Turbo Compounding (Edit: now gone VNT!)

[vwmike]

The whole point of having the VNT was that it would always have the optimum turbine aspect ratio. Under some conditions the turbine can provide less exhaust backpressure than the boost pressure generated. This is one of the reasons the VNT is so popular on diesels. With limited heat available it is important to harness what you have as efficiently as possible. A wastegates job isn't to offer optimum exhaust flow around the turbine but simply vent off the excess. The primary flow area is still through the turbine and with a small A/R or vanes that are clamped shut (essentially the same thing) you are hindering exhaust flow and increasing backpressure. The backpressure increase will cause a decrease in the overall efficiency of the engine. Remember, after all it is just a fancy air pump.

[Turbinepowered]

So what kind of controller would you suggest, Mike? Anything with a computer is out; part of the reason I'm ditching the gas engine in the car is I'm a little tired of computers and sensors and all that. Much easier for me to visualize and fix a mechanical problem than an electrical one.

[jackbombay]

Check out the videos posted by 745 turbogreasel of Named Tintin's controller.  Throttle lever closes vanes.  Boost can opens them.  

Andrew

  Yea, that is a slick little control unit finding the right stiffness spring might be a bit of a PITA, but certainly not a deal breaker.

[Turbinepowered]

Hmmmm, went out and took a look at the engine. That manual VNT controller with the accelerator linkage would need some serious cabling to get across the intake manifold and everything else in the way, to go from pump to turbo. Maybe the gasser intake manifold is more lowline, but the naturally aspirated swoops upward way too much for a simple cross-valve cover linkage to bridge. Pump is all the way at the back of the engine, too, and high on the side.

Maybe set it up with a cable, cable stop, and some springs that way?