how to do a twin vnt turbo setup on an 01 firebird

hey guys, i havent found anywhere else on the net to ask this question so here goes. I want to do a twin vnt 25 turbo system on my 2001 3800v6 firebird. I am running into problems though. Since i dont have the computer to control the actuator for the vnt how would i go about getting it to work? I was told by someone in the tubo section that i can control it like a standard wastedgate, how do i do this? Also how would i need to hook up the vacuum lines in my application? I am willing to do just about anything to get these things working on my car. any help would be greatly appreciated.

John.

[crazyace]

It would be pretty much a large waste of money getting two VNT's to just use them as regular turbos. You have two choices as it stands right now, One is to get two normal turbochargers that are properly sized for the engine and Two is get a custom designed computer to control the whole set up the way it is intended.

[CSXT404]

Try to find out how the 1989 GTA Trans Am and Grand nationals were done. You might be able to go old school and link up the computer from the old trans am. They were 3800 series motors if I remember correct. I would just put a single garret on it too. 1 big turbo is better than 2 small turbos.

Just my thoughts.
Mark

wow, um i think you are misunderstanding me. i want to use the vnt system i dont want them to be standard turbos. I am not new to turbos at all just new to VNT's. I see a pretty big advantage with them because of the quick spool up which would allow for more power under the curve. What i want to know how to do is use the vnt system on my car without the dodge computer and how to hook up the vacuum lines. Please just explain how to do this. I havent found any other vatn style turbo that i can afford or that would be the correct size. There has got to be a way to get this to work.

You don't need a computer to run a VNT-25. It uses a twin port actuator. You hook up one port to manifold vacuum, and the other to the scroll housing.

From memory, the larger port is manifold vac, but it's easy to tell. The actuator spring keeps the vanes closed. Manifold vacuum at light throttle will pull the vanes open. Once vacuum drops, the vanes close down and stay there up until 6 - 8 psi of boost or so (the actual pressure is adjustable via the actuator rod).

From that point on, the vanes open up as rpm/exhaust energy goes up, maintaining more or less a constant boost level.

The only tricky issue would be balancing the two turbos, but that's no different than balancing standard turbos.

You need to make *sure* your pressure line to the scroll housing is in good shape and clamped well. If it pops off under boost, the vanes will close and over-speed the turbo. You can also run a g-valve in the line to raise the boost like a regular turbo as well.

Boost will spike quickly to the 6-8 psi according to where the rods are adjusted, then raise a little slower as a standard turbo would to whatever maximum you have the g-valve set up for.

--Dan

ok so just to make sure i'm getting this all right. I run one line from the turbo to the manifold (i would assume just behind the TB would be ok) and then i just run one a short line from the other hose fitting on the turbo to the scroll housing on the turbo? This sounds pretty easy. Now how do i adjust the pressure with the actuator rod and what is the G-valve?

Now as for the one big turbo being better than twins. Ususally one turbo will perform just as well as two smaller ones, not better from my experience. twins have the advantage of less rotating mass which "can" reduce spool up time but this is neglegable. twins also allow for more possibilities as far as mounting locations. Also do to how my car is designed if i were to locate the single turbo in the one place it will fit (in the space in front of my engine where the extra two cylinders of a v8 would go) i would only have one choice as to where to run my down pipe... under my k-member. also the amound of piping it would take to run the exhaust from the back of my engine to the front would induce a lot of heat loss giving much less energy for the turbo to use. the only other option i have is to make custom forward swept manifolds but that is a lot more work than modifying a set of aftermarket headers to attatch to the turbos. And yes i know i will need a scavange pump since they will be mounted very low (im getting a mocal). Also i like the vnt system and wanted to take advantage of the quick spool. i have made my decision to do twins after months of working this all out and to use vnt's a while ago as well i just cant find any sites with good info about how to use them. thanks for the help thus far guys, hope to get more info soon.

Quote:

Originally Posted by tpunk ok so just to make sure i'm getting this all right. I run one line from the turbo to the manifold (i would assume just behind the TB would be ok) and then i just run one a short line from the other hose fitting on the turbo to the scroll housing on the turbo? This sounds pretty easy. Now how do i adjust the pressure with the actuator rod and what is the G-valve?

Yes. And I checked the ports again to make sure. The top (small) port on the actuator is the pressure port. The lower (larger) port is the vacuum port. Also, on the vacuum line, I use a checkvalve w/ small relief bleed so that port sees vacuum only. Otherwise you get the same boost pressure on both sides of the actuator diaphram and the spring will keep the vanes closed.

The g-valve is a grainger valve. It's a spring loaded ball check valve. But, you could use any kind of bleed for raising boost. http://www.xmission.com/~dempsey/perform/grainger.htm

The rod is threaded. To adjust it, just loosen the lock nut and screw the clevis in/out. The tighter you make the rod, the higher the boost will go before the vanes start to open. 8 psi is about the highest you can go though. Trying to go higher rusults in the motor falling on it's face. I think it's stalling the turbine. Not sure what it is, but it's very noticible when you've gone too far.

It's not exactly a pretty install, but I have some pics here:
http://www.houlster.com/amigo/turbo2/images

The 102* and 103* pics show the actuator ports lines. I'm using the actuator remote mounted in these pics, but went back to a direct mount again after I swapped out the brake booster and had the room.

--Dan

yeah i have deffinately visited your site a few times (in fact it was the most informative i have found yet). thanks for all the help, i think this is enough to get me on my way. I'll post here again when i get the system done so you guys can see how it turned out. thanks again.

John.

i like the vnt idea, but for the sake of debate...why not supercharge? the 3800 supercharger with an overdrive pulley kit is a simple, cheap, dependable method of producing that "power under the curve" i think...