A funny thing happened at the dyno...

[sjf911]

I was on my first low load pull checking the base map in second gear running about 5600 rpm and a MAP of 40 kpa when we started blowing big smoke out the back without any change in the engine numbers. I shut down and immediately went to the back to find the crank case breather hose had blown off the oil tank connection and acted like a fire hose quickly blowing 2 qts of oil ( Mobil V-Twin 20W-50) out the back. It created an oil slick about 20 feet behind the car suggesting a lot of pressure behind it.
I am running a stock SC oil pump, stock 930 high pressure oil line and check valve to the turbo and a Tilton electric scavenge pump from the turbo back to the upper left chain box. The oil tank is vented through a catch can to the atmosphere. Compression is equal in all of the cylinders without any significant leak-down and I wasn't burning any oil out the exhaust.
From what I can gather, this appears to be a result of inadequate oil pump scavenging by the SC pump at high rpm and I assume oil foaming in the crankcase as I was doing a long slow pull trying to match the rpm/MAP bins. The retaining clamp may have been relatively loose but I also think that the stock SC breather hose restrictor acted as a pressure dam and contributed as it was ejected from the hose. In any event, it suggests that there was a significant issue of inadequate scavenging from the crankcase with this sustained high rpm run and a significant increase in crankcase pressure from oil foaming.
I have actually been driving the car on the road including quite a few WOT runs to maximum boost prior to this and never had any noticeable issues. This was never an issue on previous dyno sessions before the turbo conversion (the breather hose was never disconnected at the tank), so I can only assume that it is an issue with the increased return of oil to the engine sump from the scavenged turbo oil aggravated by sustained higher rpm run. I also don't know if returning the scavenged oil to the upper part of the chain box is contributing to the foaming.
I removed the breather hose restrictor so I don't think this will happen again but it still implies that there is a foaming issue and likely significant crankcase oil returning to the tank unfiltered via the breather hose at times. The only short term solution I can think of is to reroute the turbo scavenged oil either closer to the engine sump (if significant foaming is occuring in the chain box) or directly to the oil tank. The problem with going directly to the tank is the lack of a convenient port to return the oil to the tank and needing to add another oil filter.
Suggestions? Anyone else have similar issues?
Thanks

[patkeefe]

Well, the only way to pressurize that breather is to pressurize he crankcase. I had good leakdown and compression numbers also, but always fought a high crankcase pressure also. Finally, one oil ring let go. I think the ring lands on the old CIS SC pistons couldn't stand the pressure from the turbo, and gave up. I have a well documented trail of everything that could possibly go wrong with your lubrication system with a turbo, search my username.


http://forums.pelicanparts.com/showthread.php?t=434997&highlight=piston

[sjf911]

Originally Posted by patkeefe

Well, the only way to pressurize that breather is to pressurize he crankcase. I had good leakdown and compression numbers also, but always fought a high crankcase pressure also. Finally, one oil ring let go. I think the ring lands on the old CIS SC pistons couldn't stand the pressure from the turbo, and gave up. I have a well documented trail of everything that could possibly go wrong with your lubrication system with a turbo, search my username.


http://forums.pelicanparts.com/showthread.php?t=434997&highlight=piston

These are actually new JE pistons/rings with QCS cylinders from Henry that have less than 2000 miles on them that were very carefully broken in so I believe the rings are well seated (or at least should be).