Cribbj,
Yeah, compression tests are good for what you described. Most professional engine builders I know don't really do leakdown tests because they aren't always consistent and aren't really repeatable. You could try forever to get an engine to give you even, good leakdown results... and it wouldn't make a damn bit of difference on the dyno. Blowby is a MUCH better indication of actual operational engine sealing. You can see stuff like ring flutter and sometimes detonation (causing the rings to unseat). You can also tell if a motor is getting tired and may be in need of a rebuild. With that said, some types of engines that see very stressful, short duty cycles (think drag engines) will have drastically different requirements for ring seal than say a daily driver. This is why I asked about how the Lextreme's engine builder put this particular engine together.
Now that I've blabbed on about blowby for long enough, there are about 10-15 different reasons why Lextreme's engine could be having problems with oil consumption and 'quality' after adding a turbo. Unfortunately, without a lot of data, it's a complete crapshoot as to the actual cause (or causes) of his problems. Something that is done for OE applications is to plot center housing leakage vs. pressure differential across both the compressor and turbine piston ring seals. Depending on where on the compressor map you're operating (directly related to your turbo match), the seals can leak. It doesnt mean they're bad, it's just not possbile for them to seal under all conditions you throw at them. The leakage can be pronounced when you've got a oversized compressor running low boost. I'm not sure what kind of boost you're running and power you're making. Just something to think about.
Do you have any smoke out the tailpipe on acceleration? There are about 5 different possible causes for that if there is... most of which have nothing to do with the turbo. Unless you can pull apart the turbo it's basically impossible to assess if it's the turbo of the engine.
For people that have puking oil problems, the most 2 most common problems are oversupply and poor drainage. The drains on all of our turbos MUST BE AT LEAST 1/2" INNER DIAMETER! Larger frame size journal bearing turbos can require even larger return lines sometimes. The other thing that is CRITICAL is that the oil drain back ABOVE THE OIL LEVEL IN THE PAN. If there is any possiblity that the oil can back up into the turbo, then you're almost guaranteed to have problems. The other thing that's very important is the drain line must have a generous slope back to the pan or else it is possible to get oil backed up into the center housing.
Journal bearing turbos require MUCH more oil than our ball bearing cartridge turbos. Don't confuse the GT line with ball bearings. Any turbo with the 'R' designation after it means it has the ball bearing. GT is just our current product line. GT series turbos have improved aero wheels and better wheel materials. I've seen some small oil feed fitting restrictors. A GT28 can probably get away with a .075 hole (or maybe smaller). To give you an example of oil flow requirements... the crankshaft on a 1.6L Cosworth BDA that I've been involved with uses 0.050" hole at normal oil pressures to lubricate the ENTIRE bottom end at 12,000 RPM. The best people to ask should be our performance distributors. They have direct connections with the people that run our turbos, so they could tell you what other people have run before.
Now, truth be told, I forgot that I ever put where I work on my profile. I hate to have that on there because people don't always take what you're saying with a grain of salt. I'm not the "horse's mouth" by any means. I've got my opinions, and they don't necessarily reflect the views or recommendations of Garrett. As such, I don't like to be thought of as an "expert" for turbos.
Anyway... yes, I suppose I'm biased toward choices in turbo brand. I'm going to be quite honest with you... We produce extremely high quality turbochargers. The aftermarket group at Garrett uses OE production released parts, so they're top quality in design, engineering, and manufacturing. I KNOW first hand how much engineering goes into every turbo we've ever made. I KNOW how much testing and how much history there is behind every component and every turbocharger assembly we make. If you could see what I see every day, you'ld never even consider using another aftermarket turbocharger.
The unfortunate circumstance of selling to the aftermarket is that the people in the aftermarket are generally kooks. Most turbo failures we hear about are 100% because the person using it didn't actually know what they were doing. Personally I think it's a shame that Turbochargers and Maximum Boost are the only two books that most people can read and understand. If I ever get enough motivation, I'd like to write a better turbocharger book that actually explains what's going on with turbochargers. The information is out there, but most people need to raise their level of understanding (MORE READING!!!) before they 'go turbo'. I suppose that's why I'm here answering questions...
-Kirk
