My 172mm fan is RATED for 139CFM I think. I have a Chevette heatercore + shroud. I also need to remount my CPU block, didn't do that great of a job on my last mount.
My heatercore hasn't cooled my water close to room temp since I added my GPU block. W/ my cpu only running at 2140 (1.75vcore) and my 9800 Pro @ 441mhz. Air coming into the heatercore is 20.6C, air coming out is 26C, water temp from my t-line (which is between heatercore --> CPU) is 24.1. Socket reader gives CPU temp 32.5 100% folding. GPU is not under any load.
Another day when I had my system at it's usual 2392mhz (1.8vcore), ambient was 23F, air leaving heatercore was 27C, water temp was read at 33C? This was during prime95 torture test w/ a CPU socket temp of 48C, which I'm really not use to. But I think I was running 3dmark before the reading.
Here's a very old pic of my heatercore.
Shroud is a piece of sheetmetal bent and JBwelded at the corners, then JB welded to the back (front of case side) of the heatercore at it's corners. I have a 1.25" space between heatercore and fan. I painted the shroud after masking off the finned area of the heatercore. When JB welding the 5/8" barbs on I know some JB weld dripped down onto the back side of the core which MAY be blocking some of the avanues to the "fins." But I think most of it is just stuck to the back of the tanks, above the "avanues." Fan is, of course, pulling and I have a piece of neoprene sealing the space between hc/fan.