DBW config

[ellisd1984]

I was watching this on YouTube and it seems relatively easy concept. HHowwood ypu be able to set this up in the G4X?

 

 

 

 

 

[dx4picco]

I guess the transcient going back on the throttle would be the hardest part to smooth out. 

Antilag function and a separate DBW table will make the base of it. 

If I remember, while the ALS is armed but not active, you get instant fuel cut, so combined with 2 table for dbw opening it would be the starting point.

however, how the throttle is reapplied when coming out of such event, I leave the better brains figure that out lol

 

[Adamw]

I've come across this guy's videos before and they are usually reasonably accurate, but in this case Im not entirely convinced he has it right - or perhaps he has missed some important part of the strategy out?  If I search "Porsche Dynamic Boost" pretty much all articles are linking to the same video and quoting the same "facts".  

A strategy that is fundamentally very similar to what this man describes has been used in the higher end motorsports for 10years or more, often named "pre-blip" or "blip in advance" or similar and I have never seen any mention of it improving turbo response - in fact I have probably seen it more commonly used on NA engines.  The purpose of pre-blip is to improve the timing and abruptness of the torque reversal for a quicker and higher success rate downshift.   When the driver lifts off the throttle, it is only partially closed and fuel is completely cut, when a downshift is requested the fuel is momentarily re-instated so you get near-instant torque reversal since you are not waiting for a throttle to open and the manifold to fill with air etc, this method allows you to time the torque reversal more accurately to occur at the right instant within the shift sequence.  There are a few issues however; firstly even at say 25-30%TP you have already lost nearly all engine braking effect.  Secondly, the power reintroduction becomes quite tricky, obviously, you cant just turn the fuel back on as you would go from 0% torque to 100% torque in 1 engine cycle.  You need to first almost close the throttle before you can re-introduce fuel, so that the driver has some chance of driving out of the corner etc.  There needs to be quite a few rules controlling when it is time to close the throttle, in the motorsport ecu's I have used it is often timers and lat G etc, but you have to adjust these for each track depending how long the car is off throttle for etc.  Given these Porsche's are probably mostly PDK gearboxes that need accurately timed shift events, they have paddle shift, they have long intake runners and two large plenums (poor blip response), my thoughts are this so called "dynamic boost" strategy is possibly just a blip strategy?

A further question that fuels my scepticism:  I've always heard a general rule that a turbocharger turbine makes its shaft power from roughly an equal share of heat energy Vs mass flow/kinetic energy.  Is the extra mass flow that you gain from opening the throttle (and remember you are now pumping cold air through the manifold/turbine etc) really going to make more energy than what you would have had with a normal closed throttle condition but when there is still combustion/expansion/heat doing work?  I have some doubts... 

 

 

[dx4picco]

I understand it the same as your second paragraph, without the blip part.

I guess not closing the throttle allows to keep a higher turbine shaft speed compared to a blow off valve setup (slower shaft speed decrease), that combined with the higher intake air pressure (still <BAP or close, but not 15kpa overrun) you get better throttle response when picking up the throttle out of a corner.

As you said, that doesn't explain how the torque re-introduction is happening to make it smooth.

[Adamw]

9 hours ago, dx4picco said:

I guess not closing the throttle allows to keep a higher turbine shaft speed compared to a blow off valve setup (slower shaft speed decrease)

How do you come to that conclusion though?  If half the shaft speed comes from heat, with an open throttle and 100% fuel cut you are now not adding any heat, the turbine is still consuming heat the whole time and to make matters worse you are now pushing cold exhaust gas through the manifold and turbine removing further stored energy. I would argue the loss of all that heat would exceed any increase in energy you may get from increasing mass flow.

 

9 hours ago, dx4picco said:

combined with the higher intake air pressure (still <BAP or close, but not 15kpa overrun) you get better throttle response when picking up the throttle out of a corner.

You still need to close the throttle before you can add the fuel back in.   Manifold pressure at the time you want to reintroduce power will be no different.

[dx4picco]

Fair enough on both points. that was just ideas 

my first statement was rather compared to classic overrun fuel cut than with retarded timing and closed throttle. But your point may very well be more important, with the manifold heat I didn't think about. 

We will never know what it really is then