EGR Valve info / help

g3chevy / Mr Pontiac wrote:Joe, I concur with your thoughts on the OEM PCV valves. They don't work well with modified engines. This is what I ended up with when I built my 400 sbc for my 87 El Camino. They are a bit pricey at $130 but are totally adjustable.

http://mewagner.com/

I hope nobody minds that I resurrect this post but I wanted to put in my 2¢.

I'd been chasing idling issues since I put in my latest engine into my Monte Carlo. At the heart is a Comp Cams 12-422-8 cam, advertised as the largest cam I could use with a stock torque converter and the largest cam I've ever run in my car. The specs state that this cam pulls 15" of vacuum @ idle; ~800 RPM and 16.5" @1100 RPM. Everything else seemed dialed in; I adjusted the jets, rods, accel. pump output, etc, of my Q-jet, ignition, etc., and, sure enough, the vacuum gauge read 15" @800 but she would still behave as though something was off.

After Mr. Pontiac made me aware of the M.E. Wagner PCV valve, I looked into it then found myself compelled to go deep into that rabbit hole. Among the wealth of info I absorbed was with bigger cams came a choice regarding what kind of PCV valve to use; a) one that's great for idle or b) one that's great for cruising. My daily driver application here in SoCal made that binary option daunting; sacrifice some drivability for good idle at stop lights and during the stops in stop-&-go traffic, not to mention vacuum for the brake boster and AC/heat (a different topic) or pleasant driving in-between stops with high idle in drive (i.e. ~900 RPM) to avoid sporadic surging with occasional near stalling that a lower idle would bring.

I bit the bullet and spent the $$$ to get one of these. I figured if it didn't work for my application, I could resell it at a loss and justify it as a learning experience. I purchased it late last May (2022) but didn't get around to installing it until last week.

For me, this is one of those "should have done this from the start" acquisitions. Installing this valve was the only thing I changed on my engine. I didn't mess with anything else other than the carb. The adjustment to the valve AND the carb took an entire morning. After the initial adjustment to the valve, I had to readjust the carb, then back to the valve, then back to the carb…

In the end, for my application, it was totally worth it. In hindsight, should've done a "here's what I did today" video.

Your mileage may vary.

No problem reviving the thread particularly with many unanswered questions concerning the whole issue of vacuum. This is why I feel one should go either 100% stock or 100% performance with these G3 models. There was an increasingly complicated balancing act by GM to meet emissions and also performance aspects. I know that GM was still tweaking EGR settings for the 76 Chevelle as late as 1981 or so in service updates.

Also as Joe and others note different states have various emissions requirements. I was surprised to learn that Texas requires statewide a stock Thermac installation on cars equipped with it. Also recently Nevada passed a law or state reg requiring city residents with cars as far back as 1967 to get an emissions test. The trend lines are all in this direction which is why I am trying to make the stock engine work as I am on the East Coast.

I will say that for these 1975 and later models it is vitally important to keep all vacuum exactly in spec. When I replaced all of the vacuum related parts some time ago the engine performance made a startling improvement. This happened even though the prior installed vacuum parts were operating, that is, not dead.

Great info Zucchi. Mine also was money well spent.

EGR's really did not work as intended (or better would be efficiently) until ECM were added to vehicles.  When the EGR is open at cruise speeds, timing needs to be advanced.  Once the ECM that controlled timing was added in 1981, the timing could be advanced by the computer when it opened the EGR, I believe it was advance around 20* - vacuum controls alone could not do that.  Some vehicles since the mid 1980's eliminated the EGR and replaced that function with how the camshaft was ground to achieve the same result - the Oldsmobile Quad 4 comes to mind along with some of the early 1990's LT and later LS engines.

I think we just need to appreciate the G3s for what they are rather than what they are not. They are for external reasons not going to compete performance wise with earlier or later performance car models (except for the Laguna which in its day was quite noted). Of course there are all kinds of improvements one can make but the Corvette was always the Chevy model that ignored everything but performance. The G3s though are nice looking cars, they have good handling and suspension, many were equipped with factory PS and PB and even A/C. They certainly are more comfortable and safer than earlier cars. Also it is not like GM made lots of great later models. The only 2 that I find remotely interesting are the Buick Grand National and the 94-96 Impala, the last great car that GM made IMO or likely will ever make.