Wastegate setting

[Dave Ledwitch]

Hi.

I could do with a reality check from those who have measured the Wastegate Actuator setting.

I set a rig up to check this which worked fine, and I got around 0.4mm movement at 0.6 bar.

However I did not expect to see movement until around 0.5 bar as I understand there is a return spring in the module that keeps the gate firmly closed to prevent any leakage.

I started to see movement (ok, only 0.05mm) at pressures as low as 0.1 bar with this being quite linear to the 0.4mm spec at 0.6 bar. After this the gate opened quite quickly so that at 0.8 bar the rod had moved 2 - 3 mm.

Is this consistent with other peoples experience?

Dave

[tjs98jetta]

Funnily enough I just did this myself at the weekend. I looked at the original one, and it had a noticable creep even at quite modest pressures, say 2-3 psi above atmosphere. Well below the spec 0.4 mm travel of course. It was also opening (0.4 mm+) below the spec pressure, so I adjusted by screwing in the actuator (more preload). This got it into spec, but there was still creep at lower pressures. For comparison, I tested a brand new unit from Forge motorsports and it had a very abrupt actuation, no creep at low pressure. I put this down to aging of the original unit. When I get a spring of the correct strength for the new one, I'll switch to it. Haven't tried the car after the adjustment, so I can't comment on any performance improvement, but getting it into spec must be good, I assume. Maybe the creep in the old one at lower pressures is causing me loss of boost, but I don't know how much the wastegate needs to start the by pass.

Hope this is useful

Trevor

[andydclements]

You'd expect the creep if the movement is purely linked to the spring. You'd only not get creep if the rod has slack on the spring before it moves because the spring action will be approximately linear (or non-liner if it's not a standard spring).

What ever happens, if you compress a spring that will move a given distance with a given force applied, it will move part of that distance with a lower force applied. The way to overcome this is to have the rod attached in such a way that the spring can move a part of the distance before it comes into contact with part of the spring.

If you take a car suspension spring and rest a coin on it, it will compress slightly, not enough to see, but then you probably only get an inch of movement when it has 300kgs on it at standard gravity, so 10 grams will be microscopic distance, although this is an extreme, the same will be true of the wastegate spring.

[tjs98jetta]

Andy, yes I agree with your analysis, the setup must be such that the response is non-linear. I'll have to take the Forge unit apart and see what's going on inside. The original actuator seems sealed, but the new one is assembled with allen key screws and is designed to have the option to change the spring strength.

Cheers,

Trevor

[Dave Ledwitch]

Thanks Guys.

Useful to know that a new one has some preload on the spring.

I think I will adjust mine to give a bit of preload before the rod starts to move and see if i get an improvement. I think as long as the gate starts to open before 0.6 bar i should be ok.

Dave

[gertjan]

Why don

[lotus4s]

gertjan,

To answer your question simply, because every car/wastegate is slightly different. We are dealing with tolerances in thousandths of an inch which are affected by the slight variances in the length of the rod and tension in the spring. That's why each one needs to be setup in it's own application.