I've got a 70 SS 454, big cam, hei dist. headers, flowmasters. My question is this, I have the pcv valve in the driver side valve cover and on the passenger side where the oil fill hole is I have a black rubber snap in plug. With the engine running there is a ton of vaccum in the crankcase. If you pull the plug and put your hand over the hole it's sucking pretty hard. Is this good or should there be a vented cap where the rubber plug is?
Thanks,
Fred

If you want vacuum in the crankcase, leave the plug. If you want a positive crankcase ventilation system, put a breather there.

The whole point of a PCV system is to get crankcase gasses out of the engine. Without a breather to allow fresh air in, you can't get the crankcase gasses out via the PCV valve. Put a breather in the other valve cover.

I agree with Rich, but one benefit of vacuum in the crankcase is reduced oil leaks. But it sounds like your motor is pretty well taken care of and would not have any leaks.

thanks for the reply... yep I don't think I'd have any leaks, and I just feel like it needs a vented filler cap... guess I can give it a try anyway.

thanks, I think it might be a good ideal and not that expensive to try..

I think venting it might be worth a try, don't know if it will change anything or not other than keeping the crankcase vented.. thanks

just a FYI vaccume in the crank case builds hp. thats why big time drag motors run evac systems through the exhast, to create a vaccume with out a pump. that and any blow by in oil form is burned and not spilled on the motor or track
dusty

Your throwing away free horsepower! Vacuum in the crankcase allows the pistons to travel down without having to displace air, yes another piston is going up but the air has to flow around the main cap from on pair of cylinders to the next and you are just wasting power pushing it back & forth. Like the post above says race engines use vacuum to reduce that waste of power from pumping the air. There is an additional gain in that oil flinging off the crank just flails in the air, then the crank somes around and hits it wasting more power. In a vacuum the oil stick to the block, pan etc and slides down rather than flaing around

Your throwing away free horsepower! Vacuum in the crankcase allows the pistons to travel down without having to displace air, yes another piston is going up but the air has to flow around the main cap from on pair of cylinders to the next and you are just wasting power pushing it back & forth. Like the post above says race engines use vacuum to reduce that waste of power from pumping the air. There is an additional gain in that oil flinging off the crank just flails in the air, then the crank somes around and hits it wasting more power. In a vacuum the oil stick to the block, pan etc and slides down rather than flaing around

yep:beers: