this is surely old hat to most of you folks, but being born in 1982 i've got a lot to catch up on. i'm trying to figure out how to run a '50's/'60's style breather tube on the front of the manifold on my small block chevy. my dad thinks there's some kind of tube on the back of that exits under the car. how does that hook to the manifold? i've got an old manifold that has the hole for the front tube plugged (some kind of br*** fitting...wierd?) but i can't figure out what's going on in the back. also, if there is a tube in the back, is there some sort of PCV-like deal back there? will it work as long as i get into the lifter valley with both tubes? any help is appreciated.
the blocks were different up to about 1967, they had a hole in the back behind the intake, that met up with a hole in the valley, and an oil vapor separator was in the valley stuck in that hole. Also at the front there was a hole that went down into the timing cover area that met up with the hole in the intake where the filler tube went. The hole in the back was connected to the road draft tube that went down the side of the engine and exited just below the starter, up to about 1961, then they got rid of the draft tube and put a small fitting on the block back there, connected to a PCV valve (although the plumbing arrangement for these mid 60s engines varied quite a bit, some had the PCV on the front fill tube, some had it on the base of the carb, etc) the newer blocks don't have these holes in the block, they were designed to use a PCV valve in one valve cover and a breather tube in the other.
The back pipe is a road draft tube(RDT)...it installed into a hole in the engine block, and had an oil baffle inside the lifter valley area. When PCV's first came along, the RDT was deleted and the PCV was installed there instead. Later, the PCV went to one valve cover while the air inlet for the PCV went to the other, thus giving full cross ventilation to the entire engine. You can run a PCV to one of the valve covers and still use the front mounted tube breather, or drill a hole in your intake manifold (remove it first.) for the PCV if you don't want to drill a set of finned covers or whatever. The hole is drilled into the lifter valley area (NOT a runner!) and may require a baffle to prevent oil vapor from being ****ed into the PCV system and giving you what appears to be an oil burning engine. Bottom line...if you have a PCV system now, you won't hurt its operation by running a manifold with an oil tube. To get 100% proper flow you would just need to have a non-vented cap on the tube...or use a vented cap and plug the air intake on the opposite side valve cover from the PCV if you can live without full cross flow capability. Remember...The first series of PCV equipped Chevys had NO venting to the valve covers, just thru the lifter valley...so they didn't have cross flow thru the heads either.
Will I run into issues if I run the front filler/breather as my only breather? What if I add breathers to the V/Cs?
having breathers on the valve covers is not a bad thing. if you are only running the front filler tube and no RDT
Thanks Boones. I'm gonna change a few things on my car and if I put on what I have, I won't have vented V/Cs or a PCV but I'm not opposed to putting some in. The Current set up is a PVC and A V/C breather with no filler tube. I just don't want it puking everywhere.
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