Ratling PCV update

[Wayne Kever]

Finally got to measure the vacuum on the L79 with the rattling PCV valve today. Had only a little time, and the line to the vacuum advance fit the gauge, so that's where it got measured. This is probably "ported vacuum," so not the best place. Anyway, here are the results: At idle, 8-9 inches. At ~1500RPM, 14 inches. This seems like it should be adequate to pull the valve.

I have a new theory. Something is wrong with the breather mechanism that connects into the air cleaner. There is a canister in the lifter valley that I believe is connected to the breather (didn't assemble myself, but saw the stuff apart). Anyway, have any of you seen the breather assembly put together wrong before in a way that leads to pulsating pressure on the crankcase side of the PCV?

- Wayne

[Iron Duke NCRS #22045]

Re: Ratling PCV update

Something doesn't sound right. You should pull more idle vacuum than that. What was the actual idle speed at which you measured the vacuum? I've never checked a L-79, but with a 114 degree lobe center it should be at least 12 inches at 800 to 900 RPM. My Duntov (110 deg. LC) was about 12 inches at 900 to 1000. Is the cam installed on center? BTW, it should not be a ported vacuum advance on that year ('67, right?). The "breather" you refer to in the lifter valley is a liquid vapor separator. If it's not there you might get some oil pulled into the intake, but I think you need to check your cam to see if it's installed properly. Maybe someone else on the board can give us a vacuum reading at idle speed, and please specify the idle speed.

Duke

[Wayne Kever]

Re: Ratling PCV update

Idle speed about 900RPM. Cam is not L79, it is an Isky 270int/280exh advertised, 221int/232exh @0.050, 108 lobe centerline angle.

- Wayne

[Iron Duke NCRS #22045]

No wonder the valve rattles!

I don't know who talked you into running a 108 degree LC cam on the street, but all your problems will be solved if you install the production L-79 cam, or if you want to be a little more radical go with the L-46/L-82 cam.

Duke