I've been readying all the posts about L31 heads, and that they have to be milled from .020 - .040 and use a special gasket to make the compression stock (9.3:1). Here's my question...Isn't the reason why we can run the higher compression in these 305 engines because we're pumping air back into the intake at high RPM's, and cooling the combustion process? And since Vortec intake manifolds have no EGR, aren't we going to detonate on pump gas? Does anyone make a Vortec EGR intake manifold for the Quadrajet engines? Thanks for your help in advance!

 

in a word...NO and not nessessairily and ....no

 

So milling the Vortec heads .030 and using a .017 head gasket will make roughly the same compression as stock, and even if I toss the EGR system (and the AIR system while I'm at it), I can get away with using 91 octane and let the computer worry about the timing?

 

maybe

 

If you want a factory-original Vortec intake with EGR, go to your nearest Chevrolet dealer, or gmpartsdirect.com and order p/n 12496820.

 

The whole thing about pinging without EGR is due to the timing advance curve that was implemented to counter the effects of EGR. In other words, before EGR, the factory timing curve was different than it was after EGR. So, if you aren't running EGR, you modify your timing curve to prevent pinging.

EGR does cool the combustion, but it does so by introducing exhaust into the air/fuel charge, not by "pumping air" into the air/fuel charge (lean mixtures typically raise combustion temps). The whole idea is that high temperature and pressure promote the formation of nitrogen oxide compounds, which are air pollutants. By lowering the temperature of combustion under certain conditions, NOx compound production is reduced.

If you need to run EGR for emissions testing reasons, the GM Vortec manifold (I believe it is actually manufactured by Edelbrock for GM) requires external plumbing of exhaust gases in order for it to function.

FWIW, GM found that the ZZ4 cam had enough overlap to contaminate the intake charge with sufficient exhaust gases that they eliminated the EGR in the later versions of their no-longer-available emissions-certified HO 350 Conversion Kit for factory carb'd engine 1982-1987 vehicles.

Oh, and pinging increases NOx production.

 

AFAIK all of the Vortec heads lack the exhaust passage to feed exhaust to the intake for EGR.... so it really doesn't matter if the intake has it or not, the heads by themselves don't support it. That's why you have to plumb it externally if your local emissions codes (visual inspection, like in California) require all physical devices to be present and operating.

The reason you need to mill those heads to use them on a 305, is because their combustion chambers are sized appropriately for the engine they were designed for.

9.3:1 isn't "high compression". That's 87 octane territory.

No you will not have to worry about detonation at that compression level, especially not if you put a halfway decent cam in it.

"Toss the EGR system" doesn't amount to much, when it isn't applicable to the parts at hand. The heads don't have the passage, so the intake doesn't either, and it therefore has no place to mount the valve; all that's left besides that, is the solenoid and 2 short pieces of vacuum line. Not much "tossing" to be done, after the other parts are swapped on.

I'd strongly recommend you check your local laws carefully and see what is required, before spending any money.

 

Well as far as local laws go, there is a quick visual inspection, and then a sniffer test. The visual inspection seems to amount to: raise the hood, glance, close the hood. On these carburated cars, the air cleaner body covers up the EGR anyway, so no one would know if it was there or not. Of course they can see the smog pump, so I guess I'd have to leave it alone. When I do this I'm going to replace the catalytic with a new high flow anyway, so don't you think I'd pass the emissions test without EGR? Vortec heads should burn much cleaner than old style heads .

 

RB, believe it or not, there is a GM Vortec manifold that has a boss on it for the EGR valve. You have to plumb it for exhaust gas.

http://www.gmgoodwrench.com/gmgoodwr...405&section=ep

Part # 12496820, about half way down the page.

 

You may be able to get by w/o EGR using Vortec heads.

 

Right.... that's why I said "by themselves", and "have to plumb externally", and all that. Lots of caveats in there.

 

Great, I'll just go for the special manifold. One last question...do the heads have to be unassembled before they're milled, or can they be milled with the valves assembled?

 

Colorado Air Care is doing more than "raise the hood, glance, close the hood", even if that's all it appears they are doing. I'd suggest treading lightly here. They start looking a lot closer when something doesn't look "factory" to them. At the very least have the valve on the manifold and all lines connected to it - whether it's actually functioning is another matter. Unlike earlier days in California, they aren't going to hook up a vacuum pump to the valve and verify it works. In fact, for my first emissions test on the Camaro here, my EGR passages were completely plugged (something I didn't know until later) and it still passed NOx (just came across that old print-out last night, as a matter of fact). If you pass the dyno sniffer, then most likely they aren't going to go any farther with regard to the EGR valve.

Yes, heads have to be disassembled when milled. Or, at the very least, disassembled after being milled.

 

I was referring to the "and it therefore has no place to mount the valve" part.

 

A couple more questions for you guys. Precision Engine will sell me a remanufactured 350 longblock with vortec heads for $816. I think I'm going to go for it. So I'm going to get the vortec intake with the egr, and at least make it look like I have a working egr. But my quadrajet is shot, and for the money ($349) it would cost to replace it, I think I'm going to get the Demon carburetor that is tuned for vortec heads (they apparently have a different fuel curve requirement) and yank the computer. Of course I've got to get a vauum advance HEI. Okay, here's my question: I want to keep a knock sensor that can retard the timing. How do I do that? And will Colorado allow an open element air filter on my carburetor? And will this stuff clear under my hood?

 

If what five7kid is saying is correct, either forget the open element, or save the original air cleaner and reinstall the original when you go in for the smog check. (I still remember the good old days in Denver, when all they did was hook up the sniffer).

One alternative: pick up a dual snorkel. That's what I added to my LG4 (along with a few other parts). The factory doesn't make them any more, so used is all that's available. IROCZDAVE has the air cleaner housing available on his website. I don't recall seeing any plastic scoops or hoses, but get in touch with iroczdave and see what he has available.

Although the dual snorkel is factory-original, I pull it and reinstall the original single snorkel before I got in for a smog check, just to be on the safe side.

There is a guy on this board that took his original LG4 plastic scoop, picked up another LG4 driver's side scoop and used those to funnel air to the dual snorkel air cleaner housing (which means you still need the ducts).

Can't help you with the knock sensor question.

Good luck.

 

The problem is that I doubt the recessed air cleaner body will fit over a Demon aftermarket carburetor. For that matter I wonder if it will fit up against the EGR valve. If the recessed housing will fit, I would much rather use it for stock look, cold days, and clearance issues.

 

There are a lot of guys on this board that are quite satisfied with their quadrajet. I don't know if I would be too quick to dump it. Can you rebuild it yourself?

 

Spend the $349 for the q-jet (assuming whatever problem you have is being caused by the carb). Cheap. Here's why:

1) Open element won't pass visual.

2) Demon won't pass visual. Most likely, won't pass sniffer, either.

3) Demon gas mileage will be worse than a properly performing CC q-jet.

4) Knock sensor only works with CC ignition.

I have yet to hear of a Vortec-headed engine legimately passing either California or Colorado inspection and testing. If you manage to do it, let us know.