If this isn't AT, please move.

I would like to learn more about vaccum pumps, such as when they are needed, their effects on horse power, basic components to the system, any other applicable info.

 

I'm assuming you mean as crankcase ventilation?

For every cubic inch above a piston, there's an equal amount below it. Your basic crankcase ventilation system is a simple PCV valve which sucks that air back into the engine to be reburnt. The downside is that you're sucking oil and water vapour back into the cylinders.

Racers have used other ways of keeping the crankcase clean and reducing pressure inside it. Exhaust evac systems have been around for years. They use a check valve similar to the AIR valve on your exhaust manifolds. When hooked into the exhaust system down at the end of the headers, the exhaust gasses can create enough vacuum to keep the crankcase pressure low. They pull very little from the crankcase at high rpms though.

In the last 30 years or so when the car manufacturers started using air pumps (smog pump) to inject air into the exhaust to reduce emissions, racers found that these pumps can also suck a lot of air out of the crankcase with a few modifications. Smog pumps are still used today but there are now better vacuum pumps available to do the job. Moroso makes a very good but expensive belt driven pump. GM produces an electric AIR pump for the exhaust on late model F-bodies that's supposed to work just as good for pulling the crankcase down into a vacuum.

The theory is that when the crankcase is in a vacuum, the pistons are not trying to compress air below them. This means some HP is free'd up. Having lower crankcase pressure also allows the rings to seat tighter against the cylinder walls. You'll also eliminate any oil leaks from the engine.

There are some drawbacks from running a crankcase in a vacuum. The rear main seal is designed to keep oil from going out. If the crankcase is in a vacuum, it can easily draw dirty air into the crankcase through the rear main seal. The common way to correct it is to install the seal backwards.

Too much vacuum can be hazardous. No more that 14-15" of vacuum should be used. A vacuum pump of any kind in a well sealed engine can pull 28" of vacuum. This is enough to pull the oil out of the wrist pins and bearings. The best way to limit the amount of vacuum is with a vacuum relief valve. It's preset to open if the vacuum become too great. Think of it as a controlled vacuum leak.

Dyno results vary but a 2-5% increase in HP can be expected.

 

Thanks, that's what i wanted to know. I wish i knew what happened to my air pump when i pulled it.

I suppose you would just plug the PCV on the manifold and pull vac from the valve cover (1 or both?).

Anything special needed for a supercharged setup?
I suppose this is best since PVC and boost dont mix.

What's the complete setup? [assuming my SC'd LT1]

(hose(s) from valve cover > vac relief valve > LT1 air pump > some kind of catch can?)

also, i take it you just run the pump at all times?

 

I run a belt driven smog pump all the time. If your system is sealed up then shutting off an electric pump can build up a lot of pressure inside the crankcase. I was having problems when I used to use a small electric vacuum pump. At high rpms the pump couldn't pull enough air out of the crankcase. It built up so much pressure that I was constantly blowing the dipstick out of the engine.

I have hoses running from both valve covers to the pump. A small vacuum line is also connected so I can monitor how much vacuum is being created. The outlet from the pump goes into a catch can and moisture and oil vapours are drained every few runs.

The advantage of an electric pump is that it can be turned on when the engine is shut off. When the engine cools off, the water vapours will condense and can be easily sucked out of the engine.

The vacuum relief valve can be installed anywhere. So far I don't need one because I'm underdriving the pump so it doesn't spin as fast. Usually a fitting is installed in a valve cover and the relief valve is screwed into the fitting.

There are vacuum relief valves available to racers but they're expensive. Here's what they are and can be purchased a lot cheaper here. It's the same thing as a race version but the race version is around $50
http://www.grainger.com/Grainger/pro...mId=1611718986

I'd like to get my hands on an LT1 air pump some day.

 

Also i believe the vaccum makes the piston rings seal better further increasing hp. With the theory of gained hp from the pistons not having to compress the crankcase air, wouldnt the pistons have to pull harder going up the bore from the vaccum pulling them down?

 

I think i'm gonna go with this pump. Any oppinions/suggestions?

At the bottom of this page:

http://www.speeddemonmotorsports.com...acuumpump.html

 

what kind of internal modificatins must i do if any to the smog pump if i use one as a vacuum pump? Can i use the stock pullys or should i gear them down/up? I was thinking can't i just hook up a regulator to keep the vacuum constant and adjustable?

 

i posted a thread on this in the lt1 forum, but i think this is the same thing. if we are going to delete the egr and smog **** from our cars can we use the elec vacume pump to pull crank case vacume. thanks prorac1

 

Until I'm able to find an LT1 pump, I use a belt driven one from a Ford truck. I currently have it underdriven but until I get to the track to test the new setup I won't know if it's going to work properly. I fabricated an aluminum spacer for the end of the crankshaft to mount an alternator pulley on the crank. The smog pump still uses the large pulley. A small pulley turning a large pulley is a huge underdrive but at 6700 rpm it should be about right. At an idle it pulls about 5" of vacuum. The real test will be to see how much vacuum it can pull when the engine is under load. If it isn't underdriven, it can easily pull 28" of vacuum at an idle which is way too much.

My current setup has 2 1" hoses coming from both valve covers to a Tee fitting then to the inlet of the pump. The outlet of the pump goes to a catch can in case there's too much moisture or oil vapours being sucked out.

You could just run the belts as per normal and install a vacuum relief valve in a valve cover to limit the vacuum to no more than 12"

 

Mr Gasket just released a new Electric Vacuum pump. Looking into the Part number right now, I'll post what i find. For a means of controling the vacuum on the crankcase I use a 1/8" npt jet fitting installed in the valve cover and bleed off the thing with a nitrous jet. Run a hose from the jet fitting to the air cleaner box so you pull filtered air. Do this in front of the mass air meter.

 

Unless im gettin ya wrong, i dont think your putting air into the crank case, your pulling it out, so why would you go to the air filter? What i was thinking was to use the elec air pump already on our cars as a vacume pump. wire it to a constant hot when the ignition is on and suck from the valve cover into the pump and into a puke tank, like the setup on my race cars bbc. I do agree with you (great idea ) on using a nitrous jet to restrict the amount of vacume your pulling. if you pull to much from the crank case your liable to pull seals etc. so what does every one think of my idea? Prorac1

 

First off the airpump on a lt1 is just that...a airpump.
it won't make vacuum anywhere near whats needed on a e-vac system.

The reason you run the line from the Jet to the air cleaner is so your pulling "Clean Air" into your valve cover...IE: crankcase.
Kinda like how the factory A>I>R>pump pulls clean air.
Most guys drive there cars as I do and I didn't want to suck any trash into it.
At 13 volts a true electric vacuum pump will pull 18" of vac easy, which is too much...bleed it off to 13" on a wet sump oiling system.
The jet acts as a "control'd vac leak" since we are sealing up the system with a e-vac.
The trick$ piece has a prefilter built into it so your not pulling trash into the cover.
I like the cheep and easy route, hope this help you.


Oh, ps...its also easy to install a vacuum guage into the spot where the PVC use to be used.

 

You don't want to pull air into the crankcase unless it's through a controlled vacuum leak like though a vacuum relief valve or an orifice fitting. The whole idea is to have the crankcase in a low vacuum all the time. 10-13" of vacuum is all it needs. It depends on how much the pump pulls and how well the engine is sealed up. Keeping the crankcase in a vacuum will eliminate any oil leaks also.

The last I heard, the Mr Gasket pump has been recalled. They've had some problems with it already and are planning to re-release it again later this year.

 

The A I R pump is actually used to pump air into the exhaust, not the motor itself. But in order to pump air, it has to suck it from the intake side of the pump, does anybody have any vacume readings from this pump (air) if so what were they, not to be pushy, but this idea (right, wrong, or otherwise) is just to good to let go yet . Let me know guys, thanks prorac1

 

I know of a few racers on the net that use the LT1 pump for vacuum. Any pump can suck 28" of vacuum but only a few are capable of doing large CFM.

In the early 80's GM used an electric vacuum pump on cars to assist in power brakes. It works fine in that application however it can't pull enough air to keep the engine in a vacuum at more than an idle.

For every CID above the pistion, there's an equal amount below it. 350 cubic inches of air is a lot of air that needs to be pulled out quickly. Once pulled out, there will always be air entering to replace it even with a totally sealed engine. Most of that is blowby past the rings. Compressed air from the cylinders means that even more air needs to be pulled out. 150 psi compression makes a lot more air inside the crankcase from blowby. Supercharge it and that number gets even larger. A pump needs to be able to pull a lot of CFM to be practical. The smaller vacuum pumps just don't pull enough air.

Although I don't have any flow numbers, the LT1 pump is suppose to work fine.

You could always spend a few hundreds of dollars on a Moroso 3 vane pump.