Open Loop Boost Control Duty Cycle
Turbo Mini Forums

I'm trying to create a base open loop map for the boost duty cycle.

I have a log of the boost/tps/rpm (below). Any clues on how to get a rough map from this?

I'm really only interested in mapping the WOT boost at the moment.

Edited by wil_h on 7th Oct, 2015.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Only real way Wil is either on the rollers or trial and error. Increase the duty cycle bit by bit and see what boost you get each run as you alter it.
If you are feeling keen you can manage the boost curve by altering the duty cycle through the rev range.
What ECU is it?
What effect the duty cycle has on the turbo depends on the valve, pipe work, actuator, etc.

Edited by Tom Fenton on 7th Oct, 2015.

Yeah, it's a trial and error process. Also, the actual boost you get will vary depending on the ambient conditions (temperature, barometric pressure, humidity,...).

http://www.jbperf.com/

Its a specialist components Tornado.

I was hoping for something more scientific. Ho-hum, trial and error it is.

At the moment the actuator is a 10psi one with no bleed and short piping. I've found a few best guess maps as a start I can try.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Right, after the above I went and researched the subject again. I had already done so.

Having done this I now fully understand the purpose of the map. I had been misinformed of what it was for.

Basically the duty cycle can be considered to be the amount of bleed to achieve the desired boost. You then have a target boost and the PI controller alters the duty cycle to get this required boost.

Too little duty cycle - boost target not reached.
Too much duty cycle - boost overshoot.

Looking at the previous duty cycle map I had, I now understand why the boost spiked so much.

As I only want a 2psi rise above the actuator (10psi rated), I reckon 20% will be a good start.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Wil, I think you are mixing drinks here a little.

Target boost and PID control is for closed loop boost, e.g. you tel the ECU what boost you want and it looks at the MAP signal coming in and then manages the control valve to achieve it. This is limited of course by the turbo itself, the ECU cannot make more boost than the turbo can physically supply at any given point. If you like closed loop is like Robert in his car up the strip, he has a boost figure he wants in mind, looks at the gauge, not enough boost, opens the bleed a bit more, checks again, too much boost, closes it a touch, etc etc. Closed loop is just the ECU doing this for you.

Open loop is as we are discussing above, there is no feedback loop, you are just telling the control valve to work at a given duty, this as you rightly say gives a certain amount of actuator signal bleed effect, more duty cycle = more bleed. Even though there is no feedback and hence no "active" if you like control, open loop is still very consistant, once you have set it up, it will do pretty much the same thing every time. To go back to the Robert analogy, if someone put his bleed valve where he can't alter it on the move, so the bleed is fixed, he gets the same every time, until he stops and alters the valve (alter the duty cycle in the ECU).

Edited by Tom Fenton on 8th Oct, 2015.

PS
Assuming this is your hillclimber? If so i would say open loop will suffice for what you want. Closed loop can be tricky to get setup and working well without it swinging the boost all over. Allied to the fact that open loop is usually very predictable.

Yep I understand.

The thing is, that if the open loop is there or there abouts, then the closed loop has a lot less to do.

But yes I can see how open loop would be more consistent.

And yes on the hillclimber(s)

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

The boost controller i ran you set a duty guestimate, if your guestimate was close enough it took over and went closed loop and started regulating boost itself tweaking the duty, i presume your setup is the same in which case yes start nice and easy 15-20% and slowly work up.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

That's is Denis. I'll bang a load of thresholds in to keep it as safe as I can as well.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Trial and errors is scientific !!!

test, note results, repeat..

Doesnt get more scientific than that lol

A good closed setup is good to have, problem is not all setups are that good, but they do rely on having the right info which can be difficult to get right.

But most do still require a base lookup table of duty cycles vs boost which the user/tuner needs to build manually, no different than they have to build their own fuel/spark tables.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will