A little while ago we gave you the opportunity to ask Turbosmart’s R&D department questions regarding boost control. We had a solid response to this round of Ask The Expert, and thanks to the Turbosmart tech-heads we now have answers to a bunch of them.
Let’s take a look…
Turbosmart: Thanks for so many great questions! We’d love to answer them all, if only space permitted. Before we begin, it is important to note that every car and every turbocharger setup is slightly different. When it comes to boost control, there are so many variables, and few hard and fast rules. There is almost always more than one way to achieve a set goal, and what works for one vehicle, may not work for another, and vice versa.
What are the temperature ranges an external gate can handle? More particularity the internal diaphragm. I know some are made with silicone which is usually good till 450-500ºF, how does this no burn up when the wastegates get up to 1000ºF+?
Turbosmart: The wastegate is made up of two parts – the body, and the actuator housing. It is the actuator housing that holds the diaphragm. The bodies of our wastegate range can handle a continuous 900 degrees centigrade (1650ºF) while the actuator housing can handle up to 260 degrees centigrade (500ºF) for brief periods of time. Our external wastegates range incorporate a heat shield and spacing between the wastegate body and the actuator housing assembly, which stops much of the heat from reaching the diaphragm. You’ll find that with adequate cooling and shielding that the actuator housing will stay around 150 degrees C (302ºF) while racing around a track. Temperatures in the housing actually climb dramatically when the car begins to slow down after a track session, normally during the cool down lap. Since the amount of airflow through the engine bay is reduced, the housing rapidly rises in temperature. We have seen up to 320 degrees centigrade (608ºF) after returning to the pits – which was no issue, as the car was stationary, there was no pressure applied to the wastegate at the time. Street driving will result in temperatures far lower than anything seen on the track so it is generally not much of an issue.
Temperatures are normally kept within this range by doing the following things: 1) Point the actuator away from any turbine housing and exhaust manifold and preferably at the front of the engine to receive good airflow. 2) Limit the amount of radiant heat (i.e. unshielded exhaust pipes and turbine housings) the actuator housing is exposed to. 3) Choose the correct wastegate size for the application. If the gate is too small, it can overheat as it cannot dump the exhaust gas effectively. 4) Ensure the dump pipe is correctly sized, and not convoluted in its path. Anything that impedes exhaust flow can trap heat in the gate.
Are external wastegate setups on factory exhaust manifolds ideal or should one stick with an internal turbo/wastegate? Would you prefer a tubular manifold matched with an external wastegate?
Turbosmart: A tuned-length manifold can reduce spool up time and increase turbocharger performance while a cast manifold is generally more physically reliable and compact. As long as the shape of the manifold can allow the wastegate to divert enough exhaust gas to control boost, either manifold design will work. An interesting point to note is that the Mercedes F1 power unit this year uses a simple log manifold (similar in theory to the picture) to reduce heat loss between the engine and turbocharger while allowing better engine packaging.
Can you shed some light on wastegate sizing in relation to engine size and power output, i.e. does a high horsepower motor need a bigger wastegate compared to the same motor with low horsepower output? Also, on a twin scroll manifold/turbo setup running an external wastegate will a feed from each scroll into one wastegate be okay, or to do it properly should you run two wastegates, one for each scroll?
Turbosmart: This is a tricky question, and unfortunately there is no easy answer. To determine the correct size of a wastegate you must first look at engine size and target power. This will give you the mass airflow require to produce that power – from that a turbocharger is chosen. Once you know how much mass flow the engine puts out and how much mass flow the turbine requires, you’ll then be able to determine how much mass flow the wastegate needs to bypass to keep the turbine running in its optimum range. As you can see, this throws up an infinite number of variables related to wastegate sizing. All applications differ slightly, so it is best to speak with an experienced engine builder or tuner for advice on what’s been tried and tested. If you are tossing up between two wastegate sizes, it’s always better to go larger as this gives you more ability to control boost with future modifications and it will give the wastegate better heat handling capabilities.
In terms of twin scroll turbochargers, always run twin wastegates as the turbine housing is designed to have split exhaust pulses all the way to the turbine wheel. Using a single wastegate will bridge the exhaust pulse and have a negative effect on turbocharger performance to the point where it will have slower spool up even compared to a single scroll turbocharger.
Blow-off valve placement: how much of a difference does it really make – i.e. from next to the throttle to next to the intercooler, or integrated in the compressor housing.
Turbosmart: A blow-off valve really can be mounted anywhere, just as long as it is big enough to flow enough air to keep the compressor off the surge line in the compressor map. Turbocharger manufacturers have begun integrating blow-off valves on the compressor cover as a way of isolating their product from the rest of the engine. It gives them more control over the turbocharger system without having to worry about installation issues affecting the reliability and function of the blow-off valve and turbocharger system. In a recirculating application this means the return path for compressed air returning to the intake is very direct, which enhances response. However, the air has not passed through the intercooler, so it can also be very hot (up to 100 degrees centigrade hotter than ambient air), introducing extra heat into the turbocharger system. The idea behind mounting the blow-off valve before the throttle body is that the airflow through the intake system continues to flow towards the intake manifold when the throttle is shut and the blow-off valve is venting, but when the throttle is reopened, air is still travelling in the same direction requiring less energy and time for the turbocharger to return to operating speeds. In a recirculating application the return path from the valve to the intake is much longer, however the recirculated air will be much cooler (only up to 50 degrees centigrade hotter than ambient air), thus not adding as much heat into the turbocharger system.
What are the pros and cons of a blow-off valve versus recirculation? I have heard many pointless arguments on forums debating why each is better for which application but mostly it sounds like a lot of smoke from people who really don’t know what they are talking about
Turbosmart: Blow-off valve - Pros: greater flow capabilities, does not recirculate any heated air back into the turbocharger system (even air that has been through an intercooler can be up to 50 degrees centigrade hotter than ambient air, simpler and lighter installation (no need for extra pipes and fittings to recirculate). Cons: slower response at low throttle movements as the use of a stiff spring is required to keep the blow-off valve closed at idle.
Bypass valve – Pros: fast valve response, quiet, no adjustment required. Cons: additional piping and fittings needed to recirculate air, flow limited by outlet fitting and return hose size, lighter spring can increase turbocharger spool up time, adds heat into the turbocharger system by recirculating heated air.
Why don’t manufacturers install blow-off valves in the original turbocharged cars?
Turbosmart: Back in the day, turbocharger technology was in its infancy, and there was not a lot of understanding and information about turbochargers and their ancillary systems. We think manufacturers did not install blow-off valves or bypass valves in original old school turbocharged cars, because at the time, they would have added a large cost to a vehicle, and the benefits (longer turbo life, quicker spool-up time, etc) weren’t as well understood as they are today. As turbochargers became more prevalent, and technology progressed, manufacturers realised that the benefits outweighed the extra cost of a blow-off valve or bypass valve. Today, manufacturers have a fantastic understanding of the technology and now all petrol turbocharger cars run some sort of bypass valve from the factory. Manufacturers have even gone as far as adding electronic control to the valve to minimise valve response time such as in the VW Golf 2.0L TFSI. Manufacturers don’t install vent to atmosphere blow-off valves onto current production cars because emissions laws require them to keep a closed system, where air is only allowed to enter via the air filter and exhaust to exit via the exhaust pipe.
No Subsitute For Boost
Is there any advantage to running the wastegate directly off the turbine housing?
Turbosmart: In theory, mounting the wastegate off the turbine housing will give you better control over exhaust because you’re controlling gases closer to the turbine wheel giving it better response. The problem with mounting it on the turbine housing, however, is that it spoils the exhaust flow in the location where the wastegate is mounted, and does not allow for the exhaust gas to remerge and smooth out before it hits the turbine wheel – thus affecting turbo spool up. This issue is amplified when the wastegate opens, which results in undesirable boost characteristics. Mounting the wastegate before the turbine keeps the turbine housing shape intact to smoothly guide exhaust gas into the turbine wheel.
Piston driven blow-off valves versus diaphragm – which one is superior and why?
Turbosmart: There is no superior in this argument, both are good. In general, a diaphragm valve can be shorter but wider, while a piston valve is taller but narrower. A piston valve has fewer components but is heavier than a diaphragm style valve. The operation of both valves is similar so when we are designing a new valve, we choose either a piston or diaphragm based on the size limitations, and other wanted attributes of the desired product.
How can I measure if my blow-off valve is effective/tuned enough? I still hear ‘fluttering’ at certain loads and throttle angles when letting off. Is any amount of flutter bad?
Turbosmart: A blow-off valve should be tuned so that the spring is just firm enough to keep the valve closed at idle. A spring that is tuned too soft will open at idle have an adverse effect on idle quality. A spring that is tuned too stiff will ensure good idle quality, but will not open far enough for long enough, and therefore will not vent the desired volume of air. ‘Flutter’ is most common when backing off the throttle at light loads – where the vacuum generated is not sufficient enough to overcome the spring force of the valve, and therefore does not allow the valve to open sufficiently. For a more detailed definition of flutter, check out the information our website here. Technically any amount of flutter is not ideal, however in a real world application it may be impossible to eliminate completely, so reducing it to a minimum is best.
I’m thinking about replacing my Trust blow-off valve, with a Turbosmart Race Port blow-off valve, and have a couple of questions. 1. If i did install the Turbosmart blow-off valve would I need to retune the car for the new piece of equipment to reap any benefits? Would you recommend re-tuning after install? Would it be worth installing the blow-off valve controller? Would this give additional performance increases? The car has a build EJ25/20 engine, front-mount intercooler with a GT3082R running high boost and putting down over 400kW at the wheels. Looking for every advantage I can get. Any information appreciated.
Turbosmart: You don’t need a re-tune after installing the Race Port blow-off valve. You just need to make sure that the springs chosen for the blow-off valve are right for the vacuum produced by your engine, so that the valve is closed at idle but not too stiff so that the response is diminished. You won’t need a blow-off valve controller as it is designed for use in diesel engines, where there is traditionally no vacuum to control the blow-off valve.
Age old question, which is more reliable – an electronic boost controller or a manual boost controller, and why?
Turbosmart: It depends on what you are referring to in terms of reliability; boost control reliability or functional reliability. In terms of boost control reliability, an electronic boost controller has its advantages in its ability to maintain a reliable boost curve and include safety measures – such over boost shut down and warning alarms. Electronic boost controllers are also installed in a fashion so in the case of an electrical fault, the solenoid remains in a state which reverts boost pressure back to the actuator spring pressure. A manual boost controller does not have as much scope to tune the boost curve, but has better functional reliability as there are no moving parts and there is no requirement for power – meaning there is very little to go wrong. One thing to note with any turbocharged car is that there always needs to be an ECU based boost cut or engine protection measure, in case of a mechanical failure to the wastegate (or pneumatic lines to the wastegate) which can cause overboost situations outside the boost controller’s ability to manage.
What level of analysis goes into your designs? Non-linear CFD? There are a lot of small companies making parts that ‘do the job’ so what do you do to make sure that your parts ‘do the job’ better? I’m talking about more than fit and finish here. What makes your stuff ‘performance’ instead of just ‘aftermarket’?
Turbosmart: We use a variety of methods which does include software packages to validate our designs. Our main validation is through on-road and race track testing, and data logging. Through rigorous real world testing on a number of different engines, we can ensure our new products perform as per their design specifications before they are released to the public. Our goal is always to design products which have a proven ability to increase performance or performance potential of the engine they are used with. If a new product doesn’t increase performance, and just ‘does the job’ it is refined, until a true performance advantage is seen.
Turbosmart
More Ask The Expert stories on Speedhunters
Turbosmart