Rb25det boost won't hold

[Jasper34gtt]

Hi, I just had my 25 neo tuned today on a apexi power fc. 

The engine is stock except for 3"exhaust all the way and blitz fmic. I have a turbosmart manual boost controller, set at 10psi. 

But after 4500rpm, the boost won't hold and lowers to 7psi at higher rpms. 

Is it time to start searching for boost leaks? Or is there something I'm missing? 

Thnx. Jasper

[Murray_Calavera]

Can you post up the dyno graphs for your tune?

What did your tuner say, surely it was doing this on the dyno at the time?

 

[Jasper34gtt]

He said the turbo isn't capable of delivering boost at higher rpms. It's designed for lower rpm torque. I'll post the graph when I get it from him

[GTSBoy]

4 hours ago, Jasper34gtt said:

He said the turbo isn't capable of delivering boost at higher rpms. It's designed for lower rpm torque.

Not true. Stock Neo turbo will hold 12 psi to the redline. Mine certainly does.

[admS15]

Where is the boost t plumbed in? It's probably going to be related to that.

[Jasper34gtt]

I deleted the 2 stage boost solenoid. Incoming line to the turbosmart boost T comes from the turbo, and outgoing goes to the wastegate actuator. 

Anyone else using only a manual boost controller and running 10+ psi? 

I think something is not right, it should hold boost

[KiwiRS4T]

18 minutes ago, Jasper34gtt said:

I deleted the 2 stage boost solenoid. Incoming line to the turbosmart boost T comes from the turbo, and outgoing goes to the wastegate actuator. 

Anyone else using only a manual boost controller and running 10+ psi? 

I think something is not right, it should hold boost

You didn't mention the bleed - you do have the right one going to the actuator?

To test properly for boost leaks you need to make up a plug and put about 20 psi into it. Leaks are sometimes hidden from sight and hard to hear with the motor running.

[Jasper34gtt]

The T only has one input and one output... In comes from turbo, out goes to wg actuator. 

I think that's correct 

[admS15]

Have you used the nipple from the intercooler cold pipe as the boost source like this pic, that's how i had done it many moons ago and it worked fine.

 

[KiwiRS4T]

3 hours ago, Jasper34gtt said:

The T only has one input and one output... In comes from turbo, out goes to wg actuator. 

I think that's correct 

OK so it bleeds to atmosphere. Is it supplied from a nipple in the compressor housing? Have you tried turning up the boost? I see the turbosmart instructions suggest removing the ball and spring in some applications - have you tried that?

[Jasper34gtt]

Using the cold charge pipe as feed instead of directly from the turbo housing, shouldn't matter I think. But I'll try

4 hours ago, KiwiRS4T said:

OK so it bleeds to atmosphere. Is it supplied from a nipple in the compressor housing? Have you tried turning up the boost? I see the turbosmart instructions suggest removing the ball and spring in some applications - have you tried that?

From the compressor housing yes. I tried turning it up and stopped at 11psi. Then after 4500rpm it goes back to 7psi for some reason. I will try your suggestion to remove the ball and spring. Thanks

[Jasper34gtt]

 

8 hours ago, KiwiRS4T said:

 

Just a thought... Could it be that the stock cat is too restrictive and exhaust gas pressure is pushing the wastegate flap back shut? 

[KiwiRS4T]

1 hour ago, Jasper34gtt said:

 

Just a thought... Could it be that the stock cat is too restrictive and exhaust gas pressure is pushing the wastegate flap back shut? 

It could be blocked too. Either way I would either lose it altogether or get a better flowing one. If you can without outraging the neighbours  you could try dropping the exhaust altogether to see if that is where the problem lies. 

Also, if dropping the ball and spring doesn't help you could pull the hose right off and , driving carefully so as not to overboost , see if the problem is with the wastegate.

[GTSBoy]

7 hours ago, Jasper34gtt said:

Using the cold charge pipe as feed instead of directly from the turbo housing, shouldn't matter I think

But you would be very very wrong.

There is enough pressure drop across the shitty sidemount for that to be a bad idea. Although it should result in other bad effects, not low boost.

I'd seriously be looking for boost & exhaust leaks.

[BK]

11 hours ago, KiwiRS4T said:

It could be blocked too. Either way I would either lose it altogether or get a better flowing one. If you can without outraging the neighbours  you could try dropping the exhaust altogether to see if that is where the problem lies.

Look you should drop the cat as Kiwi said just to eliminate that as a cause, but it probably isn't. I've had completely blocked cats. The side effect generally is it is pathetically gradual to build to peak boost, makes jack power everywhere, but the peak boost is still usually up the rev range. Blocked cats generally do not cause a spike to peak boost then drop like you are explaining.

I think the problem is elsewhere, but do it just to check anyway.

[Jasper34gtt]

Ok I will check the cat. 

And as for boost coming from hot or cold pipe, I just installed it exactly the way turbosmart advised. 

 

People do have good boost over the complete rev range with just a manual boost controller? Or do most people install a rb20 actuator? I thought I might give that a try... Maybe the wg spring is just too weak

22 hours ago, KiwiRS4T said:

 

 

[KiwiRS4T]

Have you actually done anything but wring your hands?

Nipple on compressor housing should be fine but lots of other things for you to check out.