[PMDRACER]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> All sounds good to me. By the way, PMDRACER where are you? You started all this and you just sit back and let us go at it while you chuckle? <HR></BLOCKQUOTE>

I'm right here soaking up the info. Unlike some people in this world (no implications to anyone here!!! Speaking of my boss.) I know when to shut my trap and listen.
Anyway, I've been doing some trial and error myself. After changing over to the cast impeller, the water temps dropped considerably on the freeway. It used to run at 200-210 all the time, even on really cold nights. (BTW - new 4 core radiator, new HD fan clutch, 160 degree t-stat, etc.) Well, a couple of nights ago the temps dropped to 50 degrees outside, and while doing 80MPH my temp sat at 160 degrees. But when I got off the freeway and drove on the street that same night, I was back to 200 degrees. What I did next was reconnect the vacuum advance. I had been running without it because of serious pinging at 200 degrees. Now I run about 180 on the street, and 160 on the freeway.
I have taken my old stamped impeller water pump and bolted a gasket and new plate to it. The gaps were all less than 1/8th inch.
When time permits, Jack Blum and I are thinking of making a flow bench of sorts and testing cast vs stamped, differences in gaps between the vanes and plates, etc.

Oh, and 4 things to add to the list.
1. No matter if you are running a flex fan or the stock solid fan with a solid spacer or clutch, the blades of the fan must stick out of the fan shroud at least 1/3. This gives the fan/shroud combo a direct in and out path, creating a moving column of air to follow.
2. Seal the shroud and the radiator together. Any gaps open between the shroud and radiator will allow air in through there, instead of pulling through the radiator. Use rubber sheet material to seal the gaps, or trunk weatherstrip glued to the inside of the shroud.
3. Same goes for the radiator to the core support. All that air being shoved through the grilles is free cooling. Make it all go through the radiator, not around it.
4. The small air dam bolted to the core support underneath the car will create a vacuum behind it, drawing more air through the radiator. The air dam for the '70 A-body the PY sells may not be correct for a '71-'72, but it fits perfectly.