I have a set of C7AE-A heads that I am going to use on the 390ci FE that I am building. They have as-cast combustion chambers. My questions are, is it possible for me to polish them myself, along with the intake and exhaust ports, or would the machine shop have to do it? If I can, how difficult is it, and how much of an advantage is it? Or am I just wasting my time?

 

Polishing your combustion chambers can be done yourself easily. This will reduce detonation. You better get your ducks in a row before you start on the port and bowl work.

 

When you polish the Combustion Chambers don't try o get them perfect. The main thing is to knock down all the tall stuff and smooth everything. Don't try to open up the chamber by making it wider or deeper. The polishing alone will open it up.

The way I would start is get a set of sand paper wheels invarious grits. about three different grit shold work well. Use the most course grit to simply get the really big stuff, you may not use this one at all. Then step down to the medium grit, probably a little more than the course but still not much. The on to the fine, you could acctually do almost all of the work with this one sanding drum. After you have them all smoothed out then you need to make them as near the same size (CC) as you can get them.

This may require some real patience. I have heard of using a large siringe, a 100 cc siringe would work great. If you go over 100 cc's you wnet way to far. Fill the chamber with water, oil, tranny fluid, etc. Then use the siringe to suck it all out. Measuring how much you remove from each. There will always be some that you can't get out. Right down the volume of each cylinder, preferably one the head so you know for sure. Start on the smallest one and go up. Try to make them all the same CC as the largest one. Leaving the largest one alone.

Something else that may be of help, look at the largest chamber and see if you can tell what makes it bigger. Try to duplicate that in the smaller chambers. Also CCing chambers before hand may not be a bad Idea. Give you an Idea of how much you have taken out (or in this case volume you added).


This is a bunch of info I know. It really isn't that hard to do. Keep us informed of your progress and let us know how they come out. By the way what heads are using??
Good luck

Scotty

 

Thanks for all the info. I am using standard 390 heads, casting number C7AE-A. They were installed on a 1967 390, have 71.2-74.2 cc combustion chambers, and do not have AIR injection. I haven't measured the chamber volume yet, but am hoping to get to around 76 cc's on the combustion chambers, giving me around a 10 to 1 compression ratio. I will keep you informed!