Small Block Chevy - Valve Cover Breather Holes

You don't have to hook up the PCV valves. That's just for emissions. Just plug it off at the carb. If its a mild performance engine, one breather in one valve cover will be fine. Just plug off the hole to filter and carb, and you're good.

Dan, I believe if you look at your original valve covers there are no vents except for the tube to the enclosed air filter so the PCV valve can suck clean air through the engine. With PCV the engine has all of the crankcase emmisions sucked through the PCV valve and into the intake so they can be burned so as to lower the overall emmissions. The laws in most states do not allow this to be changed. You could install a gromet in the valve cover for the PVC valve and use the hole you made as your filler and vent with a nice breather cap on it then your free to install an open element air breather and not have the second tube going to the air breather. It would be best to have the PCV in the opposed valve cover. For competion use there are several ways to vent the crankcase and do away with the PCV completly. You can purchase vents that bolt or weld on the sides of the valve covers that look and perform well, You can do the same thing on the tops. Another method is to have a tube run from the front of one valve cover to the other and have the breather in the center above the water neck. For circle track racing we mount two in the top of the left valve cover so making left turns there is less chance of oil finding its way out. Any vents you add need to have staggered baffles to help stop the oil and only allow the vapors to escape including the one you already have installed. The more power the engine makes the more it needs some good vents, the movement of the pistons create a lot of pressures in the crankcase and they need to have a free flow to atmosphere and if you can't vent the pressures they are going to find a weak spot be it a seal or gasket and force their way through and will probly carry oil with them. If the motor is not properl vented you can cause oil to be forced past the rings or have oil leaks you will never get rid of. Best of luck, make that mouse roar. J.Conway path

Thanks,

No competition here.

I might do the front taps and use bulkhead fittings and the Y. I'd like to keep the fins intact. Or, maybe I'll just hook the PCV to the air cleaner and not use the Y. If it blows oil out somewhere the first time I rev it up, I'll know that's not enough venting.

In Arizona, we have to retain the stock emissions components and functionality.

I have a hole/grommet in the right side already for the filler cap. I put a hole/grommet in the filler cap to accommodate the PCV. Never seem that in a store.

Lynlynch, With the PCV valve hooked up you have to have a way for filtered air to enter the crankcase to complete the loop. As I am shurr you have heard (form follows function) and the function of properly venting the crankcase should be a priority over the way it looks. Its your choice, a system that functions or one that will lead to failure. If the PCV valve doesn't have a baffled chamber under it to keep it from picking up oil you will be creating more problems that can lead to failure. Look inside your original valve covers and duplicate what you see or create something even better but do nothing less. Good luck. J.Conway

When designed correctly, your PCV valve will remove all of the crankcase blow-by. But that is only up to a given amount of blow-by. Blow-by will increase as wear takes place on moving pistons, rings, valves as well as the block and cylinder heads they rub against. Blow-by will also increase as engine RPM increases and as Cylinder pressure rises. The way that the factories compensate for the occasional WOT operation is to allow the extra blow-by to travel from the now high pressure (relatively) area to a low pressure area. That is the air cleaner assembly. When the blow-by reduces, the PCV now pulls more than the given blow-by, and the air cleaner connection now flows clean filtered air into the valve cover again.

If you work carefully, you should be able to drill and tap the corners of the valve covers in the back, top areas. This would be back, intake side of each cover. From that threaded hole run short hose fittings to a T, to the air cleaner.

Use twin 3/8" hose and you will match to volume of the OEM closely.

There is another option that I remember. Ford had a breather that removed to add oil. In the middle of it was a hole for the PCV valve. It would not be perfect as far as releasing blow-by to the atmosphere at WOT, but it might sneak through.

The oil cap was used from 1968 till around 1985. It should fit in your cover, if your cap is the twist on one.The Stant # was SO 71. NAPA # 703-1306 chrome, and 703-1305 painted. Good luck.

Seems to be several folks out there with the same 383 Stroker problems I'm having, maybe the following info. will help.

I used a Comp High Energy roller-cam & rocker setup with new World retro Torquer heads to get maximum low-midrange torque. The engine runs great, has lots of power & even gets good fuel economy for a rolling bread box.

Down-side is replacing back 4 plugs every 500 miles and gaging economy buy qts. of oil per mile.

I converted a chevy van into a 4x4 and installed a 383 stroker in it, worked out great except the engine burns 1 qt. of oil per 140 miles.

THE ENGINE IS ON A 3 DEGREE TILT TO THE REAR, WITHIN SPECS FOR A S.B.350 BUT MAYBE NOT FOR STROKERS ??

BOTH VALVE COVERS ARE VENTED & THE DRIVERS SIDE VALVE COVER ALSO HAS A PVC VALVE ROUTED TO THE 'FRONT" OF THE EDELBROCK CARB.

This oil is going down through the back 4 cylinders valve guides.. I found this out by inspecting the intake runners with a mini-cam I purchased @ Harbor Frt.. All of the back runners were free of any oil, but 'stem-side' of Intake valves were pretty carboned up.

I cut 3 'windows' in the down-side of a valve and found excess oil accumulating along the rear two cylinders. The windows show lots of oil hitting the outside of the valve cover surface & running to the rear oil drain hole.

This is likely more oil than the rear drain hole can handle under highway speeds. Especially when going uphill....

SOLUTION

I'm pop-riveting thin aluminum drain-rails, with a tilt towards the 'front' oil drain hole. Plenty of room in after market valve covers. This will also provide oil supply to the cam gear & chain assy.

Hope this helps some of you folks with oil-return problems..

Chuck

Boise, Idaho

Have you checked your valve stem seals? At 500 miles between spark plug changes in a full sized Chevy van, I would step up to platinum plugs till I could slow the oil leakage.

Hi Bob, thanks for the feedback. REF. 383 STROKER, EXCESSIVE OIL DOWN REAR CYL. VALVE GUIDES.... I've tried higher performance plugs to extend the plug change intervals, but doesn't address the excessive oil consumption problem.. Several guys with 383 Strokers out there with identical problem, burning a qt. of oil through back four cylinders in 2-300 miles. NOTE; This engine does not smoke on start-up or while running and carries 170 # of compression. When I ran a mini-cam down my intake runners, I found no oil leakage at the gasket or in the runners, BUT FOUND CARBON BUILDUP ON THE UNDERSIDE OF THE INTAKE VALVES... When I ran the engine up using the valve cover I put clear poly carbon windows in, oil-level reached between the 2nd & 3rd valve spring coil. This may be more oil than standard cup-type valve seals can handle, especially with 170 lbs. of compression?? At this point, looks like my only option is to pull the heads and have them machined for ""positive-style valve seals"". Hastings seems to think these type seals need to go on both intake & exhaust valves. Thus far, none of the guys on forums with this kind of problem have posted any resolutions to solve this issue and I've run out of 'things' to try. Extra crankcase venting & leveling the engine accomplished nothing. ON THE POSITIVE SIDE !! Now that I have my new mini-cam snake I can do my own colonoscopy checks !

There is nothing in the head design that should cause the problem. Chevy produced 400 small block with a 5 year 50,000 mile warranty.

Are your oil drain holes clear?

Are your valve guides loose?

Have you added more lift to the cam, possibly changing the rocker arm geometry? There are inexpensive plastic geometry checkers available from the cam manufacturers.

Are you using the stock valve stem seals and spring retainers, and oil deflectors? The stock seals should provide an oil tight seal between the top of the spring retainer and the valve tip. If you can find a suction cup to fit over the spring assembly, it should not leak. Another way to test is to find a section of rubber hose that will fit snugly over the spring. Then try to see if the hose will hold penetrating oil when added to the inside of the hose.

High performance spark plugs usually are a colder design to allow them to not overheat when the engine is driven hard at high rpm. If you are not working that 383 hard, the colder plugs will want to foul more than the stock plugs. By going to platinum plugs, the platinum designs are allowed to run very hot with no worries, because the platinum will not melt.

Another thing that is common is to use oil restrictors to limit the volume of oil reaching the rockers. That forces more of the oil to go to the bearings. Moroso should be able to help with this, but the engine needs to be dismantled again.

If I had the problem you are experiencing, I would look into any restrictions that might be in the return holes. After that I would go to platinum plugs. I had a 318 van with 360,000 miles on it that had never had any engine repairs to it other than a timing chain. Those valve seals had to leak. Every morning it would blow a garbage can sized puff of smoke. But the platinum plugs just kept on firing.