Internal vs external wastegated

[Duquey]

Hi guys,
I'm in the middle of my m20 turbo build and have been searching for a turbo for some time, the manifold I have is for an internally gated turbo as I was worrying about clearance on the steering shaft as it's rhd, now I see most people are running external gates, is there an issue with clearance too the inner guard or is it just a preference?

My engine will be a m20b25
Ported head
Valve seats dropped
Heavy duty ie rockers
Turbo camshaft
Arp stud
.80" mls
And looking at a garrett gt3071r .76ar
Although I am open to change if someone can
Point me in the right direction turbo wise
I'm looking at just under 400hp until my bottom end pops
Then I'll be going forged.
I want this just as a weekend car I don't want a lot of lag I would rather have a responsive ballbearing turbo I can have some fun with


Ps. I love this forum

[Mikey_Boy]

This is can of worms, but really not that controversial. There are pros and cons to both types of wastegate. Most of the drivers for an internal wastegate are mainly around packaging - can the turbo and wastegate fit into a certain space. This is of course important for car manufacturers!

That said, sizing an internal wastegate is also pretty difficult AND it has a really hard time with high temperatures so has to be made out of special materials. Also, it's not that easily adjusted because of where the actuator is and so on. External wastegates were the thing WAY back in the day (1970s) as frankly there was nothing else. They have a lot of pros to them - they can be adjusted easily, their size implies a better control of boost, they are further away from the turbo so don't get so much of a battering. BUT, exhausts are trickier with external wastegates and response time can be an issue if they aren't placed correctly or well matched to the turbo. I've had cars (not BMWS!) with both and I prefer an internal gate but that's just me.

I think for what you want to do, you could go with either honestly, driven primarily by how much room you might or might not have - you aren't trying to get 1000's of HP and there are plenty of good internally wastegated turbos out there that will flow enough air for the job.

Google is also your friend - there's a tonne of stuff online for you to read - get the kettle on!