[hotrod]

Just thought I would try and post some images of the turbo I just pulled out. It took a while to figure out how to get descent resolution images.

Richard I will send them to you by email if you could post them up as I have no place to host them.

Keep in mind a couple things:
1. On casual examination the impeller looks just fine, its only when you look close that you see a bit of errosion at the outer impeller tips.

2. I suspect I was over spraying (3%) mass air flow, and I also experimented with spraying at high idle speeds (very low throttle setting). I discovered that this would act to cool the intercooler prior to drag racing.

(note to self, very good idea for post turbocharger pre-intercooler injection point . If you could manually trigger this pre-intercooler spray prior to drag racing, or Autox event all the evaporation takes place in the intercooler and quickly cools the structure of the intercooler. Due to the engines air flow you completely eliminate any need for external fans to cause cooling of a heat soaked intercooler while the car is stationary)

I suspect during these experiments I may have had some liquid water streaming down the walls of the turbo inlet pipe. I believe, this could be a possible cause of the erosion at the compressor impeller tips.

IF that proves out to be the case, it might be useful to put a trap of some sort in the inlet tube that would re-suspend any surface water in the air flow. This could be in the form of a ridge that would stop the droplets that tend to run down the surface of the inlet tube and cause them to be ripped apart by the high speed airflow as they try to climb the lip.

3. Last but not least, it is important to note that I also made about 6 drag strip runs with this turbo using no air filter of any kind, to determine the intake air restriction the filter creates, and its effect on turbo boost. This was through a cold air intake system that had the intake in front of the right front tire and directly behind the front bumper. At the strip I run at there is a section of gravel/dirt you must drive over as you pull off the strip. I know I sucked up some dirt on at least one of those events. Shortly after that experiment, I pulled the discharge off the turbocharger and found small amounts of aluminum dust in the turbo to intercooler tube and some very fine dust. I wiped this off and it did not return after that. If you look closely at one of my pictures you will see a clear "meteor crater" impact about a quarter mm in dia. on the leading edge of one impeller blade from a piece of grit.

My personal judgement is most of the errosion is due to these no air filter tests, and the effects of the water were minimal but I cannot prove that case. After I run my current turbo for a comparable period of time I will pull the intake tube and check for similar wear without having ever made any filter free passes.


Larry