I have an F100 with a 390. Recently rebuilt an Autolite 4100 4bbl carb w/ auto choke and tranny kickdown. Put on a 1" high-heat plastic spacer and the carb and hooked everything up......except the PCV hose!? Oh ya, these Ford carbs didn't have the PCV port built in, I believe there was a short factory spacer that had a port in front.

Talked to a guy at one of my parts sources and he said he doesn't run a PCV valve/line - just uses another breather cap on the rear PS valve cover PCV hole. That I can do easy enough. First question - is this really OK to do - any performance impacts? Just air quality impacts (if any meaningful numbers)? Of course I could go out and buy (already searched a salvage yard for a Ford unit - no luck) another spacer (pliovic with PCV port), but there goes another $40 that I would rather spend on other things if not necessary. Interestingly, there might be another option that I'll look for some advice here. My Ford stock iron 4bbl intake has a blocked off port that has two smaller holes in it. Based on the runners it LOOKS like (not 100% sure) one hole goes to the runners on left side and the other goes to the right side. Can anyone confirm this is true for this intake manifold? If true then I would guess I can get a fitting to work there. It comes down to the info/facts on if the engine truely runs better with/needs a manifold vacuum being applied to a PCV valve in the rear PS valve cover (of course the front DS has the vented Oil cap)?

Thanks in advance,
daggerNC

 

I, personally would run one. This helps keep moisture out of the crankcase as well as funk that can cause sludge over time.
You can use one of the rear intake runner fittings, but it may tend to foul that plug after a while from the oil vapors sucked in. The spacer like ones from tdperformance or mr.gasket, will be sucking from directly under the carb and distribute the vapors to all cylinders eliminating fouled plugs.

 

running a PCV is a must if want any decent engine life out of it. The PCV pulls moisture and acid forming particles out of the engine.

 

jimmy and gashog - thanks, that's what I needed to know. I'm going to try that port on the stock cast iron intake that looks like it feeds both runners.

 

How about a fitting in the aircleaner? I know my 289 had the plate under the carb, but I've seen lots going into the aircleaner too....

 

The fitting in the air cleaner is for the breather filter. This is the end of the PCV system - it lets in the fresh air that the PCV valve pulls on the other end. The PCV valve itself runs off manifold vacuum and a plate under the carb or on top of the oil filler cap using a vacuum hose are two very common mounting methods.

 

fmc400 - I'm a little confused by your description of the mounting methods. I can't quite figure out how a PCV system could work if the other end (vacuum source) is the "top of the oil filler cap" option?

 

The oil filler cap has a hole in it. The PCV valve mounts in that hole. Then, a vacuum hose runs from a fitting in the intake manifold to the PCV valve. Or, there is a grommet in the valve cover, and the PCV valve sits in the grommet. The same hose runs to the valve.

However it is done, you have a vacuum source at one valve cover, and a breather filter at the other valve cover. What you're going for is circulation. The PCV valve is at one point in the system to restrict flow at low vacuum. I have seen both ways in factory setups. Hope that helps; I'll try to scrounge up some pictures later if you'd like.