how do i install this 3 port mac valve for boost control?

[r32-25t]

that’s how it’s done, its really not that hard 

[kevboost7]

4 minutes ago, r32-25t said:

that’s how it’s done, its really not that hard 

thats literally what i did!

[r32-25t]

According to your diagram you have the right side port attached to the pressure source on the turbo and the front port also attached to the pressure source on the plenum 

[joshuaho96]

2 hours ago, kevboost7 said:

@joshuaho96 I'm sorry josh , i dont know if i'm dumb or missing something here, but your original diagram makes no sense with my configuration. I have internal waste gates.

This is what you said: "Port 1 is the blue line. Port 2 is the green line. Port 3 is also the green line. The key point is that you will have to modify the vacuum line for port 3. Instead of tying port 2 and 3 together you cap the vacuum line on the combo coolant/vacuum pipe and the line on the plenum goes directly to the valve. Port 2 has unchanged routing." 

based on that description of what you said above^^ this is what the connections should look like below:

is that what you are suggesting? Port 1 on the Mac valve (vent to atmosphere) should go back to the turbo pressure?

No, look at this diagram again:

 

What you have drawn would put boost into port 1. The blue section is the intake before the turbos but after the MAFs.

[kevboost7]

2 hours ago, joshuaho96 said:

No, look at this diagram again:

 

What you have drawn would put boost into port 1. The blue section is the intake before the turbos but after the MAFs.

Okay thats what i thought you were trying to say. I will give that a shot tomorrow. 

It just did not seem right, because every diagram i see on the internet has 1 port on the 3MAC Valve with the cap that vents to atmosphere. 

I'm still confused, on this diagram below with the twins. I thought that the "turbo pressure" line was the blue line. In the RB26, where is the turbo pressure line?

Edited October 22, 2023 by kevboost7

[GTSBoy]

The "turbo pressure line" is the boost reference. This is commonly sourced from the compressor outlet. It can be from anywhere between the compressor outlet to the throttlebody. As the RB26 has a plenum UPSTREAM of the throttlebodies, the boost reference is obtained from the plenum.

Your circled (in red) line above is the green line on the coloured in RB26 plumbing diagram.

[joshuaho96]

56 minutes ago, kevboost7 said:

Okay thats what i thought you were trying to say. I will give that a shot tomorrow. 

It just did not seem right, because every diagram i see on the internet has 1 port on the 3MAC Valve with the cap that vents to atmosphere. 

I'm still confused, on this diagram below with the twins. I thought that the "turbo pressure" line was the blue line. In the RB26, where is the turbo pressure line?

Turbo pressure line is the green line from the plenum. Almost all diagrams online just vent to atmosphere which is why you're confused. This is fine on speed density systems but it will cause an unmetered air leak on MAF-based systems. Even if it's nominally ok you really don't want to make a habit of it because it just makes it harder to diagnose what's wrong in the future.

[r32-25t]

If this is that confusing for you then you really should take it to a professional 

[kevboost7]

@GTSBoy @joshuaho96 Thank you guys, and especially thank you josh for that diagram you made. It is clear for me now. Why does the 3 Port only come with 2 of the barb fittings? I will have to buy another barb fitting now. 

@r32-25t There are no professionals near me. I am learning, which is important to me and one of the reasons i got this car. 

And the one professional i took it too was my tuner, who told me to get rid of all the 30 year old hoses and just run  new hoses from the wastegates. I felt like there was a better way to do it. Thats why im on here. 

 

[r32-25t]

Most of us would agree with getting rid of the 30yr old hoses! Im surprised you haven’t had all the heater hoses let go yet 

[GTSBoy]

2 hours ago, joshuaho96 said:

This is fine on speed density systems but it will cause an unmetered air leak on MAF-based systems. Even if it's nominally ok you really don't want to make a habit of it because it just makes it harder to diagnose what's wrong in the future.

The amount of air that comes out through a bleeder is too small to worry about wrt metering.

52 minutes ago, kevboost7 said:

Why does the 3 Port only come with 2 of the barb fittings?

Because, as Josh said, most people just vent it to atmosphere. I've had the 3rd port on my MAC valve open for at least 10 years and no wasps have ever tried to build a nest in there.

[joshuaho96]

2 hours ago, GTSBoy said:

The amount of air that comes out through a bleeder is too small to worry about wrt metering.

Because, as Josh said, most people just vent it to atmosphere. I've had the 3rd port on my MAC valve open for at least 10 years and no wasps have ever tried to build a nest in there.

While true, it's just easier IMO to put the hose on the solenoid instead of pulling it off and then forgetting it somewhere.

[GTSBoy]

7 minutes ago, joshuaho96 said:

While true, it's just easier IMO to put the hose on the solenoid instead of pulling it off and then forgetting it somewhere.

The world isn't only RB26.

If I were to hook up a hose, I would have had to poke a hole into my turbo inlet pipe and weld on a nipple, because that's the only sensible place to send the vented signal air to. And....I didn't feel like doing that much extra work when I fitted the boost controller.

My previous boost controller was a pneumatic regulator based unit on an RB20. There was no venting, so my turbo inlet had no port on it for receiving vented air. And RB20s never had any boost control of any sort anyway.

[joshuaho96]

1 minute ago, GTSBoy said:

The world isn't only RB26.

If I were to hook up a hose, I would have had to poke a hole into my turbo inlet pipe and weld on a nipple, because that's the only sensible place to send the vented signal air to. And....I didn't feel like doing that much extra work when I fitted the boost controller.

My previous boost controller was a pneumatic regulator based unit on an RB20. There was no venting, so my turbo inlet had no port on it for receiving vented air. And RB20s never had any boost control of any sort anyway.

Yeah, it's very contextual. If you have to add a bunch of plumbing and general annoyance to "do it right" then I also wouldn't bother. On the RB26 venting directly to atmosphere means capping another port on that combo vaccum/coolant pipe under the plenum and figuring out how to keep track of a random hose/hose clamp 5+ years into the future. I have a mystery "firewall harness bolt" sitting in an organizer and it's taking up a non-trivial amount of my mental headspace trying to work out which of the five or so cars it could possibly have come from.

[kevboost7]

Can someone explain what the blue line is then? Green is waste gate. What is the blue?

And why is the plenum "turbo pressure"?

[GTSBoy]

Blue is the vent. This is where the air that is released via the solenoid flows away. It is connected to the turbo inlet, so that it remains metered by the AFM(s) (and for emissions reasons, as there are rules about releasing engine gases to atmosphere).

The plenum is turbo pressure because you have ITBs. The plenum is upstream of the throttles, therefore the plenum is always at whatever boost pressure is at the turbo outlet (minus pressure drop from forcing a large amount of air through smallish pipes and an intercooler).

[kevboost7]

Thanks man. Im in the garage now. Dear god, that last hose is so far back. I forgot how much of a pain in the ass it was to work under the plenum. 

[joshuaho96]

2 hours ago, kevboost7 said:

Thanks man. Im in the garage now. Dear god, that last hose is so far back. I forgot how much of a pain in the ass it was to work under the plenum. 

Every time I reach under there I have accepted that I'm shredding my gloves. Too many hose clamps and other sharp bits.

[kevboost7]

Does the factory boost gauge pressure = turbo pressure? Couldn't i just T into that line by the firewall? I mean its too late, i already shredded all the skin on my hands, but man..

https://www.gtrusablog.com/2019/06/where-do-i-tap-my-rb26-for-boost-sensor.html

[GTSBoy]

No. The boost gauge is connected to the little boost log/plenum that is connected downstream of the throttles.

The two functions are totally different.

The boost control is for what the turbo is doing. So you have to measure what the turbo is doing, so you have to measure upstream of the throttle(s).

The boost gauge is for what the engine is doing. You want to know what the inlet manifold pressure is, which is the pressure that the engine is experiencing. You have to measure that after the throttle(s).