PorKen

I had some oil squirt out of the various leak points on my cam tower seals while on the dyno the other day (at over 140MPH). I assume from crankcase overpressure.

As tested, my PCV system was free venting via a K&N breather on the oil filler cap.

My (somewhat unoriginal) new idea is to re-install the air pump, connect the intake port of the air pump to the oil filler cap via a 'T' fitting, the branch of said 'T' would retain the K&N breather. The breather would allow an air draft so as to not create too much vacuum in the crankcase.

The exhaust of the air pump would vent under the car, but I could just as well weld a tube back onto my exhaust system via a one way valve (no cat).

I've read something about a low pressure crankcase helps the oil rings seat better and/or increase horspower by providing less resistance to the piston downstroke at high RPM? Any validity to this?

Thoughts?

Or perhaps I should just run a one way valve to the exhaust, as with race cars. (The exhaust rushing past the crankcase vent inlet creates a vacuum.)

*Exhaust Vent Attempt*
*Working Version*
~thread~start~

drnick

do you think the air pump is up to the task, in terms of handling oil and also the volume of air? the one way valve onto the exhaust sounds do-able.

GlenL

The air pump idea strikes me as fairly clever but I've got reservations. The blow-by is both hot and humid. I'm not sure the pump will last with steam being pumped through it.

I've read about drawing a vacuum in the crankcase. The summary is that "it works" to raise horsepower. Does the air pump have enough strecngth to do that?

Using vacuum of a pitot tube into the exhaust stream is an established practice. There are kits to insert that at header flanges.

The vents from the engine are reasonably large. I don't think the crankcase is pressurizing...and if it is you've got bigger problems.

One last thing: I notice that the breqther is mounted sideways. The element is intended to filter stuff out in both directions. If you're getting a oil misting problem, it'll drip down on the engine. Routing that port to a catch tank is another apporach.

PorKen

Thanks for the replies.

The breather as installed doesn't drip oil at all, in fact, at impulse speeds there are rarely any emissions from there. Occasionally an oily steam vapor wafts out of it.

I drilled out the cap inside to 1/2" when I installed the K&N breather. The hose connection is 1" but at the entrance to the strainer area there is only a ~8mm hole.

I already have the check valve for the air injection system. I could weld a pilot tube (GlenL - thanks for mentioning the tube, I would have just put a surface mount!) into the exhaust after the oxygen sensor(s). Then I would measure the amount of vacuum generated and decide if pumping would be worth the added complexity/HP trade.

On the other hand, I could just stick the pump on there, no welding, and free vent it... No need for the breather (maybe put it on the output side); just let the air pump create as much vacuum as it can.

Regarding the steam: What are the guts of the air pump made of? Stamped steel or aluminum?

GlenL

I think that the body is steel, but what matters is the bearings which will not be aluminum.

If you put in a tube, angle the tip to maximize the suction. I'm thinking that if you did that, you wouldn't need the pump at all.

Do post if you rig up the pump. Mine's just tensioning the fan belt.

PorKen

GlenL - I would imagine that the bearings are of the sealed type?

Maybe an electric pump connected via relay to the WOT throttle switch would be better.

On my girlfriends 95 SAAB, the air injection pump is electric, and only operates when the car is dead cold. It runs for <30 seconds until the oxygen sensors warm up.

It is a big beefy pump, unfortunately it costs $300 new!

Try searching for electric vacuum pump on Google; most of the search results were not exactly what I had in mind...

PorKen

Upon further research: the answer is no!

The carbon sealing surfaces in the stock pump will fail quickly with oil ingestion and the pump will seize!

However I did find some good reads on 'crank evac':
____Modified belt driven air pump
____Using a GM electric auxiliary brake booster vacuum pump

I just might try the GM electric pump.

"Theoretically everyone who uses a vacuum pump whether it’s electric or belt driven should see an improvement of 2-5 percent increase in HP."

ViribusUnits

Why not tie your crank vent to the a/c by-pass line.

It's not like you'll be getting false air, if any more long. Modify an a/c bypass silinoid so it only opens when the WOT switch is switched on, so your not sucking air into the crank case seals when you let of the throtal.

There's got to be a way to make the TB ventury make your vacuum for you.

You'll amost certainly need to add a major catch can. Maybe serices of baffals and mesh screens to keep any oil mist out of the intake. Oh, I got it, add a can filled with steel wool. Well, filled with steel wool secured by a fine metal screen. Leave the bottem empty, and run a return line back from just below the screen. This away you can drain the water at the bottem off, but the oil that gets collected goes back into the crankcase.

I'll bet that would work well. Maybe solve the GTS oil mist problem...

PorKen

VU - that's basically what the stock PCV does?

Trouble is, you don't (from a performance perspective) want to use engine vacuum because you want high vacuum, and don't want to burn oil vapor (lowers octane), or suck in unburnable water vapor.

I realize now that I should do something though, not having a crank evac system is bad.

More options:

Moroso belt driven pump, $359
Vacuum relief valve, $135 from Summit

ViribusUnits

Well, use a really good catch can that has enough surface area to condense the oil vapors and no real vapors make it to the engine. From there all that remains is blow by, which is nearly the same as EGR gas, which icreases octane.

I'm not sure how much vacuum the ventury would make, hum...

PorKen

VU,
The catch can is a good idea. Maybe best put in between the engine and the vacuum source so as not to contaminate the pump. The early cars oil fill is much like a catch can with the screen inside.

Lowering the air pressure in the oil pan gives you more horsepower and torque, but I'm not sure it would be good for the racing GTSs.

Creating a vacuum in the pan lowers the oil pressure because the oil pump has to work harder to pull oil out of the the pan.

Or maybe it would be good:
"With negative crankcase pressure present, the engine's oil pump sees less resistance, therefore the pressure that the gauge will show is lower, but in turn the volume that the oil pump puts out actually increases. Because of the reduced resistance, the oil pump can flow more oil while showing less pressure on the gauge. Since the increased flow serves to pull additional heat away from the bearings and journal, however, the reduced oil pressure is compensated for, and no engine damage occurs"

ViribusUnits

I don't think it would matter.

It take a pressure defferentail to cause the oil to flow into the bearings. The oil pump creates that pressure differential. The oil never sees atmospheric pressure, so we should probably deal in absolute pressure. So if all we're worryed about is the diffrence in pressure between the oil in the lines, and that in the crank case, a vacuum shouldn't cause a problem. The oil pump is positive displacement, so as long as it's good, it's going to deliver the proper flow no matter the crank case pressure.

I would be curious as to the reason that a vacuum in the crank case would create more power however.

On the early cars, the screen is more of a filter so you don't pour paper from the bottel into the engine, than something to catch oil mist. Also, it's apperently not large enough to adquitly catch the mist. You'd need something taller, with a much finer, more extensive mesh, for a larger surface area, to really seperate the mist out.

Normy

Porken-

I think your heading into detonation land!

If you have excessive crankcase pressure, then you have have combustion pressure in your crankcase. There's a term for this- "blow by". It means that your rings are bad.

You can recycle the pressure all you want. The problem is that if you run it to the intake, you are forcing motor oil [extremely low octane] into the combustion chamber, most likely causing detonation. My '66 Ford had blown rings- it got 10 mpg, and when I basically ran a tube from the top of the valve cover to the intake via the existing PCV valve it started running bad. I decided to let the oil that blew by go from the tube into a metal juice can with a fitting soldered on. Then all I had to do was empty the can every couple hundred miles....

N!

Z

Yes.

Yes

I've measured positive crankcase pressure on several 928s of different years, including when the crankcase was vented to the atmosphere through a 5/8" hose.

The pump will pull a significantly higher crankcase vacuum than the exhaust suction based systems.

Yes, you'll need a pretty effective method of air/oil separation with any of the methods that have been mentioned to achieve any sort of significant crankcase vacuum.

On an engine without excessive amounts of blowby, two of the well done exhaust system based fittings can pull around 3"Hg of vacuum in the crankcase.

It increases ring seal, reduces ring flutter at high RPM, and reduces the oil cloud that spins around with the rotating assembly, reducing the parasitic drag from it. The vacuum also creates a less dense "atmoshere" for the rotating assembly to spin in, which means less drag on it from that as well.

PorKen

Normy - I don't notice much blowby; the whole point is not to put any blowby/oil mist/water vapor back into the engine anyway.

Zed - thanks for the input.

Went to the 'yard today, but couldn't find one of these:

Cardone 641500 - remanufactured brake booster vacuum pump

I checked online at NAPA and PartsAmerica (search for 641500) ~$160 with a $20 core.

I then called locally (82 Cadillac Cimmaron) and may have found one for $150 with no core.

I'm thinking about mounting this suction side down in the drivers side fender where the cruise motor was, with a catch can underneath/before it.

Supposedly it kicks in automatically at 5" vacuum and can pump down to 16" at 13.7V.

I plan to route the regular PCV intake vacuum from the throttle body (through a one way valve connected to the pump vacuum circuit) for low speed operation. Then at WOT the pump should come on when manifold pressure drops. While the pump is running, the one way valve from the TB will be pulled shut until the pump shuts itself off.