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Rb25 Billet Turbo Boostcreep/overboost Problem

benelli

By benelli,
in Engines & Forced Induction

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benelli Rookie

benelli

Posted
Posted (edited)

Hi,

Alirght, i've been searching on here and around the internet for the past 4 days trying to find a a solution but so far nothing 100% certain.

I had a stock RB25 turbo high flowed and worked on to take a billet compressor wheel and stage 3 turbine so turbo should be good for 450hp

The specs i got from the shop are this:

Compressor housing is stock modified stock modified/bored out for the bigger wheels

Turbine housing is the stock modified/bored out for the bigger wheels

Comp Wheel 54mm/76mm billet

Turbine Wheel Stage 3 Garrett

The turbo also had the stock wastegate actuator converted to be adjustable and was set 9psi

so from the looks of it i figure the turbo should be somewhere around a gt3071 or gt3076 equivalent.

The car has blitz return flow front mount, 550cc injectors, Turbosmart FPR, Apexi Fuel pump, 3 inch turbo back exhaust w/bell mouth 3 inch downpipe, straight pipe (ie. No cat), Apexi super suction intake kit, Nistune for RB25, Z32 MAF

For boost controll we had a Hallman MBC controller put in temporarily and then later on AEM Tru Boost would be used permanently.

Took the car to the dyno and....we can't controll the boost. It hits 15psi around 3000 and by the time it reaches 6000 it's hovering around 25psi. The boost curve on the dyno graph is a straigh 45degree line with no taper. Shoots up and keeps going up.

Took out the boost contoller and ran the Vac line from wastegate to nipple on the compressor hot side pipe and same thing happened.

Removed downpipe check for obstructions, nothign there ....just a nice big 3 inch bellmouth

Checked all the piping and no leaks, ran air compressor to wastgate and it opens normally at 9psi.

Looked at the Internal wastegate port and it's been ported/bored out to max, anymore and you compromise the exhaust housing.

Any of you have any suggestions or solutions? Maybe you guys ran into a similar problem?

Only thing I can think of at this time is the internal wastegate port is just too small and can't flow enough exhaust gas to control boost. Which means turbo probably needs external wastegate? Or the stock bored out nissan housing is way to small causing restrictions. I don't want to go external wastegate as I am really only looking for 320rwhp to 340rwhp (240rwks - 255rwkw) and its just a street car. Hoping i would be able to pull something close to that with internal WG setup.

Next step is just putting back in my old semi upgraded Stock oem turbo and dynoing that to see what i get and calling it a day.

any help would be great!

thanks!

Pic of exhaust side of turbo:

pRUoyaXl.jpg

Edited by benelli
FordyR31 Mentor

FordyR31

Posted
Posted (edited)

Is the wastegate flap opening all the way? Is anything obstructing the actuator bar when installed in the car? Could the wastegate flap be catching on the dump pipe when its fitted? The dump may be suited to a stock turbo but the larger flap may be fouling somewhere and not opening fully.

Edited by FordyR31
FordyR31 Mentor

FordyR31

Posted
Posted (edited)

He said a bit down the post he had it bored out/enlarged already.

With the turbo off or at least the dump off, disconnect the actuator rod and make sure the wastegate opens fully anyways. Hard to tell from the pics but it almost looks overlapped by the housing near the turbine wheel side of the gate.

Edited by FordyR31
r32-25t Grand Master

r32-25t

Posted
Posted

He said a bit down the post he had it bored out/enlarged already.

i skipped that bit

Either way it's not flowing enough, weather it be the flap isn't opening properly or it still isn't big enough. The other thing I've seen is someone ported out the wastegate and it still over boosted. It turned out there was no taper directing the gasses into the wastegate, so we grabed a die grinder put a taper in it and problem solved

benelli Rookie

benelli

Posted
  • Author
Posted


Wastegate actuator and the bar itself is fine and nothing is obstructing the flapper. My tuner was looking over the car and disassembled the actuator and put it back making sure it as correct.

The WG hole has been ported already and it can't be ported any further without compromising the exhaust housing.

I'll take off the dump and look at the swing valve and see if opens fully just to be sure again, but I'm pretty certain it should be ok.

At this point i'm pretty much stumped and so is the tuning shop. They even loosen the pre-tension on the WG to see if it helps but nothing is working. We're overshooting boost by 15-20psi on average.
Any of you run Hypergear turbos and run into similar problems?

This guy in the UK ran an HKS turbo and had similar troubles as me and we tried very similar steps;
http://www.skylineowners.com/forum/showthread.php?t=184880

What about a 4 inch downpipe or something?

Ben C34 Grand Master

Ben C34

Posted
Posted

Part of the problem with Highflow turbos is they are a bit of a lucky dip, unless you can see previous proven results. If you have a peak at the Hypergear thread you can see how much R and D Stao has put into his range.

I assume the supplier hasn't done one like this before, and you are a bit of a guinnea pig. It does seem like a huge turbine for the stock housing.

I am sure Stao would be able to help out, but I notice you are in Canada, so a bit far away. Maybe if you ask him nicely he might point you in the right direction.

hypergear Grand Master

hypergear

Posted
Posted

Well I don't have this problem the high flow profiles I do has been welly sorted and trailed. The configuration of this compressor appears to be too big for the turbine side. But yes I can fix it.

benelli Rookie

benelli

Posted
  • Author
Posted

THanks for all the input guys.

@

Definitely! THats what I learned the past 2 years that without proven numbers, it's almost a guessing game. I've been following Stao's threads and I am always glad that at least there is someone out there that will make products and prove their performance.

@@hypergear

Thanks for the info! Problem is im in Canada where we can freely modify anything we want...but there aren't that many good shops around to help us modify. Btw, how would you fix it? Would you have to disassemble the turbo and swap out the compressor? or is it a more simple fix?

GTScotT Grand Master

GTScotT

Posted
Posted

FYI the spec is actually equal to a t04e with a billet wheel, thus the stage 3 rear.

Have you tried watching the flapper open when it boosts? Maybe the actuator itself doesn't push it far enough

Frosty Grand Master

Frosty

Posted
Posted (edited)

THanks for all the input guys.

@

Definitely! THats what I learned the past 2 years that without proven numbers, it's almost a guessing game. I've been following Stao's threads and I am always glad that at least there is someone out there that will make products and prove their performance.

@@hypergear

Thanks for the info! Problem is im in Canada where we can freely modify anything we want...but there aren't that many good shops around to help us modify. Btw, how would you fix it? Would you have to disassemble the turbo and swap out the compressor? or is it a more simple fix?

why not just weld the wastegate shut and run an external if you can get away with it....Will solve alot of issues and more than likely have better boost control

Edited by Frosty
hypergear Grand Master

hypergear

Posted
Posted

To get a compressor as large as this to work you will need to remove the actual gate assembly and then install a 38mm disc while machining the wastegate gate whole to about 36mm. Even thou Its still very small for the compressor setup which means the turbine side will go red hot. How ever that should stop the overboosting problem. Example of some thing that we often to do XR6 turbochargers:

gate1.JPGgateopen.JPG

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