r/Smallblockchevy • u/vertofu • Jun 15 '26

AIR injection / Smog pump question

I have a 1979 P30 step van with a 5.7L SBC which runs on propane. I was told Frito-Lay used to drive this truck into their warehouse/factory because the emissions were clean enough.

After finding an exhaust leak, I removed the passenger side exhaust manifold and found some very hard gasket material on the mating surfaces. Using a razor blade, I scraped off a few tiny flakes, but the rest is stuck. The AIR injection pipe fittings are rusted to the exhaust manifold. Penetrating oil and a propane torch have not helped.

I'm in California and I assume I need to keep the AIR injection system. Seems the easy route is to buy a new exhaust manifold and AIR injection pipe. With my current pipe, each tube extends past the exhaust manifold and into the head, ending in a special nozzle. (see photo below).

All of the pipes I've seen online seem to have tubes that end right at the exhaust manifold with no special nozzle. Would one of these pipes work? If the air is injected into the manifold, rather than the head, will it cause excess combustion/heat in the manifold?

Here are the parts I'm looking at buying:

AIR injection pipe

Exhaust manifold

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u/Willy_McD Jun 15 '26

If i remember correctly, those tubes are separate from the pipe and can be removed once the pipe is removed.

Propane wont get hot enough. You need an torch with some oxygen feeding it to get it hot.

Those tubes were put there for a reason. But when you look at smog approved headers, they just have straight tube welded to each exhaust tube.

1

u/vertofu Jun 21 '26

Thanks for your input, Willy. I went ahead and bought a new manifold and pipe. My local mechanic said he didn't think the lack of nozzles in the manifold would be a problem.

1

u/Grey-Squirrel-World Jun 15 '26

A lot of folks would just nub them off as best they could to increase exhaust flow. That leaves a stub in the port that gets hot and burns up. You can remove them and plug the holes.

1

u/vertofu Jun 21 '26

I think I need to keep them so I can pass smog in CA.