how to prevent surge?

[Prophet_dlx]

I'm trying to understand this,
what does the big DV do, limit the flow or limit the prssure
if it is boost, isn't it already controlled by ECU trough mapsensor > N75 > WG in relation with RPM
So surge could be prevented with the right map....?
what is the interest of producing boost just to dump it afterwards.
Might make sense on a mechanicly controlled boost level, but not that much on motronic, right?
as my knowledge in these matters is still a bit rough (me being kind with myself I don't say anything is wrong or right.
just wanted to know what you people think of this.

[Jamo]

Real life testing results on the car in question

Small DV with stiff spring = surge

Small DV with weak spring = a bit less surge but a fluttery top end with inconsistant power delivery

Because the big DV only needs to open a minute bit in comparison to small DV to bleed of the same amount of flow you can keep the stiff spring and not have any adverse effects at high boost and high rpm. The end result being:-

Big DV with stiff spring = no surge and nuked gearbox within a 100miles

As a reference with surge the car made 459hp and 462hp tested on 2 independant dynos over 300miles away from each other after being mapped by Quattronics - he never did get back to adjust the map after the surge issue was addressed as after the gearbox blew he decided to break it as the car was too lively (Seat Ibiza) and wanted something milder out of fear he was going end up getting hurt. Asides from the fact the car was worth more in bits he didn't want to sell it to an unsuspecting driver and have their death's on his conscience either.

All I'm relaying back is the results that worked for my mate based on information that has been proven time and time again with other car brands through the years. So by opening our minds and trying something that isn't supposed to work we found a solution that was simple and effective.

It's a similar concept to running an oversized wastegate to bleed of excess exhaust gasses once the desired boost threshold has been reached. Thus releasing valuable hp by reducing backpressure, reducing egt's and subsequently allowing the advance of timing for more hp. The minute the turbo is not achieving the desired boost threshold doesn't matter how big the wastegate is it will close.
That very method was used by a reknowned tuner that made 587hp from a GT3071R on an .84 backhousing. Same principle as reducing surge with a large DV but on the other side of the engine.

I switched off after a certain word

[JP]

The big DV reduces pressure when there is too much. If you fit a big turbo that is flowing a lot of air it doesn't matter how advanced the boost controller is there is always a chance of hitting surge at low rpm or when accelerating from cruising speed.

From my limited experience of electronic boost control playing with a blitz iD spec R unit and a couple of other brand names like Greddy you set the boost you wish to make and how quick you want to get there. Sometimes that means somewhere on the curve as the boost is climbing you will get a situation on a big turbo where it is flowing more air than the engine can swallow. This then creates a pressure build up stalling the air causing the chopping surge noise as the turbo is trying to spin against a stagnant airmass. By giving an escape route for the pressurised air it allows the turbo to freely spin without surging until the engine can swallow it again at which point the alternate (DV) escape route closes.

The biggest problem I have found with all of these controllers other than the dual solenoid blitz unit, is that they are prone to overboosting as the frequency valve can't react quick enough. Ultimatelly I've seen a couple of big turbo cars go bang because of this. These same people have gone back to the old skool mechanical way of mapping boost with springs and bleeding of to atmosphere giving much more reliable peak boost control.

As I don't do mapping and will never pretend to I can't say how much control the Motronic units have, poss a question for S2central?

[JP]

I switched off after a certain word

?you lost me too technical?

[terrybullwon]

Quattronics

He ment that word. Its a Joke.

[S2central.net]

I think these things surge when people try to make them boost much too early - either by ignoring the compressor map - or having a clue what a compressor map is.

You can definitely remove / reduce surge under Motronic control by careful modulation of the WGFV... making the turbo stay within its operating limits. If you have too much duty cycle dialled in at low revs for a 'desired' boost level then its gonna surge.

The reason for some engine destruction blamed on solenoid valves is not so much that they can't go 'fast enough'... Its cos they can stick and put the turbo in a situation where boost control via the WG is being impaired. In that situation you want some way to alarm the driver that boost control is impaired and also as a failsafe that the WG valve can open by itself under exhaust gas pressure - assuming that gets high enough to relieve pressure before the engine melts down.

I still don't fully understand how these DVs are controlled in the real world for surge reduction. Its almost in the 'orrible world of bleed valves and other inefficient schemes... Which aren't so bad in knowledgable hands I suppose.

[Prophet_dlx]

AFAIK every turbo surges if you map it passed the surge line. It is a well known problem on 1,8 20v T even with the tiny K03, mainly because the intrenal wastegate can't handle the bigger amount of exhaust gazes 'cause the boost is way too high. Might be wrong though.

That only happens on weak dump valves. When you have cars producing high boost you can't use weak sprung valves as they would open under load constantly.

I'm with Jamo on that one, you could for example have surge @ 1.7 bar between 3000 and 3800 and at the same time be fine with 2.1 bar above 4k. How does a DV makes the difference between between surge and boost at wot?

just asking

[QuattroFever]

Sorry, but I dont like this idea at all. Personally wouldn't recommend it but I get were you're coming from. The dv has two +ve sides the small bore tube and the large port and the third is either recirc or atmos. when the turbo provides more air than can bleed off in a given time the small bore tube forces the piston shut. Its a very crude method and is governed by the spring tension so your output is dependant on the quality of a spring that gets cycled ALOT. As paul said with the right duty cycle on the wgfv it really shouldnt be an issue, and if your wastegate cant flow enough to keep the thing under control then ideally you should bite the bullet and get a bigger one and/or port/polish the head.

[Henkjan]

recycling pfrom the pressure side back to the inlet is exactly what a surge cotrol on an industrial compressor does. but this is governed by it's own control system, ofter a high integrity PLC given the large safety hazard an exploding comressor is... but in theory you could do the same in yr car: if you have a control valve and a controller that uses the airflow, temp, and boost pressure as input, it can keep the turbo in its safe operating range with enough flow at higher boost.

[Jamo]

Pretty fancy solution to something that can be controlled by a good ecu map!

[denniselbows]

just a few questions for you all
1 when do you get surge? is it at wot only or at any time when under load
2 when surge is pessent is there a boost pressure rise
3 how much boost pressure rise would you see and is it messurable

[Henkjan]

Pretty fancy solution to something that can be controlled by a good ecu map!

yes and no... with surge control you can in effect run in areas of the compressor map that an ECU only control would keep you out of

[Jamo]

yes and no... with surge control you can in effect run in areas of the compressor map that an ECU only control would keep you out of

But then your spending more compounding the fact you've picked the wrong turbo for the application in the 1st place.

[S2central.net]

All turbos surge when pushed excessively past that surge line... Its a fact...

Some turbos are more likely to surge than others for a given load / flow point on certain engines.

You can't build a turbo that flows enough air at 2000rpm for 500Nm of torque and has enough puff left for 500bhp at 7000rpm.
You select the turbo for the desired operating performance and that will mean some trade offs in the low-mid range of mid-high range depending on what you want.

If you disregard the surge lines then you'll get surge issues. Good turbo selection, matched to the engine characteristcis (sometimes tricky with oddball cams and/or exotic fuel for example) is the key here, but also good boost control as well... With or without Motronic - if you try to build boost too soon then you risk getting some surging. I'm not a big fan of the bleed valve methods - a bit agricultural - but I understand the story of giving the compressor a means of relieving the pressure in that way by letting the airflow somewhere if the engine can't consume it. Question is that any more effective than reducing the boost at those load points so it doesn't surge in the 1st place.... Curious.

[Ross]

I guess you could argue that the turbo would be responsive - once the engine is ready to take the air, DV closes and there's no spool-up time as the turbo is already spinning.

Personally, I'm for the right-turbo-for-correct-application and control it via WGFV. But each to their own of course... the mechanically controlled cars do have their advantages, tend to be more aggressive with less safety features but not my preference for a daily driver.