Crankcase ventilation

MReid · 10-15-07, 02:37 PM

I'm not running a PCV valve, but need to vent my valve covers. What are my options short of running a vacuum pump? Can I simply vent the valve covers to a tank to capture any oil spray with a filtered vent? Any recommended parts?

Jac Mac · 10-15-07, 03:20 PM

IMHO the best position for breather vents on any pushrod V8 is on the pushrod side of the rocker covers between any pair of cylinders. Any other position requires baffle plates to prevent oil surge from cornering, braking, acceleration. Run the lines into a tank with breather on top and a return line drain into the timing cover or oil pan just below & in front of the oil filter on a SBF. The return line should have a tap fitted so that for road use you can close it off to prevent moisture from being reintroduced to the pan. For track days the catch tank can be drained off then the tap opened to allow any oil carried over from blow-by/venting at high RPM to drain back to the pan. With dry sump units I utilise the old redundant pump to filter gallery for this purpose.

Jac Mac

Keith Hardy · 10-15-07, 04:19 PM

I used a reed valve (anti backfire) inserted @ 45 degrees into each collector to provide a positive vacuum (achieved via collector pulses) which vented the crankcase via the valve covers and helped to stabilise the rings at high rpm. Any oil mist was quickly "consumed", but then the scrutineers found it and made me fit a catch can....

A friend of mine used a similar system but didn't use a reed valve. Can you guess what happened?

It was a neat solution though but probably more suited to drags than circuit racing.....

I do firmly believe that a positive ventilation system benefits a high rpm installation but of course intake manifold vacuum is a total no no in a performance/racing set up, so where to get the vacuum from?

My Isuzu Trooper 4X4 features an alternator with the vacuum pump on the rear, providing the vacuum for all engine, brake and advance/retard functions....worth a thought.

Richard B. · 10-15-07, 04:57 PM

What are you using the car for? Is it just a driver, do you run it hard or do you race it? Also what kind of carb and induction setup are you running?

If its a driver with just some occasional hard running and you are using a regular intake and 4 barrel carb I would just hook up a pcv valve. If you are running webbers, then this really isnt an option since you would only be pulling vacuum into a single cylinder.

If you are racing it or running it hard alot, about the only options are to just vent it to the atmosphere, which you can run this through a catch tank, you can run an exhaust evac system which works fairly well, but really needs to be plumbed after the muffler so you dont get any back pressure, or a vacuum pump with catch tank.

Frank · 10-16-07, 02:06 PM

Like what Kieth says above I use a exhaust scavenge system on my Cobra. ( I have webers.)

Both valve covers are vented to the exhaust. A 5/8 pipe welded into the collector, one for each valve cover. A one way valve keeps any pressure coming back to the valve covers.

You could run lines from the valve covers into a separtor then to the exhaust to burn off any remaining oil. A car with mufflers sometines will have oil accumulate if the motor has alot of blowby.

Exhaust Evac doesn't pull alot of vacuum, but it does pull.

Ofcourse a vacuum pump would just look and work alot better.

Big-Foot · 10-16-07, 04:32 PM

I'd just run lines to a puke tank with a drain petcock on the bottom.. Simple and easy to gauge actual amount of oil residue being vented without blowing it out the tailpipe.

Also one of the bad things about crankcase vacuum pumps and pan-evac's is that they can (and have) sucked the seals out of an engine along with other gaskets - most notably the valve cover gaskets.. What little gain seen on a dyno is not worth the hassle and potential for problems down the road..

KISS method works for me every time..

Keith Hardy · 10-16-07, 07:05 PM

I think the principal of some kind of positive evacuation system in a race engine is to stabilise the rings by preventing "flutter" at higher rpm's. Too much is obviously not good either.....the collector idea works well with a small but positive contribution at all throttle openings. A small "drop" (or catch) tank in the vent line collects any "liquid" oil.

Scott Calabro · 10-16-07, 07:22 PM

What ever happened to just a push in breather in each cover?

K&N makes some good ones.

Best,
S

Richard B. · 10-16-07, 07:31 PM

There is nothing wrong with just using breathers, but, if you do have any blow by at all, they will eventually begin to drip.

I can tell you from experience back when I used to drag race, putting on an exhaust crankcase evacuations system was worth a tenth and a half. I know a super stock racer that ran the same system and had a vacuum gauge plumed into a valve cover. On a fresh engine at WOT he would get 3" of vacuum, when it dropped below 1.5" he knew it was time to freshen the engine.

With vacuum pumps people have seen some pretty impressive numbers on the dyno, but, once you go over about 10" of vacuum you will begin to start suffering other problems, most notably wrist pin gauling. Below 10" I dont know of anyone that has been seeing any problems. There are vacuum regulators made now that go in the valve cover and make it very easy to manage the vacuum level.

Scott Calabro · 10-16-07, 07:38 PM

Yeah wiping off your rocker covers with a rag is huge.

Frank · 10-16-07, 08:01 PM

(Again this is a my cobra J pipe.) But gives you an idea.

The "nipple" is welded into the J pipe about 3/4 inside. The end of the nipple has a 45 degree cut on the end. So the open potion of the nipple faces toward the direction the exhaust is going. When the gases go around the end of the nipple it pulls air out of it. The nipple itself is welded at a 45 degree angle making the inside 45 degree sitting about 90 degrees to the J pipe. Im confused now.

Then a one-way valve screws onto the welded pipe.

Not sure what this would look like on a GT.

Keith Hardy · 10-17-07, 06:42 AM

That's exactly the piece - very effective. You can find the valves on any smog car in a wrecking yard for peanuts....

Tobias · 10-17-07, 08:12 AM

normal cars vents the crank in the airbox why wouln´t it be legal to vent it in the exhaustpipe like Frank?. The only difference is that the oil is introduced before combustion on normal cars. And aftercombustion on Frank´s but it still burns i don´t believe any oil would survive being put thru the exhuast, if it does maybee its time to tear things down..

speed220mph · 10-17-07, 08:41 AM

An inline PCV valve will accomplish about all you want with little hassle. A breather cap with a nipple, inline PCV valve and a fitting in the intake is about all you need. Pictures on Club Cobra show how I did this with a dual-four tunnel ram intake on the 427 in my Cobra. Results have been rocker covers that aren't covered with oil from the mist exiting the breathers and crud getting purged from the crankcase.

At the manifold: Club Cobra Photo Gallery - PCV Manifold Inlet - Powered by PhotoPost

At the rocker cover: Club Cobra Photo Gallery - PCVCrnktoPCV0002 - Powered by PhotoPost

I did a similar modification to the HP289 in my Mustang that's fitted with a 3X2 intake. Used a PCV valve plugged into the rocker cover grommet and ran a line to a nipple at the rear of the intake. Note the PCV valve at the rear of the right-side rocker cover: Club Cobra Photo Gallery - Triple Trouble, tuned and ready to go - Powered by PhotoPost

MReid · 10-17-07, 09:40 AM

Thanks for all of your insights.

I've used a PCV valve and breather in the other cover in every car I've built with no problems. That included my 1941 Willys coupe with a Chevy 502, tunnel ram and dual 4 barrel carbs and my Factory Five Daytona Coupe with stack EFI. My dual carbed engine for the GT40 has a 3/8" nipple in each carb spacer for a PCV that I could gang together and run to a PCV, venting the other cover. To Scott's point, I could simply run two breathers, but my valve covers are not baffled and there is not enough room under them for a baffle without valve train interference. Hence, I didn't think that either of these two options would work effectively.

The bigger issue I am grappling with is suction or no suction to be blunt. I like Randy's idea of two lines to a tank with a vent on the top and petcock on the bottom. Simple and effective. I am, however, intrigued by Richard, Frank, and Keith and their experiences using vacuum to aid in evacuation.

So, to suck or not to suck. Gentlemen, that is the question!

speed220mph · 10-17-07, 10:11 AM

MReid: I had the same problem you're describing with the unbaffled rocker cover. The solution was to use the, albeit ugly, baffled breather. That solved the problem with sucking too much oil out of the engine, which is what happened before I went to this approach.

If you're looking for vacuum, the intake is the place to find it, i.e., unless you go to a vacuum-pump setup and the packaging problem such a system presents. I considered a puke tank for the Cobra, but it in itself doesn't provide the vapor evacuation that a PCV system gives.

Keith Hardy · 10-17-07, 06:24 PM

You certainly don't want a stock vacuum set up for the PCV via the intake in a performance/high rpm circuit style engine. Oil contamination would greatly reduce the octane level with attendant detonation problems.

MReid · 10-17-07, 06:39 PM

That's my other concern, Keith. This engine is a built Ford 342 of around 550 HP that will rev to 7500 rpm.

Scott Calabro · 10-17-07, 07:05 PM

Possible charge contamination is why one or two K&N stlye breathers in each cover will easily do the trick.

K I S S

Moroso sells a baffle that is aluminum (weldable) and requires minimal room inside the cover. P/N 68790

I plan on using 2 baffles and breathers in each of my Holman Moody covers.

If they (baffles) don't fit inside I'll fab a 2 inch long ally pipe (4ea.) with a baffle inside, TIG it on the outside of the cover, put on the breathers and be done with it.

When some oil gets on the covers I'll wipe it off.

Cheers,
S