| Mr. Jim Wolf concerning the issue of smoking turbos with free-flowing exhaust. Although the fundamental nature of this problem is very clear in my mind, he did offer up a few additional pieces of information of interest. Let me first detail what I had previously mentioned with regards to this problem. 1) When installing downpipes and testpipes into the vehicle, the lack of backpressure will allow oil to pass through the rear turbine seal, causing the smoking condition that a number of people have experienced. The lack of backpressure in the system allows the negative pressure side of the exhaust pulses to create a pressure differential on the rear turbine seal where the "inside" of the turbo cartridge is at higher pressure than the "outside" of the cartridge, thereby forcing a few drops of oil through the rear turbine dynamic labyrinth seal. When cats are still in place within the exhaust, these negative pressure zones in the exhaust pulse train are minimized to a point where there is not a negative pressure differential on the seal, thereby preventing oil passage through the seal. Mr. Wolf added several things to these facts of which I hadn't considered namely for the fact that they aren't specific to the Z32. Some vehicles have the turbo oil return lines plumbed into the engine at a location below the level of the oil within the pan. This causes issues with creating higher pressure within the turbo since the oil flowing out of the cartridge has to "push" the level of the oil in the pan in order to bleed off. The 350Z twinturbo folks have this problem significantly when they remove the cats since their return lines are below the oil level in the pan. A suggestion that Jim made, something that they do, is to place a restriction of some kind over the muffler tips so as to produce backpressure in the exhaust. He said that this is a very conslusive test to determine if the problem is due to insufficient backpressure. However, if your car didn't smoke with the OEM DP and midpipes and then it started smoking as soon as you installed them, there is no question what the problem is - you simply did the test in reverse. So, those of you who feel that I just pull things out of thin air and have no basis of understanding: shut the front door, now you heard it from "the man". Moving forward in the conversation, we spoke about various things concerning ballbearing turbochargers, that they are also subject to the same problems as they have the same turbine seal technology in them - we both chuckled when I made the comment that "Total-Seal" needs to start making turbine shaft seals (the kind that has no end-gap). I've got business to take care of, but just wanted to entertain you folks a little and add some substance to my statements for those of you who think I'm just pulling my ideas out of thin air.
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