Crank Case Oil Vent Leak

[Tom McCutcheon]

I was going through a quart of oil about every 9 - 10 hours. It seemed that it all ended up on the belly of my -4. I finally broke down and bought a Super Seperator from Anti Splat Aero. Once I got the leak at the "T" fixed that I installed in #3 cylinder head oil return everything seems to be working great. I also put on the vacuum valve to one of the exhausts which they claim to increase horse power. I have noticed about an extra 100 to 120 RPM. I have a Whirlwind ground adjustable propeller but I have not changed the pitch. I think I'll just throttle back and have the extra umph when I need it. Hope this is helpful to anyone considering such a move.
Tom

[PCHunt]

Originally Posted by Tom McCutcheon

..........I also put on the vacuum valve to one of the exhausts which they claim to increase horse power. I have noticed about an extra 100 to 120 RPM. I have a Whirlwind ground adjustable propeller but I have not changed the pitch......
Tom

Tom, can you elaborate? I'm not familiar with the vacuum valve you mention.

[Tom McCutcheon]

Yes, Aero Splat sells an adapter for their oil seperator. Instead of the vent tube leaving the seperator and just exiting out the bottom of the cowl, you weld this tube onto one of your exhaust pipes at about a 30 degree angle. The angel needs to be so that the exhaust creates a vacuum on the tube. On the tube is a one way valve that only allows a vacuum on the vent line. The result is there is a small negative pressure on your crank case making it easier for the pistons to go in. Less pressure on the pistons going in results in the power stroke being easier to push that piston in.

The end result is that I get about another 100 to 120 RPM's. My guess would be that it might be harder to measure the improvement on a constant speed prop. However, if it's there for a fixed pitch prop it's there for a constant speed prop as well.
Tom

[bird]

I was wondering if anything really bad would happen if the valve should fail closed, get stuck?

bird

[Tom McCutcheon]

Bird,

I'm not sure why they even have a one way valve. It would seem to me that the way we welded the tube onto the exhaust wouldn't allow pressure of the crankcase to happen. But then I haven't tried to think of every possibility either. Maybe a good question for Allan of Aero Splat.
Tom

[DanH]

Originally Posted by Tom McCutcheon

The result is there is a small negative pressure on your crank case making it easier for the pistons to go in. Less pressure on the pistons going in results in the power stroke being easier to push that piston in.

It's a case evacuator. It does reduce crankcase pressure (or more accurately, crankcase air density), in some configurations well below sea-level atmospheric.

The goal is two-fold; reduction of windage losses (a hp gain), and reduced oil droplets in suspension (less oil out the breather).

"Less pressure on the pistons going in" does not in itself result in a HP gain as it is offset for the same reason when the same or other pistons move toward TDC.

You need the one-way valve.

My favorite case evacuator was one I did in the mid 80's on a racebike, based on a reed valve cage entirely hidden inside a catch can. The rule book had nothing to say about case evacuation, so it wasn't cheating

[bird]

So if the valve failed, say stuck closed, what do you think would the result be? Possibly a momentary increase in crankcase pressure? Just wondering, I like the concept.

bird

[PerfTech]

Originally Posted by bird

So if the valve failed, say stuck closed, what do you think would the result be? Possibly a momentary increase in crankcase pressure? Just wondering, I like the concept.

bird

...This particular valve can't stick closed. They are designed so if it did fail it would be wide open and the result would be back to stock HP. These are a very dependable part that is used on virtually every vehicle built from 1970 to 2003 and I have never seen a bad one. We have installed a vacuum system on every high performance vehicle and engine for to last 35 years and every performance shop uses these as well. All NASCAR teams use this, along with a vacuum pump that pulls 18" of vacuum in the crankcase. At the high rpm that they run, it typically results in 75 to 90 HP gain. In the case of our 360 or 540cu in Lycomings at 2500 rpm we typically see about 8 to 12 HP. I have had this system on every airplane I have owned or built over the last 33 years with perfect performance. There are numerous advantages with no down side to this system and I will outline them in a video soon as a picture is worth a thousand words and I type with two fingers. Allan...

[DanH]

Allan, nothing proprietary about that valve. Give 'em a part number or application so they hit the auto parts store and cut one open.

[bird]

Ok now I understand, seems like it is similar to a pcv on an auto. I like the idea. When I get to the engine part of my build, I'll be giving you a call. thanks

bird