Hi there,

I am new to this thread, but I am not new to turbocharger control and electronics. I am from Mechatronics and computer engineering background, specialized in forced induction ECU design and research in my thesis (decades ago anyway). My first touch on VNT/VGT in gasoline is inspired from the Aerocharger VATN turbochargers (they are still around see www.aerocharger.com) .

I am working in a motorsports and performance parts business right now. We are throwing in lots of resources in VNT gasoline projects instead of treating this as a home made or school project. We have a bunch of cars here ready for test projects, including factory turbocharged cars like a series of Nissan GTR's from R32 to R34, Audi/VW/Porsche turbos , 911 NA turbo conversions and such .

Personally, I have done at least dozens of electronic boost controller installations, HKS EVC, Apex AVCR, Greddy and ECU mapping work.

I read through this thread and find that its the most active up-to-date VNT turbocharger thread in gasoline . But there is something I really need to point out. First of all, thanks to CivicTSI who has done a lot of work on reverse engineer the Holset actuator (not controller). I think he has mixed up the "controller" and the "actuator" . I don't think its a good idea to mixed up the 2 pieces into a single model. First, an actuator should accept signal for vane position (or wastegate actuation for wastegated turbochargers). Secondly, the boost controller is a unit that should send out signals to the actuator according to boost changes or with other logics (will explain further later). Whether the actuator accepts a CAN message protocol or a PWM is not important, it is just an implementation issue. What is important is how your controller will control the vanes. I hope reader is with me and is clear about what I want to point out. Garrett make two versions of their REA (rotary electronic actuator, rotary electric actuator). The second accepts a PWM signal for vane position for simplicity and the first uses a CAN message. The AVNT slide vane turbochargers found on GT37V series (GT3571VA, GT3771VA, GT3782VA, GT3788VA, GT3794VA) turbochargers all uses a PWM signal for vane position control.

VNT turbochargers control is much more complex is not as simple as wastegated turbocharger control, in a way it can be simple if you setup your control schematics clearly. Mixing the actuator and controller together will result yourself in a very difficult situation.

A VNT turbocharger can varies the A/R of the turbine, but not controlling the boost. If your turbine A/R is small, it result in high exhaust manifold pressure and causing the turbine to spin up fast (we all know that) . Open up the vanes result in a larger A/R, result in lowering the exhaust back pressure but will still keep your turbine to energize and result in speeding up the turbine (not bypassing the turbine). A wastegate bypass the turbine and deenergizes the turbine and causing it to reduce speed. Most gasoline engines have a high working range (high rpm) and high EGT . The way how turbocharger works is we pickup the energy in the exhaust gas and use it to drive the turbine. So that, in theory or in practice, open up the vanes (large A/R) doesn't mean you that you can control the boost. Gasoline engines uses a throttle to control engine load, the higher the rpm , the higher the gas flow rate and will continue to cause boost to rise unless causing your compressor to reach the stall line (refer to your compressor map) . That means, a wastegate is needed to bypass the turbine for boost control. This not happen to diesel engines because they don't use throttle so that the maximum air flow can always be determined.

If you go youtube or threads that have successful installation of VGT in gasoline, most of them (at least the ones that I saw) are all done by wastegate actuators. This way, you missed the beauty of VGT that allow you to open up vanes wide in cruise mode for reduction in pumping loss thus improve fuel economy. Another advantage of VGT is engine braking by closing up the vanes when needed. These logics can only be done by electronics, or a complex solenoid valve setup with vacuum reservoirs by a dual port wastegate actuator (Aerocharger people use this kind of setup, but no vacuum reservoir). Relying on vacuum is just unreliable because vacuum will/may run out due to driving condition changes.

To properly take advantage to a VGT turbine, what you need is to setup a controller with a mapping style control. The map should be a 3-axis (rpm+tps+targetboost) for vane position readout. As in different air flow (rpm+tps) rate there should be a desired turbine A/R according to your target boost level. When your compressor is under surge (air flow rate beyond the left line in your compressor map) the vanes should remain wide open so that your engine maintains in a highest VE to reduce compressor surge . Before you reach a certain flow rate your compressor doesn't/cannot make any boost anyway. Vane position should remains wide open so that when cruising/surge you get the best VE and thus best fuel economy. This is one advantage over wastegate turbo . A map for vane position is really needed because you don't want to close up your vane with a wide open throttle so that will cause your engine to choke, or even an unpreditable engine VE in a given situation so that you have no way to setup your fuel maps AFR properly.

I would like to point out some missing information as well. Don't mixed up turbo lag and compressor surge . There is no way to get around with compressor surge if your compressor is large (or with a high value of A/R on the compressor) in low air flow situations. Turbo lag is the time required for spool . If you pick such a large compressor for high power and you will deserve a surge line at high flow rates (only able to make boost in high rpm, thus high air flow rate). If you really need boost in low rpm (low air flow rate) the only way is to use a smaller compressor to give up some top end power. It is always good to pick compressors which has a "wide flow range" at a certain pressure ratio (the Garrett GTX compressors are good in this) . The other way to get around this issue is go for a sequential turbo with twin smaller compressors so that they can add up at the top end.

I am sorry to post such a long message but I hope this will clear up some misunderstood turbo theory from home builders .

For my own VNT projects, I vote for Garrett AVNT because the actuator (the VGT solenoid uses a electro-hydraulic) accepts a PWM signal out of the box so that we can interface it easy. There is no easy way in hacking the CAN messages because we don't know about the protocol and is really a waste of time. We bought dozens of GT37Vs out of Ford Powerstrokes and GM Duramax turbos so that we can pull them apart and pick the size of compressor wheels that suit for each engine build. For example, a 71mm or 76mm compressor will be good for a 2.0, and twin 82mm compressor will be good for a 2.6L twin turbo GTR or Porsche. One more thing to point out is that the Powerstroke turbos are not watercooled, it is no good for serious power outputs so the Duramax turbo is better but they come with stock 88mm compressor or 94mm compressor which will be too large for most of the applications .

For CivicTSI work, I strongly suggest he should separate the actuator and controller. If he can standardize his actuator implementation for the HE351VE turbocharger, it can be a very useful piece of work. It will be not difficult to use the PIC ADC to receive a PWM signal for vane position to simulate what the Garrett turbochargers can do . There is apparently a weight disadvantage for the HE351VE comparing with Garrett GT37V, also for the popularity for parts in garrett turbochargers, there is a bunch of compressors out there, or even the GTX compressors which has a better flow range .

Last post from CivicTSI is 6 months ago and not sure where is he up to now. Hope he is still working on the project or he is still viewing this thread. Its nice to see people around working on VGT and is having the same goal.

My current engineering project is the turbocharger boost controller for VNT turbochargers. We are now busy in setting up a new workshop and will have lots of equipment coming, including a dyno and a new turbo balancer for in-house turbocharger rebuild and modifications. Once we have some results and we will post some updates. Work progress is slow, but we are getting there.

Hope this information is useful to the thread. Thanks for reading.