What wastegate actuator to get?
 

I am gathering up parts for a turboization of my 1997 1.8. I got a hold of a used GT2560R for cheap (someone else decided to go bigger on their car). It's in generally nice condition, but I don't get the wastegate actuator with it. So, I need to pick out something to get.

First, what actuator pressure should I get? If I understand things correctly, the actuator pressure basically dictates the "minimum boost", in that if the turbo spools up to provide that boost pressure, the ECU can't do anything to get below it (but can get boost pressure above it by bleeding off air through the solenoid valve).
I want to start off low, just a few PSI boost, make sure everything seems to work, and slowly increase from there (aiming to eventually get to 180-200-ish hp). Does that mean I need to get an actuator with a pretty low opening pressure?

Seems cheapest way to get one would be a spare for some car with a low pressure turbo. Are there any particular models/types that are appropriate or popular?

Also, my manifold has a port for an external wastegate (plugged up). Are there any real benefits to using an external wastegate, especially at pretty low boost levels? Is it at all advisable to even do that when the turbo has an internal one (which I guess can just be bolted shut pretty easily)? Overall using the internal wastegate seems easier and slightly cheaper, which is what I would do unless there are good reasons to go for an external one.

if you have an ewg, you should absolutely use it. with a 2560 you will very likely have boost creep and other boost control issues, so if you have an ewg port, it would be really silly not to use it.

Will boost creep be an issue even with my fairly low boost levels? I plan to start out somewhere not more than 4-5 psi, and I guess i need to eventually get to 8-10 to reach my golden end-game dream scenario of close to 200hp.

It seems most actuators for "regular cars" are somewhere in the 3.5-5 psi range, and I could get one of those for next to nothing (tons of old Saab and Volvo stuff for low-boost turbos available here). Would it be sensible to start out with a cheapo actuator for the internal wastegate, and later go with an external one with higher spring rate?

I've read here and there that the ECU-controlled boost regulation works best if the actuator pressure is somewhat close to the target boost pressure. Somewhere it said "you're good with boost pressure up to twice the actuator pressure", but I suspect it's not really that simple. What's the word on that?

Also, actuators with two ports (one on each side of the actuator diaphragm) exist for both internal and external wastegates. Are those significantly better or just marginally so? Assuming you have the right kind of solenoid valve, are they as easily controllable with Megasquirt?

(this might be very nooby questions, but I didn't see much about this in the FAQs)

creep is an issue more so at low levels than high
no they're not. more like 10ish. no
the word is no
yes they are better at holding boost from sagging up top. yes.

stick around and read read read. all of this is easy stuff.

bottom line: no argument you can come up with in this scenario will make it ok to use IWG on a garrett turbo when you have a setup for EWG

Thank you. EWG it is, then. It will be some fabricating fun to get the dump tube into the downpipe, but should be manageable (no, there will be no screamer pipe).

What manifold is it? I agree that, in principle, there is no downside to using an EWG, but in practice there are some pretty dodgy EWG manifolds out there.

--Ian

There are several benefits to running an external wastegate, you should do it. Better boost control, wider range of boost levels (especially if a dual port gate). With dual ports on my old external gate, I could run 8 PSI, or 28 PSI just by adjusting my MBC. And I had ROCK SOLID boost control, paint-the-line accurate. no overshoot, no fall off up top, no wavy-ness. Within 1kPa of target at all RPMs once it spooled. They're great.

Tacotaco (from ebay).

OK. There are a few of the old BEGI/FM "FM3" manifolds floating around that used a 2-bolt EWG flange on the bottom, which are notorious for being a PITA. I dunno anything about the "tacotaco" one.

--Ian

It's this one, which also has a bottom mounted EWG port. Once mounted, I guess I have to remove the turbo to get to the wastegate, but I'm not too worried about that..