Surging?

[Dum-Dum]

It occurred to me the other day that many people talk about turbos surging and this being bad but I dont fully understand the how and why and also why its bad.

Can someone please explain it to me.

[n0v0s]

http://www.turbobygarrett.com/turbobygarrett/surge_line

And finally,

http://www.turbobygarrett.com/turbobygar...ssor_surge

Should be all you need. In your case, a large vnt creating lots of instantaneous airflow just off idle which can't all be fed into the engine (at the lower rpms), will cause surge if you just floor it. Port the f*ck out of your head and fit anti-surge housing. Sorted.

[samass]

'surging' - commonly known as 'gushing'

[darrenjlobb]

When you start surging a vnt down low, you will instantly realise why its bad, it sounds f*cking horrific

[Dave]

Lol bouncing boost 50psi back to 0 and back upto 50psi, my vnt loves it. not.

[Dum-Dum]

Lol bouncing boost 50psi back to 0 and back upto 50psi, my vnt loves it. not.

Ouch. Mines making almost 5psi of boost when cold cos its hunting so badly just 5psi to 0 and back to 5psi again.

[darrenjlobb]

That's not surging tho is it....

[Ruan]

Surging is simply where the turbo is pushing out a chronic amount of air at a low shaft speed, therefore not much intertia behind the wheel, therefore it becomes easy to cause the flow to become unstable (that's the fluttering noise you'll hear) then when it gets really bad the turbo will start stalling... Imagine a 'stall' in aircraft, simply the aerofoil stops producing lift because the airflow over the wing is too high for the requested angle of attack... The turbo stops moving air and slows rapidly, causing massive stresses on the shaft... It's the same phonemenon as when a petrol lifts the throttle and the turbo barks away as it rapidly slows down, but the difference is that you're also on the throttle, there is drive to the turbine wheel, so its trying to rapidly bend the compressor off the shaft and press the compressor wheel back and forth... Hence we say it rapes the turbo...

Ways to solve it, reduce the boost at lower RPMs, make the head flow better at low rpms, but often its a combo of inlet pressure causing high exhaust pressure, causing high inlet pressure etc etc... I.e. the turbine side can't flow enough as the vanes are set too closed, the head can't flow enough at that rpm, nor can the engine consume that much at that rpm and the compressor is spinning to slow to increase the pressure, so it stalls as that's the easiest option...

This is why I say you have to understand that with VNTs boost is easy, you need to look into how to control it well...

[strictly_perv]

That's why I'm not going to run my VNT on boost alone as it will probably surge when cruising with my short gear box.
The idea I'm hoping to use is a cable connected to the throttle arm to control the vanes but as it builds boost up a inverted VNT act' will be used to open them. I would love to do an electronic control but I'm simply not clever enough to work out all that stuff.
Thoughts?

[Matty]

That's why I'm not going to run my VNT on boost alone as it will probably surge when cruising with my short gear box.
The idea I'm hoping to use is a cable connected to the throttle arm to control the vanes but as it builds boost up a inverted VNT act' will be used to open them. I would love to do an electronic control but I'm simply not clever enough to work out all that stuff.
Thoughts?

Found that lol...

[Pompey306mark]

I have seen that set up.

Wonder how well it works.

[Jake]

I have seen that set up.

Wonder how well it works.

Looks cool though haha.

[strictly_perv]

That's why I'm not going to run my VNT on boost alone as it will probably surge when cruising with my short gear box.
The idea I'm hoping to use is a cable connected to the throttle arm to control the vanes but as it builds boost up a inverted VNT act' will be used to open them. I would love to do an electronic control but I'm simply not clever enough to work out all that stuff.
Thoughts?

Found that lol...

Exactly the one I was planning to copy! Looks a good idea, can't see why it can't work. I'd set it up so the vanes don't really move until just before half throttle maybe.

[Ruan]

You don't want it like that, trust me, once you see how good VNTs are when closed up, you'll realise why it's pointless doing it like that, you may as well have gone for a big wastegate turbo, it's not dynamic at all, the amount the vanes have to move is miniscule... People are thinking that VNTs are way less responsive than they actually are!!! Vanes fully open, you won't be getting any boost until gone 5k, it's like it's a nasp...

http://www.youtube.com/watch?v=Lzc5EDff0e0

You can't really see the boost gauge, but you can hear the turbo spin up as soon as you go near the throttle... You'll have NO midrange torque if you leave it until 50% throttle! The first part of the video where I'm accelerating lightly, that's maybe 20% throttle - the torque midrange is simply unreal with them set up well...