Closed loop boost control - or lack thereof

[Scott]

so after the pre-spool stage the PID does not cause the boost to creep up at all?

Technically PID is not used in stage 1(pre-spool stage). In stage 1 the 'Stage 1 Duty' is applied. Stage 2 then uses P and D, Stage 3 uses P and I. The help has a good diagram explaining this.

The only way I understand I have to use such high values for P is because my wastegate spring is too stiff, which causes factor P to NOT add enough % trimming to the actual WG duty cyle, because WG duty cycle values are just too low to begin with. Is this correct?

The numbers that you have to use are influenced by a lot of different factors, setups and the numbers required can vary widely. Your spring pressure will be a contributing factor.

Isn't 31% a remarkably low percentage of WG duty to reach a peak MAP of 220 kPa?

No, again numbers can vary a lot. Talking with others here 30 to 50% is not unusual.

My target boost is 220 kPa, I use a 170 kPa WG spring, and I have "Stage 2 On" set at 50 kPA.

That means that Stage 1 ends when MAP reaches a value of 220-50=170 kPa, which is the rating of the WG spring.

-> When "Boost Target 1" - "Stage 2 On" ≤ WG spring stiffness, doesn't that mean that Stage 1 Duty has zero effect at all in how boost builds up?

The way you have it set up stage 1 does not have a chance to have any effect above spring pressure, however it is still helping keep the wastegate shut below spring pressure (avoiding float).

You should change your 'Stage 2 ON' value to a lower number if you want stage 1 to be used above spring pressure.

[Thom]

Hello,

I replaced the 170kPa WG spring with a 140kPa spring, which allowed me to give some room for Stage 1 to have any effect, namely between 140kPa and 180kPa.

I notice now that spool is slightly better than before in the [140 ; 180] kPa range (but also I don't get any more spikes when flooring the throttle after having changed gears up at full load, with PID setting of 5/0.10/0. With the same settings on the 170kPa WG spring, I would get spikes).

What I can deduce from this observation is that there may be an issue during which the engine is loaded in the boost range of the WG spring.

Does that make any sense? Shouldn't the WG be forced closed regardless of the spring stiffness if Stage 1 (which I have set at 100%) takes place during the MAP range of the WG spring?

[lekonna]

btw, how is your WG connected?

I started having problems with my china WG and switched to a real turbosmart. Also modified so that it connects to the

boost solenoid from the top port.

this seems to give pretty damn good control over the boost. Also i use the MAC boost valve, i had a saab T7 solenoid

previously but it could not move enough air to keep the WG closed.

P=5,I=0.1, D=3

50kpa,20kpa,10kpa

[Thom]

I have the MAC valve too, with port 1 connected to the turbo outlet pipe (boost/vac source) and T'd to the side port of the WG, and port 2 connected to the top port of the WG. Port 3 vents to atmosphere with a small filter.

I like the shape of your MAP curve - mine looks similar!

Any reason why you set the boost target curve to be not flat?

What turbo are you running and with what size of turbine housing?

I may be on the right track but I still do not really understand why I can't get a GTX3076R with a 0.82 A/R turbine housing, on a 3L engine, to reach 200kPa as soon as 3000rpm. My boost curve looks quite similar to the one of a GT3582R when used on a similar engine... Is the billet 76mm compressor wheel of my turbo as heavy as the "old" GT3582R compressor wheel? Probably even heavier considering that my GT30 turbine is smaller than the GT35's?

[lekonna]

I have the MAC valve too, with port 1 connected to the turbo outlet pipe (boost/vac source) and T'd to the side port of the WG, and port 2 connected to the top port of the WG. Port 3 vents to atmosphere with a small filter.

I like the shape of your MAP curve - mine looks similar!

Any reason why you set the boost target curve to be not flat?

What turbo are you running and with what size of turbine housing?

i've got a holset pro52 turbo currently. its comp:71.5/98mm turbine:71/86mm with i think #16 turbine housing.

specd at 94lbs/min. it is quite a big turbo

But it works much better than the old hx50 i had with 80mm turbine, 67compressor and #23 turbine housing.

spools faster and the response to transients is much better.

The reason the boost target is curved is that i try to avoid the torque max during spool-up to keep some traction, i'm having

issues on third gear with just 1.2bar boost already, as you can see from the rpm curve.

Need some dyno time to dial in rest of the gears and full boost ..

What cams are you running, and which engine?

What is the diameter of your exhaust runners?

these i've found to have a huge effect on the spool.

I personally don't like the 3076 since its not balanced to my mind. it has too small turbine compared to the compressor, the 3582 is better in that aspect.

[Thom]

Hi,

The engine is an old design from the early 80s. it's a 3L 4 cylinder with a single OHC (2V head), derived from the 968 turbo RS.

1) the design of the combustion chamber is nowhere near as good as on your 2JZ (or any other modern 4V head) and because of that I cannot run as much timing in the spool up phase as you may be able to because the knock threshold may be way lower than on your engine. CR is about 8:1.

2) the exhaust manifold is a 4-2-1 and the turbo is on the other side of the engine, below the intake manifold. I suppose that creates an important loss of EGT between the head and the turbine, which may also contribute to the slow spool.

Because this engine is an old design and has several flaws, I cannot hope to run reliably more than 7000rpm and 220kPa of MAP, which restricts the turbine choice to relatively smaller sizes than one may choose for a modern 4V head used on a 3L engine, and in order to get "proper" spool, a relatively high level of back pressure is needed. Currently I see between 240 and 250kPa of back pressure against 220kPa of boost when nearing 7000rpm, which I think is quite good. Upside is that the engine runs and feels very healthy and derestricted above 5k rpm, downside is that turbo spool is not that great.

I currently see peak torque somewhere around ~5500rpm, as I'm running a short runner aftermarket intake manifold. For now a standard 255/257° camshaft is used, as I expect an aftermarket camshaft with longer opening times to shift peak torque to even higher RPM. The runners of the exhaust manifold have a diameter I think of 2.25 or 2.5". What do you think about it?

I would have to sacrifice top end power and fit the 0.63 A/R turbine housing to improve spool, as I think the engine could be run relatively safely with more backpressure - I expect something like 300kPa of backpressure with the smaller housing, which should be fine as these engines were running even more backpressure (say near 400kPa) back in the days of the old KKK turbine housings. For now of course I want to extract as much performance from the Vi-PEC boost controller before concluding that I need the smaller turbine housing to improve spool and possibly widen the usable torque band.

[lekonna]

Hi,

I currently see peak torque somewhere around ~5500rpm, as I'm running a short runner aftermarket intake manifold. For now a standard 255/257° camshaft is used, as I expect an aftermarket camshaft with longer opening times to shift peak torque to even higher RPM. The runners of the exhaust manifold have a diameter I think of 2.25 or 2.5". What do you think about it?

2.25" .. that cannot be right.

with a inline 4-cyl with 2.3l displacement, i've seen a almost 500rpm difference in spool with 42mm -> 38mm runner diameter, with nothing else changing. smaller diam manifold will allow for faster flow which should spin the turbine faster. of course it will start to restrict at some point when the speed of the gas raises nearer to mach 1.

Anyways, i doubt that the channels in the head are 2.25", and thats where the gas is at its hottest ..

[Thom]

Yes, that may be incorrect. I can't remember the actual size, but exhaust valves are 40mm. Exhaust runners may be very close to this value.