1UZ TT Turbo Pulsating

[Hillbilly]

Hey guys, finally got my monaro up and running and its bloody awesome.
Car has had a basic road tune and will be haeding back to get final Dyno tune done this week.
Cant believe the power these motor's make while keeping thier smooth driveabillity.
Anyway have got one issue with the turbo's. They are Garret GT28R turbo's (The unit formerly known as "the GT28R" (part number 466541-1) is now in the GT25R family. More specifically, it is now a GT2560R model).

I start by removing the air intake filters, i then get someone to hold thier hands close to the turbo intakes while increasing the engine rpm to around 3000, you can feel the turbo's suck you hands in then they blow back then suck in then so on. I have been told that they are pulsating rather like it would do if you had miss matched turbo's. Any one have any idea what this is caused by or how i can fix it.
I have a turbosmart blow off valve fitted
Is running 7lb's of boost
Front mount intercooler
Brand new matching turbo's
3inch dual exhaust

 

[JustenGT8]

2 things spring to mind...you are hitting the surge line ie the turbo is trying to make too much boost too low in the flow range which suggests to me you need the bigger a/r turbines...OR...your boost control is mismatched so your turbos are alternating making and dropping boost.

Where are you getting the wastegate control feed from?

 

[Anaema]

or your wastegates could be too big.

 

[Hillbilly]

Turbo's have internal waste gates....
Waste gate vacum line comes off the intake pipe halfway between the intercooler and the throttle body, then goes to manual boost controler and then tee's off to the waste gate actuator's...

 

[JustenGT8]

OK your vac lines to the wastegate is a good place to start. There should either be a port or a boss for a port on the compressor housing. Just run the vac line to each wastegate from the comp housing, that's the most accurate signal source for the turbos.....this is how i run my TT setup and i have never had boost control or surge issues

 

[4000GT]

The blade can only spin one way (suck), how can it blow? As in, a technical reason...

 

[Lextreme II]

If you compressor is blowing air our from the inlet that means your BOV is not reliefing the compressed air... double check your vacuum line or lines to the BOV. Second situation is that your vacuum line is too long and delaying the signal and not openging fast enough so the compressor air escape via the compressor. The third possible cause is the your BOV is too far away from the TB and create delay response. Fouth is that your vacuum line is shared with too other vacuum lines and create weak or reduced vacuum pressure and creating delay response.

 

[JustenGT8]

The blade can only spin one way (suck), how can it blow? As in, a technical reason...

Time to do some research dude...a number of situations where a pressure wave will pass backwards thru the compressor housing/wheel.

 

[4000GT]

If you compressor is blowing air our from the inlet that means your BOV is not reliefing the compressed air... double check your vacuum line or lines to the BOV. Second situation is that your vacuum line is too long and delaying the signal and not openging fast enough so the compressor air escape via the compressor. The third possible cause is the your BOV is too far away from the TB and create delay response. Fouth is that your vacuum line is shared with too other vacuum lines and create weak or reduced vacuum pressure and creating delay response.

That is compressor surge and usually promotes the compressor to stall, not reverse it. And there is no way there is enough pressure in the system to cause compressor surge by revving it.

We are talking about suck to blow right, not sucks a lot and then does suck as much?

 

[4000GT]

Time to do some research dude...a number of situations where a pressure wave will pass backwards thru the compressor housing/wheel.

Thats not a technical reason, thats just you saying it can...

 

[Hillbilly]

That is compressor surge and usually promotes the compressor to stall, not reverse it. And there is no way there is enough pressure in the system to cause compressor surge by revving it.

We are talking about suck to blow right, not sucks a lot and then does suck as much?

The compresor wheels dont stall but there is definately air coming out of the inlets.

Thanks everyone for taking time to help nut this out.
I have attached another pic that shows where vacum lines etc are placed.

BOV is a non adjustable one but will borrow one tonight and see what that acheives.

Cheers guys.

 

[krayn]

Congrats on the neat setup. Well done.

What happens if you remove your boost bleed of valve and connect the wastegate actuators directly to your boost reference point? What size lines are you running from your boost reference port to your wastegate actuators? If these are too long or too large it will take longer to build up enough pressure in the line to activate the wastegate. Is there any restrictions between your boost reference point and the actuators?

 

[JustenGT8]

Thats not a technical reason, thats just you saying it can...

Hmm kinda suggesting you do some reading yourself as the reasons are laid out in any decent turbo text. Yes this is a great place to learn but you are asking questions on someone else's thread...maybe i'm just old skool but i learnt most of what i know by teaching myself or maybe i'm just a cranky old bastard

However, free revving will easily see both surge and reversion of the throttle plate....both of which will pulse air out of the comp housing. I can do this easily any any turbo can i have owned or worked on. Third way this could happen is if the turbo wastegate control gets out of sync ie. one turbo is boosting and the other is not...the air takes the easiest path one of which will be out of the non boosting turbo

technical enough???

 

[Pro]

the only reason i can think that you are getting air coming OUT of the inlet when you free rev it, is that the turbos chosen are too small and providing +ve pressure with no load (this should never happen) and then engine is not consuming said pressure fast enough (free revving remember - no load) and the "excess" pressure is finding it's way out of the compressor inlet.

but, that bugs me because your compressor bypass valve should be operating and venting said pressure.

is it hooked up right?

 

[1ndecent]

Justen's advice is spot on, the turbos are not too small. Perhaps you should fit a true compressor bypass valve like an OE Bosch unit (as opposed to a blowoff valve), if the reversion is bothering you. You don't appear to be using an airflow meter, is the reversion actually causing a problem?

 

[JustenGT8]

Come on, i bet anyone here can get positive pressure free revving. The compressor/turbine have mass.... you give 3 or 4 good revs and i guarantee you'll get compressor surge and/or your bov giving a decent vent.

I'm currently sorting a massive TO4E on a 4cyl and i can see a good 3-4psi boost free revving. How do you think anti lag works, there's no engine load but the compressor revs are there...i've seen 15psi boost on antilag sitting in the workshop. Hell on your ears i gotta say

 

[Hillbilly]

OK should of said this before, thought i had....
But it also has this problem when i drive the car.
I can drive along at about 3000 rpm in any gear and its fine but if i decrease rpm slightly i get the surge. Under accelaration its ok and when changing gears the bov vents and i may get a little amount of surge.
It seems to be mainly at the point where the bov is not able to vent that it does it.

 

[Pro]

not counting antilag dude! geezus - that was DESIGNED to create boost from idle!!! that works by making combustion almost happen in the exhaust manifold!

hillbilly is talking about 3000 rpm here - if my turbos were making +ve pressure there - free revving - i'd be changing compressor housings.

just a thought anyways - no need to bite my head off.

 

[Pro]

then your BOV spring is set for a higher psi setting than your turbos push into the engine.

not by a bit like most, but by a fair bit more. if you're running 8psi, check it's not a 12psi spring etc

 

[Hillbilly]

Just took a couple of pics of the waste gate actuators, as you can see i had to modify one of them by moving the mounting bracket from the front of the compressor housing to the rear of it thus also had to shorten the actuator lever. Would this have any effect?