Hi All, The 350 in my Model A is a little tired and has blow by. I would like to set up a PCV system on my Offenhauser Tri-Power manifold but am stumped. The only ports available are the full manifold vacuum port that is connected to transmission/power brake booster and the center carb non-ported vacuum port on the rear of the base which is connected to the distributor advance. This kind of leaves me one port short for the PCV valve. Here are the solutions I have eliminated after researching things on the web. 1) Connect the distributor to the ported vacuum connection on the center carb and use the base port for the PCV valve. It appears there is a lot of controversy about whether a distributor should be connected to a ported or non-ported connection. I won't get into details but I prefer a non-ported connection to my distributor. 2) Use a T fitting on the non-ported manifold connection and run the transmission, power brake booster, and PCV valve off that port. Once again, research shows that to be a bad idea for numerous reasons I won't go into. 3) Use a T fitting on the non-ported carburetor connection and run the distributor and PCV off that port. From what I've read, that isn't the best solution as the distributor may not see steady vacuum and could pull blow by into the diaphragm. 4) Drill and tap the base of one of the other carburetors. I'm not even sure this is an option but even if it was, it seems kind of dicey. 5) Drill and tap a second manifold port. The problem with this solution is I don't where to drill to catch both plains (runners?) on the manifold. If I only catch one plain, I will be dumping a fair about of blow by into 4 cylinders. Below is a picture of an Offy manifold very similar to mine. Thanks in advance... Ron
If the manifold is snugged down and in it's happy place and you would rather not disturb it, you could build some cool carb spacers and drill one out for the PCV vacuum source. You only need one done this way, but I am really **** about the carbs sitting at the same height or maybe no spacer in front, little one in the center and the tall one in back drilled and ported. That can look cool. If the manifold is off the car, you could drill a runner. I would imagine you run straight linkage as opposed to progressive on that style manifold so it really wouldn't matter which runner you drilled. The one in back would be less noticeable.
Trans-dapt makes some nice 0.500" spacers and that might be a reasonable (but expensive) solution. As far as drilling a runner, since it is going to be pulling oil mist, I would prefer not dump the mist into just 4 cylinders. (To be honest, the motor has significant blowby but a rebuild isn't in the budget right now.) I thought about tapping into two runners and teeing them together but that seems like a kludge. I'm thinking the spacers might be the only solution. Or, I could pull the Tri-Power setup and go with a nice reliable Edelbrock Performer manifold and carb setup but that seems like heresy. (Anybody in the market for an SBC Tri-Power setup? )
Depending on how much blow-by you have, the PCV may not be the solution you're looking for. From experience, a tired engine with worn rings will huff more blow-by than the PCV system can get rid of, and the engine winds up blowing exhaust out of the breather anyway. The only thing I can think of in terms of alleviating the smoking is to run a crankcase evacuation system, and just keep a close eye on your oil level. That in no way fixes the blow-by issue, it just relocates where it ultimately is discharged from in the engine compartment to a more palatable location outside and behind the car.
Paragon Corvette sells 'em for $11....here is the link Paragon Corvette Reproductions - Carburetor Hollow Stud Kit
If the blowby gets to be a problem, you might try an oil separator in the PCV line. I’ve never used one, and just how you’d mount/hide it on a hot rod I’m not sure. Probably someone will chime in on whether or not they really work.
It hadn't occurred to me the motor could be huffing more blow-by than a PCV system could handle. Hum... She does use a bit of oil, about a half a quart every 1000 miles. I've been saving my pennies and dimes to freshen up the motor next year so maybe the best solution is just to deal with the mist and put any PCV system money towards the rebuild. Thanks...
Isn’t there another big manifold vacuum port on one of the other carburetors? I think mine has one on each carburetor base. That little port on the right rear of the manifold will do your transmission and vacuum advance with a T.
I personally deal with this with the engine in one of my cars. It has a lot of blow-by, and it is an old, tired big Mopar. It has a good PCV system, but there is way too much blow-by to be remediated by the PCV, so it just pours out of the breather. As long as it doesn't foul the plugs, I deal with it and honestly, I don't drive the car much anymore so it has been less of an issue. But the only way to really fix it is to rebuild the engine. Rings, valve seats and guides... it is what it is
I guess more than anything, I hate sitting at a stoplight and watching the smoke rising out of the breather/filler tube.
My original idea was to drill and tap the base of one of the other carbs. But... I worry about going to deep or not deep enough. I guess I could buy a s**** base off eBay to practice on. Thanks!
Pull a trick from the Chevy pickup from the eighties! Plumb the breather under the air cleaner and let the engine reburn the smoke! Works great! Easy to do! Bones
I'm going try drilling and tapping a port in the base of the front carb. What could possibly go wrong?
Half a qt in 1000 miles won’t be a problem. I’ve had OT motorhomes that used more than that pulling long, hard grades in the mountains. Never fouled the plugs. Go look up the “closed” systems jimmysix referenced above. If it’s the air cleaners in your avatar, there’s a recent post on how they flow. Sorry, can’t remember who it was.
Oil fill tube with pcv attached. Factory set up from the mid '60's. Or breathers in the valve covers.
If your center carb is idle/off idle (progressive linkage), you want the PCV SIGNAL source at the center carb (dual plane intake) to distribute the fumes more evenly a**** the cylinders. A center spacer as shown with matching outboard spacers (non-vacuum source) to achieve same all three carb height. Easiest way out (IMO). How is the crankcase vented now, road draft? Photos? And then you will have to try different valves to find the correct flow.
Those hollow carb studs were very common back in the day. My 348 tri power had one, circa 58-59. Was the first I had seen and I have never seen one since. Good tip on the source!
I don't think they were intended for a PCV SIGNAL SOURCE - Description says GM 1958-1962. That was before PCV. FORD used them as a vacuum source for the trans modulator valve. The vacuum source needs at the minimum a 3/8" ******.
The hollow carb stud could be used as the non-ported distributor vacuum advance. The larger port at rear of carb used for pcv.
Each of my carbs has a 1/4" pipe thread hole in the back of the base. Elbow in the back of the center carb w/ PCV. My thoughts are that post PCV carbs probably have that hole and pre PCV carbs don't. (Carb King ?) My center carb is from a '68 PU 307 w/ manual choke, end carbs from '66 283's, one Malibu and one Impala. If yours don't have the hole maybe you could find a junk carb and swap bases. For the excess blowby problem, I cut a section of old boot sock off, rolled it into a donut, slid it over the filler tube and tucked it up tight to the cap and changed as necessary.
I was looking around with a flashlight last night and what did I see but a br*** plug on the base of the rear carb. Tonight I swapped swapped the front and rear carbs and put a 1/4 MST to 1/8 MST adapter, 1/8 MST right angle, and 1/8" MST 3/8" ****** on the new front carb. I already had a set of valve covers with 1 1/4" breather holes and ordered a PCV valve and a breather cap tonight. I'll pull the front manifold oil filler tube and cap it with an expansion plug. The PCV intake will be on the p***enger side valve cover and the PCV valve on the driver side valve cover. From everything I've read, that should work.
The Jalopy Journal
