Mixing liquid cooling tube diameters

Howdy all. I am in the final stages of putting together a liquid cooling system for my new DIY rig. I am very impressed with the Thermaltake BigWater 745 and all of the reviews I have read say it is a very good system. However, I would like to get a full-card GPU+RAM cooler, and Thermaltake does not make one. From what I have read, Koolance's VID-NV2-L06 is the best video card cooler, so I'd like to get that.

The only problem is, the Koolance block uses 1/4"ID tubing, and the BigWater uses 3/8"ID tubing. I can pick up some cheap 1/4"-to-3/8" Line Reducers and convert at the card, but I don't know what effect that will have on the BigWater's efficiency.

From what I have read, one of the radiators in the BigWater kit only has a 1/4" core, so maybe dropping to 1/4" at the card wont be such a big deal. Does anyone have any advice or wisdom?

This should help some on the info needed.

Wikipedia Choked Flow

This why most people try to run all one size tubing through out their systems.

MassRaptor

That cooler is definitely not the best video card cooler. Get a Stasis Thermal or Danger Den full cover waterblock. Far superior. Also don't get the big water. While that newer big water is an OK system, get an Lang D5 (A.k.a. MCP650) or a Lang DDC (a.k.a. MCP350), an Apogee waterblock, and a Black Ice Single or Double radiator. Connect all of that with some 1/2" ID Masterklear (from mcmaster.com) or Clearflex 60 (or even cheap vinyl tubing) and fill it with Distilled water mixed with 10% Antifreeze or some Swiftech Hydrex. You can also use Distilled Water with Alcohol so long as there is no acrylic or aluminum in the loop.

If all of that seems confusing, get a Swiftech kit. Far simpler. Also, I would recommend going with an MCW60 or Maze4 GPU because you'll be able to use one of those block when you upgrade your video card. When the 7800 was released, DD had to make a new cooler because the memory chips on the 7800 are shorter than those on the 6800. its not exactly optimal to use a shim or extra TIM to fill the gap. Some ramsinks, a good waterblock, and good airflow would be better.

Alright, the way EVERY SINGLE fitting works on a system, is that it screws into something, such as a waterblock, radiator, anything in the loop. All of these fittings are called 1/4" NPT fittings and at every fitting it chokes down to 1/4" at more than one point in a system, so cutting down to 1/4" right before the block wouldnt have any effect on your system, but that kit your getting isnt the greatest, you could do better with high performance air cooling for much less money, and also what kind of video card do you have, you dont need a full face block, you can just buy ramsinks for 10 dollars and a maze block from Danger Den or this other block from swiftech its like MCW60 or something like that. If you do go with the TT bigwater kit then you should at least try and upgrade the pump.

Thermaltake+watercooling=the pits. Period. Their kits are cheap and perform accordingly.

Do yourself a favor and follow some of the recommendations above. An MCP350, BIXII or BIPII depending on the performance you want vs. silence, Maze 4 or MCW60 with some ramsinks, a t-line or a swiftech micro-res, and some tubing from mcmaster and you will have a great setup. It might cost a little more, but you won't be sorry in the long run.