Antisurge/Ported Shrouds

[Doward]

In order to understand how an 'anti-surge' compressor housing works (which is technically a 'ported shroud'), you need understand what surge is, in the first place.

Surge: The 'Surge Line' is the leftmost boundary of a compressor map. This is where flow instability occurs - This is where the compressor wheel is spinning at a high enough speed to force more air than the engine can injest. On initial thought, one might think this would just give you more pressure in the intake - and this is true, as long as you are on the compressor map. Basically, the surge line is the MINIMUM airflow needed to keep the pressure from backing up, and causing reverse flow pressure waves - these are INCREDIBLY damaging to the turbocharger!

Follow that thought a little further - when are you constantly seeing high flow of air, but little entering the intake? That's right, when you get off the throttle from boosting. This surging is what a BOV protects the turbo from. You also see this, if you have attempt to spin a compressor wheel such that it is forcing more air into the intake than the engine can take - or attempting to get more boost per rpm of the compressor wheel, than it is designed for.

That said, the ported shroud allows the surge line to be moved further left - this is because the compressor housing allows some of the air that starts to get backed up in the intake, to flow back out the housing.

Here's a pic from Garrett:
http://www.supramania.com/images/doward/Turboinfo/shroud.gif

[sneakypete]

I know im bringing this back from the dead, but at what point anti surge port be used?
reason im asking is that my turbo has an anti surge compressor housing, but i chose to leave the port closed for the time being.
thanks
-pete

[Doward]

If you have it, use it - that's my thought on it ;)

[GrimJack]

I'm not sure I understand. Doesn't this increase the time it takes to build boost?

[Doward]

I've never definitively found an answer to that question, Grim. I see no reason why it would, though.

[IJ.]

All reports I read before buying my 04z was it does add to spool time, I specced mine with a normal Comp cover and it surged like a bitch at low throttle opening/closing as the BoV springs were too heavy to allow them to respond fast enough.

[Doward]

Ian, did you ever run it with a ported afterword? I've always 'heard' that it adds to spool time, but I've never seen it verified, anywhere.

[GrimJack]

Seems logical to me. It's essentially adding a 'leak' to the pressurized portion of the intake tract, right?

[Poodles]

Ported shroud is to stop this: http://videos.streetfire.net/video/True-Turbo-Compressor_163406.htm

True compressor surge has nothing to do with a BOV...

[Doward]

Seems logical to me. It's essentially adding a 'leak' to the pressurized portion of the intake tract, right?

Watch Poodles' video - that's what real compressor surge is - when you are attempting to flow LESS air than the compressor is capable of delivering.

The ported shroud allows that airflow to circle back into the tract, preventing surge.

[GrimJack]

That makes a whole lot more sense. So this is the solution to something ENTIRELY different from what your BOV prevents.

Thanks guys.

[Poodles]

It's also what kills upgraded CT's, or any turbo with a turbine too big for the housing size.

[sneakypete]

i thought my surge was bad. its nothing compared to that video. but i know i have surge.... should i drill out the surge port?
there is an area where the surge port should be. should i open it up?
-pete

[IJ.]

Ian, did you ever run it with a ported afterword? I've always 'heard' that it adds to spool time, but I've never seen it verified, anywhere.

No I just modded the springs in the BoV's so they're more responsive to Off/On throttle and that cured my issue.

I don't know if Kristel still has the vid of when I took her for a drive but it was surging like mad during that run.

[LilMissMkIII]

I do, but it's on a disk somewhere... You need me to try and find it?

[IJ.]

Not unless someone here wants to hear what I'm talking about K

[tissimo]

Seems logical to me. It's essentially adding a 'leak' to the pressurized portion of the intake tract, right?

It will make less power then a non ported cover as well.

[Doward]

Look at the location - you're not in the 'pressurized' portion of the intake - you're just inside the inlet where compression begins.

Tissimo, you've got back to back runs to show this?

[Poodles]

Slightly less power and more lag is a good trade off for not having a turbo grenade (or grenading your engine because of it, look at the dyno in that vid...)

[slowmedown]

Im still learning about turbos/surging but am i correct in assuming if i run my stock (responsive BOV) with an aftermarket BOV like a Tial will this prevent surging?

[gaboonviper85]

Im still learning about turbos/surging but am i correct in assuming if i run my stock (responsive BOV) with an aftermarket BOV like a Tial will this prevent surging?

Nope! And what's your logic behind one recirc bov and one non recirc bov?

[tekdeus]

In this pic of my billet turbo you can just barely see the port line. It is just above the smaller set of fins, but below the larger ones.

My BOV is adjustable and I was able to only put a small amount of spring pressure on it so it opens and vents low boost very easily, but still holds 24psi without leaking.
http://www.echowavepro.com/supraphotos/hta/HTA 061.jpg

[tissimo]

Look at the location - you're not in the 'pressurized' portion of the intake - you're just inside the inlet where compression begins.

Tissimo, you've got back to back runs to show this?

There are several runs on SF where non surge covers make more power. If you think about it it makes perfect sense, the turbo can only flow so much, if you induce a leak (surge port) the air will leak through there and less flow reaches the engine.

[Doward]

Links?

[tekdeus]

How big is the difference on average? 1%? 5%?

[tissimo]

Links?
I'll look later tonight. But garrett states that you'll have a minor impact on efficiency.
How big is the difference on average? 1%? 5%?

I would say less then 5%, more in the 2-3 range.


With small turbos there is no reason to run a ported cover. But if you have a larger turbo, it (having a ported cover) would out weigh the benefits of a non ported cover however.

I'm not sure where the 7m starts running into surging problems. My 1jz with a 67 would surge just a tad in 5th ~ 4000 or so.

[Supra_Villan]

in response to the video:
i don't understand it. what are they doing throttle wise just to make it surge like that? They said they closed the bovs to ensure that they were not a factor, but that in itself is the factor to me. If the excess air cannot be released then of course its going to surge like that.. i'm so lost. :1zhelp:

[Poodles]

it's a normal dyno run, so it's WOT...

[gaboonviper85]

in response to the video:
i don't understand it. what are they doing throttle wise just to make it surge like that? They said they closed the bovs to ensure that they were not a factor, but that in itself is the factor to me. If the excess air cannot be released then of course its going to surge like that.. i'm so lost. :1zhelp:

It's really simple man...don't over analize it! That particular turbo is pumping more air then the motor wants...therefor the pressure wants to excape and it only has two places to go....either the motor takes it or the air backs up and forces itself back out the turbo....

The other type of surge is when the throttle closes and all that fast moving air and pressure bounces back and reverses travel towards the turbo....which is why gas motors have bypass valves, blow off valves, and or some crazy badass shit antilag system that routs that air into the exhaust mani....

The ported shrouds let you force even more air in as it has en escape route for air....the turbo sucks it back in ofcourse as to not create a boost leak.

[Poodles]

It's even more involved than that, it's closer to cavitation...

[gaboonviper85]

It's even more involved than that, it's closer to cavitation...

Which is why I told him to not over analize...yes there will be a point where it just won't be able to breath anymore air and proceed to chop air causing massive turbulance ect....

Another way to explain this would be why helicopter can't hover for prolong periods very close to the ground as it causes a massive vortex and the blades just start chopping instead of "flying".

[bfr1992t]

it's a normal dyno run, so it's WOT...

That was a on a load bearing dyno, notice rpm is held at just over 4000 (top left of video on dyno screen).

[Poodles]

I sure doesn't sound that way, and it's going to zero when the car is clearly on...

[bfr1992t]

I sure doesn't sound that way, and it's going to zero when the car is clearly on...

It sure is, with steady state. Note how rpms shoot up to 4k (held by the dyno even at WOT), and then boost builds. Look closely at the start of the video, you can see the a Dynapack attached to the rear hubs. They even say it in the text "On Load, On boost..."

The turbo spools fine for a bit before the charge starts stacking up, it's the chirping that is surge.

Great find however, I've never heard it so clearly.

[marcusgnf]

would a ported head help with this? just wondering when u start having this problem what can u do about it? or do u just have to get another turbo

[CajunKenny]

Good stuff right here!

[tekdeus]

Interesting how in the video, the surge slammed the boost from 20psi to 15psi in an instant, and caused dips in power to show on the dyno graph.

would a ported head help with this? just wondering when u start having this problem what can u do about it? or do u just have to get another turbo

I believe the turbo in the video did not have an antisurge housing. This is why they make turbos with antisurge/ported shrouds ;)

[IJ.]

Surge will do that as it tries to stall the Compressor and is why it can be so destructive.

[Poodles]

exactly

[AndyMac]

just for the record, I have a t04z with a surge protected housing. I get no surge whatsoever at any throttle condition.

I havent noticed any difference on spool times really either.

[IJ.]

My 04z surged like a bitch till I tweaked the BoV's.

Before the tweaks mine sounded like "Powered By 3Stooges" if I was on/off the throttle over 15psi.

[Supra_Villan]

just for the record, I have a t04z with a surge protected housing. I get no surge whatsoever at any throttle condition.

I havent noticed any difference on spool times really either.
you sir need a build thread :)

[AndyMac]

you sir need a build thread :)

I sir have one ;)

http://www.supramania.com/forums/showthread.php?t=91507

[nosechunks]

Would the surge, or stall be incurred when the exhaust push on the exhaust wheel isnt strong enough to continue to spin the shaft against the load on the compressor wheel?