Turbo questions...spooling and drive pressures

[ToddMcMilian]

Howdy gang, I have some questions about my turbo on my 2008 6.7 cummins. A few weeks back I had my turbo replaced on my after market warranty. The replacement turbo was very noisy in terms of spooling, at about 2lbs you could really here it spool up which I actually loved to hear. Unfortunately that turbo crapped out in 4 weeks when the vanes stuck so I had to have it replaced again...same model from same mfg. This time when I got the truck back, the new turbo is very quiet and I actually barely notice it until around 10 lbs of boost and then it's still not much. I also noticed on a drive I make every weekend that this one may actually be taking more exhaust pressure to drive it, almost like its tighter to spin. I am seeing some higher egts, still acceptable temps but just nothing I have seen in the past at the same speed, same hills etc. It appears to be performing at acceptable limits but it's got me wondering what makes one turbo "tighter" for a lack of a better term, than another one when it's the same model, same mfg, and nothing with the truck has changed . Truck is fully deleted running 4" pipe. I'm really close to doing a 2nd gen swap and getting away from the vgt model all around but in the meantime, I still am blessed with the need to understand what makes this new turbo act different than the previous.

 

[lpennock]

Sounds more like a boost leak with the higher EGTs.

 

[cerberusiam]

The VGT's are a finicky animal, the new one that crapped out probably had problems in how it was setting the vanes or just a bad rebuild. They should be essentially very quiet with almost no sound if stock. The higher EGT's could be a boost leak or it could just be the collar not sliding as far when commanded. As long as the temps are not extreme it is likely just the way the turbo is reacting.

FYI, the Holeset does not uses variable pitch vanes, it uses a sliding collar to control exhaust flow on the turbine.

 

[ToddMcMilian]

The VGT's are a finicky animal, the new one that crapped out probably had problems in how it was setting the vanes or just a bad rebuild. They should be essentially very quiet with almost no sound if stock. The higher EGT's could be a boost leak or it could just be the collar not sliding as far when commanded. As long as the temps are not extreme it is likely just the way the turbo is reacting.

FYI, the Holeset does not uses variable pitch vanes, it uses a sliding collar to control exhaust flow on the turbine.

That is true. I always use the wrong terminology for those. That does make sense that perhaps the collar isn't having as much travel as the old thus not using the exhaust as efficiently to drive it. I just wasn't sure of in the build process something gets set as far as tightness and perhaps this one is just tighter or something of that nature. I sure wish the sliding setup wasn't so prone to problems on these, sure isn't awesome.