Okie, nobody makes headers for our cars, so I was wondering if it would be worthwhile to port + polish the stock manifolds. I've read that in some cases it can be as good as headers, what do u guys think?

 

I am hoping to start making these things soon. But to answer your question no it would not be the same.

 

I found what seemed like (and turned out to be) a restriction in my manifolds. We have a gasket-less ("Ball") flange for our manifolds. That means there's no gasket between the exhaust manifold and y-pipe. There's a chunk of iron that's curved on one end (to fit into the y-pipe), and flat on the other (to fit flush against the exhaust manifold's output).

Since the piece goes from curved to flat, it narrows on the inside. GM didn't make this "wide to thin" transition smoothly. They basically drilled two holes- one wide, and one thinner. The holes "clash" together at one point. I used a metal rat's tail file (for the bulk of the work) and a die grinder (smoothing/polishing work) to turn that "step" into a "slight ramp".

When I put the pieces in, the car seemed to rev easier, and it seemed to have more power over the whole tach. Not too bad an improvement for a few hours of work!

There's not much to be removed inside the stock manifolds. The walls are pretty thin in some places, so don't expect to hog the manifold out to give you header-sized primaries. But, there are a few places where there's sharp corners, and a few places where casting flash sticks out. Overall, by looking at the manfolds, it's a bit of a disappointment. I never got to port my manifolds (I got a spare set from a junkyard to play with), so I'm not sure of the gains. But working on those little donuts gave a SOTP improvement on my car.

They're not much work to remove, either. Er, well, maybe they are- you need to loosen the y-pipe-to-manifold nuts. Once you loosen the nuts enough, the donuts pretty much fall out on your head. Be careful tho! I snapped one of the studs while I was loosening a nut; I had to put my junkyard manifold on. Soak those things with tons of Liquid Wrench (when the exhaust is cold!!! The stuff's flammable!) every day for a week or so before you start work on it.


------------------
-Tom P (Hot rodded 1986 Firebird 2.8l)