A sbc question about breather tubes

When did Chev make the change in the back of the block and eliminate the road draft/breather tube? Did any of the large journal small blocks still have the tube and the can in the valley? I'm trying to remember if the first 350's or the late 327's used the tube, and I just don't remember. Thanks, Rob

 

I believe the first year for elimination of the road draft tube (replaced by the PCV valve) was 1962 in California. Manufacturers then just made the change to all vehicles. Some early 327s still had the tube...no 350s ever did.

I am prepared to be challenged on this sketchy information.

dj

 

Just realized that in the early stages of "environmental sensitivity" most trucks were exempted, so it's conceivable that some trucks (including ½T pickups) were equipped with draft tubes past 1962.

dj

 

I'm gonna throw another question in the mix, not tryin to hyjack ur thread but can you run an intake breather tube, with out pcv, or valve cover breathers on a pcv engine?? I've heard that youcant, but I've seen plenty of sbc with no breathers on the valve covers no pcv, and just a breather on the intake.

 

You gotta vent the engine. Some are really clever on hiding a pcv.

 

I've always wondered about venting an engine. I ran an old AMC i6 for a couple of years with the pcv hole plugged off. It came to me that way and I never bothered to change it. Never seemed to hurt anything, always ran fine (at least till an unnoticed hole in the oil pan took it out).

I was running the 350 in my old van that way for awhile too, until a friend noticed it, completely freaked, and bawled me out. That was the first I ever heard of it being anything more than an emission control thing (I wasn't very well informed back then, I guess). I took his word for it and took the plugs out, but I've yet to hear an explanation of exactly what catastrophic effect the lack of ventilation is supposed to have. Maybe the time has come?

So, what was I doing to my engines?

 

Nationwide, Chevy went to PCV valves in '63, but I'm quite sure that the 283 and 327 blocks still had the same road draft hole in the rear of the block through '67---they just used a different fitting for the valve to hook up to.

 

you make more power without crankcase pressure. I remember an interview with STAR racing (pro stock bike) they pick up ~15 hp with a small vacuum pump, more with a 3 stage pump. and that's on 1500cc. PCV is good for everyone, not just environmentalists.

 

I've taken the intake off of a bunch of small blocks and '67 is the newest one I have ever seen with the block set up so you could run a road draft tube. I pulled the intake on a '68 last fall and it had no provision in the block for a road draft tube.

A lot of the early PVC motors ran the PVC from the oil fill tube on the front of the engine to the carb. It was an inline PVC and can still be purchased at the local parts store.

My '68 engine has the PVC in the rocker cover, The rocker covers resemble script rockers without the script. But in '68 they also had a rare setup that ran script rockers and a factory PVC. Pretty rare setup but they do pop up ocaisionally.

You need a PVC or a road draft tube or if you are a serious racer a vacuum pump. If you go the vacuum pump route the cheap way to do it is to purchase the air pump for a Ford with an air pump. But that is serious race chit, a lot of the blower/turbo guys do that around here.

 

My 67 Elcamino 283 had the hole with this hose connector for the PCV valve in the rear hole. I don't know the years for the different sized journals.

I hate the use of the term "VENT when referring to PCV systems. You "vent" a rear end to relieve pressure. An engine needs air flowing through it. Just my hang up.



This old image shows the direction of the air flow through an 8BA 48-53 Ford flat head using the road draft tube system long before the PCV invention. The air need to flow through an engine. It's not merely a vent to relieve pressure.

 

Actually the 1967 Camaro with the 350 ... did have the hole in the rear of the block ( like the 67 327's ) and used the same fitting that TOMMY shows.



The 350 was a fairly rare option for the 67 Camaro. I believe it only came in the Super Sport models ... ( mine came from a gold 67 RS/SS Camaro )

 

I thought it was in that 67/68 period, but I couldn't remember exactly when, and if the first 350's had it. Sounds like some did. Thanks Rob

 

1967.

The only 350 engine that had a road draft tube is the 1967 350SS engine! Period, end of conversation!

1968 found all SB's no longer having the cast bosses for it!

This crap fall's into the realm of "Did any 350 engine's have SJ rod's in them?" sorta stuff. There is much talk that the 1967 350SS engine had SJ rods in it but I don't think so because mine didn't.

But go hunt up Gary, (aka, GOSFAST) and ask him on both t/c boards as well as nastyz28. Please tell Gary that ol' pdq67 sent you asking because he's what I consider a buddy by me..

Seem's this might be a Canadian issue????? Like our beloved SBC's having a very short run of F** CAST RODS in them way back when smog was started in the 262/267/305(?????) engine's that NEVER got off the ground...

And guy's, I'm NOT trying to spread urban legends here!!

pdq67

 

I was told my 327 was a '68 when I bought it and it is machined for the road draft tube. I used the cannister baffle in the lifter valley and the PVC nipple from an older 283 along with a filler tube breather in the intake.

 

I seem to recall a magazine article about drilling into the intake at the rear near the distributor hole and tapping it for a PCV. I am running a 350 in my '29 and want to use early 'Vette valve covers without holes or breather provision. I am going to use an early aftermarket intake with oil filler tube.

 

The 307 (replaced the 283) and 350 (replaced the 327) are the ones with a PCV system.

 

Well, technically, there was no road draft tube after 1962. PDQ67, I know you are talking about the machined hole in the back of the block. I'm talking small blocks here, starting in 1963, all Chevrolet small blocks used some sort of PCV that utilized the machined hole in the back of block.
2 types of PCV were used from 1962 to 1967 -->
Open PCV: Tube from back of the block with an in-line PCV that went to the front of the carburetor. The oil filler tube had a vented cap.
Closed PCV: The oil filler tube had a non-vented cap and either a nipple with an in-line PCV or a threaded PCV that screwed into the oil fill tube. This went to the front of the carburetor. Tube from back of the block went to the air cleaner

 

Your are going to have to also drill your intake.

 

Actually the front oil fill, breather tube was never designed to be a breather, it was used for fresh air flow into the crankcase. Crankcase vapors would then exit through the road draft tube. In 62 they replaced the road draft tube with a pcv valve in California. In 63 all states used the pcv valve. There have been several different arrangements to getting fresh air in and vapors out. The ones where a pcv valve was plumbed to the oil fill tube, the tube used a sealed cap and fresh air was routed to rear of block where the road draft tube used to be, this resulted in air flow going from the rear of the block to the front of the engine. By 1969 all small blocks used the pcv valve in the valve cover with fresh air entering the opposite valve cover. This gave a side to side airflow through the crankcase.
At any rate which system you use front to rear, rear to front or side to side, you need this airflow to remove vapors, crankcase pressure and probably more important moisture from the crankcase.

 

My first drivable car was a 67 SS 350 Camaro. When I got it in 1970, it had the vented cap in the oil filler tube in the front of the intake, and a PCV valve inline from the machined hole in the rear of the block, same as mentioned by BigDogSS in the "Open PCV" description in Post #17. It had factory chrome valve covers without holes, other than bolt holes. Had a friend who replaced his 67 intake with a later one that did not have the oil filler tube. Worked great until he tried to add oil and found he didn't have an oil fill port. Sorry for the OT references!

 

Yup, '67 350 was the only year with the road draft style (and can under the intake) motor as per Deuce Roadster himself . I remember a post from years ago that he had one.

 

This is the system as used on 65-67 Chevy's, it was called a fresh air tube, this is the curved 66-67 Chevelle, Nova and 67/68 Camaro, version, the 64 and 65 (non fuelie) Corvette and 65 Chevelle was straight and routed on other side of the distributor.
Both are available as reproductions.
I found this oem one years ago at the Portland swap meet.
Note pcv hookup , oil fill tube, script valve covers, although this is the L79 engine in my 67 Nova, the same basic system was also used in the 67 Camaro and Chevelle.

 

Hi,
I have the same engine in my 67 L79 . I need to find the breather hose! Any ideas?
Ronnie

 

Is this one for sale?

 

The engine. I would love to have another one for another project.
Thanks

 

67 L79 what?
Malibu, Nova, or Corvette.
Most Chevy restoration suppliers should have them, such as Classic Industries, etc.

 

DDDenny: I see your setup will have the fresh air being pulled in thru the air cleaner base, into the fitting at the rear of the block, thru the engine then sucked back out by the vacuum created in the intake up thru the oil fill and into the intake thru the hose you have connected near the base of the carb, correct? I am just re-stating this to make sure I am correct. I have a '58 SBC and am going to use Corvette finned covers without any oil fills etc. Therefore I need to do something similar and just wan to make sure I do it right. Also, can the air flow can go either direction? Can you just use a non-sealed type cap on the fill tube and then just run a hose from the rear fitting to the intake?

 

All the components in my Novas' system are OEM Chevrolet issue except for the angle adapter on the pc valve going into the oil fill tube, this was a retrofit to clear the shock tower brace I built.

By the way, the 65 Chevelle l79 didnt even use a pc valve, there was a "restrictor orifice" in the carburetor that connected directly to the oil fill tube, unlike the 65 Corvette which did have a pc valve, not sure GM's reasoning for the differences.
You might read this HAMB thread from the beginning, plenty of discussion on the subject.

Here is a great Google image search on the subject.
https://www.google.com/search?biw=1..........30i10.abZuZdVKLe0#imgrc=Bwpow-0BIFKjmM:

Good info here also.
https://www.chevelles.com/forums/18-engine/616914-l79-crankcase-venting.html

 

I see your setup will have the fresh air being pulled in thru the air cleaner base, into the fitting at the rear of the block, thru the engine then sucked back out by the vacuum created in the intake up thru the oil fill and into the intake thru the hose you have connected near the base of the carb, correct? I am just re-stating this to make sure I am correct. I have a '58 SBC and am going to use Corvette finned covers without any oil fills etc. Therefore I need to do something similar and just wan to make sure I do it right. Also, can the air flow can go either direction? Can you just use a non-sealed type cap on the fill tube and then just run a hose from the rear fitting to the intake?



The answer to all of your questions is yes.

 

You guys do realize that this thread is from 2016, right?