Gt2860r-5's = Surging & Flutter

[enzan]

i also think there are two issues here (well maybe)

compressor surge of "fluttering" occurs when pressure past the compressor is beyond what the compessor can supply

ie:

workshop A hiflow and do whatever and you go and run the turbo

you dial in 15psi but forwhatever reason (mismatched combo, bad wheel, etc) then manifold pressure ramps to 22psi

the compressor wheel surge's as the pressure past the outlet is greater than what it can supply so it flutters/surge's

i would expect this problem to only occur at full throttle, wide open throttle and aggressive boost building / full load

the other scenario is the common after market twin turbo flutter / chuffing

which i think is a combo of the bov's half opening and venting back and then actuators opening/closing

in a harsh and on/off type fashion instead of soft and progressive.

this only occurs during light / medium load and usually up a hill is a good example of when it occurs

Yes, it's just as you described in your second scenario. But again how are the BOV's opening when I've blocked the vacuum supply line off to them?

[paulr33]

Yes, it's just as you described in your second scenario. But again how are the BOV's opening when I've blocked the vacuum supply line off to them?

that i cannot explain :sorcerer:

[enzan]

The wastegate is located on the Turbine/Rear of the turbo

The surging is from the comressor wheel, which is on the Intake/front side of the turbo

Comp surge (the type we are talking about here) occurs when the turbos are flowing more air than then motor can handle

The air is coming from the compressor side, and has nothing to do with wastegate operation on the rear end of the turbo.

How it is tuned out, i am not sure. I'm yet to go across that in my travels

Yer, I understand the basics of the turbo charger... but is compressor surge something that normaly occurs under full throttle/load conditions? Because this occurs just cruising along a flat section of road in a 60 zone?? But when I load up the engine (3/4 throttle say) it comes out of it??

[paulr33]

i will do some more research into it

[STATUS]

Yes, it's just as you described in your second scenario. But again how are the BOV's opening when I've blocked the vacuum supply line off to them?

the BOV's actually float on their seats more with the vacuum (and pressure to seat remmeber) line dissconected. I predominantly build car for drift and the rapid on/off throttle conditions often leave a bov lagging somewhat behind (poor response and fuel mixture control if vented) and it is common to get this surging effect (different cause but safe effect), it is one of the reasons myself and many others do not run BOV's on our engines. Originally the mechanics from signal auto enlightened me to the problem as i had a similar problem with my 180 and BAI their driver at the time lokked over with their mech and picked it up within a couple of minutes.

i think the key would be for you guys to log (not possible with std ecu, unless you have consult type logger) the AFM voltages as the "surging" 'chuffing' occurs im sure you will find it bouncing all over the joint (this will actually tell you what the airflow is doing inside the compressors and inlet tract).

it would also be interesting to log the outlet pressures of each turbo at the same time and compare them to each other and plenum pressures.

Edited March 19, 2007 by URAS

[R31Nismoid]

but is compressor surge something that normaly occurs under full throttle/load conditions?

Nope.

Because this occurs just cruising along a flat section of road in a 60 zone?? But when I load up the engine (3/4 throttle say) it comes out of it??

As i expect it would. The BOV's leak, thats what they are meant to do.

This avoids this problem... what your expiriencing i've heard of a lot, only when running A/M BOV's because they are locked tight and bring this issue up.

So its odd you get it using the stockers.

As dirtgarage said, he expirienced it. ask him more mayb

[LowRollaBoy]

Ive seen vlt's surge their heads off due to incorect timing. Also bad or mismatched highflows cause surge.

You will never get rid %100 of flutter on light loads even with a bov. Thats an issue you will have to live with, or OEM it and put an airbox on or a really weak factory recirc bov.

[bradsm87]

I believe the intake wheel of the Turbo slows down when you back your pedal off or change gears.

The excess amount of air is pushed back onto the incoming air it has tried to create.

Thus causing fluttering, the longer you drive around the softer this sound becomes.

the harder you push the car...the better the sound becomes

I know what fluttering is and how it comes about but i'm more interested it this 'surging' that can apparently be tuned out.

[bradsm87]

Ok so what do you call it when the wastegates go chu,chu,chu,chu and the car surges and carries on? please elighten me. I've already ruled out the BOV's as I said earlier.... I'm confused

That's when air is going backwards through the afm and the ece registers it as air going in. Still waiting to hear how this can be tuned out.

[700HP-GTR33]

Nah, no boost controler. Do you think it would help?

How do you moniter boost then?

What boost are you running?

More than likely...I bet the boost of the one turbo is not matched with the other then.

Do you know if the actuators are set at the same boost?

Get a boost controller.AVCR....is the best

This has a self learn program which alters the turbo's boost according to how you drive.

[enzan]

I blocked the bleed side of the boost solenoid off today and by doing so dropped the boost down a fair bit, it didn't stop the flutter but it certainly softened the effects. After work I put the boost back to 1 bar to drive home and for some strange reason it hardly played up at all?? The flutter was practically gone! I also noticed the idle was a tad lower than usual for some reason, it usually sits at around 1200rpm and today it was around a 1000, then I had I thought.... could it have something to do with the idle circuit? Obviously my idle control valve is open a fair way for it to be idling at 1200rpm on any normal day, so could this being open so far be causing havoc and confusion with the presure differences either side of the throttle butterflies? Just a thought? Maybe just clutching at straws now!

[Swiper the Fox]

That's when air is going backwards through the afm and the ece registers it as air going in.

Exactly

As i said before...our car was almost UNDRIVEABLE...with only 2530's...chuffing its guts out at light throttle especially up hills.

Tuned by Jim Souvas at Croydons...fixed...

NOTHING ELSE on the car was touched...NOT the blow off valves...NOT the wastegates...NOT the airflow meters.

JUST THE BLOODY ECU.

get it tuned. (if you need a near new power fc and hand controller i have one for sale..PM me)

p.s. with larger low mounts i.e. HKS GT-RS turbo's on a 2.6ltr its more difficult to completely tune it out. Yes even Jim had trouble tuning it out of our car. With the increased capacity of a larger bore and stroke this problem can be overcome.

[Ronin 09]

How do you moniter boost then?

What boost are you running?

More than likely...I bet the boost of the one turbo is not matched with the other then.

Do you know if the actuators are set at the same boost?

Get a boost controller.AVCR....is the best

This has a self learn program which alters the turbo's boost according to how you drive.

you know that a bleed valve can be used or the factory solenoid.

remember that turbos do not create "boost"; they just push air. It is the restriction through the pipes and head that is "boost"; "boost" is merely a measure of resistance.

the turbos themselves do not see "mismatched boost" they spin happily away and jointly create the airflow that the cylinders see.

if one wastegate opens slightly earlier than the other, it should not create a pulse, as it just means the volume of air provided by one turbo is now limited; consider that a motor with one blown ceramic wheel still makes "boost" as there is still one turbo pressurising the air.

[mambastu]

This sounds like turbo 'shuffle' to me. Its quite common on poorly setup GTR's and its nothing to do with blow off valves. Its a problem you can experience with twin parallel turbo arrangements.

You should be able to cure it completely on the 2860-5's/2530 sizes turbos as previously mentioned but the problem becomes more pronounced and more difficult to eradicate on larger twins like the GT-RS/2860-10.

The problem can be caused by exhaust gas flow differences between the turbos causing the turbos to spool at different rates. This can be corrected by tuning to some degree and also a move to a pair of exhaust manifolds with a 'bridge' pipe like the ones HKS do.

Apparently ditching the standard 'Twin Turbo' common top pipe for a hard pipe kit which has longer seperated pipes for each compressor outlet can also help reduce the the problem.

I experienced this on my RB25DETT when I first converted it to twin turbos. I had the luxury of three boost gauges on the car, one on the outlet of each of the turbos and one at the plenum. From the gauges you could see that one of the turbos was boosting slightly faster than the other one. When the 'chuffing' occurred you could see the turbo outlet gauges flicking in time with the 'chuff'.

Adjusted the actuator slightly on the 'lazy' turbo which instantly improved matters and then spent further time mapping the car which eradicated the problem entirely.

There are a few threads about this problem on GTROC.

Edited March 20, 2007 by mambastu

[paulr33]

now that makes sense