Quote:
Originally Posted by Rob@RBTurbo
T1M,
Hopefully your builder is pretty good. We've had to rebuild probably 5 sets of our turbos over the years, nearly immediately after they were rebuilt from another. In fact we just had to do exactly this a few weeks back, and we can tell you we have not heard of one occasion it has gone well... but perhaps it does at times and as such we just don't hear about it. 
As for VSR balancing an older turbo- especially one that has been used for a long while- typically the results aren't that great even if the unit was absolute perfection on initial build. As these units were originally purchased in 2012 this was in an era when we outsourced our VSR balancing function (from a shop in the UK that we later realized had some fairly antiquated equipment- and also think they may have been doing a "quickie" job which is unfortunately common when outsourcing). As for the result you achieved you mean 0.389g max correct? If so that would be damn good, REALLY good, for an old used unit. FWIW 1.5g is what is known as the "acceptable" range, however we balance all new units to ~0.1g across the entire RPM range. Having been in the business we know when you put an old used unit on the machine you are seldom going to see a brand new like 0.1g resultant.
Regarding the off Axis CNC- this is something we have never seen/corrected/etc over the years- quite frankly something I'm not sure is correct. Feel free to email us any additional info, would like to see that portion in more detail if there is anything remaining.
Overall agree with you though, we use some pretty high end stuff- cutting corners to save a buck is not really top priority over here- and outsourcing anything such as balancing is no longer in any sort of our processes (for quite a long while now). 100% wish we had the equipment we've had the past couple years and the build strategies as well since introduction; but that is just 20/20 hindsight speaking and nothing we can do to change that now.
Rob |
Cheers Rob. They do a lot of time attack and tarmac rally turbos with an excellent track record. They did my old evo and many of the guys cars I tuned turbos as well. I just updated the compressors to billet 15T spec and left the 12 blade MHI TD04L turbine and shaft alone. I trust them enough to try them, and if something goes wrong its $30 shipping and next day delivery with a week turnaround time.
Point taken about them not holding balance over time, he did say it should have been better, though. The balancing was done originally from those you outsourced to by taking material out of the back of the compressor wheel, it looked a bit shabby but I'm told a few years ago this was pretty normal for cast wheels. Billet wheels are much closer to zero, in fact one of mine after being build ran up at 0.0614 G untouched which was nice, the other took a little more work but came down to 0.0184 G after trimming. They have a <0.1G policy too but I asked them to be a bit more pedantic.
The off-axis compressor cover was noted after rebuilding, it was in the range of 0.8-1mm off and was correctable easily enough. I don't have pics of this, it was just mentioned to me after the fact as it wasn't a showstopper just a hmmm that's interesting. With any luck they'll last a long time, and they'll have a pretty easy life on my car, I'm only planning to run around 15psi.