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Author Topic: Plumb N75 into inltake manifold?  (Read 1303 times)
mushtafa
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« on: August 14, 2018, 10:20:11 AM »

I'm re-doing my front mount pipe work and don't have a take off nipple anymore for the N75 valve.

I'm thinking I'll just run it to the inlet manifold instead. In my head it might actually run better. My main concern is that it's the other side of the throttle body, and the N75 will also see vacuum.

Will this be a problem? Anyone tried it? Thoughts?

Cheers
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gman86
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« Reply #1 on: August 14, 2018, 06:54:18 PM »

I'm re-doing my front mount pipe work and don't have a take off nipple anymore for the N75 valve.

I'm thinking I'll just run it to the inlet manifold instead. In my head it might actually run better. My main concern is that it's the other side of the throttle body, and the N75 will also see vacuum.

Will this be a problem? Anyone tried it? Thoughts?

Cheers

It'll dick with pressure control. If you have a part throttle / high boost situation, the waste gate won't open to release boost pressure. If anything, it'll be getting 'sucked' shut which will increase the cracking pressure.
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mushtafa
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« Reply #2 on: August 21, 2018, 01:36:42 PM »

Drove the car for the first time today, appears to be OK at the moment. I will keep a keen eye on the boost gauge and see what happens
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prj
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« Reply #3 on: August 21, 2018, 11:37:31 PM »

Just went it to atmosphere if you have no place to put it, DON'T plug it into the intake manifold.
For the boost reference it HAS to be from the turbo compressor cover or worst case past that pre-intercooler....

In part throttle situations you have the potential to blow up your intake tract with huge boost pressures. I don't see WTF your boost gauge has anything to do with that, when the pre-tb and pre-ic pressure will be insane.

To anyone reading this, DON'T be like this guy.
« Last Edit: August 21, 2018, 11:39:40 PM by prj » Logged
mushtafa
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« Reply #4 on: August 21, 2018, 11:48:12 PM »

It's the boost source of the N75 I moved to the inlet manifold - if I vented it to atmosphere it wouldn't work.

Has anyone used these boost hose nipple take offs before? Do they seal OK?
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nyet
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« Reply #5 on: August 22, 2018, 09:12:21 AM »

IMO the main question is of how tolerant the new setup is of large boost spikes.

Using the manifold as a ref pretty much limits how extreme those can be

Plumbing the ref before the throttle plate can present the n75, the wg, and possibly the intake (if vented to intake) with large spikes.

Neither are a good thing, IMO. N75s are already notoriously failure prone.
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« Reply #6 on: August 22, 2018, 01:14:01 PM »

PRJ has me worried now, so not driven the car hard at all. I've pretty much kept it off boost.

I don't understand how it could be a bad thing. In my mind, the boost pressure inside the manifold is more important than the pressure at the turbo.

I'm obviously incorrect in my thinking, so if anyone could explain, it'll be much appreciated.
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nyet
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« Reply #7 on: August 22, 2018, 01:28:42 PM »

I don't understand how it could be a bad thing.

I thought prj did a fine job explaining why.
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mushtafa
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« Reply #8 on: August 22, 2018, 03:03:49 PM »

I thought prj did a fine job explaining why.

It doesn't explain it well enough for me to understand.

At partial throttle, the throttle plate will restrict flow, but surely it wouldn't affect the pressure. Is this where I'm incorrect?
Perhaps it's the time difference between the turbo producing the pressure to the N75 seeing it?

I'm not saying I'm right, your wrong, or I don't believe you, I just want to understand it - and at the moment, I can't.

At the end of day, if you experienced and knowledgeable people say it's no good and I need to change it, I will.
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vwaudiguy
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« Reply #9 on: August 22, 2018, 09:15:43 PM »

The wastegate pressure control system does not want to see vacuum. Also, yes there is some delay from the outlet of the turbo, and the inside of the manifold. Earlier input to the wg is better. Lastly, those boost taps work fine. What's the big deal with adding a nipple somewhere close to the turbo?
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mushtafa
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« Reply #10 on: August 22, 2018, 11:25:07 PM »

Nothing wrong with adding a nipple, it was just easier to use an empty nipple on the intake.

I'll get a nipple ordered up and change the setup.
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prj
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« Reply #11 on: August 23, 2018, 12:10:24 AM »

It doesn't explain it well enough for me to understand.

At partial throttle, the throttle plate will restrict flow, but surely it wouldn't affect the pressure. Is this where I'm incorrect?

That's exactly what you're incorrect about. The very basic physics.
Flow restriction provides a drop in pressure across throttle plate depending on opening angle.
You can have vacuum in the intake manifold and 1.5 bar pressure pre-throttle in some cases. Ponder on that and now think why what you are doing is a HORRIBLE idea.
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