Boost control with VNT15
Turbo Mini Forums

Hi,

I'd like your opinion.

I'm finishing my turbo setup on a NA 998+, CR9.3:1, SW5, 40hp at 4000RPM
The goal is to run a very low boost 200-300mbar to get closer to 90Nm torque and to 55-60hp.
I used a diesel VNT15 turbo from VW AFN 1.9TD 110hp engine.

Unfortunately I have very few space around the turbo and I can not install the vacuum control. The only option would be to use a RC servo controlled by the ECU but I don't want to go this way until I tested the car with turbo.

So I need to find a simple way to limit the boost.
VNT being a variable "Permeability" turbo I'm planning to fix the control with almost closed nozzle. I expect the exhaust to limit the flow (and thus engine VE) at some level which should limit turbo RPM and thus the boost level.
What do you think about that ?

Thanks

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

this may be of interest,

it is a PWM to 4wire stepper circuit,

it should enable a mappable boost output from an ecu to drive a stepper to control the vanes.

http://www.msextra.com/viewtopic.php?t=18971&highlight

I can do that through my ECU and with an RC servo motor: cheap, reliable, proved.
For a moment I'm more interested in understanding the strategy of the VNT control.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

I've tried using the idle valve to control the boost. This works at 2000 RPM, but at higher RPM the flow is too high, the idle passage section is too small to discharge the boost.

I managed to install a remote wastegate control. I've also modified a standard wastegate actuator to be able to change the spring as I need a very low boost level. Then added a boost control valve.

Still did not get a perfect control, the control law is very non-linear. It would require a very weak wastegate spring, not good to get a stable behavior.

Edited by alpa on 13th May, 2008.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm