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131 | Tuning Open Loop Boost Control - Link G4+

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I have an EJ 25 with a stock location internally wastegated Blouch Dom3 Twinscroll on it. I purchased a Moore Performance Dump Pipe Flange that completely separates the wastegate from the turbine. So it runs a 3" dump off the turbine and a 2" dump with a hotdog muffler off the wastegate side which ends pretty much just behind the driver seat.

When I initially installed it the first thing I noticed was a horrible oscillating sound around and coming into target boost 24psi. It had been proffesionaly tuned previously on the standard style Twinscroll Dumpipe with the MAC 3port set up on 15 kHz. I could not hear any oscillating on the old set up but that may have been a product of the two exhaust streams mixing and going out right through the system at the back of the car

I started adjusting the MAC frequency and the WG table to try and tune the oscillation out. 25kHz made an improvement. 28kHz is better but no difference if going up to 30kHz.

I rejigged the 3D WG table to bring the load axis closer above and below target boost but it wasn't quite right so it was overshooting on initial spoolup and jumping around a bit.

So I watched webinar 131 again yesterday morning and decided to simplify the issue by going back to a single line WG table to get it all on target. So now I have a nice flat boost curve and the MAC is at 28kHz. But, there is still a little oscillation sound through the system - although it is vastly improved. I just need to do a couple of minor adjustments and then I can reset the 3D table.

I'm just wondering, and this is probably the main question:

When I bought the Turbo it was strongly recommended for that boost level to purchase the Turbosmart Actuator specifically made for it rather than use the Blouch OEM one that came on it.

I am now wondering if purchasing the stronger equipment might now be a useful way to improve the situation further. To me the WG should be used and not heard, maybe the actuator is struggling to keep up which could be part of the problem.

This is a pretty common scenario with a wastegate that's dumping to atmosphere. Since the pressure signal to the wastegate is being pulse width modulated, it's physically opening and closing as the solenoid is pulsed and this is what you can hear. As you've already picked up on, changing the solenoid frequency will have a big impact on the sound you hear, however this is also related to the duty cycle the solenoid is operating at - at low DC you tend to hear the oscillation worse than at higher DC.

I'm going to assume that you meant 'Hz', not 'kHz', as the MAC valves won't operate in the kHz range. I generally find for the typical 3 port valves that a frequency between 25 and 30 Hz is their 'happy' place, and 15 Hz would definitely result in very audible osccilation. How is the wastegate on the turbo plumbed up?

Yes, Hz I meant.

The wastegate is internal, the turbine housing separates the wg flow to the back of the housing then the Moore dump flange and 2mm copper gasket separates off the back of the housing into a 2" and 3" pipes. The MAC is plumbed as per the instructions with the pressure source being the compressor cover and one of the ports vents to atmo.

Thanks for the feedback. It is a hell of a lot better now at 28Hz. The lower gears were ok at WOT but getting into 4th and above the pulses were a lot slower and didn't sound like a well tuned sports car.

What are your thoughts on the aftermarket actuator?

Thanks again Andre.