NefMoto

I am trying to get my part throttle boost under control and I can't help but wonder how other stage 3 folks are accomplishing accurate boost delivery.  What I'm noticing is that I can't seem to achieve a desired boost level at part throttle if desired < wg spring tension.  Actual boost seems to hover at ~10PSI which is the approximate cracking pressure of my Tial MVS wastegate (assuming a request of 5-7PSI) even while WGDC bottoms out at 0%.

In theory, shouldn't the lowest achievable actual boost be limited by your wastegate cracking pressure (assuming no throttle cut)?

The additional boost going unchecked is also causing torque intervention problems (boost deviation threshold already softened):


I believe it's because miist_w > milsol_w while boost is more elevated than expected, but perhaps there is more torque tuning to do.  But first I'd like to get boost under control.

The graphs below were produced at ~40% throttle.  The engine completely shut off due to the above DTC / exceeded torque.

Yup. Below 10psi the ECU has no choice but to use throttle cut to limit output torque in the slow path.

Hmm, yeah I assumed this is a physical limit.  Thanks.

I'll spend my Christmas Eve morning putting in a 5 PSI Wastegate spring. :)  Then I'll tackle the torque limit issue if it's not resolved by the wastegate.

What is the max psi you plan on hitting?  You may be swapping part throttle trouble for difficulty with controlling the high boost regions, if you go for a spring that light in an external wastegate.

I'm looking to run fairly high boost - 25PSI or more.  I haven't tested high boost with a soft spring yet, but what are the mechanics of what you're warning against?  Backpressure might open the valve instead of boost input?

yup

Thanks for the heads up.  I'll report back what I find.  I can change the spring out in about 20 minutes, so it'll be worth the investigation.  I don't miss internal gates, ha.

I think some attention needs to be given to FUEDK, and since it is impossible to give a smaller cylinder filling through boost control, FUEDK needs to be calibrated so that it gives less throttle for a certain torque request.

Excellent timing, I've been noodling on this as well.  Part-load for my tune is pretty abrupt (hybrids).  WDKMSN and MSNWDK?  I've been afraid to mess with these to this point.