The water goes through the opening and slams into the far side of the tank, then goes into the channels. Water is doing TWO 90 degree turns (sideways and then down). Overall cross-section is still the same, so no restriction. (So now what do you think hehe
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I am using same version - popped a barb on one end (for the mcp350) and just a tube stub on the other end for 7/16" ID to the rest of the loop.
The only improvement in the GDI equiv (originally got mine @ autozone) is that the holes are round and the tanks are taller to allow the round entry/exit. (which makes them in some cases just a little bigger).