Originally Posted by XwChriswX

First point - The hiss comes from having an X-Pipe. Has nothing to do with Stock cats or HFCs or test pipes. If I recall correctly it is from the equalization of backpressure between the two sides of the system... Tony will have to come in and 100% answer that one. But the only way to defeat the hiss is to have either a complete dual system or have an H pipe as with the Nismo exhaust.

Second Point - The overheating issue... When you installed your CBE/HFCs, did YOU do it or did you take it to a shop and have them do it? In either instance, did you get it tuned afterwards? If no tune did you at least pull off the negative battery terminal for a few minutes to reset your ECU? Adding these breathing mods allows your engine to flow more air = more power. However comma if you haven't reset your ECU to adapt to this, it might still be running the same cooling maps as it would for stock. Which now that you're getting more power your block is heating up faster and the ECU isn't compensating for this. If you haven't done the battery reset, I would suggest to try that, remove the NEGATIVE terminal for about 5 minutes. Then return it and crank. Let it sit and idle for about 10-15 minutes. Then take it around the block a few times without getting on it. And let your ECU learn how your engine reacts with the new mods. Maybe this will help it adapt better and keeps your temps back down where they were. Or it could just be due to the weather getting warmer/more humid...