[Gooserider]

Gooserider, is you air intake right next to your hot air outlet? I didn't quite understand that part.

Sort of... The radiator is mounted in the lower left front face of the case (An AMS CK1100B server cube). The rest of the case will be sealed so that the rad is the only significant air intake.

The rad face is approx 9.5"H x 6"W, and I have made a duct with two chambers that mounts inside the case and seals around the inside face of the rad. The two chambers are created by a partition that almost touches the face of the rad and divides it into an upper and lower section.

The upper section holds a 120mm x 38mm fan mounted parallel to the rad face, about 1.5" away from it. This fan sucks air through the rad, and blows it into the rest of the case.

The lower chamber makes a 90* turn down to the floor of the case where I have a second 120mm x 38mm fan mounted on the bottom of the case going out a blowhole. The case is on casters that hold it about 1.5" off the floor. Thus air gets sucked in through the rad, turned 90* and blown right back out the case. The inlet and outlet are close to each other but on different surfaces. If I find that I have problems with either air recirculation or exhaust noise, it should be no problem to add a 'mudflap' to the bottom front edge of the case to force the airflow and noise to go the other way.

Anyway, I was wondering why more car manufacturers don't use SP heater cores.

Well they are doing a different application, with much higher dT's, less concern about flow restrictions, and more of an issue with ease of hookup. It is far easier to hook up the core if the I/O's are next to each other, and only having to reach one end of the core makes designing the heater box easier. (Indeed if you look at the 2-342 that I'm using you will see that it has some really funky extra pipes to put the I/O's next to each other - the first mod needed for the core is to shorten them. IOW, they don't gain anything useful from using an SP core as opposed to a DP core.

I'm thinking about getting two 9.5"x6"x2" heater cores and constructing a 9.5"x6"x4" single pass radiator. Two 120mm fans will pull the cold air through it into the case (26" Dragon).

IMNSHO this is a *BAD* idea! This is the same size as the core that I'm using, and is a bigger core than the vast majority of WC systems use. I chose it because I'm building a dual processor rig, with a bunch of hot SCSI drives. The 2-342 has far greater heat dissipation ability than any reasonable load you are likely to get in a single case machine from a waterflow standpoint.

If you read the articles on applied WC thermodynamics, particularly BillA's work, both here and on OverClockers, you will note that radiator design is a compromise. The better you get with waterflow, the worse you get with airflow.

Your heat dissipation is limited to the capacity of the most limited flow - infinite water flow won't cool anything unless there is air flow to cool the water, and infinite airflow won't cool unless there is enough water flow to carry the heat to it. In almost all cases, the 'bottle neck' parameter is airflow, especially if one wants to keep the amount of fan noise down. (The reason I'm using 38mm thick fans in suction mode, they have the lowest volume losses going through the rad...) This is because air has much lower heat capacity than water does. At the same time, you will loose about 50% of the fans rated free air volume due to the restriction of a 2" thick rad core (i.e. an 80CFM fan will only actually move 40CFM through the rad).

Doubling the core thickness will reduce your airflow by half (or worse)! I would expect your temps to go up considerably if you do this. Your water flow is already fine with a single core, do more work on increasing your airflow.

I know it's not a good idea to increase case temperatures, but I'd rather have my water cold the my case cool.

I agree. However the heat budget for my system called for 80CFM worth of airflow through the rad, and I realized that there wasn't much advantage to blowing that much air through the rest of the case. By splitting the airflows I'm dumping the hottest air outside the case so I get the best of both worlds.

Gooserider