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Understanding Duramax VVT Turbos

Practical Diesel Tuning

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I have an aftermarket 65mm turbo on my LBZ Duramax and it feels like it's really slow to make boost even when I command it to close to 100% vpos. I wish I would have purchased a stealth turbo from Nick, but I got a heck of a deal on the turbo I have and couldn't afford to get a stealth. My question is, how does the Duramax know what 100% is? I'm wondering if my truck thinks it's commanding 100% but in reality it still has more to give? I've added a back pressure sensor to help have an understanding of how the turbo is working, but it doesn't seem to build very much back pressure either. I'm expecting to see upwards of a 12:1 boost to back pressure ratio from a stop and if I jam the pedal but it feels like the vanes are opened and flowing too much to allow it to spool. Ive already checked for boost leaks multiple times and installed new up pipes and can't hear or see any exhaust leaks anywhere. I've done lots of form scouring and haven't found any info, but would like to have a better understanding of how the vanes actually work. When a new turbo is installed, how does it determine what 100% vpos is? Is it possible that either my actuator or sensor are to blame or is it simply that the turbo is designed to flow too much even at 100% vpos.

I also have 60 overs so I should have enough fuel to help the bigger charger and maybe I need to tune the timing differently to help with turbo response?



The Duramax VVT turbos know their position by using the screw-in vane position sensor on the center top of the charger. The sensor is a plunger that basically reads the lift on the cam arm which is used to rotate the unison ring. I'd like to help you as much as possible but there are a few things that are 'builder specific' to these turbos which can significantly alter the way the unit works. Some builders use custom unison rings which can skew the vane position (angle) relative to the cam arm. In those situations, 70% vane position may actually be full closed. This is how Danville's Stg 2r works. Without knowing the turbo or the builder it's really hard for me to make tuning suggestions.

Also important: On a stock VVT, anything greater than ~83% closed will result in worse spool up off idle. Guys think that allowing the turbo to close up to 95% is going to make it spool quicker but in reality the exhaust gets choked and the turbo spools up worse. Just like how there's such a thing as 'not enough vane position' there's also 'too much', and the symptoms can be eerily similar.

I would experiment with vane position until you find the best response. It may not be 80%, it may be 55% or 90% depending on who set it up.



I appreciate the response! I don't know if you have any experience with Wold Fab, but that's who built the turbo.

I'm hoping that if my vane position is too tight, I will see the boost to back pressure ratio go up too high when the exhaust is choking the engine and that will be my signal to lower the vpos back down. I will have a setup to Datalog the back pressure sensor so it will be easy enough to see what the boost to drive pressure ratio is all around the map. Do you know if this is the case or will that data not help?

Do you have any suggestions on how to tune for the best turbo response? Im thinking of disabling the PID controller and then having 5 dsp5 tunes all the same besides the vpos and just offset the stock vpos table by 5-10% for each of the tunes and see which one drives the best. Do you have any tips or methods that would yield better results that you can suggest?


Im thinking of disabling the PID controller and then having 5 dsp5 tunes all the same besides the vpos and just offset the stock vpos table by 5-10% for each of the tunes and see which one drives the best.

This is a pretty good way to get things sorted out. From there you can re-enable the PID controller and log vane position into a histogram. The average values in the histogram can be used to fine tune your Desired Vane position (feed forward) table.


Nick are you in the USA?


I'm in Northern Illinois. Woodstock to be specific.

I’m installing a stainless diesel 63.5 5 blade drop in turbo on my 07 lbz. Is there anything I need to change on turbo vain position table for it work properly or just log it and see how it does with stock settings and adjust if needed?


Because each turbo supplier has their own recipe for unison ring and vane sizing it's important to ask the turbo supplier what they recommend and start from there. Unfortunately I do not have experience with SD's LBZ charger so I cannot make a recommendation. If you're totally in the dark, start with stock vane tables and watch how often the truck runs against the maximum limit. You may experiment with raising the max limit if your logs suggest a lot of time spent there. Work in increments of 5-10% vane position.


Ok will do thank you very much Nick!

Ok team. Have an issue with a 2014 2500hd silverado duramax, and on side of the road unfortunately.

Truck was going fine, now it's got no boost at all and blowing smoke.

Checked all hoses and also confirmed vanes are moving by removing plug and manually moving the plunger in and out.

Lots of oil when I opened the plug.

I haven't checked the solenoid yet (but it is the suspect) . A, it's a pain to get too and b, I don't have a way of getting power too it. Normally I'd just drive slowly home but I'm towing and there are hills both sides of me 😀

Question. If I put a spacer in to stop plunger traveling out so far will that give me some boost or does the plunger need to extend out for boost.

I will try it any way. But am interested in any advise.

Best regards too all


Hey I'm pretty sure you are right that adding a little spacer would keep the vanes tighter, but that could really cause issues and I would be concerned trying that. I'm pretty sure you have a boost leak. Do you have a scanner to display the vpos as you drive? If the vpos is staying at a low number, than there is a chance the computer is commanding a low vane position. Maybe a bad sensor causing it to think it has too much boost or something. Otherwise if you are seeing the vpos read high numbers, the turbo is doing what it can to build boost, but that air is just leaking to atmosphere and not making it into the engine.

I've had a boot blow when towing and experienced the same issue with no power and a lot of smoke. I was making a good amount of boost at the time so it was pretty obvious to hear the boost all leak out at once when the intercooler pipe blew apart.

Hope this helps and that you get back home safely!!

Thanks, Wildeman101.

Tried the spacer and it was worse, all the system is working there ( as in the plunger is moving freely and i could push the end plug in about 40mm and using a 3/4 extension hold and release it back to its seat when engine started running). Checking for leaks is a workshop thing and I'll get onto it, visually though I couldn't see anything crazy or feel anything around the joins.........,

I did manage to get where I needed too. Was able (in manual mode) to get enough revs to keep it in a power range. Over 2500rpm it started to have sporadic boost power.

Black smoke everywhere.

Will get into it over the next few days. Ordered a boost control solenoid and a position sensor so I'm not chasing ghosts.

Best Regards

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