Boost Control Essentials

[S2central.net]

Further to the thread below...

http://www.s2forum.com/forum/showthread.php?t=32889

Consider the attached to be definitive reference info for how boost control is acheived on the S2 and essential info on how the wastegate (WG) and wastegate frequency valve (WGFV) work.

It includes info on the factory setup and some alternative layouts for consideration.

In time, I'll add some info on the throttle bypass valve (TBV) as well as consideration for atmospheric dump valves.

[S2central.net]

Just found this vid of some random wastegate under test - it can clearly be seen opening and closing by control pressure in the lower chamber...

http://uk.youtube.com/watch?v=6TlcIe...eature=related

[S2central.net]

And another vid that shows a wastegate being tested on a bench with a solenoid device modulating the control port... The actual WG under test looks to be the most recent generation of aftermarket devices that offers some nice advantages - like being airtight for one thing.

http://uk.youtube.com/watch?v=UBNTWo...eature=related

[S2central.net]

MOre info on this new generation of wastegate - as an aid to understanding the inherent weaknesses of the traditional (including S2) WG design...

http://www.turbomagazine.com/tech/07...ate/index.html

A reasonably common observation on some cars fitted with a boost guage is the fluttering of the needle while building and holding boost... I have always attributed that to the ECUs adaptation of WGFV duty cycle, but I'm now more of the opinion that is some latency in the boost control mechanism caused by the WG diaphragm stretching and contracting during operation. I'll wager tired old diaphragms do more of that than shiny new ones.

[S2central.net]

Oh and here's a good vid of an S2 WG under test with a stiffer spring - its in German, but seems to show it cracking at approx 0.5bar and fully open at 0.9bar... That'll be a 1.9bar (absolute rated) spring then.

http://uk.youtube.com/watch?v=FJ_W6g04xso

[philKS2]

Thanks Paul... being a relatively non-technical person...., how much difference would that Synchronic Wastegate make to performance, and how easy to fit... AMD I couldn't see anything about price/supplier

P

[Greg_S]

Just had a read through that paul, good explanation of how it all works. Would be interesting to see how some of the other configurations work in practice on custom maps too.

[S2central.net]

Thanks Paul... being a relatively non-technical person...., how much difference would that Synchronic Wastegate make to performance, and how easy to fit... AMD I couldn't see anything about price/supplier

P

Pretty sure its a US company called Synapse that makes them... I have no affiliation or experience of them - just found some interesting vids on youtube showing these fundamental things. Biggest advantages IMO are that its air tight (unlike leaky blowby Audi item) and that there is no flexible membrane/diaphragm - both of these will result in more consistent & reliable boost control. The other advantage is that you don't just set mechnical spring pre-load on the synapse item - you can adjust the spring rate as well (somehow)... Allowing you to decide how many mm the valve opens further per psi of pressure after the valve has cracked open.

Haven't looked for price info yet - or how much pain it would be to fit one... Lots of other aftermarket suppliers of WG parts - Tial, Turbosmart to name just two...


Paul

[Jamo]

Yep it's Synapse they won the SEMA awards a few years ago for the wastegate.

There's a lot of interesting stuff on their website, they have no U.K / European distributor when I spoke to them. The owner of the company was a very accommodating gentleman when speaking to him on the phone.

[veneto rs2]

Hi Paul
That's very well done as usual from you.
Can i post the PdF and links on our Italian Club forum?
Of course if yes it will be with the due credits to you and S2Forum

Stefano

[S2central.net]

No problemo...

[veneto rs2]

No problemo...

Grazie mille!

[S2central.net]

And a wee lil videoh attached of my own... Can't be bothered registering and such on utube. A spot of lunchtime testing with a spare WG (from an RS2 crashed in Italy). It took just moments to drill out the WG cover cap with an 8mm bit and prise it out with a screwdriver. That exposed the M6 hex adjuster for the spring preload. I did not need to apply heat in order to break the loctite seal on the threads of the hex key - it released with firm but careful torque by hand.

Using an air compressor and its pressure regulator I was able to get a measure of how extra spring tension adjusts the position of the valve for increasing pressure applied to the lower chamber.

The noises of moving air are caused by blowby from the lower chamber to the escape port. By slowly increasing the control pressure you can just hear an audible change in this air noise as the WG valve opens.

Some other related findings for reference...

The factory setting is approx 2 turns clockwise from where the head of the adjustment key would sit flush with the top of threaded section. From this point I had 12 full turns until the hex adjuster bottoms out... You can feel it skipping off the threaded section and you just need to reverse it on again.

My pressure regulator is NOT ideal for this test - I need one with much lower dynamic range so my numbers aren't terribly accurate, but they did confirm that on the factory setting, the WG is open at approx 0.4bar boost. At approx 1bar boost I found the valve to be pushed all the way to the top where the sound of air rushing down the valve guide changes again - but its still not airtight on the top step.

By increasing the spring preload, I discovered it was possible to visibly reduce the amount the WG valve is open for the same control pressure. I also confirmed the valve would not completely open at the 1bar boost level... Approx 6-8 turns seems to give a good advantage in reduced creep (increased cracking pressure). More than that and I felt the much reduced valve opening at higher pressure might be problematic.

I'm going to swap this cap onto my own WG and see what mechanical pressure it provides on the road and then see how/if the ECU can adapt accordingly.

The latency in the diaphragm is interesting to observe - easy to see how one can get a fluttery boost needle as the WG valve modulates rather lazily and boosted air leaks outta the house.

With about 6 windings applied I found it was possible to open the valve by hand - well two hands holding it with thumbs forced against the valve

Very little 3GP file attached to 'enjoy' this exciting topic a bit more

I have a much better quality MP4 version but can't upload that at the moment.

[johne]

Paul, you're on the way to answering a question I had after the previous thread which is if the ECU controls the boost under closed loop control using the pressure sensor for feedback, why does the duty cycle of the WGFV matter? In fact the WGFV doesn't have a duty cycle as such, it's driven by the the duty cycle output from the ECU and as long as it can reach the required pressure within the duty cycle range the ECU can supply then any WGFV would do???

Great stuff, look forward to reading more

John

[rj scotty]

Cheers Paul

I'm finally starting to understand boost control

Well done sir !

cheers

rich