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May I suggest to delete the vent from the cam housing? The catch can on mine is only fed from the AOS and it barely fills up at all.
How does the new hotside compare with the previous one?
I do plan to give that a try. Since the dip stick was popping up when I was using the AOS side port and cam tower, I suspect the cam tower is not a great pressure vent anyway. There must be meaningful air flow restrictions to the cam tower when the lower crankcase area gets pressurized. I think my car throws off a bit more oil than others, but the AOS can handle that for sure. The only question is whether the AOS alone can vent enough air to keep the dipstick in place. Fingers crossed.
The new turbo is awesome. Backpressure is down to 1.5:1, with 1 bar at 3000 still. Seat of the pants is night and day, but that may be in part because the old hot side was looking bad when I removed it, so I was probably gradually losing power over the years as it got worse and worse. The feel of the car is back now though, with a vengeance...
I do plan to give that a try. Since the dip stick was popping up when I was using the AOS side port and cam tower, I suspect the cam tower is not a great pressure vent anyway. There must be meaningful air flow restrictions to the cam tower when the lower crankcase area gets pressurized. I think my car throws off a bit more oil than others, but the AOS can handle that for sure. The only question is whether the AOS alone can vent enough air to keep the dipstick in place. Fingers crossed.
The new turbo is awesome. Backpressure is down to 1.5:1, with 1 bar at 3000 still. Seat of the pants is night and day, but that may be in part because the old hot side was looking bad when I removed it, so I was probably gradually losing power over the years as it got worse and worse. The feel of the car is back now though, with a vengeance...
I new Vitesse turbo -- similar to the old one but with larger hot side and less back pressure. Feels very strong, and still 1 bar of boost at 3k rpms...
Sorry to bring up an older thread, but I'm finally getting around to addressing my lack of vacuum through the AOS since I installed my M-Tune a few months back.
I have the issue of my turbo not draining efficiently at idle with this lack of vacuum, thus smoking when idling after a decent pull or simply after driving around for several minutes.
I've been trying to think of the simplest solution, and then I thought of the following:
If I was to use the later style AOS-to-intake hose on my '86 (pictured below, from Lindsey Racing), would it be possible to run a vacuum from the intake manifold through a check valve, restrictor, and PCV, straight into the port on the AOS hose originally used for the pressure vent (plus a check valve towards the MAF tree so it doesn't suck air in through there)? That vent port would still technically be functioning as it was designed to do, along with all flow through the AOS, but it would simply be exaggerated by having a light vacuum running through the vent port.
Would there be any downside to this that I'm missing? Guessing I would still ideally need a catch can (really trying not to run one to keep it less cluttered under the hood)?
What turbo are you running? Are you sure you don't just need a restrictor at the oil inlet? Did this start when you added m-tune, with no other changes?
If I understand your idea, I'm not sure how much vacuum you'd get in the crankcase since you'd be t'ing into a line that is essentially open to atmosphere at the other end -- or am I misunderstanding your idea?
What turbo are you running? Are you sure you don't just need a restrictor at the oil inlet? Did this start when you added m-tune, with no other changes?
If I understand your idea, I'm not sure how much vacuum you'd get in the crankcase since you'd be t'ing into a line that is essentially open to atmosphere at the other end -- or am I misunderstanding your idea?
Stock K26/6. Yeah, it started only after the M-Tune install, no other changes involved. 67,000 miles.
The idea is to use the vent port on that AOS hose (where the little black plastic pressure relief valve normally goes in) as the 'tee' for an intake manifold vacuum to go in. So the port would no longer go to the atmosphere, but to a light IM vacuum source (after a restrictor and whatnot).
I've pondered and farted around with this whole crankcase vent issue; and over time I've come up with a simple solution.
Replace the oil filler cap with a cut piece of foam to fit into the oil filler opening. Cap off the port from the AOS to the turbo compressor. You now have an independant crankcase vent to atmosphere, where you leave the oil filler cap off, and the crankcase vents through a huge opening (the oil filler neck), but the foam traps the oil vapour. Any crankcase pressure escapes instantly and the intake track, including IC, remains squeeky clean (catch cans still let oil through, somewhat)
I'm all about function before form.
Is it redneck; yes.
Is it effective; very
Thomas,
Are you still running with this arrangement? I too am a "function over form" guy looking to eliminate positive crankcase pressure under boost. This seems too good to be true, compared to the more elaborate arrangements used by many others.
Has anyone considered a crankcase vacuum pump? These have been used successfully in race engines for years. At first to prevent pan gaskets from being blown out. Then progressing to deal with blow by from blowers, turbos, nitrous, low friction rings, etc. Crancase vacuum pumps have also proven to increase horsepower by increasing the piston ring seal.
Are you still running with this arrangement? I too am a "function over form" guy looking to eliminate positive crankcase pressure under boost. This seems too good to be true, compared to the more elaborate arrangements used by many others.
Roger
have you measured any crank pressure or just think it might be there based on some symptoms you've seen?
been reading through this thread and others on the topic and other folks' measured crank pressure even under heavy boost go from 3 psi crankcase at 17psi boost and 8 psi at 23.
have you measured any crank pressure or just think it might be there based on some symptoms you've seen?
been reading through this thread and others on the topic and other folks' measured crank pressure even under heavy boost go from 3 psi crankcase at 17psi boost and 8 psi at 23.
I haven'y actually put a gauge on it, but I would say I'm pretty certain that I'm getting excessive pressure. The engine has an unknown amount of miles, so lets just assume "over 100K". Compression is decent, 135-140 psi (cold). Under full boost (set at 15 psi) I get a fair amount of black smoke out the tail pipe. Plugs get a little black and crusty. If the oil level is high, it will sometimes hesitate/detonate under full boost, which I think may be related to the ingestion of oil vapor. Only an issue when the oil level is up towards the top of the fill range.
My front crankshaft seal started leaking, so I am going through the process of replacing everything on the front of the engine. I want to make sure I reduce the crankcase pressure so that I don't wind up blowing any of these seals out after I replace them. I'm leaning towards simply popping a little air filter on top of the oil fill tube and plugging the line going to the j-boot. I don't care about emissions, or if I smell fumes sitting in traffic (it's becoming a DE car primarily).
If you are only seeing black smoke when you boost, it may be the seals in your turbocharger.
Turbo was rebuilt last year by Evergreen. In hindsight, I wish I had drilled out the opening in the AOS at that time. But I'm not pulling the turbo off again to do that.
you should *only* drill the AOS if fitting a catch-can+breather tank combo.
drilling the AOS will drop the AOS's efficiency to the point where it can no longer S the A and O...
at that point you are using the "AOS carcass" to merely contain your oil leak, and relying on the catch can to remove oil vapor and the breather option to drop crankcase pressure.
you should *only* drill the AOS if fitting a catch-can+breather tank combo.
drilling the AOS will drop the AOS's efficiency to the point where it can no longer S the A and O...
at that point you are using the "AOS carcass" to merely contain your oil leak, and relying on the catch can to remove oil vapor and the breather option to drop crankcase pressure.
I agree you should have a catch can if you drill, but have to say I catch surprisingly little oil in the can even after drilling the AOS.
10-02-2015, 04:46 PM
