VNT Wastegate?

[Whorse]

This has been mentioned a few times, but I've never seen a definitive answer on the difference between a VNT Wastegate and a T2. From my understanding, the VNT doesn't have an actual wastegate, it just looks like one. What's the difference, and what can be done if it ruptures?

[Will Martin]

Jason,

Like you stated, the VNT doesn't have a wastegate. It's not needed because of the vanes in the exhaust housing.

Instead of having the exhaust gases (or pressure) bypass the turbine wheel (hince the name-wastegate) when the desired boost is made, the vanes are closed creating boost (high pressure) and as you reach the desired speed/or boost, the vanes open so you don't overboost and the pressure is lowered. So in theory the vanes are the "wastegate." So if you were to compare the two, you could say a wastgate 'fails' by sticking open or leaking (not fully sealing when it's closed). A VNT 'fails' by the vanes sticking in the fully closed/open position. My old '89 CSX 324 would do this sometimes, idicating that the turbo was in need of a rebuild. If you've ever taken one apart, you'll see about a billion tons of carbon build up in the exhaust section. LOL That usually causes the vanes to stick. Cleaning them off with brake cleaner an adding a light coat of oil usually does the trick.

What I did with my S60 VNT was adjust the acuator arm so the vanes stay closed a bit longer.

[Whorse]

So what's the can on top of the Turbo for if the vanes bypass the exhaust themselves internally?

[Will Martin]

Quote:

Originally Posted by Whorse So what's the can on top of the Turbo for if the vanes bypass the exhaust themselves internally?

The vanes don't bypass the exhaust, the vanes bypass the pressure (gas) that's put through the turbo. Imagine this; you give your car gas and start to build pressure-boost. The vanes in the turbo are CLOSED. The line running from VNT solenoid #3 going to the TOP canister nipple (ooooh, a dirty word lol) controls this. Now as you start to reach the preset boost (pressure)number-controlled by the computer-the BOTTOM nipple (connected to VNT solenoid #2 starts to close the vanes. This is the action of the vanes acting like a wastegate. The wastegate is connected to the cansiter on a regular turbo. On the VNT, the vanes are controlled by being connected to the canister via an actuator rod. The rod is connected to a lever on the turbo and reacts to the pressure on the canister. The lever, when moved, sits in a ring along with the turbo vane switches and as it moves, they move, controlling the position of the vanes. The vanes and the wastegate are two different things with the same function. That's why if you want to bleed a VNT, you can put it on the line running to the TOP cannister nipple and it keeps the vanes CLOSED allowing you to build pressure longer giving you higher boost until it all goes BOOM!

[Whorse]

Makes sense. The bleed I understand because I was looking into it. Turns out the recent problem I had with overspooling was just a vacuum line that came off but felt like it was still on. If you want to run less boost on a VNT in a two stage setup, can it be done using the same concept, just with the 2 VNT solenoids, or does it have to be reworked?

[Will Martin]

Hmmmm.........(Jason! Stop making me think! It hurts! LOL) Seeing how the VNT works, IN MY MIND if I was to do a "two stage" set up, it would probably go something like this. Now remember I could be wrong.

You need some kind of remote check valve in-line on the bleed line. Have it so on low setting it's RESTRICTING pressure in the line and when you flip it, it's going to let you be at a higher boost from the bleed. So maybe something like this:

VNT solenoid #3------------Bleed (preset to, let's say 18lbs)--------restrictor (connected to remote cabin switch)--------------top canister nipple.

In theory, the bleed would allow the car to boost to 18lbs, so that would be your "stage 2". The restrictor would be your "stage one". So with the switch down, the restrictor would be active, giving you lower than stock boost-stage 1. Flip it up, and it is now allowing all the boost in that was being held back and being set by the bleed-that's stage 2.

There may be an easier way of doing this, but give me a break, it's late and I'm tired! LOL

[ironbird720]

Why doesn't a Turbosmart MBC work for the vnt bleed??

[Will Martin]

Quote:

Originally Posted by ironbird720 Why doesn't a Turbosmart MBC work for the vnt bleed??

Hmm.....I'm not too sure what a Turbosmart MBC looks like, but if it's anything like the one I have in my garage, it "should" work. If you hook it up to the top vnt nipple.....Maybe one day I'll try it out.

[Whorse]

Kinda off topic. Anyhow, if it uses a restrictor and a bleed they run on 2 separate lines, unlike a normal T2 bleed.