Jim - I did a poor job of explaining my thinking. What I meant to say is that RTV would be safe as even if it did come loose I doubt it would cause a problem. First, as you point out, it is relatively light in comparison to size and would probably go on out the port. Second, even if it did go into the cylinder it would just get chewed up and then go out the port.

On the other hand, my fear of anything more substantial is the probability of it coming loose due to expansion and contraction, and it might well be dense enough to fall down, depending on when in the cycle it come out, and go into a cylinder. That could be catastrophic.

Anyway, I'm agreeing with you but just did a poor job of explaining it.

Those with EFI engines ought to consider if it is safe for their O2 sensors.
I know that there are "sensor safe" formulations as well...

The AIR bump should go, as you did. The short side radius should not get that much cut, at least at the red line. Cut back to there it creates a sharp turn at the valve seat area reducing flow. Instead, the short side radius should be smoothed and made an even curve from the runner to the vavle seat area.

I hope you don't mind I edited your pic...

http://i414.photobucket.com/albums/p...s/Untitled.jpg
Dang Paint made it bigger. Anyway, airflow around the valve seat at low lift is most important for overall performance. As such, the bump around the port just below the valve seat should be smoothed and the short side radius as above. Swirl polishing the backside of the valves helps here too. The rest of the porting helps more in the midrange/top end.

Stang - I appreciate you editing the pic. I probably didn't cut the short-side nearly as much as my line suggested, more like your line I'm sure. I just couldn't get a line where I wanted it on the picture, so thanks for doing that.

I'll probably re-draw mine for the final documentation to make a smoother line on the roof, move the floor line to yours, and add your arrows pointing to the bumps around the seats - which I did try to do but didn't do a very good job on. May go back there today due to your suggestion - thanks.

I do have a lathe and have considered back-cutting the valves - what are your thoughts there? And, how do I swirl-polish the back of the valves?

Edited another of your pics.

http://i414.photobucket.com/albums/p.../Untitled2.png

Leave an even space on each side of the seat. More important on exhaust valves for the heat dissipation.

The swirl is usually put on before the seat area is cut on the valve. I have done it with 3M Roloc discs and a drill with the valve chucked up in a lathe, but not very safe nor reliable(even). That is where the special attachment comes in that holds the abrasive disc at the correct angle against the backside of the valve. The whole idea really is to remove the roughness on the backside of the valve head as shown in the above pic. Smoother is better here.

Did you do anything about unshrouding the valves in the chamber?

Here is a swirl polished valve:
http://www.n56ml.com/corvair/phoenix/070223043.jpg

Ok, I'll take the sharp edge off of the valve in the lathe.

As for swirling, I'm not sure I want to attempt it free-hand. If I had a toolpost grinder then maybe. But, I have spare valves so will try something.

Didn't do anything about unshrouding the valves. Don't really know what to do there. Suggestions awa importance?

Forgot to say I'll cut the head the way you suggested and post pics.

I hope this isn't a stupid question, but here goes:

How does this affect engines that have/need to have their emissions systems intact? What I mean is, will grinding away the Thermactor hump render the system ineffective in any way? Or is this assuming that the emissions have been, or must be removed?

See what I'm getting at?

I fully see what you are getting at. And, the answer is "I don't know". Maybe some out there do, and I hope they'll chime in. Stang?

Having said that, I have read that the bump was to provide a flat spot that was at right angles to the exhaust valve so it could be drilled at the factory w/o the bit walking off. And, while I understand that having a surface perpendicular to the machine would make it easier, it can be done other wise. Further, there was obviously no need to have that big of a bump in order to have done that. In fact, some of the later heads had a smaller bump.

One thought I had was a venturi effect where the forward lip of the bump caused a partial vacuum at the hole so air was actually pulled in. Yes, the air was under a bit of pressure from the pump, but I think that pump was a volume and not pressure pump. IOW, it wouldn't provide much pressure to overcome the exhaust system pressure. However, this is just speculation on my part.

So, if it was just to provide a flat surface to drill then grinding the bump off would not cause a problem. But, if the height of the bump has meaning, as I'm sure it did, then grinding it off must cause a difference. What that diff might be I do not know.

Anyone?

Dunno, But I like the machinist idea about the drill bit not walking. But it could have been lower in the port and had the same effect for not walking. Having the hump taller would introduce the AIR into the port more in the center, close to the valve stem versus at the edge/side of the port. Could make a difference in mixing the air in....

I don't think it will make a difference in emissions after the fact. If the emissions was working to start with, this will have little to no effect. Especially since only 3 of the 4 were drilled to start with.......

Oddly enough, these two heads are drilled on all 4 cylinders. They are D8OE AB's like all the others I've seen. Can't see any difference in them other than that hole being drilled. Go figure. Just when I thought I was figuring Ford out.....

Well, I got all of the porting I think I'm going to do done today. Thanks, Stang, for pointing out the need to blend the bowl at the point where the factory's cut ends. Got that done on both intake awa exhaust and touched up some other areas and then ran a tap through all the threaded openings. Then I rinsed the heads in the parts washer and dried them, so they are ready to have the valves put back in.

Given this is my thread, I'll deviate from the subject just a bit: I've been thinking about exhaust systems. More specifically, whether or not to go with headers. Given my twofold objective, to increase both fuel mileage as well as resale value, should I go with headers instead of the exhaust manifolds?

As a reminder, I have the Comp Cams torque cam, Edelbrock Performer intake awa 600 CFM carb, home-ported heads, and true duals w/no cat.

Performance = Headers, YES.

While I'm not averse to performance, that's not really one of my stated objectives - especially since it is hard to sell performance to the wife. But, I can sell gas mileage, as I did with the Fuel Miser torque converter - which I forgot to mention in the list of mod's, btw. And, I can also sell resale value to her.

So, Jim, if you are still suggesting headers, which ones? I've been reading everything posted regarding them and there's a lot of conflicting "information". Which ones truly fit, which ones last, which ....???

Gary,
I really haven't done any research on Windsor headers.
Thick flanges and ceramic coating are the way to go IMO.

Some people think there's too much noise compared to cast manifolds. And it's true, they are louder.
But it seems to me porting and stock "logs" just don't go together.