VNT on non-VNT car? (w/ pic)

[arro]

Scratch that, I revised the drawing...

I had the two hose barbs on the canister wrong. I had them backwards. Per that document, the top, smaller barb is the boost, and the other one is vac.

Here's the revision:



Even though I fixed the barb arrangement, I do not know if this schematic will properly control the VNT vanes at the right time. I am still hazy as to when they are typically open vs. when they are typically closed, and what determines which. The VNT computer knows the answer to that, but I can't ask one and expect it to just tell me :P I'm also hazy about what limits boost. I had thought that boost was spooled up quick with vanes closed, and then.... ?? Does it gradually open the vanes to regulate/limit the boost?

[arro]

Another question:

When the actuator arm is fully extended, are the the vanes open or closed? I think that the vanes are OPEN when the arm is extended, but I need verification on this.

And ANOTHER question:

Is there a spring inside the canister, and if so, which side is it on? What is the spring rating in PSI?


It would seem that at idle, the vanes are closed (via spring in the canister???), and as you accellerate more, they stay closed and spool up the boost, until a point where the boost begins to defeart the spring in the other side of the canister, and pushes the vanes open by defeating the spring in the canister. If this is true, then I can see how a manual boost controller could be fitted in the line to the BOOST barb to delay the signal to that, much the same way as with a normal wastegate canister.

I'm gonna redraw the diagram again to show this.

[arro]

The revision, with boost control:



The same setup, with second manual boost controlled external wastegate (to prevent overboost and creep):



This MIGHT actually work. WITHOUT VNT computer control. 100% mechanical.

[90vntShadow]

I just looked at my turbo, and yes when the arm is fully extended the vanes would be
open all the way reducing boost pressure. The spring is on the closed side, pulling the
vanes to closed position like you stated on idle. Not sure on the spring pressure, but it
is pretty strong. What did you think about my last idea? In your last drawing, what I
was talking about is having another boost pressure line coming from the turbo barb
with a boost controller/grainger valve that opens at a set pressure and send more
pressure into the existing boost line coming from the intake, thus opening the vanes
all the way and reducing boost. Do away with the restictor orifice on the pressure side,
and the boost controller will be between the main boost line and the turbo barb. If
you bleed pressure off the line it will maintain, or cause more boost.
What do you think?

[arro]

unless you are assuming your grainger has a restictor incorporated into it (which Gus has always said is required), the pictured restrictor has to stay to relieve the pressure in the line.

I could have done away withthe Y-junction, and had the boost barb on the turbo go straight to the boost barb on the can. I just did it off the manifold with a Y-junction for simplicity.

[90vntShadow]

I read what Gus said about boost control again, he states that you should have the bleed on the vacuum side to let the vanes close at idle. He is controlling the boost by running boost pressure into the wrong side of the canister cancelling pressure on the boost side of the canister. I think the one way valve should go the other direction on the low side, that is why you have the bleed to relief pressure on idle. You need two boost lines, one with a boost controller/grainger valve that releases pressure into the negative side of the canister when desired boost is achieved. This way you control the boost by stopping the vanes at a certain boost. That is the way I understand it after reading through it again. Read it over and see what you think. Just my opinion, but I
am not sure.

[90vntShadow]

This is really confusing, I read it again and I am wrong. For every psi of pressure on the
negative side of the pod raises the boost by 1 psi. Like I thought if you stabilize the
vanes it will keep building boost. Also you have the check valve going in the right direction, but only on the negative side. He does mention that Chrysler controlled boost
with exhaust back pressure, but with his buggy experiment he used a 2.5 inch free flowing exhaust. Maybe if you did not mess with the exhaust system you would not
have an overboost problem. I think we are making this more complicated than it really
is. He talks about a few different ideas and we are trying to combine all of them.

[arro]

Still not sure you're right about needing two check valves. The way I have it in the last two drawings, the moment you put the engine under load, it will spool up the turbocharger (which will have vanes closed because of the spring in the can). As the boost rises, it reaches the manual boost controller (not pictured, just shown as two hose ends leading to it), until it defeats it. Say it is set to 12 psi. Once it reaches 12 psi, it defeats the MBC, and sends that boost signal to the boost side of the actuator can. Since it's 12 psi, it defeats the spring (which I imagine is somewhere around 5-7 psi). It pushes open the vanes, and the turbine stops spinning as fast, until it reaches the point where the boost is barely regulated by the MBC. Thus holding boost at 12 psi.

Without an MBC, it will regulate at the actuator can's guestimated 7 psi.

Under hard accelleration, it still may want to creep beyond that, or on initial boost, it may hit so hard that it overboosts a bit past the maximum set point. Use of an external wastegate as shown in the very last diagram will quickly illeviate exhaust backpressure and prevent overboost or creep on this VNT setup.

On a VNT-computer setup, you will need to leave the hose at the vac barb alone, connected to the stock solenoid. Otherwise (if I read Gary Donovan's info correctly) you will get a check engine light. But for those of us who are NOT on VNT computers, the drawing SHOULD work (knock on wood).

Some of you might ask yourself, "Why would I want a VNT? Everyone says a Garrett T3 (from a Turbo 2 car) is better." The answer is twofold.

First off, if you're only planning to run ~15 psi, you will spool WAY faster and hit boost WAY harder with a VNT25. It will feel less like a turbocharged car, and more like a supercharged one (or perhaps just like a bigger displacement engine).

Second, for those of you willing to go the distance, a VNT-S60 is a great way to boost into the mid 20 psi range, while still getting superior spool response over a T3 or a T3/T4 hybrid. While there are larger turbos to be had with more flow, a VNT-S60 is extremely tunable, and will have better low-end, and more linear power delivery. There is a reason Porche continues to use them on the newest cars. There are also many V6 turbo kits that employ twin-VNT turbochargers, to get the benefits of ungodly spool as well as the more flow of twins.

I think it will work well for me on my Neon 2.0L and even on an SRT-4 given a VNT-S60. Might be the next best turbo kit for NA cars.