Controlling a VNT (vacuum lines, boost, etc)

[manteiv]

Has anyone out there played with the vacuum line setup on a VNT to control the vanes differently?

My understanding is that, stock, you have a line going from the manifold to one of the barbs on the can. This causes the vanes to be pulled shut at vacuum/low throttle to make boost quickly, and then boost pressure causes the vanes to open for better flow, correct?

Well, I have added a line to the other barb on the can. This line has a check valve so the can only sees vacuum, and boost is blocked. This will cause the vanes to open at idle, close for boost at part throttle, and open back up at full throttle. This makes sure the vanes move around and don't get stuck, and gives a smoother transition to boost. I've been driving my VNT neon like this for over a year.

Now, this morning I removed the second line and changed back to a "stock" configuration. . .just to see the quicker boost. Well, my car would hardly run. It would idle, but as soon as I touched the throttle it would bog really bad, A/F gauge would read full rich. Once it got the rpms up a little it would boost and be fine. Am I experiencing some sort of compressor surge or something here? What have I done wrong? I hooked the second line up and it drove fine again....

Oh, and just for info. . the third configuration for a VNT would be to hook up two lines to the can without a check valve. This would cause the vanes to be open at idle, and closed under boost. Not sure why you'd do this, but if you do be sure if you do this you have an external wastegate to prevent overboosting your car.....

later,

[oddcomp]

not sure really but i have been toying witht he idea of trying to get a few people to help me develop a digital type vnt controller that takes input from rpm car mph and map/engine load and runs the vnt accordingly..
but i need to find a vnt for my project first

i think if done right it would be far better and more responsive than the stock vacum/boost vane control

[manteiv]

Quote:

Originally Posted by oddcomp not sure really but i have been toying witht he idea of trying to get a few people to help me develop a digital type vnt controller that takes input from rpm car mph and map/engine load and runs the vnt accordingly.. but i need to find a vnt for my project first I think if done right it would be far better and more responsive than the stock vacum/boost vane control

(resurrecting an ancient thread. . )

Would you use solenoids to control the pressure to the vanes, and an electronic boost controller type device? Is this what you have in mind?

I've been thinking about trying g-valves, check-valves, bleeds, and/or pressure regulators in-line to be able to tune spool-up and max. boost.

As posted initially, I've come up with a way to slow spool-up and keep the vanes moving around (preventing sticking) using a check valve, but would like to speed up spool a bit and also raise my boost.

Right now my computer wouldn't be able to control and vnt solenoids, since its a neon. I'd think a stock vnt car would have better control capabilities built into the computer.

I'm sure some people out there have played with different configs. But with a stock vnt computer too much modifying would probably throw a code. I'm wanting to control without a computer at all so code throwing isn't a problem.

Anybody want to share their experiences?



Thanks,

[Whorse]

If you want to raise your boost you can run a boost bleed on a VNT, just requires a slightly different setup. I haven't heard of anyone running lower boost with a boost controller on a VNT, but I don't see why you couldn't. You can adjust your wastegate actuator arm to change when the vanes open and close as well.

Something to consider, however, is that with the size and nature of the VNT, if you allow it to spin too fast, it will make it more likely to overspool as it gains momentum faster. You can use boost controllers to control the boost the intake manifold sees, but that doesn't stop the turbo from spinning a bit faster. I found this when I had a vacuum line come off and I was overspooling like mad. At first it wouldn't spool, but once it started to go it just skyrocketed up to 18PSI or more, which is way too high for a VNT25.

I've redone all my vacuum lines, and it works well, and makes it much easier to work on. I still haven't got my vacuum rail setup though, so I have a lot of extra line right now. I've moved all my solenoids to the drivers side of the car (moving battery over at a later date), which has lengthened some lines, but shortened some others. I'm hoping that once I get my vacuum rail, I can mount it directly behind the intake manifold, and mount my solenoids right next to it, and drastically shorten the amount of vacuum lines I'm running. I'd also consider drilling a new hole in the firewall for the boost gauge, which is quite long as it is, and a bit of a pain with the original nylon hose going through the firewall right now (too tight to run rubber as it pinches).

Results: I certainly had some problems with vacuum leaks, as I noticed an increase in power after changing the lines. Currently I have too much extra hose running around my engine bay that needs to be dealt with, so I find that I have slow torque response on the low end, but once I hit about 3000 RPM under boost, it accelerates very quickly and breathes well to about 5800 RPM.

A good rule of thumb is that any line that sees boost should be as short as possible without comprimising functionality. From what I can see in my Lebaron, running a very short line straight off the intake manifold, with the solenoids right behind it (close to vacuum rail, turbo outlets, and wastegate outlets) is the shortest, and running the boost gauge right off the vacuum rail and through the firewall beside it would be a good addition.

As for your BOV, keep the line to it short if you're using a stock one, but the best bet is to mount it right to your top IC hose if you have a metal pipe for it.

Also, there are some lines you can remove if you wish, like the lines from your throttle body to your vapor canister. You could try using some T's or a small rail off your turbo outlet, and plugging one of them to cut back on vacuum line as well if need be.

That's about all I can suggest in terms of vacuum lines based on my experiences with my VNT.

Whorse

[manteiv]

Thanks for the detailed reply. I do need to go over my lines and check for any that could be shortened/replaced or removed. I hate touching those old brittle lines because I -always- crack a few.

I'll try a bleed and see if I can't get the response improved.

Just so you know, I have the vnt on my neon and it is setup with a deltagate external wastegate in addition to the vane controller. So, I can tweak the vanes to help spool-up, and keep boost in check with the wastegate. Its a strange setup, but it works pretty well.

I also had a vacuum line pop off the other day and had boost spike over 15-psi even with the wastegate set to 7-psi! So, I understand what you mean about the vnt spiking when things aren't hooked up right.


later,

[Whorse]

I'd be interested in seeing some pictures of your wastegate setup. Might be something I'd consider if it works well.

Something that crossed my mind today was determining which lines only need to see vacuum, and putting check valves on them as well, so when boosting, they don't need to be pressurized.

Also, for your air intake, if your're running an intercooler, which I'd expect if it's a VNT (not sure though with your Neon setup), you don't need to worry about cold air induction quite as much, so you could move that as close to the turbo as possible (like guys do with K&N cones) to get some more room and have filtered air to the turbo quicker. If you're using a stock VNT airbox, this would allow you to shorten a couple lines a bit, namely the PCV.

[manteiv]

I'll see what I can do for some pics. . . not much room down there for a camera

I'm using a modified neon air intake with a cone filter directly to the turbo routed over the tranny. maybe I'll be able to get some pics of that setup too. Pretty nice since I can use the stock barb for the pcv.


later,
brian