Hey all,

So, I'm getting closer to pulling my 305 out of my car, and planning to drop in an L31 350 w/some bolt-ons (slowly, but surely, it's getting there!)

I just had a few questions regarding exhaust/emissions components with my swap. There is no way I'm gonna choke up an L31 w/the factory L03 exhaust system, so that's all being upgraded too. But I'm left wondering about the EGR/AIR components...

It's my understanding that all the AIR system really does is force additional air into the exhaust system on cold starts, in order to heat up the cat faster. If I'm planning to go w/a high flow cat, is it even going to have provisions for the AIR stuff? I'm told most modern cats don't need it.

And I'm also told that the EGR valve has to be plumbed to one of the exhaust manifolds in order to be used w/vortec heads. Is this how trucks w/L31s came equipped from the factory? And is it easy to do? I'd like to keep EGR if it isn't too tricky.

FWIW, the car becomes old enough to be smog testing exempt where I live in 2016, and the laws have actually become more lax ('09 and newer cars don't even have to be tested now). Even if I have to do one more test when I do get it back on the road, theres no visual inspection, just a tailpipe sniffer/dyno test. That aside, I'd still prefer to keep it burning as clean as I can w/the mods I want to do.

 

You need the AIR connction to the cat, if your emissions inspection is relatively strict.

THIMK... use your kidneys.... the job of the cat is to convert carbon MONoxide (and various other things, but that one component should get the point across...) to carbon DIoxide. IOW, it adds one oxygen atom to each CO molecule.

It can't just miracle up oxygen out of thin air. (har har har) It's got to get it from SOMEWHERE, modern or not. Where do you suppose that is? hmmmmm.....

Newer cars, with more sophisticated control systems than the Stone Age stuff our cars have, accomplish this by deliberately running the motor too lean for a certain fraction of the time, thereby passing enough oxygen through the engine naturally to provide what the cat needs. That's why they can get their job done WITHOUT AIR. Our cars' computers aren't able to do that.

The reason newer cars don't have to be tested, is that their onboard diagnostics are adequate evidence of legality. The computers in new cars have enough bandwidth to be trusted with things like that. Ours, ... ,, .... not so much. Consider what you were surfing the web with in 1994, and think what would happen if you tried that today.

The AIR system directs the pump's output into the manifolds during warm-up to help heat the cat up faster (flames in the exhaust), then switches to pumping into the cat once warmed up.

Vortec heads don't have the "crossover" exhaust port to the intake manifold, so yes, to retain that system, it has to be externally plumbed to the exhaust. Frankly I doubt a TBI system would miss that, since AFAIK it doesn't have the temp sensor that some systems use to detect the presence of exhaust gas flow when commanded.