RB26DETT Sketchy boost mod?

[ARB26]

Carrying out some engine due diligence before my first drive in a 260RS that has been in storage for 10+ years, and found two lines that are susposed to be plumbed into the boost control solenoid. One of the lines (the wastegate boost supply line) to actuate the gates, had a bolt in one end blocking it.

The other line (main boost signal line) from the very rear of the intake manifold (RB26DETT) and runs up to the boost controller had this pill in the end of it as seen in photos.

Other than the obvious (T28 Ceramic turbos might well be cooked) 

Can anyone shed any light on if there is any validity at all with this mod, bleeding a constant fixed rate of manifold boost pressure off through this 3mm hole? 

Is it deliberate? 

Was this a 90s Jap mod done to RB26's?

Or has someone just fitted this without any idea of what happens to ceramic T28s if they are not gate controlled?

 

 

[ARB26]

[ARB26]

I might be way off the mark here.. there must be a T junction under the manifold. That takes manifold pressure through a check valve prior to the T, one side splits out to this bleed off orifice, the other straight to the wastegate actuators. 

[djr81]

Bit difficult to follow. Have a look below and see what the standard R32 layout was like. Note there was a restrictor in place immediately before "turbocharged pressure control solenoid" that, if removed, magically got you 1 bar boost.

[joshuaho96]

2 hours ago, ARB26 said:

Carrying out some engine due diligence before my first drive in a 260RS that has been in storage for 10+ years, and found two lines that are susposed to be plumbed into the boost control solenoid. One of the lines (the wastegate boost supply line) to actuate the gates, had a bolt in one end blocking it.

The other line (main boost signal line) from the very rear of the intake manifold (RB26DETT) and runs up to the boost controller had this pill in the end of it as seen in photos.

Other than the obvious (T28 Ceramic turbos might well be cooked) 

Can anyone shed any light on if there is any validity at all with this mod, bleeding a constant fixed rate of manifold boost pressure off through this 3mm hole? 

Is it deliberate? 

Was this a 90s Jap mod done to RB26's?

Or has someone just fitted this without any idea of what happens to ceramic T28s if they are not gate controlled?

 

 

This is just a dumb way of keeping the wastegate closed to make more boost. Undo it and either follow the factory setup or redo it properly. Manual boost controllers just use a spring preload to determine when to close in response to boost pressure so it no longer vents to atmosphere.

[GTSBoy]

56 minutes ago, joshuaho96 said:

This is just a dumb way of keeping the wastegate closed to make more boost. Undo it and either follow the factory setup or redo it properly. Manual boost controllers just use a spring preload to determine when to close in response to boost pressure so it no longer vents to atmosphere.

 

Yes, but it's not dumb or dodgy. You can build a perfectly good boost controller from a pressure reg, a relief valve (looks same same as a reg if all from Norgren or SMC, for example) and a check valve. I ran one for years. Only superceded with  EBC because I could get one for cheaps and wanted finer control.

 

THis mod is certainly not a sketchy boost mod, provided the boost is kept below the "spin to death" threshold of the turbos.

[ARB26]

2 hours ago, GTSBoy said:

 

Yes, but it's not dumb or dodgy. You can build a perfectly good boost controller from a pressure reg, a relief valve (looks same same as a reg if all from Norgren or SMC, for example) and a check valve. I ran one for years. Only superceded with  EBC because I could get one for cheaps and wanted finer control.

 

THis mod is certainly not a sketchy boost mod, provided the boost is kept below the "spin to death" threshold of the turbos.

So could it be assumed it has been installed intentionally with potentially a power FC boost controller kit? 

[ARB26]

 

36 minutes ago, ARB26 said:

So could it be assumed it has been installed intentionally with potentially a power FC boost controller kit? 

Or do we think it was installed to give 1 bar of boost max, all day, everyday?

[GTSBoy]

Not this

On 12/08/2025 at 7:42 PM, ARB26 said:

So could it be assumed it has been installed intentionally with potentially a power FC boost controller kit? 

But this

On 12/08/2025 at 8:19 PM, ARB26 said:

Or do we think it was installed to give 1 bar of boost max, all day, everyday?

 

[Duncan]

Manual boost controllers (where a little of the boost was bled off) were quite common back in the day, because they were cheap and easy. Generally they had a manual adjustment screw rather than being fixed like yours.

Down side is they always bleed boost, not just when you want them to so an electronic boost controller that uses a solenoid will have less lag.

[ARB26]

Thanks Duncan, that's the best info I've read. Furthermore after learning about the PCM programming side controlling the factory boost solenoid, the purpose of the solenoid is to "bleed" boost when pin 25 is earthed, thus allowing spring pressure in the wastegate actuator to overcome diaphragm boost pressure, thus closing or reducing the position of the wastegate flap creating more boost as the turbo is able to spin faster.

It's pretty cool to see a designated Pill to do exactly this, would have liked to have seen it with a tiny filter over the end for those moments in vacuum. 

The constant bleed pill has now been removed completely from the system and solenoid boost control has been restored once again.

 

Case closed 😂

[GTSBoy]

52 minutes ago, ARB26 said:

It's pretty cool to see a designated Pill to do exactly this, would have liked to have seen it with a tiny filter over the end for those moments in vacuum. 

The constant bleed pill has now been removed completely from the system and solenoid boost control has been restored once again.

 

Case closed 😂

There's restrictor pills in the stock boost control hoses. That's how they set the amount that was bled off and hence the "high" boost setting. The usual mod in the day was to remove it and send the "high" boost setting up to about 14 psi.