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External Wastegate more boost

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Hi everyone,

im tuning a 1.8t 20v engine with a gtx28 / 44mm GFB wastegate 22 psi springs and Link G4+ ecu and im struggling to hold 30 psi even with the duty cycle at zero for the N75 valve

Ive leak checked both the air system and wastegate and have the it plumbed in as the manual states

Any top tips out there ?

Thanks Chris

There are multiple ways to plumb an external gate so it's not clear what you are doing. Do you have the solenoid controlling the top port of the gate? Post a diagram (screenshot of a manual page or an MS paint thing you made).

"even with the duty cycle at zero"?

Shouldn't your duty cycle be at 100% if you want to achieve the highest possible boost pressure(Which I'm assuming... its not clear what you want to achieve)?

This is how i have it plumbed, I have switable boost maps and my 1.4 bar map works great with good control but cant seem to get above 2.0 bar

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Plumbing diagram is correct, can you post duty cycle table?

I dont have it to hand sorry but mine works 0 = more boost

i have wastage pressure for map 1 so duty is 100% across the table and it works good

for map 2 even at 0 across the table i can only just can 1.95

I can control fine to lower the boost to say 1.6, 1.7 etc but can go no higher than 1.95 ish

What happens with a stiffer wastegate spring?

That's a pretty weird situation as it seems you've got everything correctly installed. Something is odd there though as in the Link G4+ 0% duty should result in minimum boost and 100% should give maximum. Particularly if you wanted to use the closed loop control then this is an essential aspect.

It's important to realise that you don't have an infinite range of boost pressure with a wastegate but you should be able to get from 22 psi through to perhaps 35 or even 40 with no trouble. One aspect that might be worth checking is the frequency for the boost control solenoid. I find that the popular MAC 3 port valves like a frequency of between 20 and 30 Hz. Another test you could do as a sanity check is to temporarily configure the output for your boost solenoid as a 'Test (on)' which just drives the solenoid fully on. That will give you the maximum allowable boost. Be careful when you're testing this that you don't end up with an inadvertent over boost though - I'd recommend making sure your MAP limit is set sensibly first.

Ok thanks, I have the VW N75 valve fitted and the frequency set to 10hz at the moment I’ll try changing it to 20 and 30hz and do the test suggested.

as you say it’s weird that my duty is the opposite way round but maybe this is how the factory valve works ?


I've honestly never had good results with the N75 plumbed for external wastegates like you've showed in the diagram.

I'm sure, if you plumb a MAC solenoid like that you'll get the boost control you want and it'll work the correct way. But for now, I'd check for leaks in the system and for exhaust backpressure. This may also cause the need of more duty cycle for a given boost pressure.

Sorry I missed the part about the N75 valve. This isn't a valve I use or recommend however I think that is your issue. I seem to recall having a similar issue years ago with an external wastegate. My recollection is that these valves are designed to work as a bleed-off style with an internal wastegate and if my memory is right, the valve actually pushes open when plumbed as you've shown for an external and basically leaks. I'd dump it and fit a MAC 3 port solenoid.

awesome guys thanks for your help ill get a MAC 3 port ordered and report back

awesome guys thanks for your help ill get a MAC 3 port ordered and report back

Hi guys,

Just reporting back after fitting a 3 port MAC valve my boost control is awesome !

set it at 20hz and can dial in as much or as little as i need

also it made 18hp more at the same boost setting and as it spools earlier

Thanks Chris

glad we could help ;)