Interesting. I assume you stayed with a stock replacement, was the original just worn out and leaky, not pumping enough air? I've only been involved with replacing 1 turbo, and that was on an 11 liter Cat I think, I'm not even sure if I'd recognize the signs of a bad turbo beyond the obvious oil consumption or screaming bearing. What made you decide to replace it?
It's a really small turbo, or so I've been told. It's the Holset H1C, and this particular version of the H1C was only used in the '89 and '90 (apparently there were some slight differences in the '91-up). Anyways, I replaced it because it had 420,000 miles of use on it, and I started getting a lot of smoke from cold starts. Also, the impeller was starting to kiss the housing (the evidence was a polished area in the aluminum housing). The impeller could be moved up and down a bit when I was checking for movement, though I later found that this kind of movement is typical when not running, as the tolerance in the bearing is taken up by oil when running. However, I also had some fore-and-aft play, which is completely unacceptable (or so I read). Oh, and when I disassembled the unit, I could see scarring on the impeller blades and a sharpness to the edges as a result of the scraping.
After I replaced the turbo, I noticed a few different things. First, I can hear a hint of whine/whistle when it's spooling up, or when I let off, albeit briefly. There was no such sound from the old unit. Additionally, the rig accelerates better. It's quite noticeable. It's still a slug in the grand scheme of things, but not quite as bad as it was. And then finally (and I really do have a hard time believing this, myself), I picked up some top-end. Seriously. I hit 80 mph with it, which is something that the ol' boy has been incapable of for over a decade. I wasn't trying to do that speed, I just looked down and realized it was doing it. 72 mph was the limit prior to the new turbo. Not sure why that's the case, but whatever...I'll take it. Of course, I'm more of a 60-65 mph guy, myself.
As for the smokey cold starts, I haven't had anything close to what I was dealing with when the old unit was in. I still get some oil smoke under acceleration, but it disappears once the engine is nearing full operating temperature, and then it's gone. With that kind of mileage on the engine, I figure I should expect a little smoke. It's earned the right to do so.
