Flaking cast iron?

[SeaSlugs]

This is a header off a 1978 chevette - what looks like a layer of crud flaking off is actually metalic and magnetic and very hard to scrape. It reveals grey cast iron underneath. I cant say ive ever seen cast iron flake off. Did someone get this header ridiculously hot? Bad casting? Some other explanation? Is it OK to use?

[Mitch]

It's from rusting so if it is solid just go ahead and use it. If you want to get fancy bead it in the cabinet and paint it up. Don't forget it is still a chevette

[SeaSlugs]

yea i plan to blast it - couldnt tell if it was ages of baked on oil leaks and road dirt or what was going on. Ive never seen cast iron peel like this. Seems solid but after blasting will tell. Its going on my 1980 that had that weird PAIR system so there were four 1/2" pipe ports on each exhaust manifold tube that the exhaust pulses were supposed to operate some sort of bellows that introduced air (oxygen) to the exhaust stream to make the catalytic converter work its best. Theres no more converter, egr, or PAIR system now so looks really goofy with plugged off ports.

[Tom Wesenberg]

Does PAIR stand for "pulse air"?
I never cared for the pollution systems used on 70's and early 80's cars, but I do recall that exhaust system that sucked in air when the exhaust valve closed.
The pulse of fresh air was supposed to help burn any raw fuel going out. Fuel injection sure was a vast improvement.

[SeaSlugs]

Does PAIR stand for "pulse air"?
I never cared for the pollution systems used on 70's and early 80's cars, but I do recall that exhaust system that sucked in air when the exhaust valve closed.
The pulse of fresh air was supposed to help burn any raw fuel going out. Fuel injection sure was a vast improvement.

you got it - square canister a bit bigger than a coffee mug with 4 lines from each exhaust port going to it and a big hard tube from under the air cleaner. such a vacuum lined mess that gets in the way of everything. shaved at least 5 lbs of brackets and crap off the car. the 82 year had a half bastard computer controlled system that was awful then 83 or 84 they went with a kinda smart one that changed the A/F ratio by monitoring the exhaust via O2 sensor. 81 and down basic holley carb.

[Mitch]

1982 Chevrolet Chevette L4-98 1.6L

Vehicle » Powertrain Management » Emission Control Systems » Pulsair Valve » Description and Operation

• Description and Operation

Fig. 75a Pulse Air Injection Reactor System. (typical)

This system uses exhaust pressure pulsations to draw fresh air into the exhaust manifold, through a series of pipes and check valves.

Engine operation causes positive and negative pressure pulsations in the exhaust flow which depend on exhaust valve position--is seated or not.

• If pressure is positive, the disc is forced to the closed position--allowing no air flow into the exhaust system.
• If pressure is negative, the disc will open allowing fresh air flow into the exhaust system.
• Due to inertia--at high engine rpm--the disc cannot respond to pressure pulsations and air flow into the exhaust system ceases.
• Throttle closure--during deceleration--momentarily causes air fuel mixtures too

[MikeK]

The flaking areas were subject to near red heat. The normal orange/red surface rust is hydrated iron(III) oxides in varying forms as nH2O- iron(III) oxide-hydroxide (FeO-(OH), Fe-(OH)3. It is porous and atmospheric free oxygen (O2) readily passes through it. At elevated temperatures the hydroxyls are dissociated and free oxygen penetrating the surface reacts to form a combination of three products: Iron(II) oxide (FeO), anhydrous iron(III) oxide (Fe2O3), and iron(II,III) oxide (Fe3O4, also known as magnetite). This is the same as the grayish "mill scale" seen on hot rolled structural steel.

This is generally not problem for a cast iron exhaust manifold unless you're planning to enter the engine in a beauty contest. Repeated excursions to that temperature will, however, promulgate dimensional distortions if the casting is not well supported. Such is the case with the well-known Model A rear exhaust port sag, with occasional high temperature excursions caused by improper mixture and timing.

You may want to check the timing advance mechanism on that '78 chevette. Likely running somewhat retarded.

[SeaSlugs]

Engine and car have started returning to the earth on the 78. Theres no weight hanging from this besides a basic 3ft exhaust pipe thats supported on the other end by a 4 bolt flange. yea my guess someone didnt have the carb set right. My 80's manifold looks to be normal rusty and runs beautifully. I think the model A has more pep sadly.