Hi,
First here are my mods:

2005 G35 6MT
Mods: Ztube, KN Drop-In, Motordyne ISO Thermal MREV, FI 300Cell Metallic Cats, Strup Headers, FI Intimidator Exhaust, Technosquare Reflash

Question: The Fast intentions exhaust is awesome but insanely loud with my headers and metal cats for my 30 mile daily commute, so I installed electronically controlled exhaust gates that choke the flow and sound by 40% when closed, the car runs fine and sounds almost stock. Am I damaging anything by choking the flow a little bit sometimes? I realize I might be running a little rich and performance is not all there. I can control this gate from a switch inside the car (adjust the flow to any %) and I love this mod. Thanks for any info.

 

This might be affecting your performance to a degree. You have an acoustic pulse as your exhuast valve opens. Thiss travel down the heards and so on, and enters the atmosphere and creates a negitive pressure wave that will travel back up the exhuast. If everything is working correctly and tuned correctly this wave enters the combustion chamber just before the exhuast valve closes. That wave helps pull out the last of the exhuast gas. You are limiting the amount of exhuast gas the is let out of the cylinder. This will equal more exhuast gas in the cylinder therefore making it hard to get the rest of that waste out of the combustion chamber and allowing new air/fuel to enter. Even though air is entered into the cylinder at a very high rate, you want as much exhaust gas to get out of there as possible. This mod might also affect the wave that is traveling back into the exhaust to help expel that little bit of exhuast gas in the combustion chamber. Then again this comes into play when it comes down to fine tuning but still the basics are working all the time.

I don't think you are "hurting" you engine by doing this. While you might not get the gas mileage you want and the performance you want I dont see why this would hurt the engine other what I just talked about. This is atleast how I understand it to be.