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I've seen it mentioned that some people should port their wastegate on their turbocharged vehicles. Usually, this seems to be recommended in some situations where the car is overboosting past the boost limit, but it is unclear to me if careful tuning or other solutions could also work.

What exactly does porting the wastegate entail and what conditions would I want to do that?

  • I kinda think this question deserves a wastegate tag as well (if someone feels like we should create one). I figure this question would be more accessible with that tag. – Ellesedil May 24 '16 at 7:40
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Porting your wastegate allows increased flow rates through the gate itself.

The gate is a little metal flap (operated by a vacuum operated actuator) that covers a small hole in the rear of the turbo housing hot-side (exhaust side).. The flap usually extends past the diameter of the gate port/hole so that no air can leak. When the flap opens, it allows boost pressure to escape, and the turbo doesn't over-boost.

Porting the wastegate entails using a dremel (or similar) to increase the diameter of that port. Usually, you mill enough material out so that the stock flapper still can cover the hole completely. Sometimes, people upgrade that also when going larger (although at this stage you'd be looking at an external gate - this means that the internal gate hole is sealed shut, and a separate wastegate is attached to the exhaust manifold).

Generally, you'd be wanting to port the gate out when you're experiencing 'wastegate creep'. This means that the exhaust flow is exceeding the flow capacity of the wastegate, allowing for an uncontrolled rise in boost pressure.

Usually, you won't experience this on a stock turbo.

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  • So, I was doing some research on this as I know just enough to be dangerous. A few things I've noticed so far. 1) One of the top Google results explicitly says that enlarging the hole is a common misconception, since the actual goal is to improve the flow of gases through the wastegate and there are other avenues to do so. 2) In the exceptions to "Usually, you mill enough material out so that the stock flapper still can cover the hole completely", don't you now have a boost leak? – Ellesedil May 24 '16 at 18:13
  • And 3) For some Subarus, I know that overboost can occur on stock turbos but with aftermarket downpipes. For instance, it is known to occur on Legacies, which is why I'm interested in this to begin with. The better exhausts increase the exhaust flow out of the housing, but neglect to also increase the flow out of the wastegate. So, when it's opening, it isn't as effective anymore and contributes to overboosting. How do these points fit into the info you have here? – Ellesedil May 24 '16 at 18:16
  • @Ellesedil Upgraded exhausts are much less restrictive stock, allowing exhaust gasses to flow at higher rates. Say your stock exhaust allows 8 arbitrary volume units of Exhaust gas Per Minute (EPM), and adding an aftermarket downpipe allows 10 EPM. The higher EPM flow rate means the engine doesn't have to work as hard on the exhaust stroke - thus increasing power. If you're pushing 10 EPM past a stock waste gate that was only designed to see 8, it will not be able to release the extra pressure, creating the over-boost situation. – MooseLucifer May 24 '16 at 18:52
  • @MooseLucifer: Yup, got that, although it might not be quite as simple as that in all situations. I'm trying to avoid making this question hyper-focused on my situation. But, in some cases (and in my case, may be a factor), it appears that simply optimizing how the wastegate gases flow and combine back into the exhaust can impact the amount of gases the wastegate can move. Instead of widening a river, simply smoothing some corners or adjusting how it joins into a larger river can increase how much water it can move. – Ellesedil May 24 '16 at 18:59
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    @Ellesedil Sorry, didn't mean to dumb it down, I misinterpreted your question with regards to Aaron's answer. I have done a good amount of research and used the trusty butt dyno to experiment with N/A intake tuning, where general consensus (as you said) is to port the transitions between every piece of your system such that the air can achieve laminar flow across the surface. There is a debate, however, regarding the optimal surface finish to reduce drag from the boundary layer. Either way, you can almost always improve OEM flow rates by porting and sanding out casting lines. – MooseLucifer May 24 '16 at 20:00

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