TURBO (Frequently Asked Questions)
Q: What are the primary tuning issues with Turbos?
A: Engine setup - ignition timing - fuel delivery are the most important areas. Under boost, if any of these areas are insufficient detonation, or ping, will occur. Detonation is the heat and pressure inside the cylinder chamber begin to build and detonate before the engine is prepared to. You can eliminate this issue by tuning the air/fuel ratio to run a little rich which acts as a cooling effect on the combustion gases. Tuning the ignition advance to ensure that combustion chamber pressures stay below the level that causes unburned fuel to ignite ahead of the advancing flame front.
Q: What is the difference between a Single Turbo and a Twin Turbo setup?
A: A "Single turbo system" setup receives exhaust flow from one exhaust manifold and supplies air to all cylinders usually found on 4 cylinder engines.
The most common type of twin turbo setup is the "Parallel system" where each turbo is fed by ½ of the engine's cylinders. Two turbo compressors supply compressed air to the intake manifold simultaneously. Most drag racing setups on 4 cylinder and In-line 6 cylinder engines utilize the power of a single big turbo for convince, power delivery, and overall efficiency
"Sequential twin turbo systems" utilize one of the turbos at low engine speeds and convert over to two parallel turbos at a predetermined engine speed and/or load. In theory, sequential turbo setup have big potential however have proven to be rather unpredictable and hard to create the environment where both turbos can work seamlessly
There are also twin turbo systems found on some diesel engines where one turbo feeds the other turbo for greater air compression which means more power delivery.
Q: What is Twin charging?
A: Twin charging is a method utilizing both turbo and superchargers strengths and mitigating the weaknesses of each on the same power plant. (In other words it is a turbo supercharger.)
Q: What is Turbo Lag?
A: Turbo lag is the delay period it takes the turbo to build air pressure. This boost response or air pressure (psi) builds after the throttle is opened. The lag occurs when the engine RPMs are above the optimal boost threshold. Turbo lag is a result of many factors, including turbo size relative to engine CC's, tuning, the inertia of the turbo's rotating group, turbine efficiency, restrictions in the intake plumbing, and exhaust back pressure. There are extended tip turbo setups that eliminate lag through various methods and turbo wizardry.
Q: What is Boost Threshold?
A: Boost threshold is the engine speed at which there is sufficient exhaust gas flow to generate positive manifold pressure (PSI), or boost.
Q: What is a boost leak?
A: A boost leak means that somewhere in the turbo or intake, there is an area where the air (boost) is escaping. Check for a bad seal, cracked housing, or hole in your intercooler piping If you have a boost leak the turbo will still be able to generate boost, but it may not be able to sustain it at a constant level and it will drop off in proportion to the size of the leak.
Q: How can I adjust the turbo boost?
A: Adjusting the boost is rather simple. It depends on the type of boost controller you have if you have one. You can also adjust the boost at the Wastegate. For a standard Wastegates actuator, simply re-calibrate the actuator to open (more or less) for a given pressure. Changing the length of the rod that attaches to the Wastegates lever accomplishes this adjustment.
Mechanical boost control systems, adjustments may involve changing the setting on a regulator valve(s).
Electronic boost control systems, adjustments may need to be made to the vehicle's engine management system.
External Wastegates, adjusting the boost often requires turning the adjustment screw (when equipped) to increase/decrease spring load, changing Wastegates springs, or shimming Wastegates springs.
IMPORTANT: ADJUSTING THE BOOST IS A SIMPLE PROCEDURE, MODIFICATIONS TO THE ENGINE FUEL DELIVERY ARE ALSO NECESSARY!
Tuning an engine is creating a perfect equilibrium for combustion. If you add more air you have to add more fuel, if you add more power potential, you must increase the engines ability to expel the extra exhaust created.
Q: What is boost spike?
A: A boost spike is a brief period of uncontrolled higher boost, usually encountered in lower gears during the onset of boost. This occurs when the boost controller cannot keep up with the rapidly changing engine conditions, or the wastegate actuator is not functioning properly or malfunctioning entirely in the closed position.
Q: What is boost creep?
A: Boost creep is a condition of rising boost levels past what the predetermined level that has been set. Boost creep is caused by a fully opened Wastegate dump not being able to flow enough exhaust to bypass the housing via the Wastegates itself. i.e. if your boost is set to 14psi, and you hit full boost, you will see a quick rise to 14 or 15psi, but as the rpm's increase, the boost levels also increase beyond the stock or predetermined settings. Boost creep is typically more pronounced at higher rpm's since there is more exhaust flow present for the Wastegates to bypass. How to fix the problem. Port the wastegate dump area on the turbine housing.
Q: What is compressor surge?
A: The surge region, located on the left-hand side of the compressor map (known as the surge line), is an area of flow instability typically caused by compressor inducer stall. The turbo should be sized so that the engine does not operate in the surge range. When turbochargers operate in surge for long periods of time, bearing failures may occur. When referencing a compressor map, the surge line is the line bordering the islands on their far left side.
Compressor surge is when the air pressure after the compressor is actually higher than what the compressor itself can physically maintain. This condition causes the airflow in the compressor wheel to back up, build pressure, and sometimes stall. In cases of extreme surge, the thrust bearings of the turbo can be destroyed, and will sometimes even lead to mechanical failure of the compressor wheel itself.
Common conditions that result in compressor surge on turbocharger gasoline engines are:
The outlet plumbing for the BOV bypass valve is too small or restrictive
The turbo is too big for the application
Q: How does a wastegate work?
A: A pressure actuator, controlled by boost pressure determines whether the wastegate is open or closed. In its resting position allows boost pressure to build and force is applied to the actuator. When the boost pressure exceeds the spring value, the actuator will progressively open the wastegate, allowing the exhaust gases to expel therefore maintaining the boost pressure at the set level. To put it simply – a wastegate prevents the boost pressure from climbing indefinitely and consequently blowing the engine.
Q: What is the difference between a BOV and a Bypass Valve?
A: A Blow Off Valve (BOV) is a valve that is mounted on the intake pipe after the turbo but before the throttle body. BOV's prevent compressor surge. When the throttle valve is closed, the vacuum generated in the intake manifold acts on the actuator to open the valve, venting boost pressure to the atmosphere in order to keep the compressor out of surge.
Bypass valves are also referred to as compressor bypass valves, anti-surge valves, or recirculating valves. The bypass valve serves the same function as a BOV, but recirculates the vented air back to the compressor inlet, rather than to the atmosphere as with a BOV.
Q: What is turbo shaft play what causes it?
A: Shaft play is caused by the bearings in the center section of the turbo wearing out over time. When a bearing is worn, shaft play, a side to side wiggling motion of the shaft occurs. This in turn causes the shaft to scrape against the inside of the turbo and often produces a high-pitched whine or whizzing noise. This is a potentially serious condition that can lead to internal damage or complete failure of the turbine wheel or the turbo itself. Axial/radial axial shaft play (in/out) Radial (side-to-side) should be minimal and nearly undetectable when moved. A ball-bearing turbo is designed to have clearance between the bearing cartridge and center housing for hydrodynamic damping. Hydrodynamic damping uses the incompressible properties of a liquid (oil in this case) and the space around the bearing cartridge to dampen the shaft motion of the rotating assembly. As long as the shaft wheel spins freely and the wheels don't contact their respective housings, the assembly will function properly but may demonstrate some wear.
Q: What is causing my turbo to sound like a whistle?
A: The "sewing machine whistle" is a distinct cyclic noise cause by unstable compressor operating conditions known as compressor surge. This aerodynamic instability is the most noticeable during a rapid lift of the throttle, following operation at full boost.
Q: Which turbo kit should I get?
A: Picking a turbo charger is like picking a mail order bride from a catalog, either way you are going to have to live with your decision for better or worse. Things to think of when choosing a turbo setup are boost response, peak power and total area under the power curve. If you need specifics go to the turbo calculator and play around for a while and make that informed decision. (TURBO CAL LINK) I hate to say it, but the recently popular EBAY (turbos) made in China get a lot of criticism from tuners. But the fact of the matter is they are cheap, they get the job done, they do last for a considerable amount of time and they do produce good power. Are they as good as name brand turbos, well, sort of, but no not really. Is it the best bang per buck? Sure. Especially when you get tired of it and want to go a bigger setup it is easier on the pocket. But, buy American when you can. God knows we need it.
Choosing between a single or parallel twin turbo setup is mainly a issue of space limitations or a personal preference. Adding two turbo increases the amount of labor, time, weight, and headaches. If you are running into space issues for the larger single turbo setup, purchase or fabricate an inverted exhaust manifold, cut a hole in the hood, stick it out the top = problem solved. Besides it looks nasty!
Turbo charging versus supercharging
In contrast to turbochargers, superchargers are not powered by exhaust gasses but are connected directly or indirectly to an engine. Belts, chains, shafts, and gears are only a few of the ways this is performed. Most automotive superchargers are positive displacement pumps, such as the Roots supercharger. Some superchargers are compressors such as World War II piston aircraft engines, specifically the Rolls-Royce Merlin and the Daimler-Benz DB 601, which utilized single-speed or multi-speed centrifugal superchargers.
A supercharger uses mechanical energy from the engines crank to drive the supercharger pulley. For example, on the single-stage single-speed supercharged Rolls Royce Merlin engine for instance, the supercharger uses up about 150 horsepower (110 kW). Yet the benefits outweigh the costs, for that 150 hp (110 kW), the engine generates an additional 400 horsepower and delivers 1,000 hp (750 kW) when it would otherwise deliver 750 hp (560 kW), a net gain of 250 hp (190 kW). This is where the principal disadvantage of a supercharger becomes apparent: the internal hardware of the engine must withstand generating 1150 horsepower.
In comparison, a turbocharger does not place a direct mechanical load on the engine. It is more efficient because it converts the waste heat of the exhaust gas into horsepower used to drive the compressor. In contrast the principal disadvantages of turbo charging are engine back pressure and the inefficiencies of the turbine "turbo lag" versus direct drive proportional to the engine RPMs.
A combination of an exhaust-driven turbocharger and an engine-driven supercharger can mitigate the weaknesses of the other. This technique is called twin charging.
Intercooler Continue to INTERCOOLER FAQ