That Drop !

[r34unit]

Is it just me or does every Garrett gt3076 on a rb25 manifold drop boost in the top end ?

[Lithium]

It's just you.

[scotty nm35]

I assume you are talking internal gate housings Angelo? Most setups I have seen hold nicely near spring pressure, as you try and bleed them up it can all go to crap due to manifold pressure.

It's not such a bad thing to drop a little boost in the top end, the engine is ingesting a lot of air up there and boost is only a measure of the engines lack of airflow. Why overspin the compressor when most of the time it is just producing hotter air...

A larger turbo and or housing will always help top end flow.

[r34unit]

I'm running a gt3076 on a rb25 manifold with a 38mm external gate welded off it. It does not spike at all but in the top end it drops from 19psi to 16,15 psi.

I'm using a blitz sbs dual solenoid ebc.

Might need to test for a boost leak !

But if any other ideas come to mind on what it could please let me know !

[wolverine]

Which turbine housing?

[r34unit]

Gt3076s -56t

[Ben C34]

Same question.... what housing?

[Lithium]

I don't think there is a housing which will cause that issue - when I had a .63 housing on mine I struggled to keep it UNDER that boost level, it was hitting 20psi by 5700rpm and trying to climb hard. The only reason the turbo itself would not be able to hold boost (assuming it's healthy) is if it is struggling to keep up with the airflow requirements of that engine at that boost level. Even a .63 GT3076R shouldn't have issues, really the compressor and turbine should be able to hold 20+psi "all in" so if it's not holding, it will be something to do with the setup - wastegate/boost controller/boost leak/exhaust leak/something...

[scotty nm35]

I'm running a gt3076 on a rb25 manifold with a 38mm external gate welded off it. It does not spike at all but in the top end it drops from 19psi to 16,15 psi.

I'm using a blitz sbs dual solenoid ebc.

Might need to test for a boost leak !

But if any other ideas come to mind on what it could please let me know !

Pressure test the intake by all means.

What spring are you using in the wastegate?

Are you using a MAC valve to hold the gate closed also?

[r34unit]

My apologies! I've just realized It's a Garrett gt3037s 56t in a .82 rear housing !

I'm using the big black blitz dual solenoid.

Now I'm wondering if the .82 rear is too big ? And I should change to a .74

[scotty nm35]

No, you just need to sort out your boost control. Shouldn't be too difficult to work out.

Just slapping an electronic controller won't make a 4psi spring hold 30psi, you need to first match your spring to be close to your desired output, then the controller might have a fighting chance of holding what you set it at.

If that fails, you need to hold the gate shut using pressure to the top port on the gate. You would need to swap to a 4 or 5 port MAC valve to do this properly, simply cut the old solenoid out and solder the MAC in it's place.

[r34unit]

I've got two springs in the waste gate.

Combined they are rated 16psi from memory !

[scotty nm35]

So bump another in there, or control the top port. Easy fixed.

[r34unit]

Haha might have to come past again Scotty and get another spring then.

Well the blitz ebc is meant to be controlling the top and bottom of the gate !

[GTScotT]

It sounds like a boost control issue, otherwise you have all the parts to support what you want to do.

Obviously you should still check for leaks, but move to boost control if you cant find any leaks.

[wolverine]

If you have 16psi on the gate then the boost controller should be able to hold it at 19psi easily if set up correctly.