Silvia Club of NSW

I have a T518z on my S14 and its surging pretty bad. In 3rd/4th gear <3500rpm, the turbo can easily produce >1bar of boost and thats when it starts surging its guts off and wont stop unless I ease off the throttle a bit. Its kind of sad really, because its great being responsive at lower RPM but the surge is making the whole affair ugly! The surging goes away past 4500rpm. I understand surge occurs when the motor is unable to 'swallow' the airflow provided by the turbo.

Any ideas on how to stop it? Sure I can turn the boost down but you can't say no to 1.3bar at 3500rpm! I'm thinking it might be a camshaft issue (HKS Step 1s)? NVCS not functioning properly? Less retard on exhaust cam (-2 retard atm)?

The only way you will stop it is to make the engine breath better at that point or to reduce the efficiency of the turbo by changing up the exhaust housing size.

What size step ones? 256/256 or 256/264 ? and where's the exhaust cam timing set atm?

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meh

Less retard on exhaust cam (-2 retard atm)?

Why is the exhaust cam retarded?

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oops, i missed that

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meh

Pardon my lack of experience but how exactly do you know when the turbo is surging? What are the symptoms? or is it more of a feeling thing?

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I didn’t break it, I just modified the operational status...
There are 10 types of people in this world, those that understand binary, and those that don't.

Boost fluctuations, you can hear the thing chopping at the air in the same way that a car without a bov does on gear changes, can cause the car to shudder pretty badly in extreme cases

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meh

So this is basically an overboost condition for limited throttle position? Shouldn't the BOV take care of this? Hmmm on second thoughts I am guessing this condition occurs before the BOV has reached the point where it activates...

Probably not a good comparision but is this something like running out of fuel? that kind of surge?

My Haltech allows me to alter the boost controller percentage for given load point, Busky2k do you have this option?

_________________
I didn’t break it, I just modified the operational status...
There are 10 types of people in this world, those that understand binary, and those that don't.

Thanks for the replies guys.

The surge sounds like a rapid 'choo choo choo' type flutter once theres more than 1 bar made under 4000rpm. The car does buck very slightly but its nothing major. On the dyno I first noticed it as the air intake pipe was shuddering with the aformentioned noise as the operator was loading up the car for the run.

HKS Step 1s 256/264. -2 retard was where the previous tuner put it at, and I believe thats a good thing? I don't know the exhaust housing size. It might be an 8cm. Any way to tell via serial numbers?

Maybe this is just an excuse to go larger on the turbo? lol.

This is starting to sound familiar.. Got a feeling I may have read about it in an old turbocharging book.

Not sure a bigger turbo will help the problem if you have too much boost now. (guess you know that) Is there a restriction between the turbo and the intake?

_________________
I didn’t break it, I just modified the operational status...
There are 10 types of people in this world, those that understand binary, and those that don't.

interesting, did this only start happening recently or has it always been like this ?

Didn't see your reply as I posted mine 182Go! Anyways the BOV is definitely not activating as its on the opposite side of the car. I don't believe its overboosting because the AVCR does not see it, and it'll do it even with the throttle wide open (so there goes the theory of the turbo overboosting into a partially open throttle plate). Fueling is OK as reported by my wideband.

The only restriction I can think of is the yumcha FMIC but its a bar & plate design and doesn't appear to be restrictive at all. But who knows?

Its always done it but hasn't really bothered me because I only drive the car a few times a month. But last week when I went on a hills run, it drove me nuts because every time I stabbed the throttle at midrange RPM it would make the surging sound (although it still drove OK!). It won't happen in lower gears. I'm just worried the surge is murder on the thrust bearings of the T518z too.

Might put the exhaust cam back to 0 deg. Although I can't see how that'll fix anything.

compressor surge under load definately isnt doing your turbo any favours, especially since yours is journal bearing.

have you tried a different boost controller ? try running a direct vacuum feed to the wastegate, i know you will get slower spool up but its good for eliminating possibilities, whos knows maybe your AVCR is screwed.

i dont think it will be your FMIC, if it was too restrictive you would probably get surging over a larger rpm range as flow just increases

Dont take this as gospel as I have no real life experience of this condition and I am only offering suggestions to try help... but from what I can remember of what I read the turbo can reach this unstable condition both sides of the optimal curve. Is this condition been caused by lack of air???

You mentioned the intake was pulsing is the air filter too restrictive causing it to pulse?

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I didn’t break it, I just modified the operational status...
There are 10 types of people in this world, those that understand binary, and those that don't.

i think the left side of the islands on the compressor map was surge, and the right side was choke which was the compressor maxxing out and also the turbo reaching too high an rpm, so its a different condition

if it was lack of airflow though, the car wouldnt be making power, and hence wouldnt be making boost either to cause this sort of compressor surge

Yeah I started thinking that myself after I posted... it wouldn't possibly reach those boost figures at those rpms if it was not enough air.

_________________
I didn’t break it, I just modified the operational status...
There are 10 types of people in this world, those that understand binary, and those that don't.