Como said:
alright, but being a double pass wouldnt the bottom tank not have a divider? i would think the flow would come out of one pipe into the tank, then into the other pipe, no divider...
Anyways i need 3 because i'm doing WC for the noise, and theres going to be verry little airflow.
its actually closer to 2 1/2, i have to chop away quite a bit of one to make it fit...can i get away with that?
the 2-342 would be an easier way to go if you need single pass cores (provided they will fit). The dimensions on the 342 are roughly 11 1/8" x 6 1/4" x 2" (that is including the tanks).
If those won't work, you can convert the 2-302 ('77 b'ville w/ac) to dual channel, single pass by adding an outlet in the bottom tank. the top 2 will serve as inlets. The water will be split between the channels on either side of the core due to the divided top tank but the flow resistance will be about the same as a 2-342 core.
side note - I called it dual channel, single pass because that is the easiest way to describe the conversion considering the divided top tanks will split the core into 2 sides. A more accurate description would be dual-six-channel single pass. The 2-302 normally has 12 channels that water flows thru - 6 on each side. Oddly enough, the 2-199 ('77 b'ville w/o ac) has 13 channels - if you are looking at the core with the pipe fittings facing you, it has 6 channels on the left side and 7 channels on the right. Since I mentioned the 342 earlier, it has 13 channels with all the flow handled by undivided tanks on both sides.
edit: normal flow path for a dual pass core:
water enters thru either side of the divided top tanks - it then moves down one side of the core thru whatever channels are fed by the tank on the inlet side of the core - the water then moves into the bottom tank and across to the other side of the core where it moves up the channels on the other side of the core to the tank on the outlet side.
single pass - water moves into the top tank and then moves down all of the channels where it enters the bottom tank and then out of the core thru the outlet fitting.
dual pass -- water flow is in, down, across, up and out. All waterflow is thru 6 or 7 channels when moving in either side thru the core.
single pass -- water flow is in, down and out. Waterflow is thru 13 or so channels, all in the same direction.
see where the difference in resistance comes from?
that being said, if your pump has enough head & flow, the performance difference from flow rate will be overuled by raw surface area (i.e. a dual pass core with larger surface area [less flow, more surface area] will outperform a single pass core that has roughly 90-95% of the surface area of the dual pass core [more flow, less surface area].
a more useful restatement of that - a 302 will slightly outperform a 342 provided the pump will push water thru it well enough. the exact amount of head and flow rate where that no longer applies is still an open question...but I will get around to it sooner or later. Also, I am going to put the single pass vs. dual pass question to rest as I have two identical cores with different tanks on them - that test is going to be done with a regular pump as opposed to the Captain Insano pump I normally use.