A
Anonymous
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I just finished my 1979 Fairmont head rework and it worked out well!
Here's some things I saw in this 1978 casting (3.3L engine) that might be in yours, too:
1. There is a stiff, almost sharp ridge that leads up to the sparkplug boss in the chamber. This ridge directly divides the squench-induced flow during compression, which can delay fuel ignition in an erratic fashion. When you have you head open, grind this ridge down, rounding it evenly in all 6 head chambers. Don't remove it wholesale, because the compression will drop too far.
2. The intakes valves in these later castings are very shrouded. Open the chamber along the wall about .030" if you are going to mill the head .010" and open it .060" or more if you're going to mill .020". I don't think I would mill more than the depth of the squench deck, in any case, because the head does not have enough wedge angle to control knock if you go too small on the chamber volume.
3. The chamber volumes varied by .75cc in my head. It's easy to see where the castings varied: I matched them all "by eye" before milling and they came out to less than .25cc difference afterward. This is worth the effort.
4. The intake port shape on this head was good, but the transition across the valve seats was varied from one chamber to the next, all poor. I removed as much as .100" of material to smooth out this transition into the head.
5. The exhausts were surprisingly even and equal. If I were going for a (non-catalytic) high-breathing exhaust, I'd open the tops of the exhaust ports into a "D" shape to improve the flow exit. The exhaust manifold may have to be slightly reshaped to accomodate this, but on my catalytic-equipped Fairmont, this is a waste of effort.
6. The edges of the chamber are almost all within the combustion area, so round off the edges of the chamber to improve flow-over during compression and reduce the hotspots that those edges will become at higher RPM.
7. The squench area of these heads is a surprising 28% of total area! This is a lot, so it will have a considerable effect on the efficiency of this engine. Keep this squench height low, .040" to .020", by either decking the block or by using the steel head gaskets or the "C" series FoMoCo composite types.
8. If you have the $$, get your intake valves back-cut to 30 degrees. Leave the exhaust valves alone unless you are going to use headers: then you'll want to reshape the exhaust ports, too.
...just the rantings of an ex-racer that's now putting to & from the grocery store....
Here's some things I saw in this 1978 casting (3.3L engine) that might be in yours, too:
1. There is a stiff, almost sharp ridge that leads up to the sparkplug boss in the chamber. This ridge directly divides the squench-induced flow during compression, which can delay fuel ignition in an erratic fashion. When you have you head open, grind this ridge down, rounding it evenly in all 6 head chambers. Don't remove it wholesale, because the compression will drop too far.
2. The intakes valves in these later castings are very shrouded. Open the chamber along the wall about .030" if you are going to mill the head .010" and open it .060" or more if you're going to mill .020". I don't think I would mill more than the depth of the squench deck, in any case, because the head does not have enough wedge angle to control knock if you go too small on the chamber volume.
3. The chamber volumes varied by .75cc in my head. It's easy to see where the castings varied: I matched them all "by eye" before milling and they came out to less than .25cc difference afterward. This is worth the effort.
4. The intake port shape on this head was good, but the transition across the valve seats was varied from one chamber to the next, all poor. I removed as much as .100" of material to smooth out this transition into the head.
5. The exhausts were surprisingly even and equal. If I were going for a (non-catalytic) high-breathing exhaust, I'd open the tops of the exhaust ports into a "D" shape to improve the flow exit. The exhaust manifold may have to be slightly reshaped to accomodate this, but on my catalytic-equipped Fairmont, this is a waste of effort.
6. The edges of the chamber are almost all within the combustion area, so round off the edges of the chamber to improve flow-over during compression and reduce the hotspots that those edges will become at higher RPM.
7. The squench area of these heads is a surprising 28% of total area! This is a lot, so it will have a considerable effect on the efficiency of this engine. Keep this squench height low, .040" to .020", by either decking the block or by using the steel head gaskets or the "C" series FoMoCo composite types.
8. If you have the $$, get your intake valves back-cut to 30 degrees. Leave the exhaust valves alone unless you are going to use headers: then you'll want to reshape the exhaust ports, too.
...just the rantings of an ex-racer that's now putting to & from the grocery store....
