Just finished my VNT install!!

[Bajaman]

WOW! This thing feels like a totally different vehicle. Though I don't think my old turbo was functioning properly, so maybe its a little unfair comparison wise. Similar to others who have done this install, full boost (11 psi in my case) can be achieved by about 2k. I will have pics posted later with all of the modifications I did to install this. Not necessarily for the faint of heart, but by far the best modification that I have done hands down. My black smoke has also mysteriously disappeared

As for the control, I used the stock (Liberty) vacuum diaphragm and reworked the VCV to operate reverse of what it normally does (0" Hg at idle 15" Hg WOT) and finally a spring operated pressure controller to limit the boost. Works perfectly. Boost builds rapidly to 11 psi then stops abruptly (I can dial this value in with the tension on the spring). Cruising boost can be varied by adjusting the VCV (>0" Hg at idle). I am glad that I decided to try this method as it is so easy to adjust and works great. It also has the side benefit of a safe fail mode i.e. loss of vacuum = no boost.

I do have one question though. Can anyone describe what surging sounds like? I can distinctly hear the normal whine of a turbo spooling up, but then above 3k WOT I get a slightly lower pitch humming for lack of a better word. Since I have never heard surging first hand, I cannot tell if that is what I am hearing.

[Bajaman]

Just watched a video of surging. Definitely not that. FI, BG you guys have this sound that I am talking about? I will try to get a clip of it.

[bgkast]

Maybe it's your exhaust vibrating?

You will have to post some pictures of your actuator set up. Sounds like you got a good system.

How did you reverse the VCV? Mounting it upside down?

[Bajaman]

As promised some pics of the install. First the adapter plate. This was made of 3/4" plate. Two 10mm bolt holes are countersunk for cap head screws, the other two are for the 8mm stud and a 10mm threaded (I screwed up so it ended up being 1/2"). Then of course the other three holes tapped 8mm. I took all the dimensions from this post. (Thanks bgkast). I also added a 1/4 NPT for the thermocouple and tapped a 1/8" NPT for pressure measurements.


Next up is the exducer adapter. This is a 1-1/4" x 1-1/2" exhaust pipe adapter with 1/4" square welded on one side (thanks again bg), and 3/8" square on the other end with some machining on a lathe. The inner part of the flexible coupling slides right in.

Here is the whole mess installed. I used a GM 3.8 air box which fit very nicely in front of the turbo. No K&N for me thank you very much. I also used a 240 oil separator (not finished in pic). The vent gas will go into the clean side of the air box in place of the OEM pressure transducer?

Also if you look close in this pic you will see the boost limiter on the intake manifold, which cracks open at a given psi and bleeds off vacuum to limit boost.

Finally, the modified VCV. I disassembled a VCV and bent the linkages as shown. This just reverses the rotation of the shaft with pedal travel


This is the schematic of how it works

[bgkast]

The schematic does not work for me.

Looks good!

[KarTek]

I can see the schematic but not the pictures... Turbo surge happens when the engine RPM is too low for the amount of air the turbo is trying to move. This happens when it's lugging in a particular gear below a given RPM. On my truck it sounds like ch-ch-ch-ch-ch-ch with the pitch going up with the throttle position, sometimes morphing into more of a woo-woo-woo-woo sound at higher power levels.

In my case, the limits before surge are no more than 10 PSI below 1800 RPM and anything goes above that.

[bgkast]

Originally Posted by KarTek

I On my truck it sounds like ch-ch-ch-ch-ch-ch with the pitch going up with the throttle position, sometimes morphing into more of a woo-woo-woo-woo sound at higher power levels.

[Bajaman]

Originally Posted by bgkast

Looks good!

Thanks!!
I changed the images to urls maybe that will work

[Cervan]

Installing a blow off valve will remedy any compressor surge. Not a cheap one that makes a huge WHOOOSH every time you let off of the throttle, i mean a good solid tial or greddy BOV.

Originally Posted by Cervan

Installing a blow off valve will remedy any compressor surge.

Adjusting the minimum vane setting (should be a little set scre under the lever) is the easiest remedy. Having the vanes just a little more open from the start will reduce backpressure on acceleration and get rid of the surge.

[bgkast]

Originally Posted by Bajaman

Thanks!!
I changed the images to urls maybe that will work

Yep, they work now.

[Deni]

They don't work for me. It says file not found.

Same here, file not found except the schematic.

EDIT: I think its not allowing direct linking. Entering the link while on the 404 page displayed the pictures.

[Bajaman]

Can everyone see them now?