Soarer Central: New Turbos

Soarer Central Mechanical - TT Turbo Talk New Turbos - big problem!

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Matthew Crawford
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Victoria
Soarer TT

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Monday, February 25, 2008 - 09:00 pm, by: Matthew Crawford (Doink)

Cihan Aday wrote on Monday, February 25, 2008 - 05:30 pm:
Sorry Matt, i didn't read your post properly..
If its on and off at low boost as you say - its definitely compressor surge. Happens with twins as the flow through each compressor is halved at that pressure ratio so they're more likely to surge.

T3G's and generally any high flow will do it under light throttle.

Nothing to worry about. If you hear it at 20psi - thats when you've got a problem.

Ah cool - a weight off my mind, sounds bloody ricey though!! - any idea how lessen this anyone?

If i block off the BOV will it make it sound like a bloody VL turbo?
te last thing I want is that SSChhhh vvvv v v v v v v crap.

Maurice Diggler
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Monday, February 25, 2008 - 09:44 pm, by: Maurice Diggler (Mau_rice)

VL sounds FTW!

Steven Nanevski
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D Day has almost arrived....

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Monday, February 25, 2008 - 09:46 pm, by: Steven Nanevski (Imprestik)

Yeah I noticed this with my new HKS T3G setup as well....

Matthew you obviously would have a set of Lews dumps or something similar?? If not, will a set of Lews dumps prevent this?? I am presuming no??

Michael Keen
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Tuesday, February 26, 2008 - 06:22 am, by: Michael Keen (Spoilt)

Matthew Crawford wrote on Monday, February 25, 2008 - 09:00 pm:

Cihan Aday wrote on Monday, February 25, 2008 - 05:30 pm:
Sorry Matt, i didn't read your post properly..
If its on and off at low boost as you say - its definitely compressor surge. Happens with twins as the flow through each compressor is halved at that pressure ratio so they're more likely to surge.

T3G's and generally any high flow will do it under light throttle.

Nothing to worry about. If you hear it at 20psi - thats when you've got a problem.

Ah cool - a weight off my mind, sounds bloody ricey though!! - any idea how lessen this anyone?

If i block off the BOV will it make it sound like a bloody VL turbo?
te last thing I want is that SSChhhh vvvv v v v v v v crap.

restrict your intake more i guess. are you using the standard air box? what setup you got on that side of things.

Matthew Crawford
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Tuesday, February 26, 2008 - 07:12 am, by: Matthew Crawford (Doink)

Yes Steven, I'm using Lews dumps - altough there is a tiny crack in one of the welds of the dump pipe flange that i need to get sorted.

As for the intake - it's a Greddy AirNX pod.

Cihan Aday
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JZZ30

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Tuesday, February 26, 2008 - 09:33 am, by: Cihan Aday (Cihan)

Restricting your intake won't make any difference (you'll simple lose peak power) so thats an unfounded suggestion.

The problem is *mechanical*, i'll reiterate; the turbo's are making more boost than they can sustain at those revs and throttle opening (low velocity). The air simply bounces off the throttle body and pushes itself past the compressor housing and stalls the compressor momentarily.

Common causes are mismatched compressor and exhaust side turbo sizing. More common with ball bearing units because they tend to come on boost more rapidly.

The only way to get rid of it to some degree is through tuning.

Matthew Crawford
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Tuesday, February 26, 2008 - 10:12 am, by: Matthew Crawford (Doink)

Well that gives me more of an excuse to get it on the road faster and have you slap the emanage on it eh?

Michael Keen
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Tuesday, February 26, 2008 - 05:52 pm, by: Michael Keen (Spoilt)

Cihan Aday wrote on Tuesday, February 26, 2008 - 09:33 am:
Restricting your intake won't make any difference (you'll simple lose peak power) so thats an unfounded suggestion.

The problem is *mechanical*, i'll reiterate; the turbo's are making more boost than they can sustain at those revs and throttle opening (low velocity). The air simply bounces off the throttle body and pushes itself past the compressor housing and stalls the compressor momentarily.

Common causes are mismatched compressor and exhaust side turbo sizing. More common with ball bearing units because they tend to come on boost more rapidly.

The only way to get rid of it to some degree is through tuning.

when i said, restrict, i meant, ie run a large pipe to pick up further down. sum kind of muffling( make the intake tube longer as you can, then the noise wont be as loud.. i think you are wrong saying that it is a misfounded idea.

you cant tell me that a stock system is just as loud as a pod filter straight on the turbo.
have you not seen, sum new cars, with little chambers that run of the intake pipe. this is make it quiter. cheers

i cant see how they turbos are mismatched since they are 2 standard units.

Matthew Crawford
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Tuesday, February 26, 2008 - 06:22 pm, by: Matthew Crawford (Doink)

My Pod is way down in the stock position.

Michael Keen
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Tuesday, February 26, 2008 - 08:01 pm, by: Michael Keen (Spoilt)

move it further away.
i agree yes the turbos, arn't properly matched, but it will be ok. and to get rid of the noise move the pod further away from the turbo. .

Matthew Crawford
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Tuesday, February 26, 2008 - 09:21 pm, by: Matthew Crawford (Doink)

Where do you want me to move it!?? its already behind the headlight!

Michael Keen
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Wednesday, February 27, 2008 - 05:46 am, by: Michael Keen (Spoilt)

down near front bar. just further away, i'm not sure about your set up. it not going to fix the problem but will fix the symptons.

Daniel Clarke
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Wednesday, February 27, 2008 - 09:39 am, by: Daniel Clarke (Dieseltrain)

What about Making Twin intakes? Each turbo having a seperate intake pipe? WOuldnt this eliminate the pulsing caused? Is the pulsing caused from 2 turbos trying to suck through the same small stock pipes?

Cihan Aday
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Wednesday, February 27, 2008 - 12:29 pm, by: Cihan Aday (Cihan)

Michael Keen wrote on Tuesday, February 26, 2008 - 05:52 pm:
when i said, restrict, i meant, ie run a large pipe to pick up further down. sum kind of muffling( make the intake tube longer as you can, then the noise wont be as loud.. i think you are wrong saying that it is a misfounded idea.

you cant tell me that a stock system is just as loud as a pod filter straight on the turbo.
have you not seen, sum new cars, with little chambers that run of the intake pipe. this is make it quiter. cheers

No, i don't see the correlation between restricting the intake and the position of the pod filter. The problem is unrelated to piping, even if piping/resonance chambers/more filters etc did help, it would simply be masking the noise and you'd still feel the loss of torque as the turbo's surge.

The standard airbox has an anti reversion section which restricts reverse airflow through the filter. Most turbo cars do.

The noises you speak of are resonating waves. The longer the piping the lower the frequency of the waves will be - long or short, muffled or un-muffled, the surging problem will still remain.

Think of the bottom x-axis (Air Flow) to be a representation of where your foot is + where the engines revs are. The more throttle you put in, and the higher the revs are ie. The more Air Flow there is.

Think of the side y-axis (Pressure Ratio) as boost. 1 = atmospheric, this means no boost. 1.5 would be nearly 0.5BAR or 7psi.

So, with your foot on the pedal half way and the engine revs at 2000rpm let assume we have 16pounds per minute of airflow (unlikely at 2000rpm, just using to illustrate a point). The graphs use the term 'corrected' because total airflow varies with temperature and atmospheric pressure. Because its a twin turbo setup, each turbo flows only HALF the total airflow the engines actually consuming; that gives only 8lb/min per turbo.

Lets assume our mis-matched turbo combination (like most highflow twins) makes 7 psi with 50% throttle at 2,000rpm. This puts our little green dot about here;

As you can see, the flow through our turbos is under the red dashed surge line. Going over it will cause a surge condition.

Lets say we release the throttle to 25%, flow through the engine (hence turbo compressor) drops. Flow may drop to 12lb/min. Both turbos start to slow down but they're still spinning fast enough to compress the intake to 5psi. This leaves us with a green dot here;

As you can see, flow through the engine is now over the red dashed surge line. The compressors lose their 'grip' on the airflow. Air takes the easiest path so it reverses its direction and pushes its way past the compressor housings. The pulsing sound comes from resonance through induction path. The noise that comes out of the air filter is determined by the overall length of the piping associated with your setup and the velocity at which the air is moving when the compressors 'lose their grip' or 'stall' (ie. surge).

The reason most high flows surge is simple. Toyota (hitachi in our case) designed the CT12a according to the 1JZs airflow characteristics under all throttle conditions. They aren't such a 'big' turbo to begin with, even at part throttle, even if they are getting only half the rated airflow - they dont surge. Bumping the size of each turbo to 300hp plus means each compressor requires more airflow to sustain smooth operation, fitting them with ball bearing CHRA's amplifies the regularity of surges and their severity because they spool fast enough to make even more boost at light throttle openings and low revs.

Is it a real concern (in terms of longevity)? No, not at all.
Is there anything you can do about it? Little, just use some more throttle when they surge.

Matthew Crawford wrote on Tuesday, February 26, 2008 - 10:12 am:
Well that gives me more of an excuse to get it on the road faster and have you slap the emanage on it eh?

Matt, when ever you are ready mate