than a single turbo setup.

Symptoms of Excessive Turbo Lag

  • Noticeable delay in power delivery after pressing the throttle, especially from a standstill or low RPM.
  • A sudden surge of power once the secondary turbo engages, rather than a smooth transition.
  • Difficulty maintaining boost during part-throttle driving; the system may drop out and then spike.
  • Higher than expected EGTs (exhaust gas temperatures) during the lag period because the primary turbo is working harder.

Root Causes of Turbo Lag in Compound Systems

  • Primary turbo too small or too large: The primary must be correctly sized to feed the secondary. If the primary is too small, it cannot supply enough flow to spool the secondary; if too large, it may not spool quickly enough.
  • Excessive backpressure in the exhaust manifold or up-pipes: Restrictive flow between the primary outlet and secondary inlet slows spool.
  • Incorrect wastegate spring setting or control strategy: If the wastegate remains open too long during low load, exhaust bypasses the secondary, causing lag.
  • Pressure drop in the charge air piping: Long or narrow intercooler pipes can delay boost build.

How to Reduce Turbo Lag

  • Optimize the primary turbine housing: A smaller A/R (area/radius) housing will increase exhaust velocity and spool the primary faster. However, this may limit top-end power. Tial offers a range of turbine housings for their turbos.
  • Upgrade to a ball-bearing center cartridge: Tial’s ball-bearing cartridges reduce friction and improve transient response significantly.
  • Improve exhaust manifold flow: Ensure the manifold has smooth, equal-length runners. Port-match the manifold to the primary turbo inlet.
  • Adjust tuning parameters: Work with a tuner to set the wastegate duty cycle and boost onset timing. For compound systems, many ECU tuners use a boost-by-gear or RPM-based boost curve to manage the transition.
  • Install a boost controller: An electronic boost controller like the Tial MVR (manual boost controller) or a digital unit can help fine-tune spool.

4. Oil Starvation – The Fastest Route to Turbo Failure

Turbochargers depend on a continuous supply of clean, pressurized oil for lubrication and cooling. In a compound system, two turbos mean twice the oil demand. A restricted oil feed or drain line can starve a turbo in seconds, leading to bearing seizure, shaft play, and ultimately failure. Oil starvation can also result from improper oil pressure, wrong oil viscosity, or an incorrectly installed oil restrictor.

Symptoms of Oil Starvation

  • Whining or grinding noise: A high-pitched squeal from the turbo, especially at idle or light throttle, indicates bearing damage.
  • Blue smoke from exhaust: Oil leaking past damaged seals into the turbine or compressor housings produces blue or gray smoke during deceleration or after idle.
  • Excessive shaft play: When the turbo is removed, push the shaft radially and axially—excessive movement means bearing wear.
  • Oil deposits in intercooler and piping: A starving turbo often vents oil through the compressor seal into the charge air system.

How to Prevent Oil Starvation

  • Verify oil supply line sizing: Tial recommends a minimum -4AN feed line (or 1/4″ ID) for each turbo. Use a tee from the oil pressure port or an adapter block that provides two separate feeds. Do not use a single restrictor for both turbos.
  • Install oil restrictors only when needed: Ball-bearing turbos often require an oil restrictor (e.g., 0.040″ orifice) to prevent over-pressurization. Journal-bearing turbos typically need full flow. Check the Tial technical bulletin for your specific turbo model.
  • Ensure proper drain line routing: The oil drain must be gravity-fed, with a minimum slope of 30 degrees downward from the turbo to the oil pan. Use a -10AN or 3/4″ ID drain line. Avoid sharp bends or uphill sections. If the drain is restricted, oil will back up into the bearing housing and cause seal leaks.
  • Maintain correct oil level and pressure: Regularly check engine oil level and use high-quality synthetic oil of the correct viscosity (typically 0W-40 or 5W-40 for turbo engines). At idle, oil pressure should be at least 10 psi; at high RPM, maintain 40–60 psi.
  • Install a pre-turbo oil filter: Fine metallic debris from engine wear can clog turbo oil passages. A high-quality in-line filter protects both turbos.

Repairing a Starved Turbo

Once a turbo shows symptoms of oil starvation, it is rarely repairable. The center housing rotating assembly (CHRA) must be replaced. Tial sells replacement cartridges for most models. Follow the Tial turbo rebuild instructions to swap the core. After replacement, flush the oil lines and the engine’s lubrication system before restarting to avoid contaminating the new turbo.

5. Overheating – Managing Heat in a Compound Setup

Compound turbo systems generate significant heat due to the high boost pressures (often 40+ psi) and the dual compression stages. Excessive heat can cause pre-ignition, detonation, and thermal fatigue of turbo components. Overheating may also be a symptom of other underlying issues such as lean air/fuel ratios, insufficient intercooling, or exhaust restrictions.

Symptoms of Overheating

  • High exhaust gas temperatures (EGT): Tied to the primary turbo outlet, EGTs exceeding 1600°F (870°C) for prolonged periods can damage turbine wheels.
  • Loss of power with rising temperature: The ECU may pull timing as IAT (intake air temperature) climbs, resulting in a noticeable performance drop.
  • Visible smoke or burning smell: Paint on the turbo housing may blister or smoke; burning oil smells indicate oil coking in the bearing section.
  • Coolant temperature spikes: Overheating engine coolant can result from the additional heat load of two turbos.

How to Fix Overheating Issues

  • Upgrade the intercooler system: A single air-to-air intercooler may not be sufficient for compound boost. Consider a larger core (3.5″ to 4″ thick) with cast end tanks, or an air-to-water intercooler for more consistent IATs. Ensure the intercooler has enough surface area to handle the total airflow of both turbos.
  • Improve engine cooling: Install a high-capacity radiator, electric fans with proper shrouding, and a coolant expansion tank. Tial recommends a thermostat with a lower opening temperature (160–170°F) for track use.
  • Add a turbo blanket: Ceramic blanket wraps for the turbine housing reduce under-hood temperatures and keep exhaust heat from radiating into the engine bay. This also helps spool by retaining heat energy in the exhaust stream.
  • Inspect wastegate and boost control for overboosting: If the wastegate fails to open, the secondary turbo will continue to compress air beyond the system’s capacity, generating excessive heat. Verify the wastegate is functioning correctly (see Section 2).
  • Check for exhaust restriction: A clogged catalytic converter, muffler, or downpipe can trap heat in the turbo system. Measure exhaust backpressure with a gauge plumbed into the downpipe before the secondary turbo; anything above 10 psi at full boost indicates a restriction.
  • Enrich the air/fuel ratio at high boost: A slightly richer mixture (11.5–12.0:1) under heavy load provides cooling via fuel evaporation. Consult with your tuner to adjust the AFR map. Never exceed 12.5:1 at boost pressures above 30 psi.

Preventing Future Overheating

Incorporate a heat management strategy from the start. Use thermal barrier coatings on exhaust manifolds and turbo housings. Install a large oil cooler (at least 19-row core for the engine oil, and a separate cooler for the turbo oil if using a ball-bearing cartridge). Monitor IATs with a dedicated gauge, and set up a warning light if intake temperatures exceed 140°F (60°C). Finally, let the engine idle for 30–60 seconds after a hard pull before shutting off to prevent oil coking in the turbo bearings.

Maintaining Your Tial TS-Double System Long-Term

Preventive maintenance is the key to avoiding these common issues. Create a regular inspection schedule that includes:

  • Every oil change (3,000–5,000 miles): Inspect all boost pipes, hoses, and clamps. Check oil lines for leaks or abrasion. Clean or replace air filters.
  • Annually: Remove and inspect the wastegate valve for carbon buildup. Perform a boost leak test. Verify wastegate spring cracking pressure with a hand pump.
  • Every 20,000 miles: Inspect turbo shaft play by removing the intake pipe and compressor inlet. Replace oil feed line restrictors if used. Flush the intercooler for oil deposits.

By following these procedures and addressing problems promptly, your Tial TS-double compound turbo system will deliver reliable, high-power performance for many seasons. For additional support, consult the Tial technical support portal or join the Tial owner’s forum to connect with experienced builders. Remember, compound turbo tuning is an art—patience and attention to detail pay off in the end.