Is there a benefit to applying vacuum to the crankcase and has anyone done it? Here's why I ask:

1974, custom 355 motor, serpentine conversion. (I have an aggressive cam compcam 12-602-4, but the lack-of-vacuum-for brakes-&-headlights- question will be the subject of a different thread.)
Application: resto-mod, (really) spirited driving, occasional track time.

I have the option of keeping the smog pump from the 92 caprice donor car and re purposing it as a vacuum pump for the crank case. This is just an idea based on cursory research. Is there any benefit to putting effort into vacuum motor (converted smog pump) on a gen1 sbc motor for crankcase ventilation?

 

Why not just use a PCV ? Doesnt require any horsepower.

 

unless you have a race motor cranking >7k rpm regularly, you won't see any benefit. add a larger PCV if you want, or go old school and put in a road draft tube....either way, repurposing a big A.I.R. pump is probably the least efficient way to go. a small secondary air pump from a VW jetta is easy to adapt, it's electric and quiet and smaller to boot, and available at junkyards for a couple bucks if you wanted to experiment...

 

with the others

Engines with a lot of stroke/rpm maybe

Hope you got some deep gears/converter for that cam!

 

To everyone so far it seams to be no , but I disagree 100% .

Cleaner crank case oil

Moisture removed

Engine parts stay cleaner.

More hp from motor because the blow by gasses are not being pushed around under the pistons on the down stroke.

I see it as win / win .. if your only worried about cost then it is not win / win from that perspective.

 

not disagreeing with you in theory, but, how much HP? how much cleaner? moisture and blowby are removed normally, so how much faster will that happen with a vacuum system?

getting to the cost/benefit ratio here, with race motors in certain circumstances, the benefits may outweight the costs, more than slightly. with the OP's motor, I doubt that is the case. can it hurt? no, but is it worth it? only the OP can decide...

 

I found this article to be helpful: http://www.dragzine.com/tech-stories...up-horsepower/

Admittedly, it's overkill for my application. I'm probably going to end up in the 400+/- hp range at the crank with this build. But I have the parts and without much modification effort, i can make something work. (I get pure joy out of tinkering with stuff like this.) I can't answer how much hp/moisture removed/engine seals life extended/oil leaks prevented/ etc.

Whatever my results are, i'll post 'em.

-Overkill-Phil

 

As much as 25 , insanely cleaner if you could see what is pulled from the crank case you would never run with out one LOL..

And normally is a compromise , all that crap gets re-burned back into the combustion cycle. And as i mentioned if you could see what drains out of the catch can you would be sorta stunned. I sure was the first time I saw one drained.

And yes cost can be an issue however as creative as people are it can also be cheap. I chose a mechanical system from aerospace components

 

Saving 25 hp??? You must be smokin' that stuff that comes out of the crankcase!

PCV system uses negligible energy...and it's energy that the engine CAN'T turn into usable torque. It's simple, inexpensive and WORKS.

But, as always, do what your 'heart' tells you to do.....

 

Dont come at me with I must be smoking something

Simply placing the crank case under a vacuum yields serious benefits in ring seal and eliminating crank case pressure that your pistons are pushing through on every down stroke.


I do invite you to show us that in no way can a belt driven pump FREE up hp your engine is losing with out one and a PCV works as effectively as a pump does because it uses "negligible energy"


So come back with facts and leave out your sarcasm

 

so why don't you disconnect the system you have and put a pressure gauge on the crank case and post the pressure numbers? all 8 pistons do not move down at the same time. some go down as others go up. I have read up on the subject, no where have I seen substantiated claims of anywhere near 25hp gains on a stock or mild build.

do what you want, it really can't hurt, and some engine designs it certainly helps, but for the average pre-90's motor it is overkill...the problem with DI motors is that the vapors hit the valves which do not have any fuel to wash them off and cool them so the crud gets cooked on due to the injection being in the cylinder, not the intake. a normal induction system does not have that problem. those engines require valve tear down every 40-50k miles...a stock small block goes 100k or more with out needing that with stock PCV.

 

That "theory" is right up there with putting a wind turbine on top of your car to 'GAIN' energy....

Pistons move up and down. Any gain from the down-moving pistons would be negated by the UP-moving pistons. {you gotta be kidding me}

 

Ignorance is bliss .... And in the confusion of modern life I would not like to be the guy accused of wrecking someones bliss.

So you are dead right I am wrong a VACUUM pump does nothing ..

It is as you stated "like a wind mill on the roof of a car" ..

 

Wouldnt the vacum cause additonal drag on the piston traveling in the up position? just trying to wrap my head around this one and I dont see the power benefit of a stronger vacuum? Ive read the seals arent designed for this and air could easily be pulled in through some of them... I and picturing the distributor seals and even the dipstick hole sucking air while the oil is in motion... Maybe I'm off base with this?

 

I don't believe that would be the case.

With the vacuum pump you are not drawing an actual vacuum in the crank case. The pressure in the crank case is likely not going to fall below atmospheric pressure without a really good pump.
What you are doing is evacuating the pressure created by the blowby from the rings. At best you are eliminating pressure created in the crank case, maybe drawing it slightly below atmospheric pressure, in many cases probably only reducing it to some degree.
At low RPM's and small throttle openings this is effectively done by a PCV through the vacuum provided by the intake manifold.

Consider high RPM/ large throttle openings However.Manifold vacuum drops to nil at that point. Thus the pressure in the crank case has to be pushed out, pressurizing the engine. This significantly increases windage losses and potential ring seal unseating leading to more power loss.
In addition with the PCV all that contamination is still being ingested by the intake further reducing power due to intake charge contamination.
Diehard has a valid point. I believe that you could and most likely do see a significant power improvement over a PCV arrangement.

In the OP's case I would add a catch can on the recovery side and an adjustable valve on the suction side to be able to vary the amount of vacuum to the engine.
Exhaust evacuation seems the simplest solution, but with little control over the level of vacuum and no control over the waste products from the crank case. Although I suppose you could put a catch can between the valve cover and the exhaust evacuation port.

 

"Diehard has a valid point. I believe that you could and most likely do see a significant power improvement over a PCV arrangement".


About time someone added knowledge to this topic. I felt like I was falling in a dream that was never going to end.

 

Can you quantify these losses? Hey, you're making the claim, so you need to back it up.

Uh, you just said "high RPM/ large throttle openings However.Manifold vacuum drops to nil at that point". How can the PCV pull all that contamination in when there is no vacuum?

 

There's pressure in the crankcase from blowby at that point pushing through the pcv right? And then vacuum at the lower rpm ranges?

 

Not with a large throttle opening.

 

In a perfect, unicorns and pixie dust for everyone world, that would be true. But it's not. Air (and oil mist) has mass. It doesn't move for free (the no free lunch rule again). It takes energy to move/accelerate a static mass. This can only come from the piston (bottom), that gets its energy from the combustion process on top of the piston, or from the crank during an intake stroke. This process reduces the net power at the crank/flywheel.
But hey, this moving air (and oil mist) just goes to the opposite cylinder and pushes it up, right? Everything cancels out, right? Um, No. These are Vee engines, not flat boxer engines. There's no straight path from one downward moving piston to the corresponding upward moving piston (due to balance issues, I don't recall seeing this ideal scenario in boxer engines either). Also, the crankshaft is in the pathway between opposite banks, screwing up the "easy" movement of air (and mist) mass between cylinders. There's also a wall friction/obstruction issue reducing the efficiency of pumping air around in the crankcase.

All in all it's a power waster moving a lot of air mass in unproductive ways. Reducing the mass of air constantly being accelerated and decelerated should result in a net power increase at the crank/flywheel, depending on the efficiency/power requirement of the evacuating pump.