RB30DET can only run 7PSI

[Guilt-Toy]

I just got the LT12 in the rb30det.. goes great on 6 7 psi.. but cannot get anymore...

I have tried to open the bleed valve right up.. no more boost.. even tried a huge spring on the wastegate which made NO difference.

The turbo is a RX7 hitachi / t4 60ar combo.. it was making 17 18psi with the rb25...

[Cubes]

Made any other changes apart from the motor? Exhaust manifold?

Sound more like a dodgy wastegate or issue within the exhaust... What condition is the cat in?

[Guilt-Toy]

Cat is not the problem =)

I do have a HKS supa dragger mufler at the rear with twin outlet. maybe its not flowing very well? zorst is 3" mandrell

[Cubes]

I tend to think its the wastegate.

Some times things happen coincidently.

Unless the head is flowing much much better for some reason and the 6-7psi is maxing out the turbo's airflow.

[Guilt-Toy]

might have to cable tie the wastegate shut and see wot boost it makes....

So maybe the turbo wont make more then 7psi with my configuration?

[Lithium]

A leak somewhere? Maybe even on the hose to the boost gauge?

[Guilt-Toy]

oh forgot to mention the turbo is running a 5psi vg30 actuator..... maybe this is the problem??

[Guilt-Toy]

A leak somewhere?  Maybe even on the hose to the boost gauge?

I wouldnt think so.. il have to check it out.. but even the map sensor is only reading 7psi on the microtech laptop software....

[Cubes]

So the turbo is a VG30 turbo?

What power did it make on the dyno at 6-7psi?

With bleeders I've always experienced boost drop with anything above 2-2.5psi what the wastegate is. The only way I found to get around this was to either use an EBC with fuzzy logic (SBC-iD in Auto mode or an AVCR) or mod the actuators bolt up holes reducing its travel.

This makes 16psi on the RB20t without any form of bleeder/boost control, just the actuator its self.

If you look at the actuator's bracket that bolts on to the turbo there are a couple of bolt holes that secure it.

These are the holes I elongated so that I was able to 'tighten' up the wastegate.

Be carefull when adjusting it as boost will easily creep and shoot through the roof at high rpm if adjusted too much.

[Guilt-Toy]

Turbo spec is

RX7 Series 4 or 5 core and rear wheel (huge wheel) cropped and machined into a VG30 single turbo .71 rear housing and the front is a Garret T04 6.0 ar front housing and wheel.

wouldnt the spring with shitloads of pressure do the same as tighten up the wastegate? if so we have tried that

[Cubes]

wouldnt the spring with shitloads of pressure do the same as tighten up the wastegate? if so we have tried that

Well sort of.. but not really..

I have reduced the travel of the actuator/wastegate to the point where it doesn't open up fully. Hence it forces it to make the boost.

A spring is unable to do this UNLESS it is a 16psi spring and is strong enough to hold back the exhaust pressure in the exhaust housing.

To work out the exhaust pressure on the wastegate that the 16psi spring can hold before being forced open can only be worked out by the known and measuring the leverage, surface area of wastegate etc.

So.. by reducing its travel even if the pressure in the exhaust housing is too high and forces the wastegate open it won't be able to force it open any more as the actuator diaphram can only open so much. Understand what I'm talking about?

[Guilt-Toy]

Because i am using a T04 front housing we had to make a custom mount for the waste gate actuator to bolt onto the front housing bolts that hold the compressor housing onto the backing plate.

I am not quite sure I understand what your sayin Joel but id like to give anything a try.. 12 psi on this thing would be animal

[R34GTT-R]

Still got the factory pop off valve on inlet manifold??.bleeding excess boost (than standard)away maybe.

[discopotato03]

I built up a turbo years ago along the same lines as this (minus the cropped turbine) and used a Dash 24 TO4B comp wheel in the .60AR housing . The first impression was no or very little boost on a two liter FJ20ET . I then tried the middle sized RB25 exhaust housing (reprofiled) to excite it . This time round the dreaded surge set in . If I had these dramas with two liters you will have major mayhem with three . I would check the compressor wheel to see if it is eight bladed and if so ditch it for one of the six bladed versions . The VG30 exhaust housing is designed to work with a small diameter ceramic turbine so carving heaps out of these housings destroys most of the nozzle area , resulting in higher turbine inlet pressure and low turbine efficiency . Too late now but I'd have used the VG30 turbo standard , it was designed for three liters , and saved up for something better down the track . If you still have the std RB25 turbo and can get another std VG30 exhaust housing this combination is a reasonable stepping stone .

Cheers A .

[Cubes]

I was under the impression that with small motors you are more likely to experience surge due to the engine not being able to consume the amount of air being forced in to it.

Larger motors = more air is able to be consumed especially at the critical low and mid range.

Hence the surge issues with the GCG Stage 2 500hp on the RB20DET..

That same turbo doesn't have any surge issues on the RB25DET..

[09ONE_32]

yeah my car had bad surge with The CGC stage 2 high flow. Was quite dissapointed with the result really. Kinda got me nowhere. I had more power than stock turbo, but not as much as the boys who went full aftermarket. And these other 2 groups didn't have any surge problems.

[Guilt-Toy]

the wastegate is closed fully now and it still makes the same amount of boost. (used welding wire)

the car makes nice power for 6psi... remember that the rb25 with exact same setup everywhere else could push over 17psi no problems...

500cc would not cause this.. i think i may have a boost leak

[Sydneykid]

I think you may have a boost leak.

[discopotato03]

Does anyone know which GTBB CHRA goes into these GCG Hi Flows ? I suspect its one of the GT30 turbine based TO4S versions but have never seen one . If the compressor is seven bladed thats all I need to know .

Back to the RB30 , a GT30R I feel would have been a better choise than the 2835 giving more turbine and compressor flow and lots cheaper . Out of interest I went back to the Garrett PDF and looked up this turbo with the 1.06 exhaust housing and its flow rating (exhaust) is very similar to the GT35R/ .82AR combination . In big housing/s form this could be the go .

Cheers A .

[Doctor 30]

you will have a leak. I had one from the charcoal cannister. It will be in the inlet manifold. Check every hose that it is connected. (since then I am running 13psi without beeding at all)