The Stovebolt Site Forums The Shop Area Engine Shop Down draft tube

I was checking out a guys 59 apache and his 235 has a big Down draft tube on the passenger side of the block.
My 59 with a 235 doesn't have one. Was their a change in models or where the engine was manufactured, or was their something that the PO did to my 235?

I dont know at what time, but chevy went to using a pvc valve instead of the old draft tube.

All 235s have a spot for the tube. I know California cars had it blocked off and used a PVC system as far back as 1954 and maybe earlier, Washington cars used the tube through 1962.

Some big trucks had a pcv system also.

Dave, you are right on with that one. The 235 in my 61 has a Road Draft Tube. How hard a swap is that?

I have a '59 apache 235 with the pcv system. It was sold new in California and the pvc system looks stock.

Adam

Anyone have pics of the pvc in place of the down draft tube? And showing the return to the manifold?
thanks

Is the pvc or down draft tube required? What would the result be of not using either of them? Or would it even matter.

the engine has to breathe. if you dont put anything there it will work fine but you'll have an oily mess in no time.

The PCV (Positive Crankcase Ventilation) system also works as an emissions device, by taking the gasses in the crankcase and putting them back into the intake air to be burned again. This will reduce the HC's (gasoline) that goes out the tailpipe and pollute.

In the morning I can take a picture of the PCV system in my '59. The PCV valve attaches to the valve cover and then there is a hose that goes into the top of the oil bath air cleaner.

Adam

here's a tech. tip on it www.speedprint.com/Deves50/pcvinstall.php

The setup on my '59 is a little different than the one on the above web site. There is a hose that comes out the side of the valve cover and then to the PCV valve and then another short hose that goes into the intake manifold, right under the carb.

There is a separate hose that goes from the top of the valve cover and then into the air cleaner with no PCV valve.

I always assumed this was the factory setup, but I may be wrong.

The link has a couple photos. Hope this helps.

http://www.flickr.com/photos/11159813@N00/

Adam

I like this idea,would like to know how well it works.I also like the nostalgia look of the down draft tube.

I was hoping to avoid that hose look and have the simple look. Is there a performance issue here or is it for more current smog laws that won't apply to my 46.
Thanks

I don't think you will gain or lose any performance using a PCV valve. The carb will be adjusted to suite the needs of the engine anyway. The PCV is more for smog. Just make sure the crankcase can breathe in some way.

Adam

Thanks guys,
My truck was made and still resides in California.

California…always has to be different.

What symptoms can accrue when the PVC valve gets clogged? Or does it ever get clogged? I know they do on Mopar 318's.

Has anyone tried simply drilling the down-draft tube for a grommet and PCV valve at the top. I think a low mounted valve in the draft tube hole would pick up more oily fumes and the additional 5-6" higher mount on the top of the road draft tube would work out better. Obviously, the valve cover mount with a baffle under the valve would be the optimum if you didn't mind drilling your cover and mounting a baffle (which is a MUST) This way the tube, which would be plugged would serve as the baffle to keep splash out of the valve.

Lack of a PCV valve and a plugged draft tube will fix you up with excessive crankcase pressure, oil leaks and some sludged up oil pronto. Just my $.02....gained from....

Guys there was a previous post on this with very detailed explanation.

here is the link ...
http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=009879#000001

Here is a diagram of PCV system on a 1954 261 engine.

Here is a picture of the road/down draft-tube side of the engine - there is no longer a "draft" tube but there is a tube that goes into that hole in the block.