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Discussion Starter #1
Hi guys,

I have a thread going on the SXOC but as it's an RB related problem I thought I would post here too.

Had the car on the rollers last Saturday and it wasn't making quite the power I'd hoped for. All is healthy, and it was soon spotted that the boost is trailing off as the revs climb. Initially hits the 0.8 Bar it's set to, then trails off down to 0.5. Just refuses to hold the boost.

My spec is as follows:

Internally stock RB25
Hybrid T3 from 4x4 Cossie (360 thrust bearing and built to cope with 22PSI, has only covered about 2500 miles)
Forge motorsport adj actuator
Dawes device mechanical boost controller
Standard Recirc DV
FMIC
Apexi filter
3" turbo back Exhaust system
Power FC

From asking on the SXOC the actuator should be fine, as the previous owner of the actuator had the diaphragm replaced and the previous owner of my car fitted a stiffer spring to it to try and cure this boost dropping problem.

He has also confirmed that it did this PRIOR to the dawes device being fitted. This was my number one suspect after the actuator, but appears this may no longer be the case.

I don't believe it's a boost leak, as the car isn't running rich at all and there aren't any of the running problems I'd assiociate with such a leak, unless it's very very small or only occurs under pressure (recirc leaking perhaps?).

Basically wondering if anyone on here has had anything similar, and if so what did you do to cure it?

Any ideas or suggestions welcome.

Thanks all :)

Del
 

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1,237 Posts
Could be under higher pressure a pinhole that may exist becomes a bigger hole....justa sugestion I would deffy be looking at all my boost hoses....old ones tend to crack and leak...
 

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Discussion Starter #5
I will have to find out, cheers for the suggestion Rising Sun :)

Bought the car in present spec but the previous owner should know, afaik it's the standard housing size of a cosworth 4x4 turbo, and I'm sure other GTS25t owners are running this kind of turbo with no problems?

Also, if it's not too much trouble would you mind explaining how an incorrectly sized exhaust housing could cause the problem? I think I have an idea but I like to try and learn and understand everything like this as I don't like the thought of being one of those people just trying things because they're told to :)
 

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Discussion Starter #6
Actually, just a thought, the T3 that's on there is certainly bigger (Compressor housing and Exh Housing) than the stock turbo and that can hold boost higher than 0.5Bar higher up the rev range can't it??
 

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R33 GTST Owner.
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244 Posts
Airflow problem?

Had this problem myself on my old starlet and it was probably down to the airflow, my mate moved his filter to the front bumper to get more cold air feed and got boost creep!!!

Sounds like the turbo is struggling to get enough air to keep the boost up.
 

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When does it hit the 0.80bar and how quickly does it tail down to 0.50bar.
 

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Thats holding boost quite well neal, something like a greddy profec B sould be able to sort that out and dial in some extra gain at top end.
 

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R33 GTST Owner.
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244 Posts
Thats holding boost quite well neal, something like a greddy profec B sould be able to sort that out and dial in some extra gain at top end.
Moving the filter to the front of the bumper also helps it out as its getting more cold air higher up the rev range!
 
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