PCV Valve

[Don C.]

Re: PCV Valve

Joe

I've completed the rocker ratio research and am now set-up with 1.5 GM rockers on the exhaust. The actual measured ratio at POML for the selected 8 rockers is 1.49-1.51. I've installed 1.6 rockers on the intake (actual measured ratio 1.57-1.58). I set each valve with a slightly different lifter setting to achieve what I determined to be an optimum rocker geometry. With my set-up that worked out to 1 1/2 to 1 3/4 turns from zero lash or somewhat further down than the midpoint in the lifter bore. Just did one test run to 6300RPM and engine showed no sign of valve float, and SOTP indicated no rolloff in power at that point.

Wow,195CC on the intake ports! The work I did on mine -also non X 461's - where I raised the roof and opened the pushrod area a bit, increased the ports from 159-163 up to 162-165. I suspect my 1.94's vs your 2.02's is also a factor.

I have less concern about crankcase scavaging during low vacuum conditions (read high power short burst in my case) than I do about the instantaneaous mixture leaning created by the PCV valve under those conditions, so I opted for the fixed orifice, I have no emperical reasearch data to back-up that concern, and I suppose the carb accelerator system can compensate for that condition. I just don't like the idea. But that's just me.

All the best with your work.
The work you are doing is very similar to what I have done. Let's compare quarter mile stats when your done.

[Joe L.]

Re: PCV Valve

Yes, it is. It is a replacement for 3972110 and 3972116, Z28/LT1.
These originals are getting VERY expensive. I found a real nice manifold last year after quite a bit of looking, at a very good price. The boss for the front oil fill tube exists, but must be bored to accept tube. There are other service replacement numbers which were made with the front hole bored and fitted with a Dorman plug.

Other casting numbers:

3917610...........67-68 Z28
3932472...........69 Z28
3972110...........70 Z28/LT1
3972116...........replacement for 3972110
14044836.........replacement for 3972116

They are listed in descending order of going price.
There are differences among them as to the config of the oil fill tube bore, or boss, t-stat housing location, temp sensor and heater hose taps.

Joe

Joe-----


Actually, if one is not concerned about "numbers", "dates", and exact elements of configuration (which none of the above-referenced manifolds would meet for a C2 Corvette anyway), then, performance-wise, I think one could do just as well with an Edelbrock Performer RPM manifold. Also, the Performer RPM has a machinable surface for the oil fill tube so even that requirement can be met, if necessary. WAY, WAY cheaper than finding an original GM manifold.

[Joe C.]

Re: PCV Valve

Joe

I've completed the rocker ratio research and am now set-up with 1.5 GM rockers on the exhaust. The actual measured ratio at POML for the selected 8 rockers is 1.49-1.51. I've installed 1.6 rockers on the intake (actual measured ratio 1.57-1.58). I set each valve with a slightly different lifter setting to achieve what I determined to be an optimum rocker geometry. With my set-up that worked out to 1 1/2 to 1 3/4 turns from zero lash or somewhat further down than the midpoint in the lifter bore. Just did one test run to 6300RPM and engine showed no sign of valve float, and SOTP indicated no rolloff in power at that point.

Wow,195CC on the intake ports! The work I did on mine -also non X 461's - where I raised the roof and opened the pushrod area a bit, increased the ports from 159-163 up to 162-165. I suspect my 1.94's vs your 2.02's is also a factor.

I have less concern about crankcase scavaging during low vacuum conditions (read high power short burst in my case) than I do about the instantaneaous mixture leaning created by the PCV valve under those conditions, so I opted for the fixed orifice, I have no emperical reasearch data to back-up that concern, and I suppose the carb accelerator system can compensate for that condition. I just don't like the idea. But that's just me.

All the best with your work.
The work you are doing is very similar to what I have done. Let's compare quarter mile stats when your done.

Don,

I figure I'll tweak the WOT A/F ratio by secondary main jets and/or secondary float level, so I'll compensate for PCV flow. My carb has mechanical secondaries, so I'll also install a vacuum gauge next to the tach, and learn how to drive the damn thing so as to keep the vacuum "on the bubble" by keeping any transient dips to a minimum.

My Zeitronix meter works great, as I'd been fooling with it before I tore the engine down. Only requires plugin to an onboard laptop.

Hopefully will have some results by end July.

Joe

[Joe C.]

Re: PCV Valve

Joe-----


Actually, if one is not concerned about "numbers", "dates", and exact elements of configuration (which none of the above-referenced manifolds would meet for a C2 Corvette anyway), then, performance-wise, I think one could do just as well with an Edelbrock Performer RPM manifold. Also, the Performer RPM has a machinable surface for the oil fill tube so even that requirement can be met, if necessary. WAY, WAY cheaper than finding an original GM manifold.

Joe,

I wanted the look of a GM intake, so that any "unwashed" car crazies would not know that its not the "correct" intake. It has the Winters snowflake, the GM casting number, and even a very pretty bowtie logo.

As far as the Edelbrock is concerned, yes, you are correct about the Performer RPM. I was willing to give up the all-GM "look" ONLY if I could use an RPM Air Gap intake. The RPM Air Gap is very slightly taller still, than the Performer, but even more important, it has no boss up front for the oil fill tube. It would also have forced me to use a BBC hood, which I am not willing to do. If the hood was not an issue, I'd have immediately settled on a Victor Junior.

Besides, my intake is not "numbers' matching" for ANY production Chebby. It is a service replacement, and although more expensive than the Performer, still auctions for about 1/2 the price of a 3917610, 3932472 or 3972110. I bought this manifold for a very, very good price. Only slightly more than the price of the Performer

Joe

[Joe C.]

Re: PCV Valve

Whooops......hit the "unsubscribe" link by mistake.
Am I "resubscribed" now? Yup.

[Joe C.]

Re: PCV Valve

Hi Don,

How are you progressing on your rocker arm ratio research?

I have ported my (non - "X") 461 heads and have gotten all intake ports safely, to 195cc!!!!

I want to eliminate the fixed orifice, so as to have better scavenging at lower manifold vacuums. At very low manifold vacuum, the .090 orifice limits ventilation of the crankcase.

Joe

I am happy to make a correction:

Make that 175cc, not 195cc.
Thank God!