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Got Over 400kw Atw?

T04GTR

By T04GTR,
in Engines & Forced Induction

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colinhunt
colinhunt

Let's not turn yet another thread into a discussion about your car, please.

Lithium
Lithium
SiR_RB
SiR_RB

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GTRNUR Grand Master

GTRNUR

Posted
Posted

Matt Tang was telling me his vcam RB28 would push the -5's into surge occasionally. A combination of the added displacement providing a little more exhaust flow than a 26, and vcam inducing more overlap to to gain more mid range torque earlier in the rev range. The advice I heard Racepace gave Matt was that the surge could be tuned out, but at the expense of low end torque, most likely making the vcam retard the intake earlier.

So what we can take from this is that if your engine is optimised to the limit, even -5's will push into surge.

(I'm talking surge here, not shuffle... don't confuse the two)

R31Nismoid Grand Master

R31Nismoid

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Posted

My -5s will surge only on a 5-8 degree morning, full load in 5th coming onto boost. Could be tuned out if i really wanted as you said, any warmer and it was fine so it wasnt a problem. It was more conditions than anything else - such a rare thing that happens maybe once/twice a year.

What is the difference between shuffle and surge as I am not aware?

Same thing, different words

GTRNUR Grand Master

GTRNUR

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Posted

In your case Ash they'd retard the ignition which would make more doey to drive when its hot, and not as fun when its cold...I'd rather have surge than shuffle.

Shuffle can be seen on a data logger when the airflow values read from your twin maf sensors wildly fluctuate. I had big problems with this at around 1800-2000 rpm with my GTRS's as they start making around 0.4kg/cm under full load at this speed. However as exhaust flow isn't enough to spin the turbo's up to wastegate opening speeds, and the engine is running in a vacuum at the throttle bodies the effect is that one turbo will spin up and stall the airflow into the other. Once this happens the exhaust pressure in the stalled turbo swings the shuffle the other way. The GTRS's suffer for this because the compressor is too big for the turbine.

This is why a HKS balance pipe exhaust manifold helps dampen the effect. Also it explains why the split/baffeled twin turbo pipe helps so much, as it allows air velocities out of each turbo to be established before mixing them back into one air stream before the intercooler.

For me, I still get shuffle if I stand on the throttle in 4th at 2000 rpm. It will shuffle (till full boost at 5000 rpm), where exhaust flow and back pressure is sufficent to overcome the shuffle effect. You can drive around this though as really you'd drop back to 2nd or third anyway if you wanted to go faster.

Surge won't effect response, in fact surge is the result of too much response (for a given engine speed). The turbo's are being over driven by exhaust gas flow for a given engine speed. The rate of airflow into the engine (from the filters to the intake valve) is below what is the optimal air speed for the given compressor speed. The effect is your turbo makes terrible sounds as the airflow stalls out and bleeds back to the intake of the turbine housing, which can lead to turbine damage.

I hope that makes some sense. Im operating on minimal speel and 2 glasses of red at the moment...

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

I'd argue the point of surge not hurting response, if its bad enough it can basically have the car "stall" at a given point in RPM until it pushes through.

If low enough in the RPM this can take quite a while.

When i can get mine surging, low rpm/5th/6 degree ambient - it will not go past that RPM point at all even if i hold it there for 10 seconds. I have to drop back to 4th, pass that RPM window (about 300rpm) and then it's fine.

zebra Grand Master

zebra

Posted
Posted

They way I understand surge is that airflow stops because it cant go anywhere, except bleed back out the turbo inlet, so would I be rightin think that airflow stops or even reverses to an extent?

I remember my old highflow would surge like crazy at around 3000rpm in 5th when cruising down the highway, send the PFC Haywire and the motor would cough and splutter then clean up for a few seconds and repeat

could hear it surging a mile away...like a Chappel st VL lol

driving down the highway going tutuutututut constantly

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