Installed new 350 ci gm crate low hp engine, 2703 Edelbrock intake with oil fill/breather tube & alum valve covers. Drilled & tapped 3/8 npt in back of each cover & attached 5/16" vent tubes. When I drive the car (64) ,I remove the vent cap & place a rubber vent hose over the tube. Aprox 1" I'd. To reduce internal pressure & route oil vapors & condensation under the car, instead of sucking them thru the air cleaner & on carb & intake. Know this is somewhat unorthodox, but is this a way to reduce internal engine pressure & minimize piston blow-by. Have read several posts as to engine damage with too much pressure build up. Would appreciate any input on this. Really don't want to drill breather holes or PVC valve holes unless I have to. Thanks

 

I am, speechless!

 

Nothing unorthodox about it, you just went around your butt to get to your elbow to reinvent a road draft tube....and a sorry imitation at that.

Its less efficient than a PCV setup, sends out more pollution, keeps your oil dirtier, and, without the proper liquid/vapor separator ("tomato can" show below) you're prob dripping oil on the road the whole time you drive...




Unlike a PCV system, road draft devices don't scavenge vapors at idle either, they depend on the moving car to create a low pressure drop across the tube to suck vapors out of the crankcase. Hence the word "draft" in the phrase road draft tube as opposed to the word "positive" in the phrase positive crankcase ventilation...

Most road draft tubes are cut with a distinct angle on the lower end to increase draft surface area which I'm sure your homemade "tubes" don't have:



Proper PCV systems don't "pressurize" your crankcase so I don't know what that bit of concern is about... Your fear is totally unfounded... Even if a crankcase does get pressurized through some malfunction the worst that usually happens is that the oil dipstick gets blown out of its tube...

And what you've done doesn't "minimize" piston blowby one iota...

You need to step back and rethink this...a proper PCV system can be added to your engine for a few bucks that will work superbly.... A GM "crate" motor should allow installing a PCV system without much trouble...

And you don't want to drill holes for a proper PCV system but you drilled holes in the back of the valve covers for this setup ? Not getting that at all....

 

You're assembled a draft tube that requires finagling each time you run the engine? More trouble than installing a real PCV system, and introduces an opportunity to forget about it and have a Bubba result.

Nevermind than one more car with a non-functioning emissions system won't matter, but is this Bubba system a protest over the most benign emissions system ever, and which also provides engine protections (PCV systems were initially invented for WW2 tanks, and not for pollution control).

Short answer: why bother and why go to so much trouble to develop a poorly-engineered alternate for a PCV system? Makes no sense.

 

A 3/8" NPT in the back of each valve cover is very small compared to the approximate 1" draft tube and fresh air tube on the old motors.
In order to expel air, air must be taken in to the engine, so is one of the 3/8" tubes fresh air in??? I won't venture to guess whether 3/8" hose is large enough to do the job on a fresh motor, may be as the blow by should be minimal after the rings seat. The two hoses should help prevent over pressurization of the crankcase and thus blown gaskets due to internal engine pressure.
Without a baffle of some kind inside the valve covers or an oil separator in the tubes, you are probably going to lose a significant amount of oil to the atmosphere and road. The fast engine speed, the more pressure, the more oil loss.

I am not opposed to your inventive efforts. I enjoy tinkering myself (too much at times). All old engines pollute the environment. I think you should consider increasing size of the hole in one valve cover to install a fresh air inlet and installing some kind of baffle in both valve covers to help minimize oil being lost thru the hoses. An oil separator in one hose external to the valve cover and then a PCV valve to a vacuum source on the engine may increase the efficiency of your design. A filter of some kind on the fresh air hose may be needed to prevent debris from being sucked into the engine. You don't want dust and dirt in the new engine.

That said, dirt track racers and drag racers have for years plumbed the crank case ventilation to the headers to scavenge the oil vapors out and burn them off rather than dump them on the ground. Not to EPA standards, but works better than the passive system of the 50s and early 60s before the PCV systems.

Don't let negative comments deter your imagination, most are meant to be constructive criticism, which is sometime helpful. Pick the constructive comments out of the rubbish and improve your crankcase ventilation system.

 

My post was well-intentioned and based on a lot of experimentation on my 61.

Even if the OP replicated a factory road draft system it’s sub-optimal and not really solving his stated concerns.

 

I may have misunderstood what you wrote but I believe you say you have a 1" tube venting as well as the 2 5/16 lines. First off and most important with any attempt at ventilation is baffling. If you don't have baffles in you valve covers they are just open leaks or if you do have a pcv valve a place to vacuum oil out of your engine. You must have baffles on either set up. There is a ton of oil being splashed around in your valve covers as you drive and air being forced out those tubes at fairly decent pressure is going to take oil with it. Second you don't have to have a source of fresh air for venting the engine the only purpose is to let internal pressure escape. All of that said I would run a pcv valve but you MUST have proper baffles.

Racers don't run evacuation tubes to the headers to keep oil from dripping on the ground. The rapidly escaping exhaust creates a vacuum at the hose and sucks pressure out of the engine. It's done to lower back pressure and improve ring seal at high rpms. It's a super sonic road draft tube.

One of the last engines I machined when I had an engine shop was for a guy that was going to build it his self. He found out where I lived and drove his truck to my house. He complained that I didn't hone it right because every time he drove it it pushed the dip stick tube up and blew oil everywhere. I glanced at it real quick and said you don't have any engine ventilation. He had nowhere for gases to vent no breather at all.

Modern engines run the crank case under vacuum they aren't vented to the atmosphere.

 

All the comments so far are meant to be constructive, whether you like the way they're worded or not. Seems like your comments were negative as well. Nothing wrong with teliing someone they took a wrong turn.

In addition to using imagination on a system revision, it'd be a good idea to bone up on how a crankcase evacuation is supposed to work correctly.

 

Setting aside everything else, Roberts61 brings up a very good point - opening up any holes in the valve covers without baffling to control splashing and spraying oil from passing out, is going to be a very messy and leaky ventilation system.

 

I brought that up in post #3 along with a lot of other issues

 

Thanks R66, appreciate your comments, yes I have 3 vents, one each on back of each valve cover and the large one on the oil fill tube, have monitored all three for oil leaks/loss. Only a few drops total on a 100 mile run. Installed a cloth screen on each vent to monitor. I will cut an angle on the large tube. I will use what I like out of the rest of the comments ,I only drive 1000 miles a year living in a northern climate. Am invirmently concerned for the most part, recycle a lot, I had stated ,I didn't want to install a PVC valve because of cosmetic reasons. I have a rather thick skin, and expected a few rude comments, just wondering it seems like the number of posts have declined lately. Don't think I will be asking/ posting any more ignorant questions.

 

I read your major concern being about internal engine pressure foremost and cosmetics as secondary. My post was addressed accordingly.

If you’re happy I’m happy for you.
You will find no better source of info on these cars than right here.

There are members here who actually worked at the factories, others with survivor, original cars, master level NCRS judges and dolts like me that blunder around and come up with solutions to stuff...and sometimes they work...

All stuff no book will provide.

 

This is the system I have on my 57 with a crate 350 and dual quads. When I first put the set up on, I only had a vented oil fill cap. Found that I had oil mist all over engine, so I put a generic pcv valve on rear of driver’s side and connected it to base of front carb. No baffle, just the valve. Maybe dumb luck, but oil stays amazingly clean and I have no problem with oil being “sucked out”. Yes, I’ve had several tell me it’s wrong, but just as many commend my effort. I don’t worry about looks as long as it works!

 

You almost surely have the tomato can in the lifter galley and that separates the fluid from the vapors...
To me, what you've done is not unsightly at all...

 

WOW. I just saw this! My advice would be what Mike suggested earlier: study PCV systems and how and why they work, and then re-install a functional PCV system to your car. Your current situation is inferior to even the original road draft systems, by a whole bunch. You are guaranteed to: get dirty oil fast; leak oil on the road and chassis; increase wear and blow-by; and have a smelly car and clothing. Bad Ju-ju.

 

Here's a feature article I wrote several years ago that explains what a PCV system does and how it operates - you might bone up on this and reconsider the design of your crankcase ventilation system.

 

Look again he's not going to the tomato can the pcv valve is in the valve cover. If you don't drive very much it isn't going to suck the oil out but if you drove it a lot it more than likely would consume oil.

 

Nope, actually I’ve driven all day long at highway speeds, as well as local shorter trips - never uses a drop of oil.

 

For those of you who have lost sight of the original stated objective. This was it!!!!!!!

If the OP just wanted to reduce any internal crankcase pressure, he's on the right track with his "imagination". He could have improved his position a little by just leaving one of the valve covers off. His system as designed won't do a thing for reducing any "piston blow by" pressure but it will help with the pressure created by the pistons dropping on the down stroke and creating some pressure.

Poorly stated objectives caused the concern here. Not the answers received. Your opinion may vary. As stated several times now, he needs to bone up on the proper way to evacuate and engine crankcase.

 

My apologies to all.

I mis-read the original post about the 1" oil fill tube being a vent / inlet also. Don't know how I did that. Your system will probably work as well as the early V-8s that used no PCV valve, as long as it is not sucking oil. No harm, no foul.

Ron