ebay fabricated valve covers leaking....

Jack, yours is a street car?

 

Yes, it is and it runs 11.50 1/4's.

 

I've run both setups on the same vehicle for comparison many times(and actually just hacked off my evac kit when I detuned my 383 Blazer recently).. and still prefer closed PCV setups for mild to moderate street cars that rarely drive around revving against 4.xx rear gears(with no verdrive) and still use "street mufflers". The basic reality is that header evac kits only work efectively if you typically.. and continually.. like to rev the snot out of it everywhere you go.. and will do absolutely nothing at lower rpm's when exhaust velocity is too low. I know this this to be fact because I've had pressure gauges on many types of evac systems to evaluate and tune them thru the years. Even just using the old "plugging the hose with a finger" trick can show it well enough.

Also consider that header evac kits won't keep the engine as "clean" if you drive the car more realistically on the street since they don't pull much vacuum at lower rpm's and trying to overcome mufflers/full exhausts. And unbeknownst to some folks.. sealed PVC will still pull light vacuum at WOT if designed correctly and the right valve/fresh air inlet sizing is used.

I've also run both setups simultaniously(header evac & closed PCV using MUCH smaller fresh air inlet from the air cleaners pan) which shows sort of the best of both worlds effect.. but you need to run custom bungs off the rear of the cover with oil seperators to do it correctly.

 

Groberts,
That's funny, you must have been reading my mind because I was just thinking this morning that if the header evac is great for more WOT and racing stuff and the PCV system is just fine for all around driving then why couldn't I run both together as long as the header evac doesn't suck back through the PCV. Now you said you used a PCV valve in the valve cover connected to the base of the air cleaner, does that draw enough vacuum at idle and low speed to relieve crankcase pressure? I would think you would want the PCV attached to the bottom of the carb for manifold vacuum and let the header evac take care of the rest. Because on a conventional system the PCV valve goes to the base of the carb and the vent on the other valve cover goes to base of air cleaner. The reason for this is manifold vacuum(PCV side) goes away at full throttle and suction in the air cleaner increase so the two kind of overlap. You would basically be replacing the air cleaner connection with the header connection.

 

yeah.. it's a traditional closed PCV setup(ie; as you just mentioned).. but you need to be careful about not using an intake system as the idle/part throttle vacuum can be CONTINUALLY pretty high and cause leaks in gaskets around the motor. Running both in conjunction would be simiular to running a PCV without a fresh air intake and overwhelm the gaskets at some point. Then.. as the motor gets older and the evac systems can't keep up with cranckcase pressures at various rpm's.. the motor will develop oil leaks as the positive pressures overwhelm the available vacuum from either system. You can also go overboard and actually pull raw fuel in between the rings which isn't good at all.

Sorry to complicate matters.. as I tend to do too often by just adding vague comments or personal experience into my posts which seem to cause debates more often than not.. but I'm not so sure that the motor/combo you're doing would be worth all the extra effort here. You may be better spent to put your time elsewhere on the build where you'll get better returns from it.

What compression/trans/gear are you running?.. and roughly how much power will the motor be making?

 

Mine is a 347 with 10.5:1 and hydraulic roller good to 7K. HP estimate maybe just under 400 with this cinfiguration? Upgraded heads and cam will come probably next winter. I also have a 125 HP plate system with a progressive controller.

 

Then in that case.. unless you have thinner/low tension style rings that would require vacuum to be present under high rpm(which would be getting into the realm of vac pump requirement anyways).. all you really need is the evac portion of either system to suit your needs here, IMO. If the motor is healthy enough(obviously a fresh one should be) then I'd just stick with running the evac system and enjoy the racy feeling imagined when you rev it up and/or pop the hood for others to gawk at.

The one good thing about running a sealed case with a header evac system is that it will help ring seal a bit better than the standalone PCV setup would at higher rpm's since that's where it likes to live most efficiently. Muffler's can make or break the efficiency level of such system though so be careful and be sure it's nice and loud(free flowing) to get the full effect. lol

 

The exhaust system consists of 3" pipe from the headers to a pair of 3" Magnaflows (the straight through stainless steel kind) (yes loud unfortunately!) and the rest which is not completed will be all mendrel bends in either 3" or 2.5" most likely depending on what will fit best. The carb is a worked Holley double pumper which flows around 800. I do not have an air cleaner yet. So if I understand what you're saying... you are recommending me to just use the header evac by itself. because adding a PVC attached to intake manifold vacuum in a sealed system will be too much on the gaskets & seals. And you're not recommending using a PCV attached to the air cleaner base because the header evac does this.

Do you think I will be ok and not build up CC pressure at idle or low rpm with just a header evac?

 

I think it's going to be fine. Tonight I measured the spot on the drivers side valve cover where I need to put the hole for the evac breather. I drilled a 3/4" hole in that spot and reinstalled the valve cover. I started up the engine and I now have zero crankcasenpreaaure and the valve covers don't seem to leak. Granted my wife and father in-law were watching tv in the room next to the garage so I didn't run it very long. But it's looking good so far. I will test it further this weekend after I install the mufflers. I feel like at least I'm not going to blow out any gasket or seals now.